3D muscular reconstruction and biomechanical analysis in two dicynodonts from the Rio Seco de la Quebrada Formation (middle-Upper Triassic)

Abstract

Dicynodontia was a diverse and abundant clade of synapsids in Permo-Triassic terrestrialecosystems. These specialized herbivores had a keratinous beak, tusks or maxillacaniniform processes, and an extended squamosal where the adductor musculatureoriginated. These traits are related to feeding specializations. In the Río Seco de laQuebrada Formation, Mendoza Province (Middle-Late Triassic), skulls belonging to ¨Kannemeyeria¨ argentinensis (PVL 3465 and PVL 3471) and ?Vinceria vieja? (MACN18.871) offer a great opportunity for a comparative biomechanical and paleoecologicalanalysis. The materials were CT-scanned, segmented, and digitally restored, completingmissing regions using additional specimens of the same taxa. The adductor muscles(Adductor externus lateralis, Adductor externus medialis and Adductor internuspterygoideus) were reconstructed in 3D following previous authors. The origin andinsertion areas of the main masticatory muscles (AEL and AEM) were captured using 71landmarks and semilandmarks on the 3D model and the centroid of each area wascalculated to infer the line of action of each muscle. For biomechanical analysis, the jawwas considered as a lever and the craniomandibular joint as a pivot. The input force (Fi)comes from the muscle force and the output force (Fo) from the occlusal surfaces duringthe bite. Moment arms were calculated as orthogonal lines from the pivot to the line ofaction of the muscles (Mi) and to the occlusal surfaces (Mo). The results show that theAEM has more mechanical advantage over the AEL. In addition, the mechanicaladvantage in ¨Kannemeyeria¨ argentinensis is higher in comparison with ¨Vinceriavieja¨. Our results could be reflecting differences in feeding function among these twoadult taxa, with ¨Kannemeyeria¨ argentinensis having a better capability to developforce.