Abstract
Many lizards can drop a portion of their tail in response to an attack by a predator, a behaviour known as caudal autotomy. The capacity for intravertebral autotomy among modern reptiles suggests that it evolved in the lepidosaur branch of reptilian evolution, because no such vertebral features are known in turtles or crocodilians. Here we present the first detailed evidence of the oldest known case of caudal autotomy, found only among members of the Early Permian captorhinids, a group of ancient reptiles that diversified extensively and gained a near global distribution before the end-Permian mass extinction event of the Palaeozoic. Histological and SEM evidence show that these early reptiles were the first amniotes that could autotomize their tails, likely as an anti-predatory behaviour. As in modern iguanid lizards, smaller captorhinids were able to drop their tails as juveniles, presumably as a mechanism to evade a predator, whereas larger individuals may have gradually lost this ability. Caudal autotomy in captorhinid reptiles highlights the antiquity of this anti-predator behaviour in a small member of a terrestrial community composed predominantly of larger amphibian and synapsid predators.
Highlights
Many lizards can drop a portion of their tail in response to an attack by a predator, a behaviour known as caudal autotomy
Extant lizards display two types of caudal autotomy: (1) intravertebral autotomy, where the caudal vertebrae are able to break apart along a pre-existing fracture plane that passes through the centrum and neural arch; and (2) intervertebral autotomy, where the split occurs between adjacent caudal vertebrae[2,4]
We examined a large sample of isolated captorhinid caudal vertebrae from the karst cave system at the Early Permian (Artinskian, 289–286 Ma19) Richards Spur locality, located at the Dolese Brothers Quarry in Oklahoma, U.S.A., which allowed for the first detailed anatomical and histological analysis of these structures and direct comparisons with the autotomous vertebrae in modern lizards
Summary
Many lizards can drop a portion of their tail in response to an attack by a predator, a behaviour known as caudal autotomy. Extant lizards display two types of caudal autotomy: (1) intravertebral autotomy, where the caudal vertebrae are able to break apart along a pre-existing fracture plane that passes through the centrum and neural arch; and (2) intervertebral autotomy, where the split occurs between adjacent caudal vertebrae[2,4]. The former case is only seen in extant lepidosaurs and is associated with more extensive tail regeneration[1]. The only records of fracture planes in the caudal vertebrae of captorhinids suggest that they do not pass completely through the centrum as they do in modern lepidosaurs[1,2,9] and no detailed descriptions or comparisons www.nature.com/scientificreports/
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