Date Published: February 6, 2019
Publisher: Public Library of Science
Author(s): Sungjin Lee, Yuong-Nam Lee, Anusuya Chinsamy, Junchang Lü, Rinchen Barsbold, Khishigjav Tsogtbaatar, Alex Hubbe.
Recent discoveries of new oviraptorosaurs revealed their high diversity from the Cretaceous Period in Asia and North America. Particularly, at the family level, oviraptorids are among the most diverse theropod dinosaurs in the Late Cretaceous of Mongolia and China. A new oviraptorid dinosaur Gobiraptor minutus gen. et sp. nov. from the Upper Cretaceous Nemegt Formation is described here based on a single holotype specimen that includes incomplete cranial and postcranial elements. The most prominent characters of Gobiraptor are its thickened rostrodorsal end of the mandibular symphysis and a rudimentary lingual shelf on each side of the dentary. Each lingual shelf is lined with small occlusal foramina and demarcated by a weakly developed lingual ridge. This mandibular morphology of Gobiraptor is unique among oviraptorids and likely to be linked to a specialized diet that probably included hard materials, such as seeds or bivalves. The osteohistology of the femur of the holotype specimen indicates that the individual was fairly young at the time of its death. Phylogenetic analysis recovers Gobiraptor as a derived oviraptorid close to three taxa from the Ganzhou region in southern China, but rather distantly related to other Nemegt oviraptorids which, as the results of recent studies, are also not closely related to each other. Gobiraptor increases diversity of oviraptorids in the Nemegt Formation and its presence confirms the successful adaptation of oviraptorids to a mesic environment.
Oviraptorosauria is an unusual group of maniraptoran theropods with distinctive anatomical characters such as a deep and short skull, edentulous jaws in derived forms, a short tail, and pneumatized proximal caudal vertebrae [1–4]. The origin of oviraptorosaurs is generally assumed to be from Asia based on their earliest records from the Lower Cretaceous Yixian Formation of China [5–7]. Derived forms mostly appeared in the Late Cretaceous [4, 8] when they dispersed throughout Asia and North America [9, 10]. Within the clade Oviraptorosauria, three derived families have been recognized: Avimimidae , Caenagnathidae , and Oviraptoridae . Avimimids are comprised of a single genus that includes two species from the Nemegt Formation of Mongolia [10, 11, 13] while caenagnathids and oviraptorids show high level of diversity that has especially been bolstered by recent discoveries from the Nanxiong Formation of the Ganzhou region in southern China [14–20]. Interestingly, oviraptorids are restricted to Asia although they are more diverse than caenagnathids which are reported from both Asia and North America [8, 10]. However, most of the caenagnathids are represented by fragmentary materials [12, 21–34] with only a few exceptions [8, 9, 35, 36] compared with the numerous nearly complete skeletons of oviraptorids [4, 19, 20, 37–40].
Gobiraptor minutus gen. et sp. nov. is a new derived oviraptorid represented by an incomplete skeleton including both cranial and postcranial elements. Gobiraptor is primarily distinguished from other oviraptorids by its dentary with the extremely thickened rostrodorsal end of the mandibular symphysis, lingual ridges and lingual shelves bearing occlusal foramina. The unique morphology of the mandible of Gobiraptor is probably closely related to a crushing-related feeding style and a specialized diet, which may have incorporated hard seeds or shelled organisms. Although Gobiraptor was recovered from the Nemegt Formation, its phylogenetic position showed a close relationship with three Ganzhou oviraptorids. The distant relationships among the Nemegt oviraptorids on the phylogenetic tree were reaffirmed in this study. Therefore, it is highly unlikely that the evolution of these unusually diverse animals was facilitated by a simple sympatric speciation. The presence of Gobiraptor in the Nemegt Formation, together with occurrences of other oviraptorids, also indicates that abundant oviraptorids lived in mesic environments and they were one of the most diverse and successful groups of dinosaurs in the Nemegt region.