English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The early Permian mesosaurs were the first amniotes to re-invade aquatic environments. One of their most controversial and puzzling features is their distinctive caudal anatomy, which has been suggested as a mechanism to facilitate caudal autotomy. Several researchers have described putative fracture planes in mesosaur caudal vertebrae — unossified regions in the middle of caudal vertebral centra — that in many extant squamates allow the tail to separate and the animal to escape predation. However, the reports of fracture planes in mesosaurs have never been closely investigated beyond preliminary descriptions, which has prompted scepticism. Here, using numerous vertebral series, histology, and X-ray computed tomography, we provide a detailed account of fracture planes in all three species of mesosaurs. Given the importance of the tail for propulsion in many other aquatic reptiles, the identification of fracture planes in mesosaurs has important implications for their aquatic locomotion. Despite mesosaurs apparently having the ability to autotomize their tail, it is unlikely that they actually made use of this behaviour due to a lack of predation pressure and no record of autotomized tails in articulated specimens. We suggest that the presence of fracture planes in mesosaurs is an evolutionary relic and could represent a synapomorphy for an as-yet undetermined terrestrial clade of Palaeozoic amniotes that includes the earliest radiation of secondarily aquatic tetrapods.

Conflicting evidence for the use of caudal autotomy in mesosaurs