Full Breakdown
New Mosasaur Species Tylosaurus rex Redefines Late Cretaceous Marine Predators
5/28/2026, 8:17:12 PM
Discovery and Core Description
A team led by Amelia Zietlow reexamined Texas mosasaur fossils and identified a new species, *Tylosaurus rex*, described in the *Bulletin of the American Museum of Natural History*. The holotype, found in 1979 near a reservoir in northern Texas, measures up to 43 ft (13 m) and dates to about 80 Ma.
Background
Earlier, similar specimens were assigned to *Tylosaurus proriger*, known from Kansas deposits ~84 Ma. In the 1960s, paleontologist John Thurmond noted unusually large tylosaurs in northeast Texas, informally calling them “*Tylosaurus thalassotyrannus*.” Modern reanalysis of museum collections revealed these fossils constitute a distinct taxon.
Data Summary
- Length: up to 43 ft, among the largest mosasaurs.
- Age: ~80 Ma, Late Cretaceous Western Interior Seaway.
- Specimens: >12 Texas fossils plus reassigned “Bunker” (University of Kansas) and “Sophie” (Yale Peabody Museum).
- Morphology: larger body, finely serrated teeth, distinct skull proportions versus *T. proriger*.
- Violence evidence: “The Black Knight” (Perot Museum) lacks snout tip and shows a fractured lower jaw, interpreted as injury from another *T. rex*.
Official Statements & Institutional Support
Researchers stressed that the find challenges long-standing mosasaur phylogenies and underscores the need for modern analytical tools. The study involved scientists from the American Museum of Natural History, the Perot Museum of Nature and Science, Southern Methodist University, and Harvard’s Museum of Comparative Zoology. Institutional partners highlighted museum collections and confirmed funding from the National Science Foundation, Dallas Paleontological Society, Society of Systematic Biologists, Richard Gilder Graduate School, Gingrich Fund, and Carter Fund.
Verbatim Quotes
- “Everything is bigger in Texas and that includes the mosasaurs, apparently,” — Amelia Zietlow, lead author
- “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,” — Ron Tykoski, Perot Museum
- “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.” — Amelia Zietlow
- “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.” — Michael Polcyn
Significance
The species revises perceptions of apex marine predators in the Late Cretaceous, demonstrates the importance of revisiting historic collections, and positions Texas as a focal point for marine reptile evolution. The revised morphological dataset also prompts a re-evaluation of mosasaur evolutionary trees.
Next Steps
Researchers indicate that the revised dataset will be used to re-examine additional mosasaur specimens and refine phylogenetic models.
Conflicting Reports & Gaps
The precise number of *T. rex* specimens remains approximate (“more than a dozen”), and quantitative bite-force estimates are lacking, leaving uncertainty about the species’ predatory capabilities.
