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Gertie the Dinosaur
Directed by	Winsor McCay
Written by	Winsor McCay
Starring	Winsor McCay George McManus Roy McCardell Max Fleischer
Release date(s)	September 14, 1914
Running time	12 minutes
Country	United States
Language	Silent film English intertitles

Gertie the Dinosaur is a 1914 American animated short film by Winsor McCay. Although not the first feature-length animated film, as is sometimes thought, it was the first cartoon to feature a character with an appealing personality. The appearance of a true character distinguished it from earlier animated "trick films", such as those of Blackton and Cohl, and makes it the predecessor to later popular cartoons such as those by Walt Disney. The film was also the first to be created using keyframe animation. The film has been selected for preservation in the United States National Film Registry, and was named #6 of The 50 Greatest Cartoons of all time in a 1994 survey of animators and cartoon historians by Jerry Beck.^[1]

Vaudeville[link]

The complete film

Gertie the Dinosaur was originally created to be used in McCay's vaudeville performances. McCay started performing "chalk talks" on vaudeville in 1906, as a sideline to his regular newspaper cartooning. In 1911, he began presenting animated films on stage, first an animation of Little Nemo in Slumberland, then How a Mosquito Operates. Plans for Gertie were announced in 1912. The episode of McCay's newspaper comic In the Land of Wonderful Dreams published in newspapers on the 21st of September 1913 showed the reader some of the creatures from the upcoming film: a "dinosaurus", a sea serpent and a four-winged lizard. In January 1914, the drawings were photographed by Vitagraph Studios. The first presentation of the film was at the Palace Theater in Chicago on February 8, 1914; later performances were at the Hammerstein Theater in New York City.

The performance consisted of McCay interacting with Gertie, a cartoon dinosaur based on the Brontosaurus skeleton in the American Museum of Natural History.^[2] McCay would stand on stage in front of a projection screen, dressed in a tuxedo and wielding a whip. He would call Gertie, who appeared from behind some rocks. He then instructed her to perform various tricks, similar to a circus act. He would appear to toss a prop apple to her — McCay palmed the apple while Gertie caught an animated copy of it. Gertie was also seen to swallow a large stump, play with a Mastodon, and drink an entire lake dry. At one point, McCay would scold Gertie for misbehaving, at which she would begin to cry. For the finale, McCay disappeared behind the screen just as a cartoon version of him climbed onto Gertie's head and rode off.

Movie theaters[link]

McCay's employer, William Randolph Hearst, was displeased with McCay's success outside of the newspapers, and used his contractual power to reduce McCay's stage activities. In late 1914, William Fox offered to market Gertie the Dinosaur to moving-picture theaters. McCay accepted, and extended the film to include a live-action prologue and intertitles to replace his stage patter. This is the version of the film generally seen today; the original animation comprises roughly 5 minutes of the entire 12-minute film.

McCay sketching Gertie

The film features McCay with several of his cartoonist friends, such as George McManus (creator of Bringing Up Father), Roy McCardell, and Thomas A. Dorgan. As the film opens, they are "on a joy ride", when their automobile suffers a flat tire in front of a museum. The cartoonists enter the museum, and see a "Dinosaurus" skeleton. McCay bets McManus a dinner that he can "make the Dinosaurus live again by a series of hand-drawn cartoons". He then spends six months making "ten thousand cartoons"; when McManus visits, McCay shows him the drawings, although an assistant trips and scatters a large pile of them over the floor (a gag also used in the Little Nemo film). The scene then shifts to a dinner party with the group of cartoonists. McCay begins by sketching a single drawing of Gertie. Someone complains that "your bet was that you could make it move", following which the film shifts to the original animated Gertie. McCay, through intertitles, tells Gertie to come out and bow, and continues through the same interaction as in the vaudeville show (although the "apple" that McCay throws to her is now referred to as a pumpkin, which was more appropriate for the size of Gertie's mouth). The film concludes with the group telling George (McManus) to pay for the dinner.

Production[link]

Thousands of drawings for the film

Gertie the Dinosaur was produced before the introduction of later time-saving techniques such as cel animation. To create the film, McCay himself drew thousands of frames of Gertie on individual 6.5 x 8.5 inch sheets of rice paper. He hired neighbor and art student John A. Fitzsimmons to draw the backgrounds. Fitzsimmons carefully re-traced the rocks, lake and tree from a master drawing onto each sheet of rice paper.

In creating the film, McCay came up with a number of techniques that would later become standard in the animation industry. He used registration marks to keep the background aligned from frame to frame, so that it did not appear to "swim", as often happened in early cartoons. He avoided some repetitious work by re-using drawings, in what would later be called cycling. He devised what he called the "McCay Split System", the first occurrence of keyframe animation. Rather than draw each frame in sequence, he would start by drawing Gertie's key poses, and then go back and fill in the frames between. McCay was also very concerned with accurate timing and motion; he timed his own breathing to determine how to animate Gertie's breathing, and included subtle details such as the ground sagging beneath Gertie's great weight.

McCay was very open about the techniques that he developed. During production of Gertie, he showed all the details to a visitor who claimed to be writing an article about animation. The visitor turned out to be John Randolph Bray, who later patented many of McCay's methods and tried to sue him. McCay prevailed, however, and received royalties from Bray for several years thereafter.

Other versions[link]

Fragment of Gertie On Tour

Around 1921, McCay worked on a second animated film featuring Gertie, titled Gertie on Tour. The film would have Gertie visiting New York and Washington, D.C., bouncing on the Brooklyn Bridge and attempting to eat the Washington Monument, among other scenes. The film may have been designed for performance on the vaudville stage; it exists today only in fragments and concept sketches.

A plagiarization of Gertie, from roughly 1915, was distributed for many years, incorrectly identified as McCay's film. Donald Crafton suggests that this other Gertie may have been created by Bray Productions, based on its graphical style.^[3]

McCay's son Robert, along with Disney animator Richard Huemer, recreated the original vaudeville performance for the Disneyland television program in 1955.

Dinosaur Gertie's is a soft serve ice cream location at Disney's Hollywood Studios in Walt Disney World, Florida. The building is an example of Programmatic architecture, meaning it is shaped like Dinosaur Gertie. The shop is located on Echo Lake (across from the Giant Sorcerer Hat).

See also[link]

• Animation Before Hollywood: The Silent Period
• List of films in the public domain

References[link]

Further readings

External links[link]

Wikimedia Commons has media related to: Gertie the Dinosaur

• The short film Gertie the Dinosaur is available for free download at the Internet Archive [more]
• Gertie the Dinosaur at the Internet Movie Database
• Gertie the Dinosaur at AllRovi
• Gertie on Tour at the Library of Congress
• Meeting McCay

Coordinates: 50°42′00″N 2°26′00″W / 50.7°N 2.433333°W / 50.7; -2.433333

Dorchester
Dorchester  Dorchester shown within Dorset
Population	20,101
OS grid reference	SY690906
District	West Dorset
Shire county	Dorset
Region	South West
Country	England
Sovereign state	United Kingdom
Post town	DORCHESTER
Postcode district	DT1
Dialling code	01305
Police	Dorset
Fire	Dorset
Ambulance	South Western
EU Parliament	South West England
UK Parliament	West Dorset
Website	http://www.dorchester-tc.gov.uk
List of places: UK • England • Dorset

Dorchester ( /ˈdɔrtʃɛstər/ DOR-ches-tər) is the county town of Dorset, England. A historic market town, Dorchester lies on the banks of the River Frome, in the Frome Valley, just south of the Dorset Downs and north of the South Dorset Ridgeway, that separates the area from Weymouth, 8 miles (13 km) south.

Dorchester is noted as being home and inspiration to the author Thomas Hardy, whose novels Tess of the d'Urbervilles and The Mayor of Casterbridge were both based on the town.

In the 2001 Census the official population of Dorchester was 16,171, although by 2010 this was estimated to have risen to 18,280.^[1]

History[link]

Prehistory and Romano-British[link]

Dorchester's roots stem back to prehistoric times. Settlements were first based around Maiden Castle, a large Iron Age hill fort that was one of the most powerful settlements in pre-Roman Britain, with varying tribes having existed there since 4000 BC. The Durotriges were likely to have been there at the arrival of the Romans in 43 AD.

The Romans defeated the local tribes by 70 AD. After possibly being converted from a garrison to a town, the Romans named the settlement Durnovaria. This was a Brythonic name meaning 'place with fist-sized pebbles' and appears to have taken part of its name from the local Durotriges tribe who inhabited the area. Durnovaria was first recorded in the 4th century Antonine Itinerary and became a market centre for the surrounding countryside, and an important road junction and staging post,^[2] and eventually one of the twin capitals of the Celtic Durotriges tribe.^[3]

The Romans walled the town and the remains can still be seen today. The walls were largely replaced with walks that form a square inside modern Dorchester. Known as 'The Walks' a small segment of the original Roman wall still exists today near the Top 'o Town roundabout.

Roman town house ruins in Dorchester

The town still has some Roman features, including part of the town walls and the foundations of a Roman town house, which are freely accessible near the County Hall. There are many Roman finds in the County Museum. The Romans built an 8-mile (13 km) aqueduct to supply the town with water, lengths of the terrace on which it was constructed still remain in parts. Near the town centre is Maumbury Rings, an ancient British henge earthwork converted by the Romans for use as an amphitheatre, and to the north west is Poundbury Hill, another pre-Roman fortification.

Little evidence exists to suggest continued occupation after the withdrawal of the Roman administration from Britain. Historians have suggested that the town became known as Caer Durnac, mistakenly recorded by Nennius as Caer Urnac.^[4][5] The area remained in British hands until the mid-7th century and there was certainly continuity of use of the Roman cemetery at nearby Poundbury. Dorchester has therefore been suggested as the centre of a sub-kingdom of Dumnonia or other regional power base.^[6]

Anglo-Saxon[link]

By 864, the area around Durnovaria/Caer Durnac was dominated by the newly established Saxons, who came to refer to themselves as Dorsaetas ('People of the Dor' - Durnovaria). In their own language, they referred to the town as Dornwaraceaster or Dornwaracester, combining the original name 'Dor/Dorn' from the Latin and Celtic languages with the word 'cester', which was an Anglo-Saxon word used for 'walled town'.^[7] The name would further change to Dorncester/Dornceaster until modern Dorchester emerged some time later. It continued as a thriving commercial and political centre for south Dorset with a textile trading and manufacturing industry continuing until the 17th century.^[8]

Early modern history[link]

"The town is populous, tho' not large, the streets broad, but the buildings old, and low; however, there is good company and a good deal of it; and a man that coveted a retreat in this world might as agreeably spend his time, and as well in Dorchester, as in any town I know in England". -- Daniel Defoe, in his A tour thro' the Whole Island of Great Britain (1724-1726).^[9]

In 1613 and 1725 great fires destroyed large parts of the town, but some of the mediaeval buildings, including Judge Jeffreys' lodgings, and the Tudor almshouse survive in the town centre, amongst the replacement Georgian buildings, many of which are built in Portland limestone.

