Neovenatorid theropods are apex predators in the Late Cretaceous of North America

Abstract

Allosauroid theropods were a diverse and widespread radiation of Jurassic-Cretaceous megapredators. Achieving some of the largest body sizes among theropod dinosaurs, these colossal hunters dominated terrestrial ecosystems until a faunal turnover redefined apex predator guild occupancy during the final 20 million years of the Cretaceous. Here we describe a giant new species of allosauroid -Siats meekerorum gen. et sp. nov. -providing the first evidence for the cosmopolitan clade Neovenatoridae in North America. Siats is the youngest allosauroid yet discovered from the continent and demonstrates that the clade endured there into the Late Cretaceous. The discovery provides new evidence for ecologic sympatry of large allosauroids and small-bodied tyrannosauroids. These data support the hypothesis that extinction of Allosauroidea in terrestrial ecosystems of North America permitted ecological release of tyrannosauroids, which went on to dominate end-Cretaceous food webs.

New tyrannosaur from the mid-Cretaceous of Uzbekistan clarifies evolution of giant body sizes and advanced senses in tyrant dinosaurs

“…The new midCretaceous Uzbek taxon is also approximately horse-sized, far smaller than the end-Cretaceous giants. Although it is currently only a single data point, Timurlengia indicates that tyrannosauroids remained small-to-medium-sized well into the Middle Cretaceous, during a time when late-surviving large allosauroids remained at the top of food chains in Asia and North America (42)(43)(44). Tyrannosauroids apparently developed huge size and ecological dominance suddenly, sometime around the start of the Campanian, but the trigger remains unclear.…”

Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy

“…After a comprehensive phylogenetic analysis, these authors considered megaraptorans as allosauroids closely related with carcharodontosaurid theropods, an interpretation subsequently followed by later authors (Carrano et al, 2012;Zanno and Makovicky, 2013). However, recent studies conducted by some of us (e.g., Novas et al, 2013;Porfiri et al, 2014) have suggested that megaraptorans are not representative of archaic allosauroid tetanurans, but instead argued that megaraptorans are coelurosaurs, and representatives of a basal tyrannosauroid radiation in particular (Novas et al, 2013).…”

The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia

“…The non-avian dinosaur fauna of the deltaic plains (e.g., Main, 2005;Main, 2010;Main, 2013) represented by the Woodbine Formation included large carcharodontosaurs, dromaeosaurs, ornithomimosaurs, indeterminate theropods (including possible tyrannosauroids), hadrosauroids, and nodosaurids (e.g., Main, 2005Main, , 2013. Possible allosauroid and carcharodontosaurid dinosaurs are known from the Mussentuchit Member of the Cedar Mountain Formation (Siats meekorum) (Zanno and Makovicky, 2013) and from the Turney Ranch Formation (Thayer and Ratkevich, 1995). Dromaeosaurids are also known from the Mussentuchit Member of the Cedar Mountain Formation (Garrison and Brinkman, 2007) and from the Blackleaf Formation (Ullman et al, 2012).…”

“…The Mussentuchit Member of the Cedar Mountain Formation is latest Albian to Cenomanian in age (~104-98 Ma) (e.g., Cifelli et al, 1997;Chure et al, 2010) and represents fluvial to deltaic environments (e.g., Kirkland et al, 1998;Carpenter et al, 1999;Kirkland et al, 1999;Garrison and Brinkman, 2007;McDonald et al, 2012;Ullman et al, 2012;Main, 2013;Zanno and Makovicky, 2013;Krumenacker et al, 2017), whereas the Dunvegan Formation represents a middle Cenomanian-age delta complex (e.g., Burns and Vavrek, 2014). The Lewisville Member of the Woodbine Formation, to which the Arlington Archosaur Site corresponds, is middle Cenomanian in age (~96-95 million years old) and preserves a coastal deltaic environment (e.g., Main, 2005;Main, 2013), making it closely comparable to the Dunvegan Formation and somewhat so to the Mussentuchit.…”

“…Campanian Appalachian faunas were compared to those of the Wahweap, Kaiparowits, and Kirtland formations representing southern Campanian Laramidian faunas and with the Oldman, Dinosaur Park, and Judith River formations representing northern Campanian Laramidian faunas, whereas the Maastrichtian Appalachian faunas were compared with those of the Javelina, Hell Creek, Lance, and Horseshoe Canyon formations. The Laramidian (western North American) faunas used for comparisons are among the most well known (e.g., Kirkland et al, 1998;, Weishampel, 2006Gates et al, 2010;Zanno and Makovicky, 2013;Farke et al, 2014) and represent a sampling of northern, middle, and southern faunas, both factors being considered to minimize statistical bias and error on the part of such faunas. As such, formations like the Foremost Formation, from which only a few taxa and indeterminate elements are known (e.g., Weishampel et al, 2004), were not included.…”