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Cranial muscle reconstructions quantify adaptation for high bite forces in Oviraptorosauria - PubMed

  • ️Sat Jan 01 2022

Cranial muscle reconstructions quantify adaptation for high bite forces in Oviraptorosauria

Luke E Meade et al. Sci Rep. 2022.

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.

© 2022. The Author(s).

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1

Locations of reconstructed jaw adductor muscle origin and insertion sites for Incisivosaurus gauthieri (a-c), Citipati osmolskae (d-f), Khaan mckennai (g-i), and Conchoraptor gracilis (j-l). Crania are shown in dorsolateral view (a,d,g,j) with temporal and postorbital bars removed to better show medial regions within supratemporal fenestra. The left sides of the crania are shown in anteroventral view (b,e,h,k) with lower temporal and postorbital bars removed to better show posterior and lateral regions within supratemporal fenestra. Mandibles shown in dorsolateral view (c,f,i,l), lateral muscle insertions sites are shown on the left rami, medial insertion sites on the right rami. Scale bars 50 mm. Muscle abbreviations given in results section.

Figure 2
Figure 2

Reconstructed jaw adductor musculature of Incisivosaurus gauthieri (a-d) and Citipati osmolskae (e–h) shown complete in lateral view (a,e), anterolateral view with mAMES removed (b,f), posterolateral view with mAME complex removed (c,g), and ventral view with only the mPT muscles (mPTv removed on left). Scale bars 50 mm, legend colour coded to identify individual muscles. Muscle abbreviations given in results section.

Figure 3
Figure 3

Reconstructed jaw adductor musculature of Khaan mckennai (a-d) and Conchoraptor gracilis (e–h) shown complete in lateral view (a,e), anterolateral view with mAMES removed (b,f), posterolateral view with mAME complex removed (c,g), and ventral view with only the mPT muscles (mPTv removed on left). Scale bars 50 mm, legend colour coded to identify individual muscles. Muscle abbreviations given in results section.

Figure 4
Figure 4

The relative contribution of each cranial muscle to total estimated bite force by species. Note that the condition of Citipati appears the most dissimilar to all others in its comparatively stronger mAMEM, mAMES and weaker mPTv.

Figure 5
Figure 5

Comparison of the estimated bite forces in multiple positions of Incisivosaurus and three oviraptorid oviraptorosaurians with other likely herbivorous theropod taxa that have had estimates made using similar digital volumetric methods, show the oviraptorosaurians (oviraptorids especially) are capable of much stronger bite forces both relative to body mass and absolutely. Body mass values from Zanno and Makovicky.

Figure 6
Figure 6

Estimates of the gape angle limit of optimal tension and the maximum limit of gape for muscle tension in Incisivosaurus gauthieri (a), Citipati osmolskae (b), Khaan mckennai (c), and Conchoraptor gracilis (d) from a muscle resting length at a gape angle of 5°. Bar charts show the strain factors of individual modelled muscle cylinders at optimal and maximum tension limit; anteriormost muscle cylinders suffixed ‘1’, posteriormost suffixed ‘2’. Muscle cylinders (and corresponding bars) are colour coded yellow and red when exceeding 130% and 170% of resting length respectively, otherwise green. Note that the anterior mPTv constrains gape in all species apart from Citipati which is constrained by the anterior mAMES. Scale bars 50 mm. Muscle abbreviations given in results section.

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