HETERODONTY IN MANIDENS CONDORENSIS (ORNITHISCHIA: HETERODONTOSAURIDAE), A BIOMECHANICAL APPROACH USING FINITE ELEMENT ANALYSIS IN ISOLATED TEETH

BECERRA, MARCOS G.; NIETO, MAURO N.; POL, DIEGO; DEGRANGE, FEDERICO J.; PORRO, LAURA B.

Salta

Congreso; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina 2022; 2022

Asociación Paleontológica Argentina

The postcaniniform dentition of Manidens condorensis is one of the most morphologically variable among ornithischians. It is unclear if this shape/size differentiation optimizes stress attenuation with changes in bite force (i.e., crowns with similar stress attenuation regardless tooth position), or if it reflects functional regionalization of the toothrow (i.e., crowns with different stress attenuation, more efficient at the main functional region). To test these alternatives, six teeth of Manidens representing the anterior, middle, and posterior regions of the maxillary and dentary postcaniniform dentitions (MPEF-PV 3809, 3810, 3811, 3815, 3818, 10861) were micro-CT scanned to construct 3D finite element models and scaled to the skull size of the holotype (MPEF-PV 3211; fossils repository Museo Paleontológico Egidio Feruglio, Chubut, Argentina). Bite force was calculated in each region using the 2D lever arm method. The input moment was calculated using a muscle force estimated through the “dry skull” method. The output moment was the distance of each bite point to the jaw joint. Models of each tooth were fixed at their roots, the calculated bite force was applied tothe apex, and differences in stress distribution were compared. Similarly, a second scenario was considered using the same maximal force regardless of the tooth position (i.e., without lever arm attenuation). Tooth properties were selected from published data and Finite Element Analyses were performed. A comparison of stress distributions across both scenarios tested indicates that anterior crowns (small, symmetric, sub-triangular) feature more prominent areas of high stress, while posterior crowns (low, symmetric/asymmetric, diamond-shaped) show proportionally minor areas of high stress, with closely similar but smaller areas in mid-region teeth (high, symmetric/asymmetric, diamond-shaped). Our results suggest that biomechanical performance did not drive the evolution of heterodonty in Manidens, given that in both scenarios different crowns respond differently to bite loads. General trends indicate that higher crowns in mid-region teeth show better stress attenuation than anterior and posterior teeth. Therefore, we hypothesize that such heterodonty confers another functional advantage, such as a functional regionalization of the toothrow: the middle dentition better suited for cutting, the blade-like anterior teeth adapted for cropping, and the low and mesiodistally wide posterior teeth adapted for grinding. Stress resistance indicates that cutting was likely the primary function of the toothrow, however, the enhanced grinding function by the occluding bulged bases (dentary teeth) and cingular entolophs (maxillary teeth) and double shearing during chewing unique to Manidens was at least secondarily to equally important.