Paleontologists have just named the largest predator ever discovered in North Texas waters: Tylosaurus rex, a 43-foot-long marine reptile that ruled the Cretaceous seas with a skull-crushing bite and violent combat scars. The species, nicknamed the “T. rex of the sea,” was identified by researchers at the American Museum of Natural History, the Perot Museum of Nature and Science, and Southern Methodist University, based on 80-million-year-old fossils found near Dallas. Their study, published Thursday in the Bulletin of the American Museum of Natural History, reveals a predator twice the size of a great white shark—and far deadlier.
Why the “T. rex of the sea” isn’t just a bigger mosasaur
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The new species isn’t just bigger—it’s a redefinition of what mosasaurs could do. While its cousin Tylosaurus proriger (the largest North American mosasaur known for 150 years) maxed out at 30 feet, this T. rex stretched up to 43 feet long, with serrated teeth like a steak knife and jaw muscles powerful enough to crush skulls. “Everything is bigger in Texas and that includes the mosasaurs, apparently,” said Dr. Amelia Zietlow, lead author and paleontologist at the American Museum of Natural History. The discovery also pushes back against the idea that mosasaurs were passive hunters—fossils show evidence of brutal injuries, including a specimen nicknamed “The Black Knight” with a fractured jaw and missing snout tip, likely from intraspecies combat.
What makes this finding especially striking is how it was uncovered. The holotype fossil—now on display at the Perot Museum—was discovered in 1979 by kids on a family boating trip in Lake Ray Hubbard. “The kids got a little antsy, started getting a little whiny,” recalled Dr. Ron Tykoski, curator of vertebrate paleontology at the Perot Museum and co-author of the study. “So the parents beached the boat and told their kids to get out and play on the shore.” The kids found the bones, their mother recognized them as something unusual, and scientists rushed to document what turned out to be one of the most significant marine reptile discoveries in decades.
A misidentified giant: How science corrected a 150-year-old mistake
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For over a century, paleontologists misclassified these fossils as Tylosaurus proriger, a species first described in 1869. But Zietlow and her team realized the Texas specimens were fundamentally different—not just in size, but in anatomy. While T. proriger had a toothless snout and lived around 84 million years ago in Kansas, the new species had finely serrated teeth, stronger neck muscles, and thrived 4 million years later in Texas’s Western Interior Seaway. “The holotype for the newly described Tylosaurus rex is a giant specimen displayed at the Perot Museum that was first discovered in 1979,” the researchers noted in their study.
The confusion stemmed from a classic paleontological challenge: distinguishing between closely related species based on incomplete fossils. As Dr. Michael Polcyn, an SMU paleontologist and study co-author, explained, “These findings reshape both the physical and evolutionary picture of mosasaurs, underscoring Texas as a key region for understanding ancient marine ecosystems.” The study also assembled a comprehensive dataset of 300 mosasaur specimens, updating older research with precise head-to-tail measurements—a resource Zietlow hopes will finally give tylosaurs the attention they deserve.
Violent kings of the Cretaceous: What the fossils reveal about mosasaur behavior
Texas researchers discover new species of dinosaur
The most chilling detail? These weren’t gentle giants. Fossils show signs of violent injuries—something rare in other mosasaur species. A specimen at the Perot Museum, dubbed “The Black Knight,” has a fractured lower jaw and a missing snout tip, injuries that researchers attribute to combat with its own kind. “Besides being huge, roughly twice the length of the largest great white sharks, Tylosaurus rex appeared to be a much meaner animal than other mosasaurs,” Tykoski said.
This aggression aligns with what we know about other apex predators: size alone isn’t enough to dominate an ecosystem. The serrated teeth suggest a diet of armored prey, while the powerful jaw muscles imply a hunting style more akin to a tyrannosaur than a passive filter-feeder. “Tylosaurs are already notorious for being one of the largest-sized mosasaurs that ever lived,” said Tiago Simões, an evolutionary biologist at Princeton University. “This study further supports that, making them the largest group of mosasaurs that ever lived.”
Texas as the epicenter: How amateur fossil hunters changed paleontology
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The discovery also highlights the role of citizen science in paleontology. Many of the fossils used in the study were found by amateur fossil hunters in North Texas, including the holotype specimen discovered by kids in 1979. “The study underscores the importance of amateur fossil hunters and citizen scientists in North Texas,” Polcyn said. “Many of whom helped discover and preserve fossils used in the research.”
This isn’t the first time Texas has delivered a prehistoric blockbuster. The state’s rich fossil beds—formed by the ancient Western Interior Seaway—have yielded some of the most significant marine reptile discoveries in the world. But Tylosaurus rex stands out not just for its size, but for what it reveals about the late Cretaceous ecosystem. As Barry Albright, a professor emeritus at the University of North Florida, noted, “This discovery can provide more information on what species are related, and where in history certain adaptations in the mosasaur lineage appear.”
What this means for paleontology—and why Texas is still hunting for more
The implications of this study extend beyond Texas. By reclassifying these fossils, researchers have forced a reevaluation of mosasaur evolution. The new species lived later than T. proriger and in a different region, suggesting that mosasaurs diversified more rapidly than previously thought. “The diversity of a really, really cool group that lived during the same interval of time the dinosaurs lived,” Albright said, emphasizing how much we still have to learn about these ancient predators.
For Texas, this discovery is just the beginning. The state’s fossil-rich reservoirs—like Lake Ray Hubbard—continue to yield new specimens, and the Perot Museum is expanding its paleontology exhibits to showcase these findings. With more fossils likely to turn up, the “T. rex of the sea” may not be the last giant to emerge from Texas waters.
One thing is clear: the Western Interior Seaway wasn’t just a highway for mosasaurs—it was their battleground. And in that ancient ocean, size wasn’t everything. It was the serrated teeth, the powerful jaws, and the scars of survival that made Tylosaurus rex the true king of the Cretaceous seas.
