Archosaur Hip Joint Evolution and Locomotor Behavior

Giraffatitan brancai in Berlin Museum für Naturkunde, Berlin.
Giraffatitan brancai in Berlin Museum für Naturkunde, Berlin.

My research seeks to virtually reconstruct the hip joint anatomy of extinct archosaurs. Archosaurs, a group of reptiles that includes extinct dinosaurs, as well as living birds and crocodilians, evolved a wide diversity of body forms throughout their long history on Earth. These include some of the most spectacular animals ever existed, such as multi-ton bipeds (theropods) and the largest animals ever to walk on land (sauropods). Even the two living representatives are vastly different in hind limb posture and behavior. Therefore, archosaurs provide a wealth of data on how evolutionary changes in posture and body size affect limb anatomy.


However, what's tricky is that archosaurs limb bones are very differently from those of us mammals. In mammals, the cartilage caps at the end of long bones reduce to a thin layer at adulthood, whereas in archosaurs, the cartilage caps tend to retain considerable thickness even at maturity. You can see this in modern crocs and birds, as well as museum display of dinosaur bones, where the bony surfaces of joints that supposedly go together have very different shapes and sizes. This also makes it complicated to study joint motion and limb function of extinct archosaurs, because the ends of fossilized bones doesn't represent the joint surface they used during life.


Anatomical reconstruction of archosaur hip joints will allow us to better understand the hindlimb mobility, load bearing ability, and locomotor behavior of extinct archosaurs. At the same time, because archosaur joints are so different from ours, my work will also be informative in general cartilage and connective tissue biology as well.

Henry P. Tsai



105A Biomedical Sciences Building

Dept. Ecology & Evolutionary Biology

Brown University

Providence, RI 02912-G


Mailing Address:

Box G-W, 80 Waterman Street

Providence, RI 02912-G