The first definitive carcharodontosaurid (Dinosauria: Theropoda) from Asia and the delayed ascent of tyrannosaurids

Abstract

Little is known about the evolution of large-bodied theropod dinosaurs during the Early to mid Cretaceous in Asia. Prior to this time, Asia was home to an endemic fauna of basal tetanurans, whereas terminal Cretaceous ecosystems were dominated by tyrannosaurids, but the intervening 60 million years left a sparse fossil record. Here, we redescribe the enigmatic large-bodied Chilantaisaurus maortuensis from the Turonian of Inner Mongolia, China. We refer this species to a new genus, Shaochilong, and analyze its systematic affinities. Although Shaochilong has previously been allied with several disparate theropod groups (Megalosauridae, Allosauridae, Tyrannosauroidea, Maniraptora), we find strong support for a derived carcharodontosaurid placement. As such, Shaochilong is the first unequivocal Asian member of Carcharodontosauridae, which was once thought to be restricted to Gondwana. The discovery of an Asian carcharodontosaurid indicates that this clade was cosmopolitan in the Early to mid Cretaceous and that Asian large-bodied theropod faunas were no longer endemic at this time. It may also suggest that the ascent of tyrannosaurids into the large-bodied dinosaurian predator niche was a late event that occurred towards the end of the Cretaceous, between the Turonian and the Campanian.

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.…”

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

“…However, the pace and nature of this transformation has been largely unknown due to a near 70 million year gap in the apex predator record of western North America. Discovery of Siats, a gigantic megaraptoran neovenatorid, in mid-Cretaceous ecosystems, together with new phylogenetic interpretations positing Acrocanthosaurus in a more derived position within Carcharodontosauridae 14,19,29,30 indicate that apex predator guilds of that time were composed neither of relic Jurassic theropod clades nor by early replacement by tyrannosaurids, and that two-step depictions of predator communities are insufficient to describe theropod guild evolution during this interval. Rather, these data indicate that mid-Cretaceous theropod assemblages were taxonomically unique from both prior and subsequent faunas in being composed largely of derived carcharodontosaurians (with subsidiary roles occupied by one or more clades of medium-bodied coelurosaurian) and that, minimally, a trifold characterization of apex predator guild occupancy mirroring the pattern observed in Asia 11,14 is required (Fig.…”

“…Persistence of carcharodontosaurian theropods into the Late Cretaceous has recently been invoked as an explanation for the delayed ascent of tyrannosaurids as apex predators in Asian ecosystems 14,15 . Siats not only provides the first evidence for megaraptoran allosauroids in North America, but also demonstrates that carcharodontosaurians continued to occupy apex guilds on the continent into the Late Cretaceous, possibly constraining tyrannosauroid size evolution via competitive exclusion throughout the mid-Cretaceous 11,19 .…”

“…The paucity of pre-Campanian data on top predators of North America is particularly extreme, with only a single taxon, Acrocanthosaurus 12 , described from the first 70 million years of the Cretaceous. Such sampling biases have led to the hypothesis that predator assemblages during this interval were depauperate and homogeneous across the continent 13 and have obscured the timing of major ecological events such as the ascension of tyrannosauroids to top predator roles 14 . Whether this turnover was related to out competition of endemic allosauroids or rather, release from competitive exclusion via regional extinction events as has been suggested for other Laurasian landmasses 14,15 and earlier Mesozoic radiations 16,17 remains unclear.…”

Anatomy, taphonomy, and phylogenetic implications of a new specimen of Eolambia caroljonesa (Dinosauria: Ornithopoda) from the Cedar Mountain Formation, Utah, USA

“…Most members of this clade are of Early Cretaceous age (Barremian–Albian); however, if the Santonian age of Batyrosaurus proposed by Godefroit et al [14] is accurate, then this clade persisted into the Late Cretaceous. There are several theropod clades that exhibit similar geographic and temporal distributions, with members found in the Early and Late Cretaceous of North Africa, Europe, and Asia, including Spinosauridae [102], Carcharodontosauridae [103,104,105], and Neovenatoridae [30,106,107]. …”