What did plesiosaurs eat? When I was a kid, the answer was simple. Long-necked plesiosaurs like Elasmosaurus evolved their ridiculous necks to strike out at little fish and squirmy squid.
But recent discoveries have complicated the simplicity of those old images. Gut contents, as well as the mechanics of plesiosaur necks, have shown that at least some of these marine reptiles trawled along the bottom for crustaceans and other morsels. And a new analysis of one of the last plesiosaurs shows something stranger still - at least one plesiosaur evolved a way to strain tiny tidbits through its teeth.
Two years back, at the annual Society of Vertebrate Paleontology meeting in Dallas, paleontologist F. Robin O'Keefe announced the finding. Mortuneria, a plesiosaur found almost three decades ago in the roughly 66 million year old rock of Antarctica, was a filter feeder. Now the results have been officially published. The teeth tell the tale.
In most plesioaurs, the conical teeth of the upper jaw jut downwards and the teeth of the low jaw rise up to meet them, giving them snaggletoothed grins. But in Morturneria, O'Keefe and colleagues report, the needle-like teeth of the lower jaw angle out to the side and bend downwards, meshing with the upper teeth to make a sieve. No one has seen anything quite like this in a marine reptile before.
And there's more. The jaws of Morturneria were relatively weak - not at all suited to holding struggling prey - and the hoop-shaped lower jaw increased the volume of water this plesiosaur was able to take into its mouth. The anatomy of the reptile, then, indicates that Morturneria was able to do what some experts said plesiosaurs couldn't do - it was a suspension feeder, a marine reptile that evolved a unique way to strain food from the water.
Precisely how Morturneria went about feeding is still open to investigation. But, from the anatomy of the skull and jaws, O'Keefe and coauthors propose that Morturneria scooped up sediment and then, holding its jaws slightly open, somehow pumped out the sediment-laden water and trapped amphipods and other small prey with its teeth. This would've made Morturneria the Cretaceous equivalent of a gray whale, a reptile who was sifting the seas before the ancestors of cetaceans even began to enter the oceans.
Fossil Facts
Name: Morturneria seymourensis
Meaning: Morturneria honors geologist Mort Turner, while seymourensis is after the Antarctic island the fossils were found on.
Age: Cretaceous, about 66 million years ago.
Where in the world?: Seymour Island, Antarctica.
What sort of organism?: An elasmosaurid plesiosaur.
How much of the organism’s is known?: A partial skull and associated neck vertebrae.
References:
Chatterjee, S., Small, B. 1989. New plesiosaurs from the Upper Cretaceous of Antarctica. Geological Society Special Publication. doi: 10.1144/GSL.SP.1989.047.01.15
O'Keefe, F., Otero, R., Soto-Acuña, S., O'gorman, J., Godfrey, S., Chatterjee, S. 2017. Cranial anatomy of Morturneria seymourensis from Antarctica, and the evolution of filter feeding in plesiosaurs of the Austral Late Cretaceous. Journal of Vertebrate Paleontology. doi: 10.1080/02724634.2017.1347570
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