D-FW researchers identify giant new mosasaur, Tylosaurus rex

A fossil long sitting in museum collections has been reclassified as Tylosaurus rex, a giant mosasaur from North Texas that lived about 80 million years ago and may have been one of the most formidable predators in the Western Interior Seaway.

Researchers from the American Museum of Natural History, the Perot Museum of Nature and Science and Southern Methodist University announced the finding Thursday, May 21, 2026, after reexamining more than a dozen fossils from North American museum collections. The animal, whose name means king of the Tylosaurus, was identified from specimens found primarily in northern Texas over several decades.

The holotype, cataloged as PMNS 8029, is part of the Perot Museum’s collection and is on public display in the Life Then and Now exhibit hall. Scientists said the specimen and related fossils had previously been grouped with Tylosaurus proriger until a closer look revealed a different pattern in the skull, jaw, mouth and teeth. Those distinctions were enough to separate it as its own species.

At up to 43 feet long, Tylosaurus rex ranks among the largest mosasaurs known. Its finely serrated teeth stood out as an unusual feature for mosasaurs and point to a predator built for slicing through prey in the seaway that once covered parts of North America, including what is now Texas. The species adds a larger body size and a more specialized feeding profile to the known diversity of mosasaurs, deepening what scientists can say about how these marine reptiles evolved and how they filled ecological niches in Late Cretaceous oceans.

The discovery also underscores the value of institutional collections in Texas. Perot Museum officials have emphasized that active paleontological research is central to the museum’s work and public mission, and this case shows how specimens already in storage can still alter the scientific record. A fossil already on display now carries a different significance: not just as a museum piece, but as evidence that the marine ecosystems of ancient Texas held a predator larger and more powerful than researchers had recognized.