Mosasaur tail morphology reveals burst swimming performance and ecological diversity

Reconstructing locomotor performance of extinct animals is fundamental to understanding paleoecology, yet the soft tissues that control movement rarely fossilize, leaving performance poorly constrained for extinct taxa¹. Burst locomotion is a key determinant of predatory and escape success^2,3 and is governed by well-established fluid dynamics and kinematic principles, meaning it can be modeled from skeletal morphology alone. Here, we apply a drag-based fast-start framework, which we term a "slam-start," to estimate lunge velocity in four mosasaurs, dominant seagoing predators of Late Cretaceous oceans,⁴ spanning Mosasaurinae and Russellosaurina, using skeletal and caudal muscle reconstructions to parameterize tail excursion amplitude, muscle power output, and hydrodynamic drag across a range of plausible parameters. Across all modeled conditions, lunge velocity increases with tail curl amplitude and power output, while increasing drag coefficient produces only modest reductions in performance. Russellosaurine mosasaurids (Platecarpus tympaniticus and Tylosaurus proriger), which have longer tail displacement areas, exhibit higher normalized lunge velocities than mosasaurines (Mosasaurus sp. and Plotosaurus bennisoni), and these relative differences are consistent across a wide range of drag regimes. These results support distinct hunting strategies within Mosasauridae: the faster-lunging russellosaurines were likely ambush predators, whereas the slower mosasaurines were likely pelagic cruisers. As a case study, this work demonstrates that physics-based biomechanical modeling can generate quantitative, directly comparable locomotor estimates for extinct taxa using preserved morphology as input, offering a transferable protocol for studying burst performance across marine reptiles, taxa with no living analogs, and through deep evolutionary time.