2023-04-18 15:23:30
Scientists from the University of Bristol have revealed for the first time the various swimming techniques of the ancient reptiles that dominated the Mesozoic seas.
Some of the most extraordinary bodily transformations in evolution have occurred in animals that adapted to life in the water from terrestrial ancestors, such as modern whales, turtles, and seals. During the Mesozoic, between 252 and 66 million years ago, as dinosaurs trampled the earth, many groups of reptiles took to the sea, such as ichthyosaurs, plesiosaurs, crocodiles, and mosasaurs.
In a new paper, published in the journal Palaeontology, a team of paleobiologists from Bristol used state-of-the-art statistical methods to conduct a first-of-its-kind large-scale quantitative study of the locomotion of Mesozoic marine reptiles.
The researchers collected measurements from 125 fossilized skeletons and used them to explore changes in swimming styles within lineages and over time, finding that there was no explosive radiation at the start of the Mesozoic, but rather a gradual diversification of modes of locomotion. , which peaked in the Cretaceous.
Lead author Dr Susana Gutarra, from Bristol’s School of Earth Sciences, said in a statement: “Changes in anatomy in transitions from land to sea are intimately linked to the evolution of swimming. For example “Flippers, sea lions have a relatively short forearm and large hands, very different from the walking legs of their ancestors. The rich fossil record of Mesozoic marine reptiles provided a great opportunity to study these transitions on a large scale.”
Co-author Beatrice Heighton said: “We included measurements of living aquatic animals, such as otters, seals and turtles, for which we know their swimming behaviour. This is very important in providing a functional reference for ancient species, with unknown swimming modes.” .
Following the late Permian extinction around 250 million years ago, various groups of reptiles became aquatic hunters and populated the early Mesozoic seas.
Co-author Dr Tom Stubbs said: “Following this devastating event, there was a gradual diversification of modes of locomotion, in contrast to the rapid radiation previously described for feeding strategies. This is fascinating because it suggests a pattern of ‘head first’ of evolution in certain lineages”.
This document sheds light on the swimming of specific groups. Dr Ben Moon explained: “Ichthyosaurs were highly specialized for aquatic locomotion very early in their evolution. This includes their close relatives, the hupehsuchians, which had a morphology unlike any other known aquatic tetrapod. Furthermore, we see overlap between mosasaurs and ichthyosaurs, indicating that mosasaurs evolved a mode of swimming using oscillating flippers, different from the eel-like body undulation suggested in the past.
“In contrast, we found no evidence of convergence between ichthyosaurs and metriorhynchids (the highly aquatic crocodyliform thalatosuchians). This group retained rather primitive-looking hind legs, which seems incompatible with tail-fin swing swimming.”
This study also delves into the evolution of size, a characteristic related to locomotion, animal physiology and oceanic productivity. Professor Mike Benton said: “We know that the transition to life in the water is usually accompanied by an increase in body mass, as seen in cetaceans, and one of our previous studies shows that large sizes benefit animals. by reducing the specific mass costs of hauling. Therefore, it was essential to explore this trait in the broader assemblage of Mesozoic marine reptiles.”
Gutarra added: “Body size follows a similar trend to the diversification of modes of locomotion, and the widest distribution of body size also occurred in the Cretaceous, confirming a strong connection between the two. The rate of increase and the upper limits of body size appear to vary greatly between groups. This is a fascinating observation. We need to further explore what factors influence and limit the increase in body mass in each group.”
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