Escape artist: Ancient reptile Captorhinus could detach its tail to elude predators

noreen.rasbach — Mon, 05 Mar 2018 16:05:05 +0000

Escape artist: Ancient reptile Captorhinus could detach its tail to elude predators noreen.rasbach Mon, 03/05/2018 - 11:05

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Department of Biology

Global

Research & Innovation

U of T Mississauga

Imagine a voracious carnivore sinking its teeth into the tail of a small reptile, anticipating a delicious lunch, when, in a flash, the reptile is gone and the carnivore is left holding a wiggling tail between its jaws.

A new study by a ��߲ݴ�ý research team led by Professor Robert Reisz and PhD student Aaron LeBlanc shows how small reptiles that lived 289 million years ago could detach their tails to escape the grasp of predators – the oldest known example of such behaviour. The study was published March 5 in the open source journal Scientific Reports.

The reptiles, called Captorhinus, weighed less than two kilograms – smaller than the predators of the time. They were abundant in terrestrial communities during the Early Permian period and are distant relatives of all the reptiles today.

As small omnivores and herbivores, Captorhinus and its relatives had to scrounge for food while avoiding being preyed upon by large, meat-eating amphibians and ancient relatives of mammals. “One of the ways captorhinids could do this was by having breakable tail vertebrae,” says lead author LeBlanc. “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."

The present day spiny-tailed iguana is similar to captorhinids, small reptiles that lived 289 million years ago and could detach their tails to escape the grasp of predators

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,” says Reisz, a Distinguished Professor of biology at U of T Mississauga.

The authors note that 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 ancient supercontinent of Pangaea. This trait disappeared from the fossil record when Captorhinus died out – and it re-evolved in lizards 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.

Read the research in Scientific Reports

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

This study was possible thanks to the treasure trove of fossils available at the cave deposits near Richards Spur, Okla.

The study’s research team included Reisz; LeBlanc, who is now a Killam postdoctoral fellow at the University of Alberta; research assistant Diane Scott; graduate student Yara Haridy; and Mark MacDougall, now a DAAD postdoctoral fellow at Humboldt University.

The research was supported by a discovery grant from National Sciences and Engineering Research Council (NSERC) and from U of T Missisauga.

Ancient amphibian had mouthful of teeth ready to grab you: U of T research

rasbachn — Thu, 14 Sep 2017 16:33:59 +0000

Ancient amphibian had mouthful of teeth ready to grab you: U of T research

rasbachn Thu, 09/14/2017 - 12:33

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The Early Permian dissorophid Cacops displays its fearsome dentition as it preys on the hapless reptile Captorhinus (illustration by Brian Engh)

Elaine Smith

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Elaine Smith

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Global Lens

��߲ݴ�ý Mississauga

Department of Biology

Paleontology

The idea of being bitten by a nearly toothless modern frog or salamander sounds laughable, but their ancient ancestors had a full array of teeth, large fangs and thousands of tiny hook-like structures called denticles on the roofs of their mouths that would snare prey, according to new research by paleontologists at the ��߲ݴ�ý.

In research published online in a recent issue of PeerJ, an open access journal, Robert Reisz, distinguished professor of paleontology at ��߲ݴ�ý Mississauga, explains that the presence of such an extensive field of teeth provides clues to how the intriguing feeding mechanism seen in modern amphibians was also likely used by their ancient ancestors.

The researchers believe that the tooth-bearing plates “were ideally suited for holding on to prey, such as insects or smaller tetrapods, may have facilitated a method of swallowing prey items via retraction of the eyeballs into the mouth, as some amphibians do today."

In many vertebrates, ranging from fish to early synapsids (ancestors of mammals), denticles are commonly found in dense concentrations on the bones of the hard palate (roof of the mouth). However, in one group of tetrapods, temnospondyls (which are thought to be the ancestors of modern amphibians), these denticles were also found on small, bony plates that filled the large soft part of the palate. The entire roof of the mouth was covered with literally thousands of these tiny teeth that they used to grab prey. Since these toothy plates were suspended in soft tissue, they are often lost or scattered during fossilization.

Denticles are significantly smaller than the teeth around the margin of the mouth – on the order of dozens to a couple hundred microns in length. They are actually true teeth, rather than just protrusions in the mouths of these tetrapods, says Reisz and his colleagues, Bryan Gee and Yara Haridy, both graduate students in paleontology.

“Denticles have all of the features of the large teeth that are found on the margin of the mouth,” says Reisz. “In examining tetrapod specimens dating back (approximately) 289 million years, we discovered that the denticles display essentially all of the main features that are considered to define teeth, including enamel and dentine, pulp cavity and peridontia.”

A look at the skull of a small amphibamid dissorophid called Passawioops, with the tiny palatal plates in place in the roof of the mouth, with two close-ups to the right.

In reaching these conclusions, the researchers analyzed specimens unearthed from the fossil-rich Dolese Brothers Limestone Quarry near Richards Spur, Okla. They were extraordinarily well preserved, making them ideal candidates for study.

The researchers extracted and isolated the denticle-bearing plates, created thin section slides and examined them under the microscope – no small feat since denticles on this animal were only about 100 microns long.

Reisz and his graduate students suggest that the next big question relates to evolutionary changes to the overall abundance of teeth: If these ancient amphibians had an astonishing number of teeth, why have most modern amphibians reduced or entirely lost their teeth?

The research was supported by the Natural Sciences and Engineering Research Council of Canada.