In the 17th century the town was at the centre of the Puritan emigration to America, and the local rector, John White, organised the settlement of Dorchester, Massachusetts. For his efforts on behalf of Puritan dissenters, White has been called the unheralded founder of the Massachusetts Bay Colony. (Some observers have attributed the oversight to the fact that White, unlike John Winthrop, never came to America.)^[10]

In 1642, just prior to the English Civil War, Hugh Green, a Catholic chaplain was executed here. After his execution, Puritans played football with his head.^[11] The town was heavily defended against the Royalists in the Civil War.

In 1685 the Duke of Monmouth failed in his invasion attempt, the Monmouth Rebellion, and almost 300 of his men were condemned to death or transportation in the "Bloody Assizes", held in the Oak Room of the Antelope Hotel, Dorchester and presided over by Judge Jeffreys.

Modern history[link]

In 1833, the Tolpuddle Martyrs formed the Friendly Society of Agricultural Labourers. Trade unions were legal, but due to them swearing an oath of allegiance, they were arrested and tried in the Shire Hall in Dorchester. This building still remains and is preserved as it was at the time. Under the court are the cells where the prisoners were held while waiting for their court appearance. Dorchester Prison was constructed in the town during the 19th century and the prison is still in use today, holding convicted and remanded inmates from the local courts.

Dorchester remained a compact town within the boundaries of the old town walls until the latter part of the 19th century due to the ownership of all land immediately adjacent to the west, south and east by the Duchy of Cornwall. This land composed the Manor of Fordington, and a select few developments had encroached onto it:

• The Marabout Barracks, to the north of Bridport Road, in 1794
• The Dorchester Union Workhouse, to the north of Damer's Road, in 1835
• The Southampton and Dorchester Railway and its station east of Weymouth Avenue, in 1847
• The Great Western Railway and its station to the south of Damer's Road, in 1857
• The Waterworks, to the north of Bridport Road, in 1854
• A new cemetery, to the west of the new railway and east of Weymouth Avenue, in 1856
• The Dorset County Constabulary police station in 1860, west of the Southampton railway, east of Weymouth Avenue and north of Maumbury Rings.

A map of Dorchester in 1937

This remaining Duchy land was farmed under the open field system until 1874 when the land was enclosed - or consolidated - into three large farms by the landowners and residents.^[12] Soon afterwards followed a series of key developments for the town: the enclosing of Poundbury hillfort for public enjoyment in 1876, the 'Fair Field' (new site for the market, off Weymouth Avenue) in 1877, the Recreation Ground (also off Weymouth Avenue) opening in 1880, and the imposing Eldridge Pope Brewery of 1881, adjacent to the railway line to Southampton. Salisbury Field was retained for public use in 1892, with land being purchased in 1895 for the formal Borough Gardens, between West Walks and Cornwall Road.^[12] The clock and bandstand were added in 1898.^[13]

Meanwhile, land had begun to be developed for housing outside the walls. This included the Cornwall Estate, between the Borough Gardens and the Great Western Railway, from 1876 and the Prince of Wales Estate, centred on Prince of Wales Road, from 1880. Land for the Victoria Park Estate was bought in 1896 and building began in 1897, Queen Victoria's Diamond Jubilee year. The lime trees in Queen's Avenue were planted in February 1897.^[12]

Recent developments[link]

Dorchester High West Street

Poundbury is the well-known western extension of the town, constructed on Duchy of Cornwall land (owned by Charles, Prince of Wales) according to urban village principles since 1993. Being developed over 25 years, it will eventually be composed of four phases with a total of 2,500 dwellings and a population of about 6,000. Since 2008, Poundbury is now home to Dorset Fire and Rescue Service headquarters and Dorchester fire station. Prince Charles designed the estate (as well as the local Tesco supermarket) and makes several visits throughout the year.

Dorchester became Dorset's first Official Transition Initiative in 2008 as part of the Transition Towns concept.^[14] Transition Town Dorchester is a Dorchester community response to the challenges, and opportunities, of Peak Oil and Climate Change.^[15]

The town's Woolworths shop closed in January 2009 after the high-street retail chain entered administration. The store manager, however, secured investment to re-open the store in March 2009, under the name Wellworths,^[16] although due to legal reasons it was later renamed Wellchester. In May 2009, a skatepark was opened in Dorchester after 12 years of planning and construction.^[17]

The catchment population for major food retail outlets in Dorchester is 38,500 (2001 estimate). The catchment area extends eight miles west, north and east of the town, and two miles south.^[1] Brewery Square is a new development in the heart of the town, and is planned to include a multitude of retail outlets, residential units, bars, restaurants and various cultural facilities, plus the regeneration of Dorchester South station to make it the UK's first solar powered rail station.^[18] The Charles Street development, being built on the site of the former Charles Street car park, is the newest project in Dorchester, and will include 23 new shops, a 485-space underground car park, an hotel, affordable housing, new public toilets, a public library and adult education centre provided and paid for by Dorset County Council, and offices and separate parking occupied and paid for by West Dorset District Council. The Charles Street development is predicted to create 660 new jobs (not including jobs within the council).^[19]

There is a new leisure centre being built on Coburg Road to replace the old Thomas Hardye School Leisure Centre, costing over £8 million, and will consist of a new swimming pool and sports equipment.^[20]

Government[link]

Dorchester is represented by three tiers of government. Dorchester town council, West Dorset District Council and Dorset County Council, all of whom are based within the town. The Member of Parliament for West Dorset is Oliver Letwin.

The town's coat of arms depicts the old castle that used to stand where the prison now does. The royal purple background signifies Dorchester's status as part of the private estates of the king since before Domesday. The shield within the castle depicts lions, copied from the shields of Dorset men who fought at the Battle of Agincourt on 25 October 1415, and fleur-de-lys. The fleur-de-lys on the shield are scattered (or "semée") rather than the more traditional triangular arrangement. Doing so, shows that the town had the right to bear the arms of France before 1405, when they were altered by King Henry VI. Dorchester's seal is the only one in the UK to use the fleur-de-lys in this way. The inscription 'Sigillum Bailivorum Dorcestre' means 'The Seal of the Bailiffs of Dorchester'.

In 2011 Dorchester was one of more than 20 towns across the country to apply for city status to mark the Queen's diamond jubilee,^[21] although in March 2012 it was revealed that Dorchester's bid was unsuccessful.

Media[link]

Dorchester is served by two local radio stations: Wessex FM and BBC Radio Solent (BBC Dorset). The county hospital has its own station named 'Ridgeway Radio'. Local television news coverage is by South Today or Spotlight (BBC News). Dorchester's regular print media comprise Dorset Echo and a free weekly periodical.

Transport[link]

Dorchester South railway station

The town has two railway stations. Dorchester South railway station on the South Western Main Line to Bournemouth, Southampton and London is operated by South West Trains. Dorchester West railway station on the Heart of Wessex Line is operated by First Great Western and serves Yeovil, Bath and Bristol The building at Dorchester West railway station is the original building designed and built by Isambard Kingdom Brunel. As part of the regeneration project taking place at the Brewery Site in the town centre, Dorchester South railway station will become the first solar powered railway station in the UK.

A bypass road was completed in 1988 by construction company Mowlem to the south and west of the town, diverting through traffic using the A35 and A37 from the town.^[22]

Education[link]

Dorchester has one private school, several first schools, two middle schools and one upper school. The upper school, The Thomas Hardye School, can trace its origins back to 1569, when it was founded by a merchant of that name, not the writer Thomas Hardy as commonly believed. Nineteen schools in the Dorchester area form the Dorchester Area Schools Partnership (DASP).

Kingston Maurward College is a land-based studies college based on the outskirts of the town.

Culture[link]

Local author and poet Thomas Hardy based the fictional town of Casterbridge on Dorchester. Hardy's childhood home is to the east of the town, and his house in town, Max Gate, is owned by the National Trust and open to the public. William Barnes, the local dialect poet, was Rector of Winterborne Came, a small hamlet near Dorchester, for 24 years until his death in 1886,^[23] and ran a school in the town. Statues of both men stand in the town centre; Barnes is outside St Peter's Church and Hardy's beside the Top o' Town crossroads. Cecil Day Lewis is buried in Stinsford, one mile (1.6 km) from Dorchester. Hardy is buried in London, but his heart was removed and buried in Stinsford.

On the hills to the south west of the town, stands Hardy's Monument, a memorial to the other local Thomas Hardy, Sir Thomas Masterman Hardy, who served with Lord Nelson, which overlooks the town with views of Weymouth, the Isle of Portland and Chesil Beach. Tom Roberts, Australian painter, was born in Dorchester in 1856.

Dorchester Arts, a regularly funded arts organisation based in a former school building runs a seasonal programme of music, dance and theatre events in the town as well as a range of participatory arts projects for socially excluded groups and the biannual Dorchester Festival. In 2011, Dorchester Arts became an Arts Council 'National Portfolio organisation' with enhanced funding until 2015.

Museums in Dorchester include the Roman Town House, The Dinosaur Museum, the Terracotta Warriors Museum, the Dorset Teddy Bear Museum, The Keep Military Museum, Dorset County Museum. and the Tutankhamun Exhibition. All of these museums took part in the "Museums at Night" event in May 2011 where museums across the UK opened after hours.^[24]

On 15 December 2004, Dorchester was granted Fairtrade Town status.^{[citation needed]}

Twinned towns[link]

Dorchester is twinned with three European towns:^[25]

• Bayeux in France since 1959, came about because the Dorset Regiment were the first soldiers to enter the town in 1944 as the Second World War came to an end
• Lübbecke in Germany since 1973, largely down to the special relationship between the Durnovaria Silver Band who met the Lübbecker Schutzenmusik Corps at an event in Bayeux when Bayeux was twinning with Lübbecke in 1968
• Holbæk in Denmark since 1992, resulted from a shared interest in community plays.^{[citation needed]}

Notable people[link]

• James Campbell (born 1988), cricketer
• Thomas Hardy (1840-1928), writer, was born near Dorchester and later lived at Max Gate in the town. Two of his novels were directly based on Dorchester.
• Paul Hillier (born 1949), classical singer and composer was born in Dorchester. He attended the Thomas Hardye School.

