How reptiles adapted to marine life

The inner-ear vestibular system of marine reptiles and cetaceans adapted in similar ways to open-ocean swimming, a study finds. During major evolutionary transitions, the development of new body plans allows animals to adapt to novel habitats and lifestyles. One of the most well-known examples are cetaceans, which evolved from terrestrial mammals into open-ocean swimmers, but relatively little is known about the earlier, land-to-sea transition of reptiles during the Mesozoic Era. Julia Schwab, Stephen Brusatte, and colleagues explored evolutionary trends in a key vertebrate sensory system, the inner-ear sensory system, which is involved in balance and equilibrium. Using computed tomography, the authors examined the anatomy of the inner-ear vestibular system of 18 extinct reptile species and 14 modern relatives. The authors focused on the bony labyrinth, a cavity in the inner ear that includes structures called the vestibule and semicircular canals. Compared with terrestrial species, open-ocean thalattosuchians, which are extinct crocodile relatives, had shorter, more compact labyrinths, wider semicircular canals, and an enlarged vestibule, similar to cetaceans. However, unlike adaptations of the inner-ear vestibular structures of cetaceans, those of reptiles developed after a prolonged semiaquatic stage and appeared after the first skeletal modifications for swimming. Taken together, the results demonstrate that distinct evolutionary routes resulted in similar vestibular system changes for different types of terrestrial animals that transitioned to open-ocean swimming, according to the authors.

Article #20-02146: “Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water,” by Julia A. Schwab et al.

MEDIA CONTACT: Julia Schwab, University of Edinburgh, UNITED KINGDOM; tel: 0044 7378 722702; e-mail:

[email protected]

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