Scientific Publications from the Virginia Museum of Natural History
by George E. Bennett, III
published 8 June 2012
Modern crocodilian populations display a distinct attritional age class frequency distribution, with each age class corresponding roughly to size. Hatchlings constitute the largest age class, with each successive age class containing fewer individuals. This pattern reflects the continuous growth and natural mortality rate in crocodilians.
Screen washing of microvertebrate localities in the upper Hell Creek Formation of eastern Montana has produced several hundred shed crocodyliform teeth. Two dominant species of Hell Creek crocodyliforms, Borealosuchus sternbergii and Brachychampsa montana, possess indistinguishable anterior teeth and have been combined in this study. The sample of shed teeth represents a temporally averaged and spatially constrained assemblage, whereby the effects of stochastic events that affected hatching rates in the original populations during a single season are muted.
Using a modeled population and measured tooth replacement rates through ontogeny of the extant Alligator mississippiensis, it was found that both the extant and extinct crocodyliforms studied shed proportionally similar numbers of teeth in each size category into the environment. Results indicate that: (1) the size and age structures of ancient and extant crocodyliform communities are similar; (2) microvertebrate localities in channel sands are size-sorted and should be used with caution in studies of population demographics; and (3) using unbiased collecting techniques, the community structures of other extinct vertebrates that lack modern analogues can be established.