Mystery of how the turtle's neck evolved may be solved by 150m-year-old fossil | Evolution

Mystery of how the turtle's neck evolved may be solved by 150m-year-old fossil

Examination of a fossilised turtle suggests the way modern animals withdraw both head and neck into their shells might be linked to capturing prey

It sounds like a tale worthy of Kipling, but how the turtle got its neck is a mystery that might have been solved by science.

Researchers say fresh examination of a fossilised turtle, thought to have lived around 150 million years ago, suggests that ability of turtles to withdraw their neck and head into their shells might have evolved as it allowed them to rapidly shoot their head forward to snap up prey.

The protection to the creature, the researchers add, was likely a benefit that emerged later in evolution.

“Most people believe that that particular way of retracting the head evolved for protection only,” said Jérémy Anquetin, a palaeontologist and co-author of the research from the Jurassica Museum in Switzerland. But, that, he says, is unlikely. “It has to evolve by steps, and for it to evolve by steps you have to have a value in it to be selected by natural selection.”

Writing in the journal Scientific Reports, the trio of researchers from Switzerland, Thailand and France, explain how they drew their conclusions by studying the fossil of a turtle from the Late Jurassic, known as Platychelys oberndorferi, that was discovered in Switzerland in the 19th century, but whose vertebrae had not been thoroughly examined before.

The creature, says Anquetin, was an early pleurodire – a type of turtle whose modern relatives bend their necks sideways and tuck their heads under their shells. However, the team found the animal’s neck to be surprisingly similar to those of modern creatures belonging to a second type of turtle – the cryptodires – who bend their neck vertically and can withdraw their head and neck completely into their shell.

“It is very bizarre in evolving in the late Jurassic a morphology that would evolve only millions of years later in cryptodires,” said Anquetin, highlighting that the two types of turtles evolved their neck mechanisms independently.

The discovery, says Anquetin, suggests that the neck withdrawal mechanism seen in cryptodires cropped up on more than one occasion in turtle evolution. “[We propose] that something very similar to what we have in our late Jurassic early pleurodire happened also in early cryptodires when they started to evolve vertical neck retraction,” said Anquetin.

But the fossils reveal that the ancient creature would have been unable to fully withdraw its head into its shell. That, says Anquetin, suggests that the trait might initially have evolved as a result of the benefits it offered for capturing prey, later evolving further to offer protection.

The suggestion, the team add, is supported by comparison with two living turtles, the alligator snapping turtle and the matamata, who are distantly related to each other but who both share similarities in their appearance with the fossilised creature.

“They usually live in the bottom of swamps or slow rivers and they walk in the bottom of the water amid the vegetation and they capture prey by very [quickly] projecting their head forward,” said Anquetin. “Our interpretation is that this fossil turtle probably lived in the same way as the two modern ones and that this particular neck anatomy which restricted the movement of the neck in the vertical plane was probably an adaptation to help the fast forward projection of the head to capture prey.”

While further studies are needed to back up the theory, Anquetin says the findings underscore the importance of fossils. “Evolution is always more complex than what we thought at first,“ he said.

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