A new microvertebrate assemblage from the Mussentuchit Member, Cedar Mountain Formation: insights into the paleobiodiversity and paleobiogeography of early Late Cretaceous ecosystems in western North America

Abstract

The vertebrate fauna of the Late Cretaceous Mussentuchit Member of the Cedar Mountain Formation has been studied for nearly three decades, yet the fossil-rich unit continues to produce new information about life in western North America approximately 97 million years ago. Here we report on the composition of the Cliffs of Insanity (COI) microvertebrate locality, a newly sampled site containing perhaps one of the densest concentrations of microvertebrate fossils yet discovered in the Mussentuchit Member. The COI locality preserves osteichthyan, lissamphibian, testudinatan, mesoeucrocodylian, dinosaurian, metatherian, and trace fossil remains and is among the most taxonomically rich microvertebrate localities in the Mussentuchit Member. To better refine taxonomic identifications of isolated theropod dinosaur teeth, we used quantitative analyses of taxonomically comprehensive databases of theropod tooth measurements, adding new data on theropod tooth morphodiversity in this poorly understood interval. We further provide the first descriptions of tyrannosauroid premaxillary teeth and document the earliest North American record of adocid remains, extending the appearance of this ancestrally Asian clade by 5 million years in western North America and supporting studies of pre-Cenomaninan Laurasian faunal exchange across Beringia. The overabundance of mesoeucrocodylian remains at the COI locality produces a comparatively low measure of relative biodiversity when compared to other microvertebrate sites in the Mussentuchit Member using both raw and subsampling methods. Much more microvertebrate research is necessary to understand the roles of changing ecology and taphonomy that may be linked to transgression of the Western Interior Seaway or microhabitat variation.

A new baenid, "Trinitichelys" maini sp. nov., and other fossil turtles from the Upper Cretaceous Arlington Archosaur Site (Woodbine Formation, Cenomanian), Texas, USA

“…may have had a minimal presence. The AAS turtle assemblage resembles those of other North American assemblages (e.g., Cloverly, Dakota, Cedar Mountain Fms), where freshwater aquatic cryptodiran forms are generally dominant among stem Testudines (Joyce et al, 2016b;Avrahami et al, 2018). We report no indication of chelonioid or deep water marine forms.…”

“…Baenidae is endemic to North America and became distinct from other Jurassic North American turtles (i.e., pleurosternids) in the Lower Cretaceous. Baenids remained restricted to North America, where they reached peak diversity after the Cenomanian, primarily along the eastern coast of Laramidia (Hutchison and Archibald, 1986;Hirayama et al, 2000;Hutchison, 2000;Joyce and Lyson, 2015;Joyce et al, 2016b;Lyson et al, 2016;Smith et al, 2017;Avrahami et al, 2018). Baenids are closely related to other primitive freshwater paracryptodires (i.e., Pleurosternidae, Compsemydidae) that ranged across Laurasia beginning in the Jurassic (Pérez-García et al, 2015;Joyce et al, 2016b).…”

The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends

“…Teeth, and particularly tooth enamel, are robust skeletal elements (Hillson, 2005), and most toothed theropods had 50 or more teeth that were replaced every one to two years (Fiorillo and Currie, 1994;Erickson, 1996). Consequently, theropod teeth are one of the most common fossils in terrestrial Mesozoic formations (e.g., Erickson, 1996;Smith et al, 2005;Blob and Badgley, 2007) and are constantly reported in the literature (e.g., Currie et al, 1990;Rauhut and Werner, 1995;Baszio, 1997;Zinke, 1998;Sankey et al, 2002;Sweetman, 2004;Maganuco et al, 2005;Vullo et al, 2007;Larson, 2008;Casal et al, 2009;Lubbe et al, 2009;Ősi et al, 2010;Han et al, 2011;Sues and Averianov, 2013;Larson and Currie, 2013;Richter et al, 2013;Torices et al, 2015;Kear et al, 2013;Madzia, 2014;Hendrickx and Mateus, 2014a;Cobos et al, 2014;Tavares et al, 2014;Fanti et al, 2014;Brusatte and Clark, 2015;Csiki-Sava et al, 2016;Gerke and Wings, 2016;Alonso et al, 2017;Malafaia et al, 2017a;Avrahami et al, 2018;Frederickson et al, 2018;…”

An ankylosaurian dinosaur from the Cenomanian Dunvegan Formation of northeastern British Columbia, Canada

“…The earliest records of the characteristic tail club occur in Albian to Cenomanian-aged formations in Asia (Arbour and Currie, 2015;Zheng et al, 2018). Ankylosaurids are also first documented in North America during this time period in the Mussentuchit Member of the Cedar Mountain Formation but then disappear from the North American fossil record until the Santonian (Baszio, 1997;Eaton et al, 1999;Parrish, 1999), possibly indicating a response to high sea levels in Laramidia during the early Late Cretaceous (Arbour et al, 2016), although poor sampling in the Turonian-Santonian cannot be ruled out (e.g. Upchurch et al, 2011).…”

“…Terrestrial Cenomanian assemblages are rare in North America but capture an important time which preserves a distinct and transitional assemblage between characteristic faunas of the Early and latest Late Cretaceous. The nearest comparative material of this age is derived from Dunvegan Formation outcrops in Alberta, the Cedar Mountain Formation of Utah (Avrahami et al, 2018;Tucker Published by Copernicus Publications on behalf of the Museum für Naturkunde Berlin. .…”