Saurischia

Saurischians Temporal range: Late Triassic – Present, 233.23–0 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N Possible Middle Triassic record[2]
Montage of six different representatives of saurischian dinosaurs. 1st row (early saurischians): Herrerasaurus ischigualastensis (herrerasaur), Eodromaeus murphi (basal theropod); 2nd row (theropods): Pelecanus occidentalis, Tyrannosaurus rex; 3rd row (sauropodomorphs): Apatosaurus louisae, Plateosaurus engelhardti.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia Seeley, 1888
Subgroups
†Herrerasauria? Caseosaurus? Chindesaurus? Daemonosaurus? Tawa? Herrerasauridae Eusaurischia †Sauropodomorpha Theropoda Saurischians of uncertain affinity †Alwalkeria †Chindesaurus †Daemonosaurus †Eodromaeus †Saltopus? †Tawa

Saurischia is one of the two main groups of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders,^[3] which are now generally considered unranked clades. Their hip structure was why they were put into these groups. Saurischians ('lizard-hipped') and the ornithischians ('bird-hipped') have differences in the ways bones in the hip are put together.^[4]

The saurischian pubic bones primarily pointed backward, while the ornithischian pubic bones pointed forward. Despite this pattern, the pubic bones of several saurschians, including herrerasaurids,^[5] therizinosauroids,^[6] dromaeosaurids,^[7] and birds,^[8] point forward. It's important consider than the etymology of names Saurischia and Ornithischia does not reflect the evolutionary relationships of these groups. Ornithischians were called 'bird-hipped' because their hips are similar to those of birds, but birds themselves evolved from 'lizard-hipped' saurischians.^[9]

Saurischia includes two main subgroups: Theropoda and Sauropodomorpha. Theropods are represented by bipedal, primarily carnivorous dinosaurs (such as Tyrannosaurus and Velociraptor). Birds are theropods and the only group of dinosaurs that has survive to the present day. Early sauropodomorphs were similar to early theropods because they shared a common ancestor. However, the most diverse group of sauropodomorphs, Sauropoda, was represented by long-necked herbivorous dinosaurs that often reached gigantic sizes (such as Diplodocus and Brachiosaurus).^[4]

1. ↑ Langer, M.C.; Ramezani, J.; Da Rosa, Á.A.S. (2018). "U-Pb age constraints on dinosaur rise from south Brazil". Gondwana Research. X (18): 133–140. Bibcode:2018GondR..57..133L. doi:10.1016/j.gr.2018.01.005.
2. ↑ Nesbitt, S. J.; Barrett, P. M.; Werning, S.; Sidor, C. A.; Charig, A. J. (2013). "The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania". Biol. Lett. 9 (1): 20120949. doi:10.1098/rsbl.2012.0949. PMC 3565515. PMID 23221875.
3. ↑ Seeley, H.G. (1888). "On the classification of the fossil animals commonly named Dinosauria." Proceedings of the Royal Society of London, 43: 165-171.
4. ↑ ^{4.0 4.1} Weishampel, Dodson & Osmólska 2004, pp. 21–24, "Saurischia" by Thomas R. Holtz Jr. and Halszka Osmólska.
5. ↑ Paul, Gregory S. (1988). Predatory Dinosaurs of the World: A Complete Illustrated Guide. New York: Simon & Schuster. pp. 248–250. ISBN 978-0-671-61946-6. LCCN 88023052. OCLC 859819093.
6. ↑ Weishampel, Dodson & Osmólska 2004, pp. 151–164, chpt. 7: "Therizinosauroidea" by James M. Clark, Teresa Maryańska, and Rinchen Barsbold.
7. ↑ Weishampel, Dodson & Osmólska 2004, pp. 196–210, chpt. 10: "Dromaeosauridae" by Peter J. Makovicky and Mark A. Norell.
8. ↑ Weishampel, Dodson & Osmólska 2004, pp. 210–231, chpt. 11: "Basal Avialae" by Kevin Padian.
9. ↑ Brusatte, Stephen L. (2012). Dinosaur Paleobiology. New York: Wiley, J. pp. 20–21. ISBN 978-0-470-65658-7.