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CM 9401 is a hypothetically unnamed genus of tyrannosaurine dinosaur that lived in Montana during the Late Cretaceous.


CM 9401 was collected by John Bell Hatcher in 1903 from what was thought to be the Judith River Formation. However, analyses assigned CM 9401 to the Willow Creek Formation, Fergus County, Montana. In 2022, David Evans teased that work was being done on this specimen[1].


File:CM 9401 skeltal.png

Credit: Clumsystiggy on DeviantArt.

CM 9401 is a massive right lacrimal ~75 million years old, referred to ?Tyrannosaurus sp. by Michael Urban and Matthew Lamanna (2006). The lacrimal appears to lack a horn entirely. Certain features, such as a rugosity running along the dorsal that is very pronounced at the apex and appearing more inflated, is not seen in Tyrannosaurus or even Tarbosaurus. Thus, it has been tentatively referred to the former. However, if the Campanian age is true, since much of the discovery data is unknown because Hatcher's field notes were lost, this would make it the oldest occurrence of Tyrannosaurus. However, some find this to be unlikely, since most dinosaurs would not have this far of a temporal timespan (~10 million years estimated for Tyrannosaurus). Thus, there may be some potential for splitting CM 9401 into a new taxon. It was also suggested to be a new species of Tyrannosaurus or at least a closely-related taxon due to temporal range, but this was left a hypothesis in 2006.


CM 9401 lived in the Willow Creek Formation, which is known to straddle the K-PG boundary in some spots. However, CM 9401 is known from the Campanian. 10 million years prior to the mass extinction that took place at the end of the Maastrichtian. Willow Creek is also reported in western Canada along the Willow Creek tributary of the Oldman River. In this formation, it was contemporaneous with Montanoceratops and hadrosaurids. Additionally, many dinosaur egg fragments are known, including eggs similar to indeterminate theropods, dromaeosaurs, caenagnathids and enantiornithes. This ecosystem was humid[2][3][4][5][6].