Sinocephale (meaning 'Chinese head') is a genus of pachycephalosaurid dinosaur that lived in what is now Inner Mongolia, China, during the Cretaceous period. The genus contains a single species, Sinocephale bexelli, which was originally named as a species of the genus Troodon in 1953, and later transferred to the genus Stegoceras in 1964. After decades of being considered dubious, it was re-evaluated in 2021 and recognised as a valid taxon, being given its own genus, Sinocephale. The original holotype was lost, with modern research conducted using rediscovered plaster casts. Scant material makes for limited knowledge of its life appearance, but it is distinguished by an embayment on the back of the domed skull, which would give it a heart shape as seen from above. It is a member of the subfamily Pachycephalosaurinae, related to animals such as Pachycephalosaurus and Prenocephale. The geologic context of the species has historically been unclear, but it is currently thought to originate in rocks belonging to the Ulansuhai Formation.
Discovery and naming
During the early 20th century, Swedish palaeontological expeditions were conducted in China. During one such expedition, sometime in 1930 or 1931, a specimen was discovered that would become recognized as the first evidence of Pachycephalosauria (known as "dome-headed dinosaurs") from Asia. It consisted of a parietal bone (a bone forming the top of the rear skull), largely complete along its midline and right side but missing part of the left. Discovered at the Tsondolien-Khuduk geologic locality in Inner Mongolia, the specimen among others were brought to Sweden for study in Uppsala. The specimen was named and described by palaeontologist Birger Bohlin in 1953, as a new species of the genus Troodon, with the specific name bexelli honouring Gerhard Bexel, who discovered the specimen. The genus Troodon had historically been considered a pachycephalosaur (as it was only known from convergent teeth), although it is now recognized as a theropod. By the time the paper had been published the specimen had already been returned to China's Institute of Vertebrate Paleontology and Paleoanthropology and was subsequently lost along with many other specimens. A decade later, in 1964, Oskar Kuhn reassigned T. bexelli to the genus Stegoceras as the species S. bexelli (as Stegoceras had been split from Troodon to contain the true pachycephalosaur remains).
Bohlin's species was largely ignored in the years following its original naming, only occasionally invoked to mention its significance as the first known Asian pachycephalosaur. In 1983 Hans-Dieter Sues and Peter Galton commented on the species in a paper focused on North American pachycephalosaurs, noting that based on the data from Bohlin's description the species clearly differs from definite Stegoceras material, casting doubt on its assignment to the genus. They considered the material to clearly be indeterminate and unidentifiable as a valid taxon below the family level. Robert M. Sullivan would agree with this sentiment in 2000s studies, noting it likely belonged to an Asian genus like Prenocephale but that it should be considered an undiagnostic nomen dubium. In her chapter on pachycephalosaurs in the 1990 encyclopedia book The Dinosauria, Teresa Maryańska offered an alternative opinion, noting points of anatomical distinctiveness compared to other pachycephalosaurids despite the scant nature of its material. She noted it would be worthwhile for the material to be re-examined and given its own genus. It is unclear if any of these authors after Bohlin examined the material or a cast firsthand. Further research became possible with the recognition of two plaster casts of the holotype. One is located at the American Museum of Natural History under the specimen number AMNH 2073, and the other at the Museum of Evolution of Uppsala University under the specimen number PMU 23186, with the former having a tag indicating its origination in Uppsala. These are thought to have been made by Eric Ingemar Ståhl during the original period of study, before the return of the original specimen to China. These were used as plastotypes for the species, meaning they function as stand-ins for the holotype (which was never given a specimen number) due to it being lost; the holotype remains the name-bearing specimen and is not considered replaced. In light of this discovery David Evans and colleagues redescribed the species in 2021; they noted that, based on how the specimen had been discussed in the literature, they were potentially the first people since Bohlin to study the anatomy firsthand instead of merely basing opinions on the 1953 paper. They aimed to provide a more in-depth description than the 1953 study, investigating the ornamentation and age of the animal and evaluating its phylogenetic place in the Pachycephalosauridae in light of the decades of discoveries since its naming. Finding the specimen to be a diagnostic (possessing distinguishing traits relative to other species), distinct species within the family, they gave it a new genus name, Sinocephale. It combines the prefix sino referring to China, where the specimen was found, and the Greek word kephalē (κεφαλή) meaning "head", which is a common suffix for pachycephalosaur names.
Description
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