Sport[link]

Dorchester is represented by many sports teams, the most prominent of whom are Dorchester Town F.C., a football team currently playing in the Conference South.

Harry Redknapp and former England players Graham Roberts and Martin Chivers represented 'The Magpies' during the late 1970s and early 1980s. The club have historically been based along Weymouth Avenue in the south of the town. Having previously played at the old Avenue Ground since their inception, the club moved to a new purpose built 5,000 capacity Avenue Stadium in the early 1990s - designed and owned by the Duchy of Cornwall. The site of the old Avenue ground is now a Tesco supermarket built at the same time as the Avenue stadium

Dorchester RFC are an amateur rugby union team who currently play in the Southern Counties South league.

Dorchester CC, are a cricket club, who play in the Dorset Premier League, being last crowned champions in 2009.

Aaron Cook, a taekwondo athlete who competed in the 2008 Olympic Games finishing in fifth place, was born in Dorchester.^[26]

References[link]

Bibliography[link]

• Bingham, A. (1987) Dorset : Ordnance Survey landranger guidebook , Norwich: Jarrold, ISBN 0-319-00187-3
• Chandler, J. H. (1990) Wessex images, Gloucester: Alan Sutton and Wiltshire County Council Library & Museum Service, ISBN 0-86299-739-9
• Draper, J. (1992) Dorchester : An illustrated history Wimborne: Dovecote Press, ISBN 1-874336-04-0
• Morris, J. and Draper, J. (1995) "The 'Enclosure' of Foridngton Fields and the Development of Dorchester, 1874–1903", Dorset Natural History and Archaeological Society proceedings, v. 117, p. 5–14, ISSN 0070-7112
• Pitt-Rivers, M. (1966) Dorset, A Shell guide, New ed., London: Faber, ISBN 0-571-06714-X
• Taylor, C. (1970) Dorset, Making of the English landscape, London: Hodder & Stoughton, p. 197–201, ISBN 0-340-10962-9
• Waymark, J, (1997) "The Duchy of Cornwall and the Expansion of Dorchester, c. 1900–1997", Dorset Natural History and Archaeological Society proceedings, v. 119, p. 19–32, ISSN 0070-7112

External links[link]

Wikimedia Commons has media related to: Dorchester, Dorset

• Census data
• Dorchester, Dorset at the Open Directory Project

Dinosaurs Temporal range: Middle Triassic—Present, 231.4–0 Ma PreЄ Є O S D C P T J K Pg N
Mounted skeletons of various non-avian dinosaurs, each from a different group. Clockwise from top-left are skeletons of: a predatory theropod (Tyrannosaurus rex), a large sauropod (Diplodocus carnegii), a duck-billed ornithopod (Parasaurolophus cyrtocristatus), a bird-like dromaeosaurid (Deinonychus antirrhopus), an early ceratopsian (Protoceratops andrewsi), and a plated thyreophoran (Stegosaurus stenops).
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
clade:	Dinosauriformes
clade:	Dinosauria Owen, 1842
Major groups
†Ornithischia †Stegosauria †Ankylosauria †Ornithopoda †Ceratopsia Saurischia †Sauropodomorpha Theropoda

Dinosaurs are a diverse group of animals of the clade Dinosauria. They first appeared during the Triassic period, approximately 230 million years ago, and became the dominant terrestrial vertebrates for 135 million years, from the beginning of the Jurassic (about 200 million years ago) until the end of the Cretaceous (65.5 million years ago), when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups at the close of the Mesozoic era. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic, and consequently they are considered a type of dinosaur in modern classification systems.^[1][2] Some birds survived the extinction event that occurred 65 million years ago, and continue the dinosaur lineage to the present day.

Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 9,000 living species, are the most diverse group of vertebrates besides perciform fish.^[3] Using fossil evidence, paleontologists have identified over 500 distinct genera^[4] and more than 1,000 different species of non-avian dinosaurs.^[5] Dinosaurs are represented on every continent by both extant species and fossil remains.^[6] Some are herbivorous, others carnivorous. Most dinosaurs have been bipedal, though many extinct groups included quadrupedal species, and some were able to shift between these body postures. Many species possess elaborate display structures such as horns or crests, and some prehistoric groups developed skeletal modifications such as bony armor and spines. Birds have been the planet's dominant flying vertebrate since the extinction of the pterosaurs, and evidence suggests that egg laying and nest building is a trait shared by all dinosaurs. Many prehistoric dinosaurs were large animals—the largest sauropods could reach lengths of almost 60 meters (200 feet) and were several stories tall—and while many extinct theropods were quite large, a majority evolved very small sizes, especially among birds and other advanced groups.

Although the word dinosaur means "terrible lizard," the name is somewhat misleading, as dinosaurs are not lizards. Rather, they represent a separate group of reptiles with a distinct upright posture not found in lizards. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs were sluggish and cold-blooded. Most research conducted since the 1970s, however, has indicated that ancient dinosaurs, particularly the carnivorous groups, were active animals with elevated metabolisms and numerous adaptations for social interaction.

Since the first dinosaur fossils were recognized in the early 19th century, mounted fossil dinosaur skeletons or replicas have been major attractions at museums around the world, and dinosaurs have become a part of world culture. Their diversity, the large sizes of some groups, and their seemingly monstrous and fantastic nature have captured the interest and imagination of the general public for over a century. They have been featured in best-selling books and films such as Jurassic Park, and new discoveries are regularly covered by the media.

Etymology[link]

The taxon Dinosauria was formally named in 1842 by paleontologist Sir Richard Owen, who used it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were then being recognized in England and around the world.^[7]:103 The term is derived from the Greek words δεινός (deinos, meaning "terrible," "potent," or "fearfully great") and σαῦρος (sauros, meaning "lizard" or "reptile").^[7]:103[8] Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it merely to evoke their size and majesty.^[9]

Definition[link]

Triceratops horridus skeleton, American Museum of Natural History

Under phylogenetic taxonomy, dinosaurs are usually defined as the group consisting of "Triceratops, Neornithes [modern birds], their most recent common ancestor, and all descendants".^[10] It has also been suggested that Dinosauria be defined with respect to the most recent common ancestor of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria.^[11] Both definitions result in the same set of animals being defined as dinosaurs: "Dinosauria = Ornithischia + Saurischia", encompassing theropods (mostly bipedal carnivores and birds), ankylosaurians (armored herbivorous quadrupeds), stegosaurians (plated herbivorous quadrupeds), ceratopsians (herbivorous quadrupeds with horns and frills), ornithopods (bipedal or quadrupedal herbivores including "duck-bills"), and, perhaps, sauropodomorphs (mostly large herbivorous quadrupeds with long necks and tails).

The common House Sparrow (Passer domesticus) is often used to represent modern birds in definitions of the group Dinosauria

Many paleontologists note that the point at which sauropodomorphs and theropods diverged may omit sauropodomorphs from the definition for both saurischians and dinosaurs. To avoid instability, Dinosauria can be more conservatively defined with respect to four anchoring nodes: Triceratops horridus, Saltasaurus loricatus, and Passer domesticus, their most recent common ancestor, and all descendants. This "safer" definition can be expressed as "Dinosauria = Ornithischia + Sauropodomorpha + Theropoda".^[12]

There is near universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. In traditional taxonomy, birds were considered a separate "class" which had evolved from dinosaurs. However, a majority of modern paleontologists reject the traditional style of classification in favor of phylogenetic nomenclature, which requires that all descendants of a single common ancestor must be included in a group for that group to be natural. Birds are thus considered by most modern scientists to be dinosaurs and dinosaurs are, therefore, not extinct. Birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs.^[13]

General description[link]

Using one of the above definitions, dinosaurs can be generally described as archosaurs with limbs held erect beneath the body.^[14] Many prehistoric animal groups are popularly conceived of as dinosaurs, such as ichthyosaurs, mosasaurs, plesiosaurs, pterosaurs, and Dimetrodon, but are not classified scientifically as dinosaurs, and none had the erect limb posture characteristic of true dinosaurs.^[15] Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially the Jurassic and Cretaceous periods. Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a cat, and were generally rodent-sized carnivores of small prey.^[16] One notable exception is Repenomamus giganticus, a triconodont weighing between 12 kilograms (26 lb) and 14 kilograms (31 lb) that is known to have eaten small dinosaurs like young Psittacosaurus.^[17]

Stegosaurus stenops skeleton, Field Museum

Dinosaurs have always been an extremely varied group of animals; according to a 2006 study, over 500 non-avialan dinosaur genera have been identified with certainty so far, and the total number of genera preserved in the fossil record has been estimated at around 1850, nearly 75% of which remain to be discovered.^[4] An earlier study predicted that about 3400 dinosaur genera existed, including many which would not have been preserved in the fossil record.^[18] By September 17, 2008, 1047 different species of dinosaurs had been named.^[5] Some are herbivorous, others carnivorous. While most dinosaurs have been bipeds, some prehistoric species were quadrupeds, and others, such as Ammosaurus and Iguanodon, could walk just as easily on two or four legs. Cranial modifications like horns and crests are common among dinosaurs, and some extinct species had bony armor. Although known for large size, many Mesozoic dinosaurs were human-sized or smaller, and modern birds are generally very small in size. Dinosaurs today inhabit every continents, and fossils show that they had achieved global distribution by at least the early Jurassic period.^[6] Modern birds inhabit most available habitats, from terrestrial to marine, and there is evidence that some non-avialan dinosaurs (such as Microraptor) could fly or at least glide, and others, such as spinosaurids, had semi-aquatic habits.^[19]

Distinguishing anatomical features[link]

While recent discoveries have made it more difficult to present a universally agreed-upon list of dinosaurs' distinguishing features, nearly all dinosaurs discovered so far share certain modifications to the ancestral archosaurian skeleton. Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical across Dinosauria; the earliest dinosaurs had them and passed them on to all their descendants. Such common features across a taxonomic group are called synapomorphies.

