Turtles are known for their protective shells, and one of the important features of that shell is the ability of the creature to hide inside of it by retracting their limbs and their head.
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Some turtles retract their heads sideways, which are known as pleurodires while others pull their heads backwards in a straight manner, known as cryptodires, but in both instances, the head is protected by the much harder shell and gives the turtle a lasting chance against predators.
On the other hand, a new study published in the journal Scientific Reports would suggest that turtles may not have always retracted their heads for defensive purposes, and perhaps this was a behavior that came to be by way of evolution.
Early fossils of a specific kind of turtle dubbed Platychelys oberndorferi, which date back as much as 150 million years, reveal that early turtle species weren’t able to fully retract their heads into their shells like many species today can. Instead, the head was only able to retract so far before it couldn’t go any further, and at that point, it would still be sticking out of the shell.
They were able to deduce this by looking at the preserved remnants of bones and vertebrae in the turtle fossil’s neck region. The 150 million-year old fossil was long categorized as a pleurodire, but it would seem from the formations of these bones that this wasn’t entirely accurate.
“They were shaped as they should be in a different group of turtles," said study lead author Jérémy Anquetin from the Department of Geosciences, University of Fribourg, Fribourg, Switzerland. "We didn't expect to find anything like that."
According to the synopsis, the fossilized specimen would have been able to retract its head straight back partially, but not to the side. This meant the long-standing theory that the turtle was a pleurodire was incorrect, and that it had more cryptodire-like qualities, despite not being a true cryptodire.
With this in mind, the behavior of retracting its head couldn’t have been very ‘defensive’ at the time because the head was still very much exposed to predators. So that only leaves one other option: offense.
This led scientists to think of another possible theory, suggesting that perhaps early species of turtles weren’t as timid as modern-day species. Rather than hiding their heads in their shells, they were likely much more predacious, using their head retraction tactics as a way to launch their head forward more quickly to grab unsuspecting prey.
While the idea of a turtle head cannon might seem a bit out of this world, it would seem to be a viable answer to the creature’s mysterious past.
Today, turtles have far more predators to contend with than they did millions of years ago, so the head retraction tactics probably evolved to become defensive over time.
There is still a lot more research to be done to get to the bottom of why this ancient turtle species differs so much from modern turtles in terms of head retraction behavior, but because there are such limited fossil remnants to work with, there’s very little that research can help answer at this point in time.
Still, it should be interesting to see what science helps uncover about this mystery in the future.
Source: Smithsonian Mag