In Norse Mythology, Loki, the god of mischief, and Angrboða, a giant from Jotunneim, gave birth to three fearsome creatures: Fenrir, the giant wolf, Hel, the goddess of the Norse underworld, and Jörmungandr, a sea serpent. When Odin received the prophecy that the creatures will be a menace to the power of the gods, he confined them to different realms. Jörmungandr was cast to the great ocean that was believed to encircle Midgard, the world of mortals. It was prophesized that Jormungandr would have a bitter rivalry with Thor, the god of thunder. They shall fight three times and their final battle will be at Ragnarok, the twilight of the gods, when Jormungandr will finally leave the oceans and poison the sky.
Jormungandr was first mentioned in stories from around 200 AD, and appears on several pre-Christian and early Christian rune stones and engravings. Creatures like Jormungandr are repetead elements on diferentes cosmogies aroound the world. In South Asian myths, Naga is the god of oceans, responsible for the tides, floods, and waves.
The discovery of the bodies of huge animals and fossil bones has always stimulated the imagination of local people, giving rise to myths and legends. In 1968, American writer Lyon Sprague de Camp wrote in The Magazine of Fantasy and Science Fiction: “After Mesozoic reptiles became well-known, reports of sea serpents, which until then had tended towards the serpentine, began to describe the monster as more and more resembling a Mesozoic marine reptile like a plesiosaur or a mosasaur.”
Mosasaurs were large carnivorous aquatic lizards with a global distribution that lived during the Cretaceous Period. Their first fossil remains were discovered in a chalk quarry near Maastricht, in the Netherlands, and were initially identified as a whale. A few decades later, Georges Cuvier, the ‘Father of Paleontology’, confirmed the animal’s identity as some kind of gigantic extinct lizard, with some similarities in the morphology of the bones to those of contemporary monitor lizard.
Jormungandr walhallaensis (named after the Norse sea serpent), from the Pembina Member of the Pierre Shale Formation in Cavalier County, North Dakota, is a new genus and species of mosasaurine mosasaur. Discovered in 2015, the holotype (NDGS 10838) comprises a partial skull, seven cervical vertebrae with three hypapophyseal peduncles, 11 ribs, and five anterior dorsal vertebrae.
Jormungandr walhallaensis is estimated to be about 7 meters (24 feet) long, and lived about 80 million years ago. The new taxon shares some features with Plotosaurini (a sister genus to Mosasaurus) and Clidastes (a smaller and more primitive form of mosasaur, part of the Mosasaurinae subfamily) suggesting it may represent a transitional form between the two.
References:
Zietlow, Amelia R. et al, Jormungandr walhallaensis: a new mosasaurine (Squamata: Mosasauroidea) from the Pierre Shale Formation (Pembina Member: Middle Campanian) of North Dakota, Bulletin of the American Museum of Natural History (2023). https://digitallibrary.amnh.org/items/13b0485f-c73f-47f9-8d1d-0d4ab6aaedfb