A detailed assessment of archosaur interrelations by S. Nesbitt^[20] confirmed or found the following 12 unambiguous synapomorphies, some previously known:

• in the skull, a supratemporal fossa (excavation) is present in front of the supratemporal fenestra
• epipophyses present in anterior neck vertebrae (except atlas and axis)
• apex of deltopectoral crest (a projection on which the deltopectoral muscles attach) located at or more than 30% down the length of the humerus (upper arm bone)
• radius shorter than 80% of humerus length
• fourth trochanter (projection where the caudofemoralis muscle attaches) on the femur (thigh bone) is a sharp flange
• fourth trochanter asymmetrical, with distal margin forming a steeper angle to the shaft
• on the astragalus and calcaneum the proximal articular facet for fibula occupies less than 30% of the transverse width of the element
• exocciptials (bones at the back of the skull) do not meet along the midline on the floor of the endocranial cavity
• proximal articular surfaces of the ischium with the ilium and the pubis separated by a large concave surface
• cnemial crest on the tibia (shinbone) arcs anterolaterally
• distinct proximodistally oriented ridge present on the posterior face of the distal end of the tibia

Nesbitt found a number of further potential synapomorphies, and discounted a number of synapomorphies previously suggested. Some of these are also present in silesaurids, which Nesbitt recovered as a sister group to Dinosauria, including a large anterior trochanter, metatarsals II and IV of subequal length, reduced contact between ischium and pubis, the presence of a cenmial crest on the tibia and of an ascending process on the astragalus,^[10] and many others.

Diagram of a typical diapsid skull

Hip joints and hindlimb postures of typical reptiles (left), dinosaurs and mammals (middle), and rauisuchians (right)

A variety of other skeletal features are shared by dinosaurs. However, because they are either common to other groups of archosaurs or were not present in all early dinosaurs, these features are not considered to be synapomorphies. For example, as diapsids, dinosaurs ancestrally had two pairs of temporal fenestrae (openings in the skull behind the eyes), and as members of the diapsid group Archosauria, had additional openings in the snout and lower jaw.^[21] Additionally, several characteristics once thought to be synapomorphies are now known to have appeared before dinosaurs, or were absent in the earliest dinosaurs and independently evolved by different dinosaur groups. These include an elongated scapula, or shoulder blade; a sacrum composed of three or more fused vertebrae (three are found in some other archosaurs, but only two are found in Herrerasaurus);^[10] and an acetabulum, or hip socket, with a hole at the center of its inside surface (closed in Saturnalia, for example).^[22] Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from the Late Triassic are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature.^[23]

Dinosaurs stand erect in a manner similar to most modern mammals, but distinct from most other reptiles, whose limbs sprawl out to either side.^[24] This posture is due to the development of a laterally facing recess in the pelvis (usually an open socket) and a corresponding inwardly facing distinct head on the femur.^[25] Their erect posture enabled early dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that surpassed those of "sprawling" reptiles.^[26] Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs.^[27] Some non-dinosaurian archosaurs, including rauisuchians, also had erect limbs but achieved this by a "pillar erect" configuration of the hip joint, where instead of having a projection from the femur insert on a socket on the hip, the upper pelvic bone was rotated to form an overhanging shelf.^[27]

Evolutionary history[link]

Origins and early evolution[link]

Skeleton of Marasuchus lilloensis, a dinosaur-like ornithodiran

The early forms Herrerasaurus (large), Eoraptor (small) and a Plateosaurus skull

Dinosaurs diverged from their archosaur ancestors approximately 230 million years ago during the Middle to Late Triassic period, roughly 20 million years after the Permian–Triassic extinction event wiped out an estimated 95% of all life on Earth.^[28][29] Radiometric dating of the rock formation that contained fossils from the early dinosaur genus Eoraptor establishes its presence in the fossil record at this time. Paleontologists think that Eoraptor resembles the common ancestor of all dinosaurs;^[30] if this is true, its traits suggest that the first dinosaurs were small, bipedal predators.^[31] The discovery of primitive, dinosaur-like ornithodirans such as Marasuchus and Lagerpeton in Argentinian Middle Triassic strata supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators.

When dinosaurs appeared, terrestrial habitats were occupied by various types of archosaurs and therapsids, such as aetosaurs, cynodonts, dicynodonts, ornithosuchids, rauisuchians, and rhynchosaurs. Most of these other animals became extinct in the Triassic, in one of two events. First, at about the boundary between the Carnian and Norian faunal stages (about 215 million years ago), dicynodonts and a variety of basal archosauromorphs, including the prolacertiforms and rhynchosaurs, became extinct. This was followed by the Triassic–Jurassic extinction event (about 200 million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, phytosaurs, and rauisuchians. These losses left behind a land fauna of crocodylomorphs, dinosaurs, mammals, pterosaurians, and turtles.^[10] The first few lines of early dinosaurs diversified through the Carnian and Norian stages of the Triassic, most likely by occupying the niches of the groups that became extinct.

Evolution and paleobiogeography[link]

Dinosaur evolution after the Triassic follows changes in vegetation and the location of continents. In the Late Triassic and Early Jurassic, the continents were connected as the single landmass Pangaea, and there was a worldwide dinosaur fauna mostly composed of coelophysoid carnivores and early sauropodomorph herbivores.^[32] Gymnosperm plants (particularly conifers), a potential food source, radiated in the Late Triassic. Early sauropodomorphs did not have sophisticated mechanisms for processing food in the mouth, and so must have employed other means of breaking down food farther along the digestive tract.^[33] The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of ceratosaurians, spinosauroids, and carnosaurians, and herbivores consisting of stegosaurian ornithischians and large sauropods. Examples of this include the Morrison Formation of North America and Tendaguru Beds of Tanzania. Dinosaurs in China show some differences, with specialized sinraptorid theropods and unusual, long-necked sauropods like Mamenchisaurus.^[32] Ankylosaurians and ornithopods were also becoming more common, but prosauropods had become extinct. Conifers and pteridophytes were the most common plants. Sauropods, like the earlier prosauropods, were not oral processors, but ornithischians were evolving various means of dealing with food in the mouth, including potential cheek-like organs to keep food in the mouth, and jaw motions to grind food.^[33] Another notable evolutionary event of the Jurassic was the appearance of true birds, descended from maniraptoran coelurosaurians.^[13]

Earth during the Jurassic, the period in which dinosaurs gained global distribution. The continents were in different locations from where they are today.

By the Early Cretaceous and the ongoing breakup of Pangaea, dinosaurs were becoming strongly differentiated by landmass. The earliest part of this time saw the spread of ankylosaurians, iguanodontians, and brachiosaurids through Europe, North America, and northern Africa. These were later supplemented or replaced in Africa by large spinosaurid and carcharodontosaurid theropods, and rebbachisaurid and titanosaurian sauropods, also found in South America. In Asia, maniraptoran coelurosaurians like dromaeosaurids, troodontids, and oviraptorosaurians became the common theropods, and ankylosaurids and early ceratopsians like Psittacosaurus became important herbivores. Meanwhile, Australia was home to a fauna of basal ankylosaurians, hypsilophodonts, and iguanodontians.^[32] The stegosaurians appear to have gone extinct at some point in the late Early Cretaceous or early Late Cretaceous. A major change in the Early Cretaceous, which would be amplified in the Late Cretaceous, was the evolution of flowering plants. At the same time, several groups of dinosaurian herbivores evolved more sophisticated ways to orally process food. Ceratopsians developed a method of slicing with teeth stacked on each other in batteries, and iguanodontians refined a method of grinding with tooth batteries, taken to its extreme in hadrosaurids.^[33] Some sauropods also evolved tooth batteries, best exemplified by the rebbachisaurid Nigersaurus.^[34]

There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were tyrannosaurids and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and pachycephalosaurians. In the southern continents that had made up the now-splitting Gondwana, abelisaurids were the common theropods, and titanosaurian sauropods the common herbivores. Finally, in Europe, dromaeosaurids, rhabdodontid iguanodontians, nodosaurid ankylosaurians, and titanosaurian sauropods were prevalent.^[32] Flowering plants were greatly radiating,^[33] with the first grasses appearing by the end of the Cretaceous.^[35] Grinding hadrosaurids and shearing ceratopsians became extremely diverse across North America and Asia. Theropods were also radiating as herbivores or omnivores, with therizinosaurians and ornithomimosaurians becoming common.^[33]

The Cretaceous–Paleogene extinction event, which occurred approximately 65 million years ago at the end of the Cretaceous period, caused the extinction of all dinosaur groups except for the neornithine birds. Some other diapsid groups, such as crocodilians, sebecosuchians, turtles, lizards, snakes, sphenodontians, and choristoderans, also survived the event.^[36]

The surviving lineages of neornithine birds, including the ancestors of modern ratites, ducks and chickens, and a variety of waterbirds, diversified rapidly at the beginning of the Paleogene period, entering ecological niches left vacant by the extinction of Mesozoic dinosaur groups such as the arboreal enantiornithines, aquatic hesperornithines, and even the larger terrestrial theropods (in the form of Gastornis, mihirungs, and "terror birds"). However, mammals were also rapidly diversifying during this time, and out-competed the neornithines for dominance of most terrestrial niches.^[37]

Classification[link]

Dinosaurs are archosaurs, like modern crocodilians. Within the archosaur group, dinosaurs are differentiated most noticeably by their gait. Dinosaur legs extend directly beneath the body, whereas the legs of lizards and crocodilians sprawl out to either side.

Collectively, dinosaurs as a clade are divided into two primary branches, Saurischia and Ornithischia. Saurischia includes those taxa sharing a more recent common ancestor with birds than with Ornithischia, while Ornithischia includes all taxa sharing a more recent common ancestor with Triceratops than with Saurischia. Anatomically, these two groups can be distinguished most noticeably by their pelvic structure. Early saurischians—"lizard-hipped", from the Greek sauros (σαῦρος) meaning "lizard" and ischion (ἰσχίον) meaning "hip joint—retained the hip structure of their ancestors, with a pubis bone directed cranially, or forward.^[25] This basic form was modified by rotating the pubis backward to varying degrees in several groups (Herrerasaurus,^[38] therizinosauroids,^[39] dromaeosaurids,^[40] and birds^[13]). Saurischia includes the theropods (exclusively bipedal and with a wide variety of diets) and sauropodomorphs (long-necked herbivores which include advanced, quadrupedal groups).

By contrast, ornithischians—"bird-hipped", from the Greek ornitheios (ὀρνίθειος) meaning "of a bird" and ischion (ἰσχίον) meaning "hip joint"—had a pelvis that superficially resembled a bird's pelvis: the pubis bone was oriented caudally (rear-pointing) Unlike birds, the ornithischian pubis also usually had an additional forward-pointing process. Ornithischia includes a variety of species which were primarily herbivores. (NB: the terms "lizard hip" and "bird hip" are misnomers – birds evolved from dinosaurs with "lizard hips".)

