Ancient marine predator, Unktaheela specta, discovered in the American Midwest

Researchers from Marshall University have identified a new species of ancient marine predator. The fossils provide valuable information about the diversity and evolution of marine reptiles in Earth’s past. 

The research, led by Robert O. Clark, reveals a new species of polycotylid plesiosaur known as Unktaheela specta. The marine predator roamed the inland seas of what is now the American Midwest approximately 80 million years ago.

Marine reptiles of the Late Cretaceous 

Polycotylid plesiosaurs were a distinctive group of marine reptiles that adapted to life in the oceans of the Late Cretaceous. 

They possessed a unique set of physical characteristics and behaviors, including a streamlined body for fast swimming, a diet of marine animals, and the remarkable ability to give birth to live young. 

Unrecognized subgroup of plesiosaurs 

The study not only introduces the world to Unktaheela but also illuminates the murky waters of plesiosaur taxonomy. The discovery of Unktaheela specta has led to the identification of a previously unrecognized subgroup within the plesiosaur family. The researchers have named the subgroup Dolichorhynchia. 

This revelation led to the reclassification of two polycotylids previously grouped under the genus Dolichorhynchops. The species are now recognized as distinct genera named Martinectes and Scalamagnus.

Significance of Unktaheela specta

Clark emphasized the significance of Unktaheela in understanding the evolutionary relationships within the polycotylid lineage. 

“For years, which polycotylids were more closely related to which has been really tough for paleontologists to figure out,” said Clark. “Unktaheela is exciting because it’s given us a better understanding of these relationships.”

Predatory adaptations 

Measuring just 7.5 feet in length, Unktaheela specta stands out as the smallest known polycotylid. However, what it lacked in size, it made up for in predatory adaptations. 

Unktaheela was a fast-swimming, short-necked plesiosaur with an elongated snout packed with numerous pointed teeth, large eyes, and a wide skull. 

Visual hunting strategy

The skull’s architecture, featuring forward-angled eyes for binocular vision, a narrow snout for an unobstructed forward view, and a large, flat, bony ledge over each eye, draws striking parallels to those of predatory birds. 

These features likely provided Unktaheela with an advantage as it hunted just beneath the water’s surface, shading its eyes while stalking prey in the murky depths of the Western Interior Seaway, where it shared the waters with mosasaurs, sea turtles, sharks, and ammonites.

Naming of Unktaheela specta

The choice of name for this new genus, Unktaheela specta, is a tribute to the horned water serpent of Native American Lakota lore, reflecting the distinct visual adaptations of the plesiosaur. 

The fossils that led to the identification of this new species were discovered in the Late Cretaceous Sharon Springs Formation, spanning Wyoming and South Dakota, offering a tangible link to North America’s ancient past.

This discovery not only marks a significant milestone in the study of marine reptiles from the Cretaceous period but also highlights the intricate relationships within the plesiosaur family tree. 

More about polycotylid plesiosaurs

Polycotylid plesiosaurs were a group of marine reptiles that lived during the Late Cretaceous period, approximately 88 to 66 million years ago. 

They were part of the broader Plesiosauria order, which is famous for their distinctive body plan featuring a small head, a long neck, a broad, turtle-like body, and four flippers. However, polycotylids diverged from this typical plesiosaur design in several interesting ways.

Body shape of Unktaheela specta

Unlike their long-necked relatives, polycotylids had relatively short necks and more elongated, streamlined bodies. 

This body shape suggests they were fast swimmers, possibly using their strong, flipper-like limbs in a manner similar to modern sea lions and turtles to chase down prey, including fish and other marine animals.

Highly adaptable predators 

Polycotylids had a global distribution, with fossils found in North America, Europe, Asia, and Australia. The wide distribution indicates that they were highly successful and adaptable marine predators. 

Their teeth were sharp and conical, suitable for grasping slippery prey, and their jaws were strong. This suggests they could handle a variety of food sources.

Reproductive strategy

One of the most fascinating aspects of polycotylid plesiosaurs is evidence of live birth. A fossil discovered in Kansas, USA, shows a polycotylid mother and her unborn offspring, indicating that, unlike most reptiles, polycotylids gave birth to live young rather than laying eggs. 

This finding provides crucial insight into the reproductive strategies of marine reptiles. Live birth would have been advantageous in the open ocean, since laying eggs on land could be risky.

The research is published in the journal Cretaceous Research.

Image Credit: Robert Clark

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