Mesozoic marine reptiles: Study reveals gradual evolution of swimming adaptations

Researchers recently uncovered how various marine reptiles, thriving post-Permian extinction, gradually developed advanced swimming techniques, culminating in diverse and specialized movement forms during the Cretaceous period. The study was authored by Benjamin C. Moon, Susana Gutarra, Thomas L. Stubbs, Beatrice H. Heighton, and Michael J. Benton.

According to the study, published on April 17 in the Wiley Online Library, the Mesozoic era was a period marked by dynamic ecological changes, with various reptile groups venturing into marine environments. Among them, several clades like Ichthyosauromorpha and Mosasauroidea not only successfully adapted to aquatic life but also displayed exceptional longevity and diversification. This phase, states the study, presents a unique opportunity to explore evolutionary shifts over time, particularly in marine ecosystems. While past studies have delved into the cranial diversity of these reptiles, uncovering a plethora of feeding strategies, their locomotion, a critical aspect of their ecology and biology, remains less explored.

The swimming techniques of Mesozoic marine reptiles were diverse and effective in the animal kingdom, according to the study. For instance, the plesiosaurs exhibited a unique quadrupedal underwater flight, while parvipelvian ichthyosaurs shared similarities with modern high-speed swimmers like dolphins and sharks. The study says, however, that inferring swimming modes from fossil records, especially in less specialized early lineages, poses significant challenges. Previous research has either focused on specific aspects like bone proportions or limited its scope to certain groups, leaving a broader understanding of locomotion across different clades unaddressed.

The study aims to bridge the knowledge gap in understanding the locomotion of Mesozoic marine reptiles. By examining a wide array of species, it sheds light on how these creatures adapted their swimming techniques, transitioning from basic drag-based movement to more advanced lift-based propulsion. This gradual evolutionary trajectory didn't happen overnight; instead, it spanned the entire Mesozoic, reaching its pinnacle in the Cretaceous period. The findings also highlight the early aquatic specialization in ichthyosaurs and shared physical traits between mosasaurs and ichthyosaurs. The study states that this comprehensive analysis contributes significantly to our understanding of the evolutionary paths and ecological adaptations of these ancient marine reptiles.

John Wiley & Sons Ltd: Susana Gutarra, Benjamin Moon, et al, The locomotor ecomorphology of Mesozoic marine reptiles, Palaeontology (2023). https://doi.org/10.1111/pala.12645