CONSTRAINING VARIANCE IN DINOSAUR GROWTH STUDIES

Histologically based growth studies of fossil vertebrates are becoming more common as improved sampling techniques reduce damage and interest within the paleontological community increases. Dinosaur studies in particular have received much attention both in scientific and popular presses. However, the small sample sizes common in dinosaur paleobiology often mean that the taxa under investigation are poorly sampled in number, across ontogeny and phylogeny, and over a geographic range. As a result, growth curves are calculated and compared without an understanding of the histological and ontogenetic variability that may be expected within Dinosauria. Estimates of variation can be quantified within and among individuals, populations and species if sampling is high enough. The clade Ornithopoda includes several taxa that are known from multiple ontogenetic series and are well-sampled over broad (paleo)geographic ranges. One member of this clade that meets these criteria is the Aptian-Albian basal iguanodontian, Tenontosaurus tilletti Ostrom 1970. Using this taxon, I examined and quantified variation among skeletal elements of the same individual, within and between populations from Oklahoma and Wyoming/Montana, and within the species itself. I interpret observed levels of variation in light of several factors known to affect ontogenetic rates in modern vertebrates, and compare these data with published growth studies for other Dinosaurian taxa. T. tilletti is a model system with which to estimate expected variation in histologically based growth studies, and on-going work to extend this study to other ornithopodans will enable me to investigate patterns of variation across the ornithopod phylogeny through geologic time.