A restoration of the giant, extinct sea turtle Ocepechelon.
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Art by C. Letenneur, from Bardet et al., 2013.
A restoration of the giant, extinct sea turtle Ocepechelon.

Paleontologists Ponder Suction-Feeding Sea Turtle

Turtles are weird. The evolutionary requirements of life in a shell made them so. Putting aside the nightmare-inducing sexual organs that chelonian copulation requires, turtles and tortoises are puzzlingly unique among vertebrates in having shoulders anchored inside their ribsinside their ribs. And those are just shared basics. When you get down to species specifics, turtles get stranger still.

Prehistoric forms only add oddities. In their constant sifting of the fossil record, paleontologists are continuing to find bizarre, shell-encased reptiles that deviate from our typical image of what a turtle looks like. The latest, described this week by Muséum National d’Histoire Naturelle paleontologist Nathalie Bardet and coauthors in PLoS One, was a suction-feeding giant that sculled the marine waters of prehistoric Morocco about 67 million years ago.

Named Ocepechelon bouyai, the Cretaceous sea turtle is known only from a complete, isolated skull. Not only is the skull from what must have been an enormous reptile, but the shape of the lone fossil is unlike any other turtle. Wide at the back, the 27 and a half inch long skull narrows in front of the eyes into a flattened tube. Ocepechelon didn’t have the short-faced look at modern sea turtles, but an unusual snout that recalls a toothless, beaked crocodile. The crocishness of Ocepechelon is only underscored by eyes and nasal openings oriented towards the top of the skull – marks of an ambush predator that lurked just below the surface, although one that lacked any dental armaments.

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The skull of Ocepechelon. From Bardet et al., 2013.

Among turtles, Ocepechelon is bizarre. But the ancient swimmer’s skull shape isn’t totally unique among vertebrates. The extinct turtle’s upper jaws, Bardet and colleagues suggest, bear some resemblance to the mouths of small pipefish and the larger, mammalian beaked whales. Since these animals feed by suction – creating a vacuum to draw in small prey – Bardet and collaborators suggest that Ocepechelon may have done the same. (There are living freshwater turtles who use this technique, as well, but their skull shapes are very different.) Paddling near the surface of the warm Cretaceous sea, the enormous sea turtle probably slurped “small fishes, cephalopods, and jellyfishes.”

Ocepechelon may have had some additional tricks for trapping prey. Perhaps, the researchers behind the new study speculate, the Cretaceous turtle had specialized, spiky papillae in the throat, much like modern leatherback sea turtles do. These traps not only filter water, but create a pointy obstacle to prey that may try to struggle out.

Whether or not Ocepechelon shared the frightening throat defenses of today’s leatherbacks is unknown. The fossil record did not preserve such clues. Even the body of Ocepechelon is a mystery. Presumably the turtle had paddles and a shell specialized for a life spent entirely at sea, but the bones crucial to testing those ideas have not yet been discovered. The lone fossil skull is a thread to follow back to the remnants of a time when the most impressive dinosaurs yet stomped on land and giant, suction-feeding sea turtles still swam the seas.

Reference:

Bardet, N., Jalil, N., de Broin, F., Germain, D., Lambert, O., Amaghazaz, M. 2013. A giant chelonioid turtle from the Late Cretaceous of Morocco with a suction feeding apparatus unique among tetrapods. PLoS One. 8, 7. e63586