Thursday, 23 February 2017

Prey: The Reason Turtles First Came Out of Their Shells – via Herp Digest




By  NICHOLAS ST. FLEUR FEB. 17, 2017, New York Times

If you are reading this hunched over your desk or smartphone, take this moment to loosen up your neck. Move it up and down. Now side to side. Roll it around clockwise and counterclockwise. Now retract it into your shell. Oh wait, you can’t do that — you are not a turtle. But have you ever wondered how these reptiles evolved to have such an interesting trick?

Scientists have, and now after studying the cervical bones of a 150-million-year-old turtle fossil, a team of researchers thinks that most turtles developed the ability first as a way to spring their head forward quickly to snatch prey, rather than as a means of protection, as was previously thought. The ability further evolved in some turtles to become a crucial part of their defenses. The researchers published their study Thursday in the journal 

The earliest known turtle ancestors were unable to retract their necks, but today’s modern species can. To understand turtle necks, however, you must first understand the two main types of turtles: cryptodires and pleurodires. 

Cryptodires include tortoises as well as most turtles: box turtles, sea turtles and alligator snapping turtles. They retract their necks straight back into their shells by folding the muscles vertically. Pleurodires include species that are mostly found in South America, Australia and Africa, like the matamata and snake-neck turtles. They bend their muscles horizontally to pull their necks back to the side and tuck it next to their shoulder.

Jérémy Anquetin, a paleontologist from the Jurassica Museum in Switzerland and the lead author, and his colleagues studied a 150-million-year-old turtle fossil that had some strange characteristics. The turtle, known as Platychelys oberndorferi, was from the Late Jurassic period and lived in what is today Germany and Switzerland. From its shell and skeleton the team could clearly tell that it belonged to the pleurodira group. But the shape of its two cervical bones suggested that it pulled its neck back vertically as cryptodires do, not horizontally. The neck also appeared to be unable to fully fold into the shell.

The neck retraction mechanism used by Platychelys oberndorferi and modern-day cryptodires to pull their heads straight back.

“Why did it have this neck retraction mechanism? This turtle is very peculiar,” Dr. Anquetin said. “Our fossil cannot retract it completely. It brings no value for protection, so we had to find an explanation for that.

The team homed in on the creature’s other features for clues. Its appearance was similar to modern bottom-dwelling turtles, suggesting that it was an ambush predator like the matamata turtle or the common snapping turtle. The two modern species are distantly related, but they hunt using similar tactics. They both lurk among the plants that shroud the floors of ponds, swamps and shallow lakes. Once an unsuspecting fish gets close enough, they strike.

“We can expect that our turtle was behaving the same way,” Dr. Anquetin said. He and his team report that the neck mechanisms seen in their extinct turtle and in modern-day cryptodires is an example of convergent evolution, meaning that both P. oberndorferi and present-day cryptodires evolved the ability independently of each other because of the evolutionary advantages that it offered them in their environments. The method of retracting their necks straight back allowed them to rapidly shoot out their heads and catch darting prey more easily.








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