Characters and Anatomy

SKELETAL EVOLUTION

Dinosaurs all show some major modifications of the basic archosaurian skeleton.

Archosaurian skeleton
Skeleton of Postosuchus by P. Olsen, after Long and Murry (1996)

Primitive Dinosaurian Skeleton
Skeleton of Coelophysis bauri by P. Olsen, after Paul (1988)

• A long S-shaped neck
• A stronger ankle adapted for a bipedal stance
• An antorbital fenestra, an opening in the side of the skull between the nostril and eye socket
• Loss of fifth and fourth fingers in many
• An essentially three-toed foot, with the first and fifth toes reduced or lost
• An upright posture, with a deep acetabulum (the bowl-like hollow in the side of the hip) and inturned femur head (the thigh bone)
• Three or more sacral vertebrae (the vertebrae that attach to the pelvis)

THE DINOSAURIAN HIP

Top set of hips on the left is the saurischian form, the bottom set on the left is the ornithischian form. The legs are from a theropod dinosaur (From Benton (2000)). Dinosaurs are divided into two clades based upon hip structure: Saurischia and Ornithischia Saurischian ("lizard hips") dinosaurs have a hip with the pubes pointing down and foward: includes Sauropodomorpha, and Theropoda Ornithischian ("bird hips") dinosaurs have an enlarged hip girdle, and a backwards pointing pubes: includes Thyreophora, Ornithopoda, and Marginocephalia

• Major subgroups in the phylum
• Fossil record
• Modern forms
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Author: Emma Schachner
Last updated: 13 November 2004
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