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Jormungandr: 24-foot lizard is a new link in mosasaur evolution

Scientists have uncovered a new species of mosasaur, a marine lizard that thrived during the late Cretaceous. The 24-foot beast offers intriguing clues about the evolution of these ancient creatures.

The species has been named Jormungandr walhallaensis in reference to the Norse sea serpent and the North Dakota city of Walhalla near its discovery site. 

“The tale of Jormungandr paints a wonderful picture and helps contribute to our understanding of the northernmost regions of the interior seaway, especially with the mosasaurs, and discoveries such as these can pique scientific curiosity,” said study co-author Nathan Van Vranken from Eastern West Virginia Community and Technical College.

Evolutionary questions 

Mosasaurs, as large carnivorous aquatic lizards, have long captivated the scientific community. The very term “mosasaur” even predates “dinosaur.” 

The discovery of the first mosasaur more than 200 years ago sparked numerous queries. Among them: their evolutionary journey towards developing flippers and full aquatic adaptation, which is believed to have occurred three or perhaps even four times. 

Another mystery revolves around their kinship – are they more closely related to monitor lizards or snakes? The recent study is helping to answer these questions. 

Awe-inspiring fossil

In 2015, experts unearthed an awe-inspiring fossil in northeastern North Dakota. This specimen includes an almost intact skull, jaws, cervical spine, and several vertebrae.

Amelia Zietlow, the study’s lead author and a PhD student at the American Museum of Natural History’s Richard Gilder Graduate School, provides a vivid description: “If you put flippers on a Komodo dragon and made it really big, that’s basically what it would have looked like.”

Iconic mosasaurs 

A detailed examination revealed that Jormungandr possessed characteristics found in two iconic mosasaurs: Clidastes, the more primitive and smaller variant, and Mosasaurus, a formidable creature stretching nearly 50 feet, which existed alongside the mighty Tyrannosaurus rex. 

Notably, this new species, estimated at 24 feet, boasted flippers, a shark-like tail, “angry eyebrows” due to a bony ridge on its skull, and a somewhat stumpy tail, shorter than its body.

Giant sea monsters 

“As these animals evolved into these giant sea monsters, they were constantly making changes,” said Zietlow. “This work gets us one step closer to understanding how all these different forms are related to one another.”

The study suggests that Jormungandr existed about 80 million years ago and was an evolutionary precursor to the colossal Mosasaurus.

“This fossil is coming from a geologic time in the United States that we don’t really understand,” said study co-author Clint Boyd from the North Dakota Geological Survey. “The more we can fill in the geographic and temporal timeline, the better we can understand these creatures.”

The study is published in the journal Bulletin of the American Museum of Natural History.

Image Credit: © Henry Sharpe

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