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| Artist’s reconstruction of the Permian reptile Captorhinus with an autotomous tail (inset showing anterior caudal vertebrae with fracture planes)
in LeBlanc, MacDougall, Haridy, et al., 2018.
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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.
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Figure 1 Fracture planes in captorhinid caudal vertebrae.
(a) Artist’s reconstruction of the Permian reptile Captorhinus with an autotomous tail (inset showing anterior caudal vertebrae with fracture planes). (b) Image and (c) SEM image of an isolated anterior caudal vertebra (ROM 73769) with a fracture plane passing through the centrum (black arrow). (d) Ventral view of an anterior, rib-bearing caudal vertebra (ROM 77410) showing the absence of any fracture plane. (e) Ventral view of a caudal vertebra bearing a fracture plane (black arrows) (ROM 73771) (f) thin-section through the sagittal plane of a caudal vertebra (ROM 73773) with a fracture plane (black arrow) passing through the ventral portion of the centrum. (g) Close-up of fracture plane (black arrows) in (f) passing into the notochordal canal.
Abbreviations: cb, cortical bone; cct, calcified cartilage; ce, centrum; nc, neural canal; ns, neural spine; ntc, notochordal canal.
Reconstruction by Danielle Dufault. Anterior is to the left in all of the images. |
A. R. H. LeBlanc, M. J. MacDougall, Y. Haridy, D. Scott and R. R. Reisz. 2018. Caudal Autotomy as Anti-predatory Behaviour in Palaeozoic Reptiles. Scientific Reports. 8, 3328. DOI: 10.1038/s41598-018-21526-3
Escape artist: Ancient reptile Captorhinus could detach its tail to elude predators