Taxonomy[link]

The following is a simplified classification of dinosaur groups based on their evolutionary relationships, and organized based on the list of Mesozoic dinosaur species provided by Holtz (2008).^[41] A more detailed version can be found at Dinosaur classification. The cross (†) is used to signify groups with no living members.

• Dinosauria

• Saurischia ("lizard-hipped"; includes Theropoda and Sauropodomorpha)

• Theropoda (all bipedal; most were carnivorous)

• †Herrerasauria (early bipedal carnivores)
• †Coelophysoidea (small, early theropods; includes Coelophysis and close relatives)
• †Dilophosauridae (early crested and carnivorous theropods)
• †Ceratosauria (generally elaborately horned, the dominant southern carnivores of the Cretaceous)
• Tetanurae ("stiff tails"; includes most theropods)

• †Megalosauroidea (early group of large carnivores including the semi-aquatic spinosaurids)
• †Carnosauria (Allosaurus and close relatives, like Carcharodontosaurus)
• Coelurosauria (feathered theropods, with a range of body sizes and niches)

• †Compsognathidae (common early coelurosaurs with reduced forelimbs)
• †Tyrannosauridae (Tyrannosaurus and close relatives; had reduced forelimbs)
• †Ornithomimosauria ("ostrich-mimics"; mostly toothless; carnivores to possible herbivores)
• †Alvarezsauroidea (small insectivores with reduced forelimbs each bearing one enlarged claw)
• Maniraptora ("hand snatchers"; had long, slender arms and fingers)

• †Therizinosauria (bipedal herbivores with large hand claws and small heads)
• †Oviraptorosauria (mostly toothless; their diet and lifestyle are uncertain)
• †Archaeopterygidae (small, winged theropods or primitive birds)
• †Deinonychosauria (small- to medium-sized; bird-like, with a distinctive toe claw)
• Avialae (modern birds and extinct relatives)

• †Scansoriopterygidae (small primitive avialans with long third fingers)
• †Omnivoropterygidae (large, early short-tailed avialans)
• †Confuciusornithidae (small toothless avialans)
• †Enantiornithes (primitive tree-dwelling, flying avialans)
• Euornithes (advanced flying birds)

• †Yanornithiformes (toothed Cretaceous Chinese birds)
• †Hesperornithes (specialized aquatic diving birds)
• Aves (modern, beaked birds and their extinct relatives)

Several macronarian Sauropods: from left to right Camarasaurus, Brachiosaurus, Giraffatitan, and Euhelopus

• †Sauropodomorpha (herbivores with small heads, long necks, long tails)

• †Guaibasauridae (small, primitive, omnivorous sauropodomorphs)
• †Plateosauridae (primitive, strictly bipedal "prosauropods")
• †Riojasauridae (small, primitive sauropodomorphs)
• †Massospondylidae (small, primitive sauropodomorphs)
• †Sauropoda (very large and heavy, usually over 15 meters (49 feet) long; quadrupedal)

• †Vulcanodontidae (primitive sauropods with pillar-like limbs)
• †Eusauropoda ("true sauropods")

• †Cetiosauridae ("whale reptiles")
• †Turiasauria (European group of Jurassic and Cretaceous sauropods)
• †Neosauropoda ("new sauropods")

• †Diplodocoidea (skulls and tails elongated; teeth typically narrow and pencil-like)
• †Macronaria (boxy skulls; spoon- or pencil-shaped teeth)

• †Brachiosauridae (long-necked, long-armed macronarians)
• †Titanosauria (diverse; stocky, with wide hips; most common in the Late Cretaceous of southern continents)

Various ornithopod dinosaurs and one heterodontosaurid. Far left: Camptosaurus, left: Iguanodon, center background: Shantungosaurus, center foreground: Dryosaurus, right: Corythosaurus, far right (small): Heterodontosaurus, far right (large) Tenontosaurus.

• †Ornithischia ("bird-hipped"; diverse bipedal and quadrupedal herbivores)

• †Heterodontosauridae (small basal ornithopod herbivores/omnivores with prominent canine-like teeth)
• †Thyreophora (armored dinosaurs; mostly quadrupeds)

• †Ankylosauria (scutes as primary armor; some had club-like tails)
• †Stegosauria (spikes and plates as primary armor)

• †Neornithischia ("new ornithischians")

• †Ornithopoda (various sizes; bipeds and quadrupeds; evolved a method of chewing using skull flexibility and numerous teeth)
• †Marginocephalia (characterized by a cranial growth)

• †Pachycephalosauria (bipeds with domed or knobby growth on skulls)
• †Ceratopsia (quadrupeds with frills; many also had horns)

Biology[link]

Knowledge about dinosaurs is derived from a variety of fossil and non-fossil records, including fossilized bones, feces, trackways, gastroliths, feathers, impressions of skin, internal organs and soft tissues.^[42][43] Many fields of study contribute to our understanding of dinosaurs, including physics (especially biomechanics), chemistry, biology, and the earth sciences (of which paleontology is a sub-discipline). Two topics of particular interest and study have been dinosaur size and behavior.

Size[link]

Scale diagram comparing the largest known dinosaurs in five major clades and a human

Current evidence suggests that dinosaur average size varied through the Triassic, early Jurassic, late Jurassic and Cretaceous periods.^[30] Theropod dinosaurs, when sorted by estimated weight into categories based on order of magnitude, most often fall into the 100 to 1000 kilogram (220 to 2200 lb) category, whereas recent predatory carnivorans peak in the 10 to 100 kilogram (22 to 220 lb) category.^[44] The mode of dinosaur body masses is between one and ten metric tonnes.^[45] This contrasts sharply with the size of Cenozoic mammals, estimated by the National Museum of Natural History as about 2 to 5 kilograms (5 to 10 lb).^[46]

The sauropods were the largest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest were an order of magnitude more massive than anything else that has since walked the Earth. Giant prehistoric mammals such as the Paraceratherium (the largest land mammal ever) were dwarfed by the giant sauropods, and only modern whales approach or surpass them in size.^[47] There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low-nutrient browse would have been advantageous in such environments.^[48]

Largest and smallest[link]

Scientists will probably never be certain of the largest and smallest dinosaurs. This is because only a tiny percentage of animals ever fossilize, and most of these remain buried in the earth. Few of the specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork.

Comparative size of Giraffatitan

The tallest and heaviest dinosaur known from good skeletons is Giraffatitan brancai (previously classified as a species of Brachiosaurus). Its remains were discovered in Tanzania between 1907–12. Bones from several similar-sized individuals were incorporated into the skeleton now mounted and on display at the Museum für Naturkunde Berlin;^[49] this mount is 12 meters (39 ft) tall and 22.5 meters (74 ft) long, and would have belonged to an animal that weighed between 30000 and 60000 kilograms (70000 and 130000 lb). The longest complete dinosaur is the 27-meter (89 ft) long Diplodocus, which was discovered in Wyoming in the United States and displayed in Pittsburgh's Carnegie Natural History Museum in 1907.

Comparative size of Eoraptor

There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest herbivorous specimens on record were all discovered in the 1970s or later, and include the massive Argentinosaurus, which may have weighed 80000 to 100000 kilograms (90 to 110 short tons); some of the longest were the 33.5 meters (110 ft) long Diplodocus hallorum^[48] (formerly Seismosaurus) and the 33 meters (108 ft) long Supersaurus;^[50] and the tallest, the 18 meters (59 ft) tall Sauroposeidon, which could have reached a sixth-floor window. The heaviest and longest of them all may have been Amphicoelias fragillimus, known only from a now lost partial vertebral neural arch described in 1878. Extrapolating from the illustration of this bone, the animal may have been 58 meters (190 ft) long and weighed over 120000 kg (260000 lb).^[48] The largest known carnivorous dinosaur was Spinosaurus, reaching a length of 16 to 18 meters (50 to 60 ft), and weighing in at 8150 kg (18000 lb).^[51] Other large meat-eaters included Giganotosaurus, Carcharodontosaurus and Tyrannosaurus.^[52]

Not including birds (Avialae), the smallest known dinosaurs were about the size of a pigeon.^[53] Not surprisingly, the smallest dinosaurs were theropods closely related to birds. Anchiornis, for example, had a total skeletal length of under 35 centimeters (1.1 ft).^[53][54] Anchiornis is currently the smallest dinosaur described from an adult specimen, with an estimated weight of 110 grams.^[54] The smallest herbivorous non-avialan dinosaurs included Microceratus and Wannanosaurus, at about 60 cm (2 ft) long each.^[41][55]

Behavior[link]

A nesting ground of hadrosaur Maiasaura peeblesorum was discovered in 1978.

Many modern birds are highly social, often found living in flocks. There is general agreement that some behaviors which are common in birds, as well as in crocodiles (bird' closest living relatives), were also common among extinct dinosaur groups. Interpretations of behavior in fossil species are generally based on the pose of skeletons and their habitat, computer simulations of their biomechanics, and comparisons with modern animals in similar ecological niches.

The first potential evidence for herding or flocking as a widespread behavior common to many dinosaur groups in addition to birds was the 1878 discovery of 31 Iguanodon bernissartensis, ornithischians which were then thought to have perished together in Bernissart, Belgium, after they fell into a deep, flooded sinkhole and drowned.^[56] Other mass-death sites have been subsequently discovered. Those, along with multiple trackways, suggest that gregarious behavior was common in many early dinosaur species. Trackways of hundreds or even thousands of herbivores indicate that duck-bills (hadrosaurids) may have moved in great herds, like the American Bison or the African Springbok. Sauropod tracks document that these animals traveled in groups composed of several different species, at least in Oxfordshire, England,^[57] although there is not evidence for specific herd structures.^[58] Congregated into herds may have evolved for defense, for migratory purposes, or to provide protection for young. There is evidence that many types of slow-growing dinosaurs, including various theropods, sauropods, ankylosaurians, ornithopods, and ceratopsians, formed aggregations of immature individuals. One example is a site in Inner Mongolia that has yielded the remains of over 20 Sinornithomimus, from one to seven years old. This assemblage is interpreted as a social group that was trapped in mud.^[59] The interpretation of dinosaurs as gregarious has also extended to depicting carnivorous theropods as pack hunters working together to bring down large prey.^[60][61] However, this lifestyle is uncommon among modern birds, crocodiles, and other reptiles, and the taphonomic evidence suggesting mammal-like pack hunting in such theropods as Deinonychus and Allosaurus can also be interpreted as the results of fatal disputes between feeding animals, as is seen in many modern diapsid predators.^[62]

Artist's rendering of two Centrosaurus apertus engaged in intra-specific combat.

