Scientists have identified a massive new species of mosasaur, a marine reptile that lived alongside the dinosaurs and dominated prehistoric oceans. The newly described predator, named Tylosaurus rex (or T. rex), measured up to 43 feet long and ranks among the largest mosasaurs ever discovered.
The research was led by scientists from the American Museum of Natural History, the Perot Museum of Nature and Science in Dallas, and Southern Methodist University. Fossils of the giant reptile were found mainly in northern Texas and date back about 80 million years.
“Everything is bigger in Texas and that includes the mosasaurs, apparently,” said Amelia Zietlow, lead author of the study published in the Bulletin of the American Museum of Natural History.
Zietlow, now at the History Museum at the Castle in Wisconsin, began investigating the fossils while working as a Ph.D. student in comparative biology at the American Museum of Natural History’s Richard Gilder Graduate School. Her research started after she noticed that one fossil in the museum’s collection appeared to have been incorrectly identified as another species, Tylosaurus proriger.
Fossils Reveal a Different and More Powerful Mosasaur
After comparing the specimen with the original T. proriger fossil housed at Harvard University’s Museum of Comparative Zoology, researchers realized the Texas fossils represented a different species altogether. More than a dozen similar fossils stored in museums were eventually linked to the newly identified predator.
The team found several differences between the two species. The new mosasaur was larger, possessed finely serrated teeth rarely seen in mosasaurs, and came from a different place and time period. Most T. proriger fossils have been found in Kansas and date to roughly 84 million years ago, while the new species primarily lived in what is now Texas about 80 million years ago.
Researchers chose the name Tylosaurus rex as a tribute to paleontologist John Thurmond. In the late 1960s, Thurmond recognized that giant tylosaurs from northeast Texas appeared unusually large and may have belonged to a separate species. He informally referred to them as “Tylosaurus thalassotyrannus,” meaning “sea tyrant.”
The holotype specimen for T. rex is currently displayed at the Perot Museum in Dallas. The fossil was originally discovered in 1979 near an artificial reservoir outside the city.
Evidence Suggests Violent Battles Between Sea Predators
Beyond its enormous size, researchers believe Tylosaurus rex was built for strength and aggression. The species had adaptations linked to especially powerful jaw and neck muscles, making it a formidable hunter.
“Besides being huge, roughly twice the length of the largest great white sharks, T. rex appeared to be a much meaner animal than other mosasaurs,” said study co-author Ron Tykoski, vice-president of science and curator of vertebrate paleontology at the Perot Museum. “Through our study and examination of well-preserved fossils collected throughout the north Texas region, we have evidence of violence within this species to a degree not previously seen in other Tylosaurus specimens.”
Scientists point to one famous specimen nicknamed “The Black Knight” as evidence of this violent behavior. The fossil, housed at the Perot Museum, is missing the tip of its snout and shows a fractured lower jaw. Researchers say the injuries were most likely caused by another member of the same species.
Other famous mosasaur fossils previously identified as T. proriger are now being reassigned to T. rex. These include “Bunker,” a massive fossil displayed at the University of Kansas, and “Sophie,” which is exhibited at the Yale Peabody Museum.
Discovery Challenges Longstanding Ideas About Mosasaur Evolution
The study also tackles a major issue in mosasaur research. Scientists noted that the main dataset used to study evolutionary relationships among mosasaurs has changed very little over the past three decades.
To address this, the team created a revised dataset and developed a new evolutionary framework for tylosaurs. Their findings suggest that many previous studies may need to be revisited.
“This discovery is not just about naming a new species,” Zietlow said. “It highlights the need to revisit long-standing assumptions about mosasaur evolution and to modernize the tools we use to study these iconic marine reptiles.”
Co-author Michael Polcyn from Southern Methodist University said the discovery expands understanding of both the animals themselves and the ancient ecosystems they inhabited.
“These findings reshape both the physical and evolutionary picture of mosasaurs, underscoring Texas as a key region for understanding ancient marine ecosystems and signaling a new era of research into the evolutionary history of these formidable predators.”
Support for the research came in part from the National Science Foundation, the Dallas Paleontological Society, the Society of Systematic Biologists, the Richard Gilder Graduate School, the Gingrich Fund, and the Carter Fund.