Diversity and variation of theropod dinosaur teeth from the uppermost Santonian Milk River Formation (Upper Cretaceous), Alberta: a quantitative method supporting identification of the oldest dinosaur tooth assemblage in Canada

Abstract

The Santonian Deadhorse Coulee Member of the Milk River Formation preserves the oldest dinosaur body fossils found in Alberta. However, vertebrate remains consist almost exclusively of isolated elements and microvertebrate assemblages. Here, 1572 relatively complete shed non-avian theropod teeth from 20 localities in the Deadhorse Coulee Member are measured and analyzed to assess species diversity. Teeth are referred to or similar to Tyrannosaurinae indet., cf. Richardoestesia gilmorei , cf. Richardoestesia isosceles , Dromaeosauridae indet., Dromaeosaurinae indet., Velociraptorinae indet., and cf. Paronychodon lacustris . For the taxa identified, the large sample size allows for the assessment of their range of variation and accurate identification, without the benefit of comparable material of this age. Multivariate statistics, including a principal component analysis and a canonical variate analysis, provide reasonable separation of all taxa, although better results are achieved by separate analyses based on qualitative observations of denticle shape. The best results of the canonical variate analysis identified 96.0% of specimens correctly. This corroborates the qualitative identification of specimens and illustrates a valid way of evaluating diversity in areas and formations from which no described jaw material is known.

The oldest North American pachycephalosaurid and the hidden diversity of small-bodied ornithischian dinosaurs

“…Unlike mammals, the less complex and stereotyped tooth morphology in most major dinosaur groups provides poor information on a-diversity patterns at low taxonomic levels, and therefore microvertebrate assemblages likely provide little meaningful insights into the species richness of small-bodied dinosaurs. Extensive work on variation in small theropod teeth over the last three decades has allowed modest resolution of their diversity in vertebrate microfossil assemblages [51][52][53] , but the generalized foliform morphology of isolated ornithischian teeth has made inferences of taxonomic diversity in small-bodied herbivorous dinosaurs based on vertebrate microfossil assemblages much more difficult 2,54 , beyond the presence or absence of major groups 22,55 . Pachycephalosaurs likely had broadly similar ecological requirements and, with the exception of the robust frontoparietal domes, had comparable preservation potential to other groups of small-bodied ornithischian dinosaurs, including leptoceratopsids, small-bodied ornithopods and heterodontosaurs.…”

Small Theropod Teeth from the Late Cretaceous of the San Juan Basin, Northwestern New Mexico and Their Implications for Understanding Latest Cretaceous Dinosaur Evolution

“…The Milk River sample is larger than that of the Hosta Tongue (number of lateral teeth = 28) and includes teeth smaller than any reported from the Hosta Tongue (the smallest has a FABL of 4.57 mm; [23]). These have a mean FABL of 11.79 [23] and a denticle density similar to that of the Hosta Tongue sample.…”

“…Large Morphology” from the late Maastrichtian of Montana (the specimen upon which this is based, UCMP 187178 is reported to be Paleocene based upon a specimen search of the UCMP database and we conclude that it likely reworked from the underlying Hell Creek Formation) that appears to be distinct from the troodontid Pectinodon that has been reported from the late Maastrichtian Lance and Hell Creek Formations of the northern Rocky Mountain region [20], [23]. Therefore it is probable that there is more than one lineage of troodontid in the latest Cretaceous of the northern Rocky Mountain region, and that this small-bodied theropod group may have been more diverse immediately before the end-Cretaceous extinction than previous suspected.…”

On the earliest record of Cretaceous tyrannosauroids in western North America: implications for an Early Cretaceous Laurasian interchange event

“…Tyrannosauroid teeth have been identified from the Mussentuchit Member of the Cedar Mountain Formation (Cenomanian) Cifelli et al 1999), Dakota Formation (Cenomanian) and Straight Cliffs Formation (Turonian -early Campanian) Parrish 1999) of Utah and the Milk River Formation (Santonian) of Alberta (Larson 2008). These isolated tyrannosauroid remains help to fill an otherwise persistent void in the chronostratigraphic distribution of the clade in North America and thereby provide essential paleobiogeographic data.…”