The crests and frills of some dinosaurs, like the marginocephalians, theropods and lambeosaurines, may have been too fragile to be used for active defense, and so they were likely used for sexual or aggressive displays, though little is known about dinosaur mating and territorialism. Head wounds from bites suggest that theropods, at least, engaged in active aggressive confrontations.^[63]

From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the Gobi Desert in 1971. It included a Velociraptor attacking a Protoceratops,^[64] providing evidence that dinosaurs did indeed attack each other.^[65] Additional evidence for attacking live prey is the partially healed tail of an Edmontosaurus, a hadrosaurid dinosaur; the tail is damaged in such a way that shows the animal was bitten by a tyrannosaur but survived.^[65] Cannibalism amongst some species of dinosaurs was confirmed by tooth marks found in Madagascar in 2003, involving the theropod Majungasaurus.^[66]

Comparisons between the scleral rings of dinosaurs and modern birds and reptiles have been used to infer daily activity patterns of dinosaurs. Although it has been suggested that most dinosaurs were active during the day, these comparisons have shown that small predatory dinosaurs such as dromaeosaurids, Juravenator, and Megapnosaurus were likely nocturnal. Large and medium-sized herbivorous and omnivorous dinosaurs such as ceratopsians, sauropodomorphs, hadrosaurids, ornithomimosaurs may have been cathemeral, active during short intervals throughout the day, although the small ornithischian Agilisaurus was inferred to be diurnal.^[67]

Based on current fossil evidence from dinosaurs such as Oryctodromeus, some ornithischian species seem to have led a partially fossorial (burrowing) lifestyle.^[68] Many modern birds are arboreal (tree climbing), and this was also true of many Mesozoic birds, especially the enantiornithines.^[69] While some early bird-like species may have already been arboreal as well (including dromaeosaurids such as Microraptor^[70]) most non-avialan dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, in particular, has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run,^[71] whether diplodocids could create sonic booms via whip-like tail snapping,^[72] and whether sauropods could float.^[73]

Communication[link]

Artists impression of a striking and unusual visual display in a Lambeosaurus magnicristatus

Modern birds are well known for communicating using primarily visual and auditory signals, and the wide diversity of visual display structures among fossil dinosaur groups suggests that visual communication has always been important to dinosaur biology. However, the evolution of dinosaur vocalization is less certain. In 2008, paleontologist Phil Senter examined the evidence for vocalization in Mesozoic animal life, including dinosaurs.^[74] Senter found that, contrary to popular depictions of roaring dinosaurs in motion pictures, it is likely that most Mesozoic dinosaurs were not capable of creating any vocalizations (though the hollow crests of the lambeosaurines could have functioned as resonance chambers used for a wide range of vocalizations).^[75][76] To draw this conclusion, Senter studied the distribution of vocal organs in modern reptiles and birds. He found that vocal cords in the larynx probably evolved multiple times among reptiles, including crocodilians, which are able to produce guttural roars. Birds, on the other hand, lack a larynx. Instead, bird calls are produced by the syrinx, a vocal organ found only in birds, and which is not related to the larynx, meaning it evolved independently from the vocal organs in reptiles. The syrinx depends on the air sac system in birds to function; specifically, it requires the presence of a clavicular air sac near the wishbone or collar bone. This air sac leaves distinctive marks or opening on the bones, including a distinct opening in the upper arm bone (humerus). While extensive air sac systems are a unique characteristic of saurischian dinosaurs, the clavicular air sac necessary to vocalize does not appear in the fossil record until the enantiornithines (one exception, Aerosteon, probably evolved its clavicular air sac independently of birds for reasons other than vocalization).^[74]

The most primitive dinosaurs with evidence of a vocalizing syrinx are the enantironithine birds. Any bird-line archosaurs more primitive than this probably did not make vocal calls. Rather, several lines of evidence suggest that early dinosaurs used primarily visual communication, in the form of distinctive-looking (and possibly brightly colored) horns, frills, crests, sails and feathers. This is similar to some modern reptile groups such as lizards, in which many forms are largely silent (though like dinosaurs they possess well-developed senses of hearing) but use complex coloration and display behaviors to communicate.^[74]

In addition, dinosaurs use other methods of producing sound for communication. Other animals, including other reptiles, use a wide variety of non-vocal sound communication, including hissing, jaw grinding or clapping, use of environment (such as splashing), and wing beating (possible in winged maniraptoran dinosaurs).^[74]

Reproductive biology[link]

Nest of a plover (Charadrius).

All dinosaurs lay amniotic eggs with hard shells made mostly of calcium carbonate.^{[citation needed]} Eggs are usually laid in a nest. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows.^[77] Some species of modern bird have no nests; the cliff-nesting Common Guillemot lays its eggs on bare rock, and male Emperor Penguins keep eggs between their body and feet. Primitive birds and many non-avialan dinosaurs often lay eggs in communal nests, with males primarily incubating the eggs. While modern birds have only one functional oviduct and lay one egg at a time, more primitive birds and dinosaurs had two oviducts, like crocodiles. Some non-avialan dinosaurs, such as Troodon, exhibited iterative laying, where the adult might lay a pair of eggs every one or two days, and then ensured simultaneous hatching by delaying brooding until all eggs were laid.^[78]

When laying eggs, females grow a special type of bone between the hard outer bone and the marrow of their limbs. This medullary bone, which is rich in calcium, is used to make eggshells. A discovery of features in a Tyrannosaurus rex skeleton provided evidence of medullary bone in extinct dinosaurs and, for the first time, allowed paleontologists to establish the sex of a fossil dinosaur specimen. Further research has found medullary bone in the theropod Allosaurus and the ornithopod Tenontosaurus. Because the line of dinosaurs that includes Allosaurus and Tyrannosaurus diverged from the line that led to Tenontosaurus very early in the evolution of dinosaurs, this suggests that dinosaurs in general produced medullary tissue.^[79]

Fossilized egg of the oviraptorid Citipati, American Museum of Natural History

Another widespread trait among modern birds is parental care for young after hatching. Jack Horner's 1978 discovery of a Maiasaura ("good mother lizard") nesting ground in Montana demonstrated that parental care continued long after birth among ornithopods, suggesting this behavior might have been common to all dinosaurs.^[80] There is also evidence that other non-theropod dinosaurs, like Patagonian titanosaurian sauropods (1997 discovery), also nested in large groups.^[81] A specimen of the Mongolian oviraptorid Citipati osmolskae was discovered in a chicken-like brooding position in 1993, which indicates that they had begun using an insulating layer of feathers to keep the eggs warm.^[82] Parental care being a trait common to all dinosaurs is supported by other finds. For example, the fossilized remains of a grouping of Psittacosaurus has been found, consisting of one adult and 34 juveniles; in this case, the large number of juveniles may be due to communal nesting.^[83] Additionally, a dinosaur embryo (pertaining to the prosauropod Massospondylus) was found without teeth, indicating that some parental care was required to feed the young dinosaurs.^[84] Trackways have also confirmed parental behavior among ornithopods from the Isle of Skye in northwestern Scotland.^[85] Nests and eggs have been found for most major groups of dinosaurs, and it appears likely that all dinosaurs cared for their young to some extent either before or shortly after hatching.

Waste[link]

Like other reptiles, dinosaurs are primarily uricotelic, that is, their kidneys extract nitrogenous wastes from their bloodstream and excrete it as uric acid instead of urea or ammonia via the ureters into the intestine. In most living species, uric acid is excreted along with feces as a semisolid waste.^[86][87][88] However, at least some modern birds (such as hummingbirds) can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia.^[89] They also excrete creatine, rather than creatinine like mammals. This material, as well as the output of the intestines, emerges from the cloaca.^[90][91] In addition, many species regurgitate pellets, and fossil pellets that may have come from dinosaurs are known from as long ago as the Cretaceous period.^[92]

Physiology[link]

Comparison between the air sacs of an abelisaur and a bird

Because both modern crocodilians and birds have four-chambered hearts (albeit modified in crocodilians), it is likely that this is a trait shared by all archosaurs, including all dinosaurs.^[93] While all modern birds have high metabolisms and are "warm blooded" (endothermic), a vigorous debate has been ongoing since the 1960s regarding how far back in the dinosaur lineage this trait extends. Originally, scientists broadly disagreed as to whether non-avian dinosaurs or even early birds were capable of regulating their body temperatures at all. More recently, endothermy for all dinosaurs has become the consensus view, and debate has focused on the mechanisms of temperature regulation.

After non-avian dinosaurs were discovered, paleontologists first posited that they were ectothermic. This supposed "cold-bloodedness" was used to imply that the ancient dinosaurs were relatively slow, sluggish organisms, even though many modern reptiles are fast and light-footed despite relying on external sources of heat to regulate their body temperature. The idea of dinosaurs as ectothermic and sluggish remained a prevalent view until Robert T. "Bob" Bakker, an early proponent of dinosaur endothermy, published an influential paper on the topic in 1968.^[94]

Modern evidence indicates that even non-avian dinosaurs and birds thrived in cooler temperate climates, and that at least some early species must have regulated their body temperature by internal biological means (aided by the animals' bulk in large species and feathers or other body coverings in smaller species). Evidence of endothermy in Mesozoic dinosaurs includes the discovery of polar dinosaurs in Australia and Antarctica (where they would have experienced a cold, dark six-month winter), and analysis of blood-vessel structures within fossil bones that are typical of endotherms. Scientific debate continues regarding the specific ways in which dinosaur temperature regulation evolved.^[95]

In the saurischian dinosaurs, higher metabolisms may have been supported by the evolution of a bird-like repiratory system characterized by an extensive system of air sacs that extended the lungs and invaded many of the bones in the skeleton, making them hollow.^[96]

Early dinosaurian respiratory systems with air sacs may have been capable of sustaining higher activity levels than mammals of similar size and build can sustain. In addition to providing a very efficient supply of oxygen, the rapid airflow would have been an effective cooling mechanism, which is essential for animals that are active but too large to get rid of all the excess heat through their skin.^[97]

Origin of birds[link]

