Gabriel S. Ferreira - Lower jaw functional morphology of the largest freshwater turtle, Stupendemys geographica, suggests an herbivorous diet

SCIMED - Geosciences - Turtle Evolution Symposium 2024

12:20, 1 July, English, 3 views

The Miocene of Northern South America witnessed the largest freshwater turtle ever, Stupendemys geographica. This podocnemidid was known only from fragmentary postcranial remains, but recent discoveries of a rich fossil record from the Tatacoa Desert (Colombia) offer new opportunities to explore the paleobiology of this incredible turtle. Here we report the first attempt to understand the feeding behavior of Stupendemys using functional morphology. A complete and mostly undeformed mandible (VPPLT-979) shows an upturned symphyseal hook and an almost flat but relatively broad triturating surface, lacking rugosities and including a long midline ridge. The coronoid process and adductor fossa are greatly developed, suggesting powerful external adductors. We digitalized that specimen with photogrammetry and modelled the adductor muscles to simulate biting scenarios using Finite Element Analysis. We tested three models: the original-sized (jaw length = 24 cm, carapace length = 134 cm), an upscaled (JL = 54 cm, CL = 280 cm), and a downscaled (JL = 12 cm, CL = 72 cm). The maximum bite force obtained from the largest to smallest models were 6700, 1200, and 142 N. Although the bite force of the largest Stupendemys proved to be comparable to similar-sized crocodiles, it is lower than expected for biter turtles, but match nicely those expected for herbivorous species when upscaled to CL = 280 cm. Thus, together with the triturating surface anatomy, the biomechanical analyses suggest that Stupendemys was herbivorous, similar to its extant podocnemidid relatives.

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