The osteology of Shaochilong maortuensis, a carcharodontosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Asia

Abstract

Large-bodied theropod dinosaurs from the Early-mid Cretaceous of the northern continents (Laurasia) are poorly known. One of the most complete and intriguing theropods from this interval is Shaochilong maortuensis Hu, 1964 from the Turonian (< 92 Ma) Ulansuhai Formation of Inner Mongolia, China. The phylogenetic placement of Shaochilong has long been a subject of debate, as it has been referred to several disparate theropod groups (e.g., Megalosauridae, Allosauridae, Tyrannosauroidea, Maniraptora). In a recent taxonomic reassessment, Shaochilong was identified as the first Asian member of Carcharodontosauridae, a clade of allosauroid theropods that was once thought to be restricted to Gondwana and includes some of the largest terrestrial predators to ever live. However, the characters supporting such a placement were only briefly discussed, and a full anatomical description of Shaochilong has yet to be presented. We provide a detailed osteological description of the lectotype and paralectotype series, show that Shaochilong is a small-bodied and short-snouted carcharodontosaurid, and highlight numerous cranial features shared with other carcharodontosaurids. We argue that the vicariant hypothesis of allosauroid biogeography, in which lineages split in concert with the fragmentation of Pangaea, is poorly supported. Finally, large-scale patterns of theropod evolution and faunal replacement are discussed, and it is argued that allosauroids persisted as large-bodied predators later in the Cretaceous than previously thought.

New Information on the Cranial Anatomy of Acrocanthosaurus atokensis and Its Implications for the Phylogeny of Allosauroidea (Dinosauria: Theropoda)

“…This crest is proportionally wider in Carcharodontosaurus and Giganotosaurus , and in these taxa the transverse nuchal crest is shifted forward to overlap the posteromedial corner of the supratemporal fossa [41], [75]. The relative size and length of the supratemporal fossa in Acrocanthosaurus are similar to that of Eocarcharia , and both taxa have proportionally longer and larger fossae than in Carcharodontosaurus , Giganotosaurus , and Shaochilong , but smaller than in Sinraptor and Allosaurus [76].…”

“…In Giganotosaurus and Carcharodontosaurus , this region clearly preserves an interorbital septum that connects the orbitosphenoid to the parasphenoid region [41]. The interorbital septum is absent in Allosaurus , Eocarcharia , Shaochilong , and Sinraptor [76].…”

“…Frontal fusion also occurs in the holotype specimen of Acrocanthosaurus [23], and in Carcharodontosaurus , Giganotosaurus , Eocarcharia , and Shaochilong [41], [49], [75], [76]. The frontals of the allosauroids Allosaurus and Sinraptor are unfused [76]. The frontal of Acrocanthosaurus contacts the posterior margin of the nasal with a flange-like triangular process.…”

Continental fossil vertebrates from the mid-Cretaceous (Albian–Cenomanian) Alcântara Formation, Brazil, and their relationship with contemporaneous faunas from North Africa

“…Although most previous authors Schultz, 2001a, 2002;Medeiros et al, 2007) have referred these teeth to Carcharodontosaurus, Candeiro and Martinelli (2005, p. 12) reinterpreted this material as pertaining to indeterminate carcharodontosaurids due to its lack of genus-level diagnostic features. Since carcharodontosaurids were widespread during the mid-Cretaceous (occurring in North America, Asia, South America, Africa, and possibly Europe [e.g., Brusatte et al, 2010;Ortega et al, Fig. 4.…”

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“…The quadrate of Carcharodontosauridae is relatively well-known due to its detailed description for Acrocanthosaurus atokensis (Eddy and Clarke, 2011), Shaochilong maortuensis (Brusatte, Chure, et al, 2010) and Mapusaurus roseae (Coria and Currie, 2006).…”