Saurischia — the lizard-hipped dinosaurs that dominated 230 million years

When and where

Saurischia appeared around 233 million years ago in the Late Triassic. The earliest fossils come from the Ischigualasto Formation in Argentina. From there the clade spread across every continent, including Antarctica. Saurischians survived the Triassic-Jurassic extinction 201 million years ago and dominated until the end-Cretaceous event 66 million years ago.

How we know

British paleontologist Harry Seeley divided dinosaurs into Saurischia and Ornithischia in 1888 based on pelvic anatomy. The saurischian pelvis points the pubis bone forward and downward, like living lizards and crocodiles. The group splits into two major lineages: the long-necked Sauropodomorpha and the carnivorous Theropoda. In 2017, a large-scale phylogenetic analysis by Baron and colleagues challenged this classic split, but the traditional definition remains in wide use. Complete skeletons of early sauropodomorphs such as Plateosaurus and early theropods such as Eoraptor have anchored the clade in the fossil record.

Source: https://en.wikipedia.org/wiki/Saurischia

What set it apart

The hip is the giveaway. In saurischians the pubis points downward and forward, while the ischium points backward. This lizard-hipped design contrasts with the bird-hipped Ornithischia, in which the pubis runs parallel to the ischium. The clade includes the largest land animals ever — Argentinosaurus, a sauropodomorph, reached 30 metres and perhaps 70 tonnes — and the most famous carnivores, including Tyrannosaurus rex and Velociraptor. Feathers evolved within theropod saurischians, making birds the last living saurischians.

For collectors and classrooms

A saurischian figure offers a gateway to the full span of dinosaur history. Models of early theropods such as Eoraptor or classic sauropods such as Brachiosaurus illustrate the two great branches that emerged from this single clade. Use them to teach pelvic anatomy, evolutionary branching, or the sheer scale of life on land.

Pick up a detailed Eoraptor figure here.