Cranial muscle reconstructions quantify adaptation for high bite forces in Oviraptorosauria

Luke E Meade,Waisum Ma

doi:10.1038/s41598-022-06910-4

Abstract

Oviraptorosaurians are an unusual and probably herbivorous group of theropod dinosaurs that evolved pneumatised crania with robust, toothless jaws, apparently adapted for producing a strong bite. Using 3D retrodeformed skull models of oviraptorid oviraptorosaurians Citipati, Khaan, and Conchoraptor, along with the earliest diverging oviraptorosaurian, Incisivosaurus, we digitally reconstruct jaw adductor musculature and estimate bite force to investigate cranial function in each species. We model muscle length change during jaw opening to constrain optimal and maximum gape angles. Results demonstrate oviraptorids were capable of much stronger bite forces than herbivorous theropods among Ornithomimosauria and Therizinosauria, relative to body mass and absolutely. Increased bite forces in oviraptorid oviraptorosaurians compared to the earliest diverging oviraptorosaurian result from expanded muscular space and different cranial geometry, not changes in muscular arrangement. Estimated optimal and maximum possible gapes are much smaller than published estimates for carnivorous theropods, being more similar to the herbivorous therizinosaurian theropod Erlikosaurus and modern birds. Restrictive gape and high bite force may represent adaptation towards exploiting tough vegetation, suggesting cranial function and dietary habits differed between oviraptorids and other herbivorous theropods. Differences in the relative strength of jaw adductor muscles between co-occurring oviraptorids may be a factor in niche partitioning, alongside body size.

Highlights

Oviraptorosaurians are an unusual and probably herbivorous group of theropod dinosaurs that evolved pneumatised crania with robust, toothless jaws, apparently adapted for producing a strong bite
The muscular origin and insertion sites interpreted in the cranium and mandible of each species are identified in Fig. 1; the 3D reconstructed cranial adductor muscles are shown in Fig. 2 (Incisivosaurus and Citipati) and Fig. 3 (Khaan and Conchoraptor)
The origin site of the m. adductor mandibulae externus medialis (mAMEM) is less clear than others of the mAME group[31] and we reconstruct it, as others have done, in the posterior portion of the supratemporal fossa[12,13,16] where it is constrained anterolaterally and anteromedially by the positions of m. adductor mandibulae externus superficialis (mAMES) and m. adductor mandibulae externus profundus (mAMEP) (Fig. 1)

Summary

Introduction

Oviraptorosaurians are an unusual and probably herbivorous group of theropod dinosaurs that evolved pneumatised crania with robust, toothless jaws, apparently adapted for producing a strong bite. The skull morphology of oviraptorid oviraptorosaurians appears to be adapted towards producing a powerful sustained bite[3,4,5,6] Though their crania are heavily pneumatised, they are short and tall, have expanded spaces for jaw musculature, and are equipped with a deep mandible and a robust palate terminating in a toothless beak. We assess how the reconstructed adductor muscle anatomy may have constrained the maximal angle of gape in each s pecies[23] This set of four 3D skull models and myological reconstructions allows us to compare bite forces, adductor muscle anatomy, and jaw function between the earliest diverging oviraptorosaurian and later diverging oviraptorids, and between oviraptorosaurians and other herbivorous theropods.

Methods

Results

Discussion

Conclusion