Comparison between Reptiles and Dinosaurs to Clarify their Differences and Similarities pp. 127-140
Authors: (Ryunosuke Kikuchi, Centro de Estudos de Recursos Naturais, Ambiente e Sociedade (CERNAS), Instituto Politécnico de Coimbra, Bencanta, Coimbra, Portugal)
Abstract: There is a popular question as to whether dinosaurs and reptiles are different or similar. It seems to be a basic and interesting topic in reptile biology and paleobiology. In order to answer this question, the present chapter compares these two species. The earliest reptiles are known from the early Pennsylvanian (323–317 million years ago), and the amniote egg evolved in the earliest reptiles. This allowed for the first true occupation of the land by tetrapods. The term ―archosaur‖ had come to include crocodiles, dinosaurs, and a wide variety of primitive Triassic reptiles. The continuity of meaning is intended to prevent confusion about what the term ―dinosaur‖ means. There is a wide consensus among paleontologists that birds are the descendants of theropod dinosaurs. The skeletal structures of saurischian dinosaurs are interpreted as osteological correlates of air sacs and pneumatic diverticula similar to that of birds, but no evidence of air-sac respiration has been found in ornithischian dinosaurs. The pelvis in the saurischian dinosaurs resembles that of still-extant reptiles, but in the ornithischian dinosaurs the pubic bone of the pelvis has forward and backward extensions that resemble those found in birds. That is, it is possible to consider that modern birds are extant dinosaurs, and it is also possible to recognize dinosaurs as a group of extinct reptiles. In conclusion, it is not logical to classify all dinosaurs in a single order; therefore, two types of dinosaur should be at least distinguished by respiratory and structural differences.