Exploring the effect of craniomandibular morphology on hydrodynamic performance in mosasaurids (Squamata, Mosasauridae)

Mosasaurids represent a diverse clade of predatory marine reptiles from the Late
Cretaceous, exhibiting a cosmopolitan distribution and a range of inferred ecologies. Some taxa
are interpreted as specialized durophages (e.g. Globidens) or ichthyophages (e.g.
Ectenosaurus), whereas a large number of species are considered as more generalist predators
(e.g. Mosasaurus), feeding on a variety of slow, fast, soft, shelled, large, and small prey items.
All known mosasaurids were fully aquatic, and therefore subject to the same physical
constraints of living in an aquatic medium, regardless of their dietary specialisations.
In this study, we elucidate how head shape influenced drag and pressure-wave
production during swimming across mosasaurids, used high-resolution 3D scans of skulls to
simulate hydrodynamic performance. Skulls of a wide range of mosasaurs were scanned, with
the bones composited into as-life craniomandibular reconstructions in Blender™, with retrodeformation
where necessary. A 3D “skin” was applied to simulate the dermis and soft tissues
of the animal. Each cranial reconstruction was uniformly smoothed and analysed using highdensity
geometric morphometrics to quantify head shape. In the absence of full skeletons for
all species, a standardised body shape was included (built in PALEOMASS) to aid in
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hydrodynamic comparisons. As we focused on how shape affects performance, all models were
scaled to projection area. Computational fluid dynamic simulations were conducted at steady
flow velocity (1 ms-1), using turbulent flow motion to approximate realistic water conditions.
Results comparing craniomandibular shape with fore-aft drag force and frontal pressurewave
production indicate a noteable effect of shape on performance. As expected, pressurewave
characterization indicated larger waves with slower dissipation in species with more
brevirostrine skull morphologies (e.g. Globidens) than longirostrine species (e.g.
Ectenosaurus). Inferred ichthyophagous species exhibited comparatively lower drag and
swifter bow-wave dissipation, supporting ecological interpretations for these species. Our study
represents a further step towards understanding (and validating) inferred ecologies of Late
Cretaceous marine predators using a computational biomechanical perspective.