Some Thoughts on Interspecific Mandibular Morphology in Fossil and Modern Alligator

Abstract

Alligator is diagnosed in the fossil record using discrete morphological characters. These characters are used with systematic analyses to determine hypothetical phylogenetic relationships. Examined here are two such characters for applicability in fossil species determination and relationship. One is the curvature of the dentary between the fourth and tenth alveoli (observed in several taxa), while the other is a further investigation into the anterior extent of the splenial (in modern Alligator mississippiensis and the early Pleistocene A. hailensis). In a small sample size, the curvature of the dentary exhibits wide variability in character states both intraspecifically and interspecifically, bringing into question its utility in fossil crocodylian systematic applications. The anatomy of the anterior extent of the splenial is phylogenetically informative, and a new method for inferring its presence as a basal or derived state (as a scar on the dentary) is described.