Discovery Jörmungandr and Halaensis, a new species of mosasaurus, provides critical insights into the evolution of these ancient marine lizards and the geological history of Late Cretaceous North America. This transitional species, found near Walhalla, North Dakota, bridges the gap between primitive and more advanced mosasaurs, and suggests new details about their aquatic adaptations and lineage. Rebuild two Jörmungandr and Halaensis Mosasaurus fight. Credit: Henry Sharp
Jörmungandr, a massive 24-foot-long marine lizard that lived 80 million years ago, has been discovered to be a transitional species between two known mosasaurs.
Scientists have recently identified a new one Classify Mosasaurs, large carnivorous aquatic lizards that lived during the late Stone Age Cretaceous period a period. With “transitional” features that place it between two famous mosasaurs, the new species is named after a sea serpent in Norse mythology, Jörmungandr, and the small North Dakota town of Walhalla near where the fossil was found. paper describing Jormungandr walhallaensis It was recently published in Bulletin of the American Museum of Natural History.
Comparative features and historical context
“If you put fins on a Komodo dragon and made it really big, this is basically what it would have looked like,” said study lead author Amelia Zietlow, Ph.D. student in comparative biology at the Richard Gilder Graduate School of the American Museum of Natural History.
The first mosasaur was discovered more than 200 years ago, and the word mosasaur predates the word dinosaur. But many questions remain about these animals, including how often they developed flippers and became fully aquatic — researchers believe this happened at least three times, and possibly four or more times — and whether they were more closely related to monitor lizards or snakes. Researchers are still trying to determine how different groups of mosasaurs related to each other, and the new study adds a new piece to that puzzle.
Line drawing of a skull Jörmungandr and Halaensis. Credit: Henry Sharp
Discovery of fossils
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: an almost complete skull, jaws, and a cerebral spine, as well as a number of vertebrae.
After extensive analysis and superficial scanning of the fossil material, Zietlow and her collaborators found that this animal is a new species that contains a mosaic of features seen in two famous mosasaurs: Clydastis, a smaller and more primitive form of the mosasaur; And Mosasaurusa larger form that has grown to nearly 50 feet in length and lives side by side Tyrannosaurus rex. The specimen is estimated to be about 24 feet long, and in addition to fins and a shark-like tail, it would have had “angry eyebrows” caused by a bony protuberance in the skull, and a somewhat stubby tail that could have been even shorter. From her body.
Evolutionary insights and geological significance
“As these animals evolved into giant sea monsters, they were constantly making changes,” Zitlow said. “This work brings us one step closer to understanding how all these different shapes relate to each other.”
The work suggests this Jormungandr It was an introduction to Mosasaurus And he lived about 80 million years ago.
“This fossil comes from a geologic age in the United States that we don’t really understand,” said co-author Clint Boyd, of the North Dakota Geological Survey. “The more we can fill out the geographic and temporal timeline, the better we can understand these creatures.”
“A story,” added co-author Nathan Van Vranken of Eastern West Virginia Community and Technical College Jormungandr It paints a fascinating picture and helps contribute to our understanding of the northernmost regions of the Interior Seaway, especially with mosasaurs, and discoveries like this can spark scientific curiosity.
Reference: “Jörmungandr and Halaensis“A new mosasaurine (Squamata: Mosasauroidea) from the Pierre Shale Formation (Pembina Member: Middle Campanian) of North Dakota” by Amelia R. Zietlow, Clint A. Boyd, and Nathan E. Van Vranken, October 30, 2023, Bulletin of the American Museum of Natural History.
doi: 10.5531/sd.sp.60