A giant sea predator that lived around 80 million years ago has been recognized as a new species after paleontologists revisited fossils stored in museum collections. Named Tylosaurus rex, the predator reached up to 13.2 meters (43 feet) in length and may have been one of the dominant hunters of its time.
The discovery did not begin with a spectacular new excavation but with a closer look at fossils that had already been collected decades ago. What researchers first thought belonged to one known species turned out to represent something different.
Mosasaurs were marine reptiles that lived during the Late Cretaceous, roughly between 100 million and 66 million years ago. They are often grouped with dinosaurs in popular discussions, even though they were actually more closely related to modern monitor lizards and snakes.
Among the different mosasaur groups, tylosaurines stood apart because of their elongated bodies, streamlined shape and unusual toothless snouts. They were also the first mosasaurs to reach giant size, with some individuals growing beyond 8 meters (26 feet). Fossils of these reptiles have been found across multiple continents, although North America’s ancient Western Interior Seaway remains one of their best-known habitats.
A Museum Fossil Turned Into A New Species
The study started when Dr. Amelia Zietlow, a paleontologist at the American Museum of Natural History, noticed that one fossil in the museum’s collection did not quite match its label. According to the researchers, the predator had been identified as __Tylosaurus proriger__.
After comparing it with the original reference specimen of that species, the team concluded that the predator fossil belonged to something else entirely.
That finding led to a broader review. More than a dozen similar fossils preserved in different institutions were examined and eventually reassigned to the same newly described species: Tylosaurus rex.
The differences were clear enough to stand out. The animals appeared larger than Tylosaurus proriger and had finely serrated teeth, something not commonly seen among mosasaurs. Dr. Zietlow summed it up with a simple observation:
“Everything is bigger in Texas and that includes the mosasaurs, apparently.”
Bigger, Younger And Mostly Found In Texas
One of the details that helped separate the two predator species was where and when they lived. As explained in the study, published in the __Bulletin of the American Museum of Natural History__, most fossils of Tylosaurus proriger come from present-day Kansas and date to around 84 million years ago. The fossils now assigned to Tylosaurus rex are mostly from Texas and appear to be about four million years younger.
“The holotype for the newly described Tylosaurus rex is a giant specimen displayed at the Perot Museum that was first discovered in 1979 along an artificial reservoir near Dallas,” said the authors.
Researchers estimate that Tylosaurus rex reached around 13.2 meters in length. The fossils also show features linked to especiallystrong jaw and neck muscles, pointing to a predator built for powerful feeding.
Fossils Hint At A Harsh Ancient Life
Size was not the only thing that caught researchers’ attention.Dr. Ron Tykoski, curator of vertebrate paleontology at the Perot Museum and co-author of the study, explained that several specimens show evidence of injuries that suggest unusually aggressive behavior. He said that:
“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.”
One specimen in particular, nicknamed The Black Knight, preserves a missing snout tip and a fractured lower jaw. Researchers said those injuries could only have been caused by another predator of the same species.
The reclassification also changes the identity of some familiar museum specimens. Bunker, displayed at the University of Kansas, and Sophie, housed at the Yale Peabody Museum, will now be recognized as Tylosaurus rex.
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