A new species of mosasaur, an enormous carnivorous aquatic lizard that existed in the late Cretaceous period, has been found by scientists. The new species, which has “transitional” characteristics that situate it between two well-known mosasaurs, is named after Jormungandr, a sea snake in Norse mythology, and Walhalla, a small North Dakota town near where the fossil was discovered. Jormungandr walhallaensis is described in detail in the Bulletin of the American Museum of Natural History, which was published.
“If you put flippers on a Komodo dragon and made it really big, that’s basically what it would have looked like,” Amelia Zietlow, a Ph.D. student in comparative biology at the American Museum of Natural History’s Richard Gilder Graduate School, said of the study’s lead author.
More than 200 years ago, the first mosasaur was discovered, and the term “mosasaur” predates the term “dinosaur.” However, many uncertainties remain concerning these species, such as how many times they evolved flippers and became entirely aquatic (researchers believe it was at least three, and possibly four or more), and whether they are more closely related to monitor lizards or snakes. Researchers are still attempting to figure out how the various groups of mosasaurs are linked to one another, and this latest study adds another piece to the puzzle.
This fossil comes from a geologic time in the United States that we don’t really understand. The more we can fill in the geographic and temporal timeline, the better we can understand these creatures.Clint Boyd
The fossil on which the study is based was discovered in 2015, when researchers excavating in the northeastern part of North Dakota found an impressive specimen: a nearly complete skull, jaws, and cervical spine, as well as a number of vertebrae.
After extensive analysis and surface scanning of the fossil material, Zietlow and her collaborators found that this animal is a new species with a mosaic of features seen in two iconic mosasaurs: Clidastes, a smaller and more primitive form of mosasaur; and Mosasaurus, a larger form that grew to be nearly 50 feet long and lived alongside Tyrannosaurus rex. The specimen is estimated to be about 24 feet long, and in addition to flippers and a shark-like tail, it would have had “angry eyebrows” caused by a bony ridge on the skull, and a slightly stumpy tail that would have been shorter than its body.
“As these animals evolved into these giant sea monsters, they were constantly making changes,” Zietlow said. “This work gets us one step closer to understanding how all these different forms are related to one another.”
The work suggests that Jormungandr was a precursor to Mosasaurus and that it would have lived about 80 million years ago.
“This fossil comes from a geologic time in the United States that we don’t really understand,” said North Dakota Geological Survey co-author Clint Boyd. “The more we can fill in the geographic and temporal timeline, the better we can understand these creatures.”
“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,” coauthor Nathan Van Vranken of Eastern West Virginia Community and Technical College added, “and discoveries such as these can pique scientific curiosity.”