Unlike most plesiosaurs, Serpentisuchops pfisterae had both a long neck and large, elongated jaws.
Serpentisuchops pfisterae lived during the Maastrichtian age of the Cretaceous period, some 70 million years ago.
The marine reptile was more than 7 m (23 feet) long, had both a long serpentine neck and long crocodile-like jaws. That makes it an evolutionary oddball and a surprise for scientists.
“For comparison, your own neck has a mere seven vertebrae. Serpentisuchops pfisterae had 32 vertebrae,” said Professor Scott Persons, a paleontologist with the Mace Brown Museum of Natural History at the College of Charleston and the Glenrock Paleon Museum.
Serpentisuchops pfisterae was a member of Polycotylidae, a derived family of plesiosaurs with a cosmopolitan distribution throughout the Cretaceous oceans.
Its fossilized remains were recovered from the Pierre Shale in Wyoming, the United States.
During the life of Serpentisuchops pfisterae, a shallow sea covered much of North America’s interior. Many other marine reptiles swam in those waters.
Besides other plesiosaurs, of both the long- and short-necked variety, there were multiple kinds of mosasaurs.
“The abundance of other competing marine life may have been the very thing that led to the new plesiosaur’s unconventional body plan,” Professor Persons said.
“It’s called ecological niche partitioning. To avoid direct competition with each other, species have a tendency to evolve adaptations that let them access or specialize in a particular source of food, or other resource, that other species struggle to make use of.”
Professor Persons and his colleagues think Serpentisuchops pfisterae was especially good at snagging smaller and quick-swimming prey, like tiny fish or squid.
“The articulation joints between the basal neck vertebrae grant a lot of lateral flexibility,” Professor Persons said.
“You combine that with broad vertebral attachment surfaces for powerful neck muscles, and you have an animal that can rapidly swing its neck side-to-side.”
“The elongate and narrow jaws extended the animal’s reach that much farther and could be swished through the water with a minimum of drag.”
“What I think we have here is a fast, effective, sideways-striking fish snapper.”
Paleontologists, studying other species that are known from only isolated or neck-less fossil material, have generally assumed that, if their plesiosaur has long jaws, then it also must have a short neck. Serpentisuchops pfisterae proves that’s not necessarily true.
“Our scientific description of the new find, multiple older plesiosaur species now need to be carefully reassessed to make sure these animals’ neck sizes haven’t been underestimated,” the authors said.
“Once that’s done, Serpentisuchops pfisterae may prove to be much less unusual.”
The discovery is reported in a paper in the journal iScience.
Walter Scott Persons IV et al. A long-snouted and long-necked polycotylid plesiosaur from the Late Cretaceous of North America. iScience, published online September 26, 2022; doi: 10.1016/j.isci.2022.105033
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