New Alberta tyrannosaur blends two T. rex subfamilies — SkimNews
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- Mark Powers of the University of Alberta and colleagues classified the new species Tromerosaurus solumons from fossils first unearthed in southern Alberta in 2010 and 2011.
- Tromerosaurus solumons lived 77 million years ago, measured 8 metres long, and had lengthy, lean legs, making it a rare addition to a sparsely populated branch of the tyrannosaur family tree.
- The specimen has a hole near the front of its upper jaw, matching the tyrannosaurine Daspletosaurus, combined with a small sinus system characteristic of the albertosaurine Gorgosaurus libratus—yet was placed as an early albertosaurine.
- Powers said the species was "so different and so unique that it was very clearly a new species," with the feature mixture prompting calls to re-examine whether other tyrannosaurs have been correctly sorted into subfamilies.
- The find challenges the "stepwise growth into T. rex" evolutionary narrative, with Powers suggesting multiple tyrannosaur lineages coexisted until the end-Cretaceous rather than converging on a single endpoint.
- Jared Voris of the University of Calgary said researchers now need to examine fossils in 78- to 79-million-year-old rocks to clarify the evolutionary story of early albertosaurines.
Why it matters: The specimen violates the diagnostic traits that paleontologists use to split tyrannosaurs into two clean subfamilies—one jaw-hole links it to *Daspletosaurus*, while a sinus pattern links it to *Gorgosaurus*—forcing a re-examination of how those groups are defined and reshaping the textbook evolution leading to T. rex.
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