A PRELIMINARY BIOMECHANICAL

ANALYSIS OF PHYTOSAUR LIFE HABITS

William P. Wall

Dept. of Biology, Georgia College & State University
Milledgeville, GA 31061

Adrian P. Hunt

Dept. of Geology , Univ. of Colorado at Denver
Denver, CO 80217

Vincent L. Santucci

Dept. of Parks & Recreation, Slippery Rock Univ.
Slippery Rock, PA 16057

 

Three distinctive cranial patterns are recognized in phytosaurs. Dolichorostral types have a long, narrow snout; brachyrostral taxa have a massive, relatively broad snout; and altirostral animals have an intermediate condition. Modern crocodilians exhibit a similar range in cranial diversity. Phytosaur skull patterns are linked to characteristics of the dentition. The teeth in dolichorostral species are homodont. The other two types exhibit primarily heterodont dentition, but tooth differentiation tends to be more extreme in the brachyrostral type.

Dolichorostral phytosaurs, such as Rutiodon carolinensis, were probably piscivorous. The long, narrow snout is designed to capture fast moving prey. The relatively weak homodont teeth were capable of holding and positioning fish for swallowing, but could not have produced significant shear.

"Rutiodon" gregorii is a good example of the brachyrostral pattern. We believe this animal fed on larger vertebrates. Its massive skull, jaws, and teeth could produce sufficient bite force to kill large prey. The large anterior teeth were adapted for puncturing while the medio-laterally flattened posterior teeth were used to shear the carcass into chunks suitable for swallowing (both types of teeth probably contributed to killing the prey).

Pathologic evidence indicates brachyrostral phytosaurs used their jaws in intraspecific combat. This behavior might explain the spacing between the two sets of enlarged "fangs" in these animals. The smaller teeth in the middle would have punctured the opponents snout while the larger teeth restrained it. The brachyrostral morphology probably evolved from altirostral phytosaurs which we interpret as generalist feeders (like the modern alligator). If combat was a significant selection pressure in these phytosaurs, more massive jaws would clearly have had an advantage. This selection pressure may in turn have prompted the shift to a more active predatory life style (or the two behaviors could have mutually reinforced each other).