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

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.

Isolated archosauriform teeth from the Upper Triassic Candelária Sequence (Hyperodapedon Assemblage Zone, Southern Brazil)

“…Zinke, 1998;Smith & Dodson, 2003;Larson & Currie, 2013); • Analysis of denticle shapes (square, rectangular or subquadrangular); • Shape of the basal cross section (leaf shape or oval shape); • Crown base width (CBW), roughly similar to the tooth basal width (BW) of some authors (e.g. Zinke, 1998;Smith & Dodson, 2003;Larson & Currie, 2013); • Extension of the area without denticles, if present (both in the apical and basal portions); • Presence or absence of enamel wrinkles; • Symmetry; • Size of the grooves present in denticles;…”

“…This is particularly the case for teeth, which compose a substantial portion of the fossil record of vertebrates (e.g. Rauhut & Werner, 1995;Zinke, 1998;Heckert, 2004;Larson & Currie, 2013;Sues & Averianov, 2013;Hendrickx et al, 2015). In areas where other osteological elements are rare or absent, the dental record may provide important information about the faunal composition of a locality.…”

A new species of troodontid theropod (Dinosauria: Maniraptora) from the Horseshoe Canyon Formation (Maastrichtian) of Alberta, Canada

“…Little skeletal material has been described, and skull material is particularly rare (Carpenter 1982;Fiorillo et al 2009;Makovicky and Norell 2004;Russell 1969;Zanno et al 2011), hindering assessments for taxonomic diversity in the group. Despite this, isolated troodontid teeth are relatively common through the Campanian and Maastrichtian of western North America (Cullen and Evans 2016;Larson et al 2016;Larson and Currie 2013). Historically, the genus Troodon has been reported to occur throughout the Campanian and Maastrichtian, and across most of western North America , based on referrals of isolated teeth and the few, and generally fragmentary, available fossils (Zanno et al 2011).…”

“…In a subsequent morphometric study of isolated small theropod teeth from the latest Cretaceous of western North America, Larson and Currie (2013) also concluded that their diversity is underestimated, and that T. formosus sensu stricto is only definitively known from the Judith River and Dinosaur Park formations, implying teeth from other units may represent distinct taxa.…”

“…Larson and Currie 2013). Previous reports include two troodontid braincases referred to Troodon formosus from the Prince Creek Formation of Alaska (Fiorillo 2008;Fiorillo et al 2009), and a perinate dentary and basioccipital from the Lance Formation (Carpenter 1982).…”