Functional anatomy of a giant toothless mandible from a bird-like dinosaur: Gigantoraptor and the evolution of the oviraptorosaurian jaw

Abstract

The Oviraptorosauria are a group of theropod dinosaurs that diverged from the typical carnivorous theropod diet. It includes two main lineages – Caenagnathidae and Oviraptoridae – that display a number of differences in mandibular morphology, but little is known about their functional consequences, hampering our understanding of oviraptorosaurian dietary evolution. This study presents the first in-depth description of the giant toothless mandible of Gigantoraptor, the only well-preserved stemward caenagnathid mandible. This mandible shows the greatest relative beak depth among caenagnathids, which is an adaptation seen in some modern birds for processing harder seeds. The presence of a lingual triturating shelf in caenagnathids more crownward than Gigantoraptor suggests a possible increased specialization towards shearing along this lineage. Like other oviraptorosaurs, the possession of a dorsally convex articular glenoid in Gigantoraptor indicates that propalinal jaw movement was probably an important mechanism for food processing, as in Sphenodon and dicynodonts. Oviraptorid mandibles were more suited for producing powerful bites (e.g. crushing-related) compared to caenagnathids: oviraptorids generally possess a deeper, more downturned beak, a taller coronoid process prominence and a larger medial mandibular fossa. This disparity in caenagnathid and oviraptorid mandible morphology potentially suggests specialization towards two different feeding styles – shearing and crushing-related mechanisms respectively.

Histology of Caenagnathid (Theropoda, Oviraptorosauria) Dentaries and Implications for Development, Ontogenetic Edentulism, and Taxonomy

“…Furthermore, it is incongruent with current evidence from Gigantoraptor , the mandible of which is remarkably similar to that of Beibeilong (Ma et al, ; Pu et al, ). The dentaries of Gigantoraptor lack any occlusal ridges or grooves (Ma et al, ), despite presumably being relatively mature compared to Beibeilong and therefore contradict Wang et al's () suggestion. It is possible that Gigantoraptor and Beibeilong differed in the development of the mandible, but their close phylogenetic relationship and the similarity of their mandibles make this unlikely.…”

The skull evolution of oviraptorosaurian dinosaurs: the role of niche partitioning in diversification

“…The mandible and lower beak form data sets include specimens of basal oviraptorosaurs, caenagnathids and oviraptorids, allowing us to assess large‐scale form variations between these major groups. The wide separation between caenagnathids and oviraptorids in the mandible form morphospace is not surprising, as their differences in mandibular anatomy are well noted (Funston et al, ; Funston, Mendonca, Currie, & Barsbold, ; Longrich, Barnes, Clark, & Millar, ; Longrich, Currie, & Dong, ; Ma et al, ; Osmolska et al, ). The lower beak form morphospace also displays a similar pattern, with most caenagnathids and oviraptorids situated at the opposing sides and basal oviraptorosaurs located between them on PC1.…”

“…Oviraptorosaurs exhibit skull forms that deviate strongly from other nonavian theropods: their skulls are relatively robust and tall, and show different levels of tooth reduction (Brusatte, Sakamoto, Montanari, Harcourt, & William, ; Foth & Rauhut, ; Osmolska, Currie, & Barsbold, ; Xu et al, ). Derived oviraptorosaurs—caenagnathids and oviraptorids—possess an edentulous beak and sometimes a tall cranial crest, which is pneumatized and elaborated into a variety of shapes and sizes (Lü et al, ; Ma et al, ; Osmolska et al, ). The unusual skulls of oviraptorosaurs probably enabled distinctive diets compared to most theropods, although feeding habits are controversial.…”

Cranial Musculature in Herbivorous Dinosaurs: A Survey of Reconstructed Anatomical Diversity and Feeding Mechanisms

“…Although nonavian theropods were primarily carnivorous, herbivory has been hypothesized to have evolved in three major clades of nonavian theropods. Studies reconstructing temporal musculature in herbivorous nonavian theropods include those of oviraptorosaurs (Barsbold, ; Smith, ; Ma et al, ), ornithomimosaurs (Cuff and Rayfield, ), and therizinosaurs (Lautenschlager, , ; Lautenschlager et al, ). These reconstructions are largely consistent with each other in terms of temporal muscle attachment sites, which are described and summarized by Holliday () and summarized above.…”