Paleontologists have unveiled a colossal new species of Mosasaurus, measuring an impressive 13.2 meters (43 feet) in length, and equipped with serrated teeth, leading to its intriguing name: Tylosaurus rex.
Reconstruction of Tylosaurus rex in the Cretaceous Western North American Interior Seaway. Image credit: Alderon Games / Path of Titans.
Mosasaurs, ancient giant marine reptiles, thrived during the Late Cretaceous Period, approximately 100 to 66 million years ago.
Often likened to dinosaurs, these creatures are actually more closely related to contemporary monitor lizards and snakes.
The family Mosasaurs is categorized into four main subfamilies: Mosasauridae, Plioplatecarpinidae, Tylosauridae, and Halisauridae, each showcasing unique adaptations like flippers, streamlined bodies, and significant size variations.
Among them, Tylosaurid mosasaurs are characterized by a toothless snout, elongated tail, and minimally ossified limbs, adaptations that facilitated their life in open waters.
These ancient reptiles were among the first to achieve true gigantic sizes, surpassing 8 meters (26 feet) in length.
Tylosaurid fossils have been discovered across Europe, Asia, New Zealand, Africa, and Antarctica, with a remarkable abundance along the Western Interior Seaway of North America.
“Everything seems to be bigger in Texas, including mosasaurs,” stated study lead author Dr. Amelia Zietlow, a paleontologist from the American Museum of Natural History.
Dr. Zietlow’s research journey began as a doctoral student, when she identified what seemed to be a misclassified mosasaur fossil from the museum’s collection, previously labeled as Tylosaurus proliger.
Upon comparing her specimen with the holotype Tylosaurus proliger, she and her team concluded that their find, along with over a dozen similar fossils from various institutions, belonged to an entirely different mosasaur family.
This distinction was significant; the fossils of Tylosaurus proliger displayed finely serrated teeth, a rarity among mosasaurs.
While the typical Tylosaurus proliger specimen was found in present-day Kansas and dated to around 84 million years ago, the newly discovered fossils, primarily from Texas, are roughly 4 million years younger.
“The holotype for the newly categorized Tylosaurus rex is an impressive specimen displayed at the Perot Museum, first located in 1979 near Dallas,” remarked paleontologists.
Beyond its massive size, the newly identified Tylosaurus rex showcased a range of adaptations that contributed to its formidable jaw and neck muscles, indicating it was a powerful predator.
“Being approximately twice the length of the largest great white shark, Tylosaurus rex appears to have been a much more aggressive creature compared to other mosasaurs,” explained co-author Dr. Ron Tycosky, curator of vertebrate paleontology at the Perot Museum.
“Studies of well-preserved fossils gathered from across North Texas revealed unprecedented levels of internal conflict within this species, unlike any other Tylosaurus fossils previously documented.”
“Evidence of this aggressive behavior includes the “Black Knight,” a specimen housed in the Perot Museum that is missing the tip of its nose and has a fractured jaw, injuries likely caused by its own kind.”
“Other notable mosasaurus specimens previously known as Tylosaurus proliger, now reclassified as Tylosaurus rex, include the remarkable specimen ‘Bunker’ discovered in 1911 and exhibited at the University of Kansas, as well as ‘Sophie’ at Yale University’s Peabody Museum.”
The research team’s published paper appears in today’s Bulletin of the American Museum of Natural History.
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Amelia R. Zietlow et al.. 2026. A new giant species of Tylosaurus from Texas (Mosasauridae), and an updated character list for phylogenetic analysis of Mosasauridae. Bulletin of the American Museum of Natural History 482; doi: 10.1206/0003-0090.482.1.1
Source: www.sci.news