The possibility that dinosaurs were the ancestors of birds was first suggested in 1868 by Thomas Henry Huxley.^[98] After the work of Gerhard Heilmann in the early 20th century, the theory of birds as dinosaur descendants was abandoned in favor of the idea of their being descendants of generalized thecodonts, with the key piece of evidence being the supposed lack of clavicles in dinosaurs.^[99] However, as later discoveries showed, clavicles (or a single fused wishbone, which derived from separate clavicles) were not actually absent;^[13] they had been found as early as 1924 in Oviraptor, but misidentified as an interclavicle.^[100] In the 1970s, John Ostrom revived the dinosaur–bird theory,^[101] which gained momentum in the coming decades with the advent of cladistic analysis,^[102] and a great increase in the discovery of small theropods and early birds.^[21] Of particular note have been the fossils of the Yixian Formation, where a variety of theropods and early birds have been found, often with feathers of some type.^[13] Birds share over a hundred distinct anatomical features with theropod dinosaurs, which are now generally accepted to have been their closest ancient relatives.^[103] They are most closely allied with maniraptoran coelurosaurs.^[13] A minority of scientists, most notably Alan Feduccia and Larry Martin, have proposed other evolutionary paths, including revised versions of Heilmann's basal archosaur proposal,^[104] or that maniraptoran theropods are the ancestors of birds but themselves are not dinosaurs, only convergent with dinosaurs.^[105]

Feathers[link]

The famous Berlin Specimen of Archaeopteryx lithographica

Archaeopteryx was the first fossil found which revealed a potential connection between dinosaurs and birds. It is considered a transitional fossil, in that it displays features of both groups. Brought to light just two years after Darwin's seminal The Origin of Species, its discovery spurred the nascent debate between proponents of evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, at least one specimen was mistaken for Compsognathus.^[106]

Since the 1990s, a number of additional feathered dinosaurs have been found, providing even stronger evidence of the close relationship between dinosaurs and modern birds. Most of these specimens were unearthed in the lagerstätte of the Yixian Formation, Liaoning, northeastern China, which was part of an island continent during the Cretaceous. Though feathers have been found in only a few locations, it is possible that non-avian dinosaurs elsewhere in the world were also feathered. The lack of widespread fossil evidence for feathered non-avian dinosaurs may be because delicate features like skin and feathers are not often preserved by fossilization and thus are absent from the fossil record. To this point, protofeathers (thin, filament-like structures) are known from dinosaurs at the base of Coelurosauria, such as compsognathids like Sinosauropteryx and tyrannosauroids (Dilong),^[107] but barbed feathers are known only among the coelurosaur subgroup Maniraptora, which includes oviraptorosaurs, troodontids, dromaeosaurids, and birds.^[13][108] The description of feathered dinosaurs has not been without controversy; perhaps the most vocal critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that protofeathers are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' integument,^{[109][110][111]} and that maniraptoran dinosaurs with barbed feathers were not actually dinosaurs, but convergent with dinosaurs.^[105][110] However, their views have for the most part not been accepted by other researchers, to the point that the question of the scientific nature of Feduccia's proposals has been raised.^[112]

Skeleton[link]

Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the multiple skeletal features also shared by the two groups represent another important line of evidence for paleontologists. Areas of the skeleton with important similarities include the neck, pubis, wrist (semi-lunate carpal), arm and pectoral girdle, furcula (wishbone), and breast bone. Comparison of bird and dinosaur skeletons through cladistic analysis strengthens the case for the link.

Soft anatomy[link]

Pneumatopores on the left ilium of Aerosteon riocoloradensis

Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to an investigation which was led by Patrick O'Connor of Ohio University. The lungs of theropod dinosaurs (carnivores that walked on two legs and had bird-like feet) likely pumped air into hollow sacs in their skeletons, as is the case in birds. "What was once formally considered unique to birds was present in some form in the ancestors of birds", O'Connor said.^[113] In a 2008 paper published in the online journal PLoS ONE, scientists described Aerosteon riocoloradensis, the skeleton of which supplies the strongest evidence to date of a dinosaur with a bird-like breathing system. CT-scanning of Aerosteon's fossil bones revealed evidence for the existence of air sacs within the animal's body cavity.^[114][115]

Behavioral evidence[link]

Fossils of the troodonts Mei and Sinornithoides demonstrate that some dinosaurs slept with their heads tucked under their arms.^[116] This behavior, which may have helped to keep the head warm, is also characteristic of modern birds. Several deinonychosaur and oviraptorosaur specimens have also been found preserved on top of their nests, likely brooding in a bird-like manner.^[117] The ratio between egg volume and body mass of adults among these dinosaurs suggest that the eggs were primarily brooded by the male, and that the young were highly precocial, similar to many modern ground-dwelling birds.^[118]

Some dinosaurs are known to have used gizzard stones like modern birds. These stones are swallowed by animals to aid digestion and break down food and hard fibers once they enter the stomach. When found in association with fossils, gizzard stones are called gastroliths.^[119]

Extinction of major groups[link]

The discovery that birds are a type of dinosaur showed that dinosaurs in general are not, in fact, extinct as is commonly stated.^[120] However, all non-avian dinosaurs as well as many groups of birds did suddenly become extinct approximately 65 million years ago. Many other groups of animals also became extinct at this time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, and many groups of mammals.^[6] This mass extinction is known as the Cretaceous–Paleogene extinction event. The nature of the event that caused this mass extinction has been extensively studied since the 1970s; at present, several related theories are supported by paleontologists. Though the consensus is that an impact event was the primary cause of dinosaur extinction, some scientists cite other possible causes, or support the idea that a confluence of several factors was responsible for the sudden disappearance of dinosaurs from the fossil record.

At the peak of the Mesozoic, there were no polar ice caps, and sea levels are estimated to have been from 100 to 250 meters (300 to 800 ft) higher than they are today. The planet's temperature was also much more uniform, with only 25 °C (45 °F) separating average polar temperatures from those at the equator. On average, atmospheric temperatures were also much higher; the poles, for example, were 50 °C (90 °F) warmer than today.^[121][122]

The atmosphere's composition during the Mesozoic is a matter for debate. While some academics argue that oxygen levels were much higher than today, others argue that biological adaptations seen in birds and dinosaurs indicate that respiratory systems evolved beyond what would be necessary if oxygen levels were high.^[123] By the late Cretaceous, the environment was changing dramatically. Volcanic activity was decreasing, which led to a cooling trend as levels of atmospheric carbon dioxide dropped. Oxygen levels in the atmosphere also started to fluctuate and would ultimately fall considerably. Some scientists hypothesize that climate change, combined with lower oxygen levels, might have led directly to the demise of many species. If the dinosaurs had respiratory systems similar to those commonly found in modern birds, it may have been particularly difficult for them to cope with reduced respiratory efficiency, given the enormous oxygen demands of their very large bodies.^[6]

Impact event[link]

The Chicxulub Crater at the tip of the Yucatán Peninsula; the impactor that formed this crater may have caused the dinosaur extinction.

The asteroid collision theory, which was brought to wide attention in 1980 by Walter Alvarez and colleagues, links the extinction event at the end of the Cretaceous period to a bolide impact approximately 65.5 million years ago. Alvarez et al. proposed that a sudden increase in iridium levels, recorded around the world in the period's rock stratum, was direct evidence of the impact.^[124] The bulk of the evidence now suggests that a bolide 5 to 15 kilometers (3 to 9 mi) wide hit in the vicinity of the Yucatán Peninsula (in southeastern Mexico), creating the approximately 180 km (110 mi) Chicxulub Crater and triggering the mass extinction.^[125][126] Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth's atmospheric temperature, while others claim that it would have instead created an unusual heat wave. The consensus among scientists who support this theory is that the impact caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun). Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid, being down to hours rather than years.^[127]

In September 2007, U.S. researchers led by William Bottke of the Southwest Research Institute in Boulder, Colorado, and Czech scientists used computer simulations to identify the probable source of the Chicxulub impact. They calculated a 90% probability that a asteroid named Baptistina, approximately 160 km (99 mi) in diameter, orbiting in the asteroid belt which lies between Mars and Jupiter, was struck by a smaller unnamed asteroid about 55 km (35 mi) in diameter about 160 million years ago. The impact shattered Baptistina, creating a cluster which still exists today as the Baptistina family. Calculations indicate that some of the fragments were sent hurtling into earth-crossing orbits, one of which was the 10 km (6.2 mi) wide meteorite which struck Mexico's Yucatan peninsula 65 million years ago, creating the Chicxulub crater.^[128] In 2011, new data from the Wide-field Infrared Survey Explorer revised the date of the collision which created the Baptistina family to about 80 million years ago. This makes an asteroid from this family highly improbable to be the asteroid that created the Chicxulub Crater, as typically the process of resonance and collision of an asteroid takes many tens of millions of years.^[129]

A similar but more controversial explanation proposes that "passages of the [hypothetical] solar companion star Nemesis through the Oort comet cloud would trigger comet showers."^[130] One or more of these comets then collided with the Earth at approximately the same time, causing the worldwide extinction. As with the impact of a single asteroid, the end result of this comet bombardment would have been a sudden drop in global temperatures, followed by a protracted cool period.^[130]

Deccan Traps[link]

Before 2000, arguments that the Deccan Traps flood basalts caused the extinction were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68 million years ago and lasted for over 2 million years. However, there is evidence that two thirds of the Deccan Traps were created in only 1 million years about 65.5 million years ago, and so these eruptions would have caused a fairly rapid extinction, possibly over a period of thousands of years, but still longer than would be expected from a single impact event.^[131][132]

The Deccan Traps could have caused extinction through several mechanisms, including the release into the air of dust and sulphuric aerosols, which might have blocked sunlight and thereby reduced photosynthesis in plants. In addition, Deccan Trap volcanism might have resulted in carbon dioxide emissions, which would have increased the greenhouse effect when the dust and aerosols cleared from the atmosphere.^[132] Before the mass extinction of the dinosaurs, the release of volcanic gases during the formation of the Deccan Traps "contributed to an apparently massive global warming. Some data point to an average rise in temperature of 8 °C (14 °F) in the last half million years before the impact [at Chicxulub]."^[131][132]

In the years when the Deccan Traps theory was linked to a slower extinction, Luis Alvarez (who died in 1988) replied that paleontologists were being misled by sparse data. While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim. Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as a drop in sea level and massive volcanic eruptions that produced the Indian Deccan Traps, and these may have contributed to the extinctions.^[133]

Failure to adapt to changing conditions[link]

Lloyd et al. (2008) noted that, in the Mid Cretaceous, the flowering, angiosperm plants became a major part of terrestrial ecosystems, which had previously been dominated by gymnosperms such as conifers. Dinosaur coprolite–fossilized dung–indicate that, while some ate angiosperms, most herbivorous dinosaurs ate mainly gymnosperms. Statistical analysis by Lloyd et al. concluded that, contrary to earlier studies, dinosaurs did not diversify very much in the Late Cretaceous. Lloyd et al. suggested that dinosaurs' failure to diversify as ecosystems were changing doomed them to extinction.^[134]

