Classifying Dinosaurs

Pelvis Shape

The pelvis (hip bones) of dinosaurs comes in two different shapes.

• Those where the pubis bone points forward and down
• Those where the pubis bone points in the same direction as the spine and ischium

The group with the pubis pointing forward and down is called Saurischia.
They have a pelvis shape very similar to reptiles like lizards.

It is believed that Saurischia diverged at an early stage into a primarily carnivorous group (Theropoda) and a primarily herbivorous group (Sauropodomorpha).

In contrast, the group where the pubis points in the same direction as the spine and ischium is called Ornithischia. They have a bird-like pelvis shape.

While some dinosaurs belonging to Saurischia evolved into birds and have descendants living today, dinosaurs belonging to Ornithischia became extinct at the end of the Cretaceous period. (It was the "Saurischian theropods" that later evolved into birds, not the "Ornithischian dinosaurs" with the similar pelvis.)

In the next section, let's classify Saurischia and Ornithischia in more detail.
Please continue to <Further Classifying Dinosaurs | Dino Tail>.