Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time

Derek W Larson,Philip J Currie

doi:10.1371/journal.pone.0054329

Abstract

Isolated small theropod teeth are abundant in vertebrate microfossil assemblages, and are frequently used in studies of species diversity in ancient ecosystems. However, determining the taxonomic affinities of these teeth is problematic due to an absence of associated diagnostic skeletal material. Species such as Dromaeosaurus albertensis, Richardoestesia gilmorei, and Saurornitholestes langstoni are known from skeletal remains that have been recovered exclusively from the Dinosaur Park Formation (Campanian). It is therefore likely that teeth from different formations widely disparate in age or geographic position are not referable to these species. Tooth taxa without any associated skeletal material, such as Paronychodon lacustris and Richardoestesia isosceles, have also been identified from multiple localities of disparate ages throughout the Late Cretaceous. To address this problem, a dataset of measurements of 1183 small theropod teeth (the most specimen-rich theropod tooth dataset ever constructed) from North America ranging in age from Santonian through Maastrichtian were analyzed using multivariate statistical methods: canonical variate analysis, pairwise discriminant function analysis, and multivariate analysis of variance. The results indicate that teeth referred to the same taxon from different formations are often quantitatively distinct. In contrast, isolated teeth found in time equivalent formations are not quantitatively distinguishable from each other. These results support the hypothesis that small theropod taxa, like other dinosaurs in the Late Cretaceous, tend to be exclusive to discrete host formations. The methods outlined have great potential for future studies of isolated teeth worldwide, and may be the most useful non-destructive technique known of extracting the most data possible from isolated and fragmentary specimens. The ability to accurately assess species diversity and turnover through time based on isolated teeth will help illuminate patterns of evolution and extinction in these groups and potentially others in greater detail than has previously been thought possible without more complete skeletal material.

Highlights

Vertebrate turnover and diversity approaching the end-Cretaceous mass extinction has been the subject of many recent studies [1,2,3,4,5,6,7]
Principal measurements included fore-aft basal length (FABL), crown height (CH), basal width (BW), and posterior denticles per millimetre (PDM) or their closest approximation if different measurements were employed in the literature (Fig. 1)
The discriminant function analysis (DFA) hit ratios combined with tests of significance from the Multivariate analyses of variance (MANOVA) show that many of the qualitative morphotypes are distinct when they occur in different formations (Table 2; Fig. 4B)

Summary

Introduction

Vertebrate turnover and diversity approaching the end-Cretaceous mass extinction has been the subject of many recent studies [1,2,3,4,5,6,7] Taxa such as large-bodied dinosaurs [8,9], turtles [10,11], and amphibians, fish, mammals, and reptiles known from vertebrate microfossil localities [12,13] have good fossil records in the Upper Cretaceous leading up to the terminal Cretaceous mass extinction. In North America, Currie et al [14] examined theropod teeth from the late Campanian Dinosaur Park Formation and used associated skeletal remains to confidently identify specimens. The study was intended to include teeth from the geographically similar but younger latest Campanian Horseshoe Canyon and Maastrichtian Scollard formations

Methods

Results

Conclusion