This May Be 'Missing Link' in T. Rex Evolution

Ancestor 'Daspletosaurus wilsoni' offers further evidence of linear evolution
By Arden Dier,  Newser Staff
Posted Nov 29, 2022 10:05 AM CST

Paleontologists have uncovered a new species of tyrannosaur that they say serves as a "missing link" in the evolution of Tyrannosaurus rex. Experts from the Badlands Dinosaur Museum in North Dakota were digging at the Judith River Formation in Montana in 2017 when paleontologist Jack Wilson spotted a flat bone sticking out from the bottom of a cliff, Live Science reports. It would be another four years before jackhammers could cut through 26 feet of solid rock to reveal the fossilized skull and bone fragments of what's now dubbed Daspletosaurus wilsoni. The dinosaur lived about 76.5 million years ago, some 8.5 million years before T. rex emerged.

Researchers believe D. wilsoni descended from Daspletosaurus torosus but preceded Daspletosaurus horneri, which is thought to have emerged between 75 million and 77 million years ago. "The new species displays a mix of features found in more primitive tyrannosaurs from older rocks, like a prominent set of horns around the eye, as well as features otherwise known from later members of this group (including T. rex), like a tall eye socket and expanded air-pockets in the skull," paleontologists Elias Warshaw and Denver Fowler, lead authors of the study published Friday in Paleontology and Evolutionary Science, write in a release.

This adds further support to the theory that Daspletosaurus evolved in a single lineage, with species "very finely separated in time from each other, forming consecutive ladder-like steps" ultimately leading to T. rex. It also "seems to suggest that linear evolution is more widespread in dinosaurs, with branching evolution being less frequent than previously thought," according to the release. As opposed to linear or "anagenesis" evolution, "cladogenesis" evolution is marked by "successive branching events [that] produce many species that are closely related ... but represent evolutionary 'cousins' rather than ancestors and descendants," the researchers note. (Read more dinosaurs stories.)

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