Bilateria

Megalosaurus (meaning "Great Lizard", from Greek, μεγαλο-/megalo- meaning 'big', 'tall' or 'great' and σαυρος/sauros meaning 'lizard') is a genus of large meat-eating theropod dinosaurs of the Middle Jurassic period (Bathonian stage, 166 million years ago) of Europe (Southern England, France, Portugal). It is significant as the first genus of dinosaur (outside of birds) to be described and named.

Megalosaurus may have been the first dinosaur to be described in the scientific literature. Part of a bone 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 1676. He correctly identified the bone as the lower extremity of the femur of a large animal and he 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, such as those mentioned in the Bible. The bone has since been lost but the illustration is detailed enough that some have since identified it as that of Megalosaurus.