Possible Paleocene survivors[link]

Non-avian dinosaur remains are occasionally found above the Cretaceous–Paleogene boundary. In 2001, paleontologists Zielinski and Budahn reported the discovery of a single hadrosaur leg-bone fossil in the San Juan Basin, New Mexico, and described it as evidence of Paleocene dinosaurs. The formation in which the bone was discovered has been dated to the early Paleocene epoch, approximately 64.5 million years ago. If the bone was not re-deposited into that stratum by weathering action, it would provide evidence that some dinosaur populations may have survived at least a half million years into the Cenozoic Era.^[135] Other evidence includes the finding of dinosaur remains in the Hell Creek Formation up to 1.3 meters (51 in) above (40000 years later than) the Cretaceous–Paleogene boundary. Similar reports have come from other parts of the world, including China.^[136] Many scientists, however, dismissed the supposed Paleocene dinosaurs as re-worked, that is, washed out of their original locations and then re-buried in much later sediments.^[137][138] However, direct dating of the bones themselves has supported the later date, with U–Pb dating methods resulting in a precise age of 64.8 ± 0.9 million years ago.^[139] If correct, the presence of a handful of dinosaurs in the early Paleocene would not change the underlying facts of the extinction.^[137]

History of study[link]

Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese, whose modern word for dinosaur is konglong (恐龍, or "terrible dragon"), considered them to be dragon bones and documented them as such. For example, Hua Yang Guo Zhi, a book written by Zhang Qu during the Western Jin Dynasty, reported the discovery of dragon bones at Wucheng in Sichuan Province.^[140] Villagers in central China have long unearthed fossilized "dragon bones" for use in traditional medicines, a practice that continues today.^[141] In Europe, dinosaur fossils were generally believed to be the remains of giants and other creatures killed by the Great Flood.

Marsh's 1896 illustration of the bones of Stegosaurus, a dinosaur he described and named in 1877.

Scholarly descriptions of what would now be recognized as dinosaur bones first appeared in the late 17th century in England. Part of a bone, now known to have been the femur of a Megalosaurus,^[142] was recovered from a limestone quarry at Cornwell near Chipping Norton, Oxfordshire, England, in 1676. The fragment was sent to Robert Plot, Professor of Chemistry at the University of Oxford and first curator of the Ashmolean Museum, who published a description in his Natural History of Oxfordshire in 1677. He correctly identified the bone as the lower extremity of the femur of a large animal, and recognized that it was too large to belong to any known species. He therefore concluded it to be the thigh bone of a giant human similar to those mentioned in the Bible. In 1699, Edward Lhuyd, a friend of Sir Isaac Newton, was responsible for the first published scientific treatment of what would now be recognized as a dinosaur when he described and named a sauropod tooth, "Rutellum implicatum",^[143][144] that had been found in Caswell, near Witney, Oxfordshire.^[145]

William Buckland

Between 1815 and 1824, the Rev William Buckland, a professor of geology at Oxford University, collected more fossilized bones of Megalosaurus and became the first person to describe a dinosaur in a scientific journal.^[142][146] The second dinosaur genus to be identified, Iguanodon, was discovered in 1822 by Mary Ann Mantell – the wife of English geologist Gideon Mantell. Gideon Mantell recognized similarities between his fossils and the bones of modern iguanas. He published his findings in 1825.^[147][148]

The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in 1842 the English paleontologist Richard Owen coined the term "dinosaur". He recognized that the remains that had been found so far, Iguanodon, Megalosaurus and Hylaeosaurus, shared a number of distinctive features, and so decided to present them as a distinct taxonomic group. With the backing of Prince Albert of Saxe-Coburg-Gotha, the husband of Queen Victoria, Owen established the Natural History Museum in South Kensington, London, to display the national collection of dinosaur fossils and other biological and geological exhibits.

In 1858, the first known American dinosaur was discovered, in marl pits in the small town of Haddonfield, New Jersey (although fossils had been found before, their nature had not been correctly discerned). The creature was named Hadrosaurus foulkii. It was an extremely important find: Hadrosaurus was one of the first nearly complete dinosaur skeletons found (the first was in 1834, in Maidstone, Kent, England), and it was clearly a bipedal creature. This was a revolutionary discovery as, until that point, most scientists had believed dinosaurs walked on four feet, like other lizards. Foulke's discoveries sparked a wave of dinosaur mania in the United States.

Othniel Charles Marsh, 19th century photograph

Edward Drinker Cope, 19th century photograph

Dinosaur mania was exemplified by the fierce rivalry between Edward Drinker Cope and Othniel Charles Marsh, both of whom raced to be the first to find new dinosaurs in what came to be known as the Bone Wars. The feud probably originated when Marsh publicly pointed out that Cope's reconstruction of an Elasmosaurus skeleton was flawed: Cope had inadvertently placed the plesiosaur's head at what should have been the animal's tail end. The fight between the two scientists lasted for over 30 years, ending in 1897 when Cope died after spending his entire fortune on the dinosaur hunt. Marsh 'won' the contest primarily because he was better funded through a relationship with the US Geological Survey. Unfortunately, many valuable dinosaur specimens were damaged or destroyed due to the pair's rough methods: for example, their diggers often used dynamite to unearth bones (a method modern paleontologists would find appalling). Despite their unrefined methods, the contributions of Cope and Marsh to paleontology were vast: Marsh unearthed 86 new species of dinosaur and Cope discovered 56, a total of 142 new species. Cope's collection is now at the American Museum of Natural History in New York, while Marsh's is on display at the Peabody Museum of Natural History at Yale University.^[149]

After 1897, the search for dinosaur fossils extended to every continent, including Antarctica. The first Antarctic dinosaur to be discovered, the ankylosaurid Antarctopelta oliveroi, was found on Ross Island in 1986, although it was 1994 before an Antarctic species, the theropod Cryolophosaurus ellioti, was formally named and described in a scientific journal.

Current dinosaur "hot spots" include southern South America (especially Argentina) and China. China in particular has produced many exceptional feathered dinosaur specimens due to the unique geology of its dinosaur beds, as well as an ancient arid climate particularly conducive to fossilization.

The "dinosaur renaissance"[link]

Paleontologist Robert T. Bakker with mounted skeleton of a tyrannosaurid (Gorgosaurus libratus)

The field of dinosaur research has enjoyed a surge in activity that began in the 1970s and is ongoing. This was triggered, in part, by John Ostrom's discovery of Deinonychus, an active predator that may have been warm-blooded, in marked contrast to the then-prevailing image of dinosaurs as sluggish and cold-blooded. Vertebrate paleontology has become a global science. Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including India, South America, Madagascar, Antarctica, and most significantly China (the amazingly well-preserved feathered dinosaurs in China have further consolidated the link between dinosaurs and their conjectured living descendants, modern birds). The widespread application of cladistics, which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in classifying dinosaurs. Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary fossil record.

Soft tissue and DNA[link]

One of the best examples of soft-tissue impressions in a fossil dinosaur was discovered in Petraroia, Italy. The discovery was reported in 1998, and described the specimen of a small, very young coelurosaur, Scipionyx samniticus. The fossil includes portions of the intestines, colon, liver, muscles, and windpipe of this immature dinosaur.^[42]

In the March 2005 issue of Science, the paleontologist Mary Higby Schweitzer and her team announced the discovery of flexible material resembling actual soft tissue inside a 68-million-year-old Tyrannosaurus rex leg bone from the Hell Creek Formation in Montana. After recovery, the tissue was rehydrated by the science team.^[43]

When the fossilized bone was treated over several weeks to remove mineral content from the fossilized bone-marrow cavity (a process called demineralization), Schweitzer found evidence of intact structures such as blood vessels, bone matrix, and connective tissue (bone fibers). Scrutiny under the microscope further revealed that the putative dinosaur soft tissue had retained fine structures (microstructures) even at the cellular level. The exact nature and composition of this material, and the implications of Schweitzer's discovery, are not yet clear; study and interpretation of the material is ongoing.^[43]

The successful extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions, but, upon further inspection and peer review, neither of these reports could be confirmed.^[150] However, a functional visual peptide of a theoretical dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of related modern species such as reptiles and birds.^[151] In addition, several proteins, including hemoglobin,^[152] have putatively been detected in dinosaur fossils.^[153][154]

Cultural depictions[link]

Outdated Iguanodon statues created by Benjamin Waterhouse Hawkins for the Crystal Palace Park in 1853.

By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured the popular imagination and become an enduring part of human culture. Entry of the word "dinosaur" into the common vernacular reflects the animals' cultural importance: in English, "dinosaur" is commonly used to describe anything that is impractically large, obsolete, or bound for extinction.^[155]

Public enthusiasm for dinosaurs first developed in Victorian England, where in 1854, three decades after the first scientific descriptions of dinosaur remains, the famous dinosaur sculptures were unveiled in London's Crystal Palace Park. The Crystal Palace dinosaurs proved so popular that a strong market in smaller replicas soon developed. In subsequent decades, dinosaur exhibits opened at parks and museums around the world, ensuring that successive generations would be introduced to the animals in an immersive and exciting way.^[156] Dinosaurs' enduring popularity, in its turn, has resulted in significant public funding for dinosaur science, and has frequently spurred new discoveries. In the United States, for example, the competition between museums for public attention led directly to the Bone Wars of the 1880s and 1890s, during which a pair of feuding paleontologists made enormous scientific contributions.^[157]

The popular preoccupation with dinosaurs has ensured their appearance in literature, film, and other media. Beginning in 1852 with a passing mention in Charles Dickens' Bleak House,^[158] dinosaurs have been featured in large numbers of fictional works. Sir Arthur Conan Doyle's 1912 book The Lost World, the iconic 1933 film King Kong, the 1954 Godzilla and its many sequels, the best-selling 1990 novel Jurassic Park by Michael Crichton and its 1993 film adaptation are just a few notable examples of dinosaur appearances in fiction. Authors of general-interest non-fiction works about dinosaurs, including some prominent paleontologists, have often sought to use the animals as a way to educate readers about science in general. Dinosaurs are ubiquitous in advertising; numerous companies have referenced dinosaurs in printed or televised advertisements, either in order to sell their own products or in order to characterize their rivals as slow-moving, dim-witted, or obsolete.^[159] Even fine artists have featured dinosaurs in their works.

See also[link]

Wikimedia Commons has media related to: Dinosauria

Dinosaurs portal

• Evolutionary history of life
• List of dinosaurs
• List of dinosaur-bearing rock formations
• Physiology of dinosaurs
• Prehistoric reptile

Notes and references[link]