Prehistoric plesiosaur filter-fed like a whale

New research shows that a prehistoric marine reptile fed by filtering small animals out of the water using their long ‘needle-like’ teeth. A team of scientists from South America and the USA re-examined the fossilised skull of the plesiosaur Morturneria seymourensis and uncovered the first known case of filter feeding in a marine reptile. This research has been published in the Journal of Vertebrate Palaeontology.

“This fossil has puzzled me since I first saw it in 1997. The morphology is so bizarre. I couldn’t figure out what the parts were and how they fit together” said the lead researcher Robin O’Keefe.

Morturneria  seymourensis was first described from fossil skull fragments discovered on Seymour Island in Antarctica in the early 1980’s. By referencing new fossil material from closely related plesiosaur species, scientists were finally able to piece the fragments together and reveal how this extinct creature once looked.

Morturneria
Life reconstructions of what Morturneria seymourensis may have looked like. Sculpted by S.J. Godfrey

In doing so they made the surprising discovery that the teeth of Morturneria did not meet end to end like other plesiosaurs. Instead they pointed outwards to form a network of interocking spines.

“I think the teeth really tell the story; they are oriented at such a strange angle. But the angle makes sense if you are dragging the mandible through the sediment… It’s an adaptation for benthic feeding, straining invertebrates from the mud at the bottom,” said O’Keefe.

Unlike other fossil plesiosaurs that had narrow skulls Morturneria had rounded ‘hoop-like’ jaws that hinged far back at the base of the skull. This combined with an arched palate meant that the oral cavity of Morturneria could filter large amounts of water.

“The oral cavity is big, particularly in comparison with other elasmosaurs… We can’t make a quantitative estimate because we don’t know how stretchy the floor of the mouth was,” said O’Keefe.

Furthermore, the structure of Morturneria’s snout have lead researchers to think that it could have closed off its nostrils with a small muscular valve, thus allowing them to push water forwards through their delicate teeth to filter out food particles.

A similar method is used by modern day crabeater seals (Lobodon carcinophaga) whose specialised lobed-teeth form a sieve-like network. Whilst crabeater seals can still use their jaws to tackle bigger prey, such as fish and squid, most of their diet consists of small crustaceans filtered out of the water with their teeth.

crabeater-seal-541832_1920
Crabeater seal (Lobodon carcinophaga). Image: Pixabay

Despite being reliant on small food items, filter feeding is such an effective feeding method that is sustains the largest animals to have ever existed on our planet. Whales feed by filtering krill out of the water using large ‘baleen’ plates that hang from their upper jaws.

Morturneria probably also relied on small crustaceans as a major food source. The researchers found that the Morturneria skull shares similar features with modern day grey whales (Eschrichtius robustus), such as an arched palate with a midline-keel, showing a remarkable case of convergent evolution between these two unrelated animals.

Morturneria  seymourensis existed over 66 million years ago during the Late Cretaceous period. The researchers believe that these fossil fragments are from a juvenile and ongoing research on additional Mortuneria fossil fragments will allow researchers to estimate how big these creatures could have been.

Dr Robin O’Keefe is an Associate Professor at Marshall University, West Virginia, USA.

 


IMG_8491Article by James O’Hanlon

James is a research scientist and science communicator currently based at the University of New England, Armidale. He hosts the In Situ Science podcast and is sick of hearing people say bad things about spiders.

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