Tuesday, February 11, 2020

[Paleontology • 2020] Thanatotheristes degrootorum • A New Tyrannosaurine (Theropoda: Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides Insight Into the Evolution and Biogeography of Tyrannosaurids

Thanatotheristes degrootorum 
Voris, Therrien, Zelenitsky & Brown, 2020
Illustration: Julius Csotonyi facebook.com/JuliusCsotonyi

• A new genus of tyrannosaurid from the mid Campanian Foremost Formation of southern Alberta is described.
• The new genus is found to be the sister taxon to Daspletosaurus spp., and together form the new clade Daspletosaurini.
• Tyrannosauridae is revealed to be comprised of multiple, multigeneric clades rather than a series of monogeneric branches.
• Geographic segregation of clades provides evidence for provinciality of Tyrannosauridae within North America during the Campanian.

Late 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 tyrannosaurid from the mid-Campanian Foremost Formation of Alberta, Thanatotheristes degrootorum gen. et sp. nov., which helps fill this gap. Thanatotheristes is found to be the sister taxon to the late Campanian tyrannosaurine genus Daspletosaurus based on several synapomorphies, such as an extremely coarse subcutaneous surface of the maxilla, a constricted jugal ramus of the maxilla, a shallow angle of the anteroventral corner of the maxilla, a high tooth count, a wide prefrontal, and a dentary chin located ventral to either the third alveolus or third interdental plate. Together, these taxa provide evidence for the existence of a clade of long-, deep-snouted tyrannosaurines endemic to northern Laramidia during the Campanian. Our study demonstrates that Tyrannosauridae consists 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.

Keywords: Theropoda, Tyrannosauridae, Campanian, Evolution, Provinciality, Biogeography

Dinosauria Owen, 1842 
Theropoda Marsh, 1881 
Tetanurae Gauthier, 1986 
Coelurosauria von Huene, 1914 

Tyrannosauridae Osborn, 1906 
Tyrannosaurinae Osborn, 1906 

Daspletosaurini clade nov.  

INCLUDED TAXA: Daspletosaurus torosus Russell, 1970, Daspletosaurus horneri Carr et al., 2017, and Thanatotheristes degrootorum gen. et. sp. nov. 

Skull reconstruction of Thanatotheristes degrootorum holotype TMP 2010.5.7. Known bones appear in white. Missing bone morphologies and proportions are based on the holotype of Daspletosaurus torosus (CMN 8506). Scale bar equals 10 cm.

Thanatotheristes gen. nov. 

Thanatotheristes degrootorum gen. et sp. nov. 

ETYMOLOGY: From Thanatos, the Greek god of and embodiment of death, and theristes (Greek), one who reaps or harvests, a reaper. The specific name, degrootorum, is in honor of John and Sandra De Groot of Hays, Alberta, who discovered the holotype specimen and have been supportive of paleontological research in the area.  

 Jared T. Voris, François Therrien, Darla K. Zelenitsky and Caleb M. Brown. 2020. A New Tyrannosaurine (Theropoda: Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides Insight Into the Evolution and Biogeography of Tyrannosaurids. Cretaceous Research. In Press - 104388. DOI: 10.1016/j.cretres.2020.104388  

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