Abstract :
[en] The coexistence of sympatric predatory marine reptiles in the Late Cretaceous suggests ecological
partitioning of higher trophic niches. The Western Interior Seaway, a vast inland sea that stretched across
a significant portion of North America, was home to a diverse array of marine life, most notably a
multitude of reptilian predators. Previous studies have utilized tooth morphology and dental microwear
as proxies for inferring the feeding habits of marine reptiles. However, teeth are only part of the feeding
apparatus. Ecological insights may be elucidated through biomechanical simulations of craniodental
remains, focusing on mechanical performance. Here, we performed the first, large-scale, comparative
study on WIS marine reptile jaw performance using high-definition three-dimensional models and
muscle-driven finite element analyses (FEA). The jaws of mosasaurids and polycotylid plesiosaurians
from the Campanian-Maastrichtian were 3D scanned and processed for FEA simulations. For
comparative purposes, mosasaur jaws were modeled with a fused symphysis and immobile
intramandibular joint, forming a single functional element. Muscle insertions were identified to
reconstruct jaw adductor muscles and assess respective muscle and bite force. We used Metafor to
simulate realistic, muscle traction dynamics during biting, including simulations at different opening
angles and biting locations. Results revealed distinct stress distributions per morphotype, demonstrating
biomechanical variation between robust mosasaur mandibles (e.g. Globidens) and the more gracile
mandibles of polycotylids and the mosasaurid Clidastes. Integrating mechanical efficiency with the
deformation sustained by the jaws provided additional ecological inferences. High deformation values in
polycotylid jaws suggest that maximum bite force (estimated from muscle attachments) was not exerted,
resulting in divergent feeding techniques to mosasaurs (e.g., snapping and swallowing). Moreover,
polycotylids and some mosasaurid taxa (e.g., Clidastes and Jormungandr) appear better adapted to
biting at wider gape angles, whereas mosasaurids with high mechanical efficiency at wide and narrow
gape angles (e.g., Mosasaurus and Prognathodon) are more suited to prey on larger items with powerful
bites. Our results align with niche partition inferences from dental remains and offer deeper insight into
feeding techniques in Late Cretaceous marine predators, providing a unified canvas and protocol to
assess niche partitioning in sympatric marine reptiles from well-sampled (and well-preserved) regions.
