Permian Reptiles Could Detach Their Tails to Escape from Predators

Friday, March 9, 2018

This is an illustration of Captorhinus, a captorhinid reptile that lived during the Permian period, showing breakable tail vertebrae. Image credit: Robert Reisz.

A new study shows how a group of ancient reptiles called captorhinids could detach their tails to avoid predation.

Captorhinids, also known as cotylosaurs, are a group of small to very large lizard-like reptiles.

They first occured in the Late Carboniferous of North America. In Late Permian times they gained a near global distribution but dissapeared from the North American fossil record, and finally they became extinct by the end of the Permian.

As small omnivores and herbivores, captorhinids had to scrounge for food while avoiding being preyed upon by large carnivorous amphibians and early mammals.

“One of the ways captorhinids could do this was by having breakable tail vertebrae,” said study first author Aaron LeBlanc, a Ph.D. student at the University of Toronto Mississauga.

Like many present-day lizard species, such as skinks, that can detach their tails to escape or distract a predator, the middle of many tail vertebrae had cracks in them.

It is likely that these cracks acted like the perforated lines between two paper towel sheets, allowing vertebrae to break in half along planes of weakness.

“If a predator grabbed hold of one of these reptiles, the vertebra would break at the crack and the tail would drop off, allowing the captorhinid to escape relatively unharmed,” said University of Toronto Mississauga’s Professor Robert Reisz, senior author on the study.

“Being the only reptiles with such an escape strategy may have been a key to their success, because they were the most common reptiles of their time, and by the end of the Permian period 251 million years ago, captorhinids had dispersed across the supercontinent Pangea,” the paleontologists said.

“This trait disappeared from the fossil record when these reptiles died out; it re-evolved in lizards only 70 million years ago.”

The researchers were able to examine more than 70 tail vertebrae (both juveniles and adults) and partial tail skeletons with splits that ran through their vertebrae.

They compared these skeletons to those of other reptilian relatives of captorhinids, but it appears that this ability is restricted to this family of reptiles in the Permian period.

Using various paleontological and histological techniques, the team discovered that the cracks were features that formed naturally as the vertebrae were developing.

Interestingly, the scientists found that young captorhinids had well-formed cracks, while those in some adults tended to fuse up.

This makes sense, since predation is much greater on young individuals and they need this ability to defend themselves.

The study was published online this week in the journal Scientific Reports.


A.R.H. LeBlanc et al. 2018. Caudal autotomy as anti-predatory behaviour in Palaeozoic reptiles. Scientific Reports 8, article number: 3328; doi: 10.1038/s41598-018-21526-3