Browsing by Author "Voris, Jared Thomas"

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    A new tyrannosaurine (Theropoda:Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids
    (Cretaceous Research (Elsevier), 2020-01-23) Voris, Jared Thomas; Therrien, Francois; Zelenitsky, Darla Karen; Brown, Caleb Marshall
    Upper Cretaceous tyrannosauroid material from North America was primarily known from upper Campanian through Maastrichtian formations until the recent discovery of derived tyrannosaurid taxa from lower-to-mid Campanian deposits in the southwestern United States. However, diagnostic material from contemporaneous deposits further north in Alberta (Canada) and Montana (USA) has yet to be documented. Here we report the discovery of a new tyrannosaurine tyrannosaurid from the mid- Campanian Foremost Formation of Alberta, Thanatotheristes degrootorum gen. et. sp. nov, which helps fill this gap. The new tyrannosaurine, diagnosed by five autapomorphies, is found to be the sister taxon to the late Campanian genus Daspletosaurus. Thanatotheristes is distinct from Daspletosaurus based on several features, and lacks at least two apomorphies of the latter taxon. Together, these taxa form the newly established Daspletosaurini, a clade of long-, deep-snouted tyrannosaurines endemic to northern Laramidia during the Campanian. Our study demonstrates that Tyrannosauridae is composed of several geographically-segregated clades rather than a series of monogeneric successive sister taxa as recovered by previous studies. The geographic segregation of tyrannosaurid clades within North America provides renewed evidence for provinciality among large theropods during the Late Cretaceous.
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    Mandibular force profiles and tooth morphology in growth series of Albertosaurus sarcophagus and Gorgosaurus libratus (Tyrannosauridae: Albertosaurinae) provide evidence for an ontogenetic dietary shift in tyrannosaurids
    (Canadian Journal of Earth Sciences (Canadian Science Publishing), 2021-01-26) Therrien, Francois; Zelenitsky, Darla Karen; Voris, Jared Thomas; Tanaka, Kohei
    The albertosaurines Albertosaurus sarcophagus and Gorgosaurus libratus are among the best represented tyrannosaurids, known from nearly complete growth series. These specimens provide an opportunity to study mandibular biomechanical properties and tooth morphology to infer changes in feeding behaviour and bite force through ontogeny in tyrannosaurids. Mandibular force profiles reveal that the symphyseal region of albertosaurines is consistently stronger in bending than the mid-dentary region, indicating that the anterior extremity of the jaws played an important role in prey capture and handling through ontogeny. The symphyseal region was better adapted to withstand torsional stresses than in most non-avian theropods, but not to the extent seen in Tyrannosaurus rex, suggesting that albertosaurine feeding behaviour may have involved less bone crushing or perhaps relatively smaller prey than in Tyrannosaurus rex. The constancy of these biomechanical properties at all known growth stages indicates that although albertosaurines maintained a similar feeding strategy through ontogeny, prey size/type had to change between juvenile and mature individuals. This ontogenetic dietary shift likely happened when individuals reached a mandibular length of ∼58 cm, a size at which teeth shift from ziphodont to incrassate in shape and bite force begins to increase exponentially. The fact that large albertosaurines were capable of generating bite forces equivalent to similar-sized tyrannosaurines suggests that no significant differences in jaw-closing musculature existed between the two clades and that the powerful bite of Tyrannosaurus rex is the result of its large body size rather than of unique adaptations related to a specialized ecology.