Scientists discover giant sea predator Tylosaurus rex that terrorized ancient oceans

Science News from research organizations Scientists discover giant sea predator Tylosaurus rex that terrorized ancient oceans

Meet Tylosaurus rex: a school-bus-sized “sea tyrant” that may have been the most fearsome predator in Earth’s ancient oceans.

Date: May 23, 2026 Source: American Museum of Natural History Summary: A colossal new sea predator named Tylosaurus rex has been identified from fossils found in Texas, revealing a brutal 43-foot-long hunter that ruled ancient oceans 80 million years ago. The discovery not only introduces one of the biggest mosasaurs ever known, but also shakes up long-standing ideas about how these marine reptiles evolved. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY

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.

• RELATED TOPICS
  • Plants & Animals
    • New Species
    • Animals
    • Fish
    • Behavioral Science
  • Fossils & Ruins
    • Fossils
    • Evolution
    • Dinosaurs
    • Ancient Civilizations

• RELATED TERMS
  • Tyrannosaurus
  • Fossil
  • Feathered dinosaurs
  • Dinosaur
  • Sea water
  • Homo heidelbergensis
  • Homo ergaster
  • Marine conservation

Story Source:

Materials provided by American Museum of Natural History. Note: Content may be edited for style and length.

Journal Reference:

1. Amelia R. Zietlow, Michael J. Polcyn, Ronald S. Tykoski. Supplemetal material for \'A gigantic new species of Tylosaurus (Squamata, Mosasauridae) from Texas and a revised character list for phylogenetic analyses of Mosasauridae (Bulletin of the American Museum of Natural History, no. 482)\'. Bulletin of the American Museum of Natural History, 21 May 2026 DOI: 10.5531/sd.sp.84

Cite This Page:

• MLA
• APA
• Chicago

American Museum of Natural History. "Scientists discover giant sea predator Tylosaurus rex that terrorized ancient oceans." ScienceDaily. ScienceDaily, 23 May 2026. <www.sciencedaily.com/releases/2026/05/260522023111.htm>. American Museum of Natural History. (2026, May 23). Scientists discover giant sea predator Tylosaurus rex that terrorized ancient oceans. ScienceDaily. Retrieved May 23, 2026 from www.sciencedaily.com/releases/2026/05/260522023111.htm American Museum of Natural History. "Scientists discover giant sea predator Tylosaurus rex that terrorized ancient oceans." ScienceDaily. www.sciencedaily.com/releases/2026/05/260522023111.htm (accessed May 23, 2026).

Explore More

from ScienceDaily RELATED STORIES Giant Sea Monsters Lived in Rivers at the End of the Dinosaur Age Dec. 15, 2025 — Giant mosasaurs, once thought to be strictly ocean-dwelling predators, may have spent their final chapter prowling freshwater rivers alongside dinosaurs and crocodiles. A massive tooth found in North ... Scientists Assess How Large Dinosaurs Could Really Get July 24, 2024 — Could T. rex have been much bigger than we ever imagined? A new study using computer modeling suggests so—by as much as 70% more massive than the largest fossils found. Researchers argue that ... A New Species of Extinct Crocodile Relative Rewrites Life on the Triassic Coastline July 10, 2024 — The surprising discovery of a new species of extinct crocodile relative from the Triassic Favret Formation of Nevada, USA, rewrites the story of life along the coasts during the first act of the Age ... 'Juvenile T. Rex' Fossils Are a Distinct Species of Small Tyrannosaur Jan. 2, 2024 — A new analysis of fossils believed to be juveniles of T. rex now shows they were adults of a small tyrannosaur, with narrower jaws, longer legs, and bigger arms than T. rex. The species, Nanotyrannus ... Ancient Superpredator Got Big by Front-Loading Its Growth in Its Youth Nov. 28, 2022 — Whatcheeria, a six-foot-long salamander-like creature that lived 340 million years ago, was the T. rex of its time: the biggest, baddest predator in its habitat. A new study reveals how they grew to ... Famous Sterkfontein Caves Deposit 1 Million Years Older Than Previously Thought June 27, 2022 — Fossils found at the Sterkfontein Caves in South Africa reveal nearly four million years of hominin and environmental evolution. The Sterkfontein Cave has become famous for the hundreds of ... TRENDING AT SCITECHDAILY.com

Scientists Finally Think They Know Why T. rex Had Tiny Arms

This Alien Planet Has Rock Clouds That Vaporize Before Sunset

The Coldest “Stars” in the Galaxy Might Actually Be Alien Megastructures

Scientists Are Turning Ocean Trash Into Roads – and It’s Actually Working