Swimming giant: 80 million years ago there was also a T. rex in the sea, as fossil analyzes reveal. It is Tylosaurus rex, a newly discovered species of giant marine dinosaur. The marine predatory dinosaur had teeth like a steak knife, particularly strong jaw and neck muscles – and did not shy away from attacks on members of its species, as the paleontologists report. The up to 13 meter long Tylosaurus rex was one of the top predators in the Cretaceous seas.
While dinosaurs like Tyrannosaurus rex dominated the land, large marine dinosaurs were the top predators in the ocean. In particular, the mosasaurs, which were up to 17 meters long, developed into prehistoric rulers of the seas. Typical for these marine iguanas were long, toothy snouts, legs converted into fins and long tails with shark-like caudal fins. The first mosasaurs to grow to enormous sizes were the tylosaurs.
“Unique combination of features”
Now paleontologists have identified a new species of tylosaur that was among the largest and possibly most aggressive of its time. The fossils of these marine dinosaurs, which are around 80 million years old, were discovered more than 40 years ago in various former marine sediments in Texas. Some of these specimens have also been exhibited in museums for decades. But only now are comparative analyzes revealing that these tylosaurs, which are up to 13.20 meters long, represent a separate species.
“Our new species is characterized by a unique combination of features, including strengthened jaw and neck muscles,” report Amelia Zietlow from the American Museum of Natural History in New York and her colleagues. This, combined with its enormous size and saw-toothed teeth, made the marine dinosaur a fearsome predator of the sea. The team therefore named the new species Tylosaurus rex – the king of the tylosaurs.
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“Not only was the new T. rex huge, it also appears to have been more aggressive than other mosasaurs,” reports co-author Ron Tykoski from the Perot Museum of Nature and Science in Dallas. “Our analyzes of the well-preserved fossils from North Texas have revealed levels of intraspecific violence not previously known from other Tylosaurus species.”
An example of this is the fossil of a tylosaur nicknamed “The Black Knight” on display at the Perot Museum. He is missing the tip of his snout and his lower jaw is broken. As paleontologists explain, these serious injuries could only have been caused by a member of its own species.
New perspective on mosasaur evolution and diversity
The discovery of the new tylosaur species is also exciting in view of the family tree of these marine dinosaurs. Until now, paleontologists assumed that the tylosaurs had hardly changed over millions of years. “Of all the subgroups of mosasaurs, the tylosaurs show the most conservative anatomy: although they have existed throughout almost the entire history of mosasaurs – 94 to 66 million years ago – their species differ only minimally from one another,” the team explains.
It was also unclear until now whether the striking size differences between the tylosaurs were due to the individual age of the specimens or whether they were species-specific differences. The new analyzes now show that quite a few fossils that were previously assigned to the species Tylosaurus proriger actually come from the marine T. rex. “Our discovery therefore not only identifies a new species, it also highlights the need to revise some long-standing assumptions about the evolution of mosasaurs,” says Zietlow.
According to paleontologists, other previously unrecognized species could be hidden among the already known fossils. “We assume that the Tylosaurinae and the mosasaurs as a whole were probably more species-rich than previously assumed,” they write.
Source: Amelia Zietlow (American Museum of Natural History, New York) et al., Bulletin of the American Museum of Natural History, 2026; doi: 10.1206/0003-0090.482.1.1