A new tyrannosaurus was discovered in the United States

A team of paleontologists has announced that they have identified the remains of a new tyrannosaurus in Montana. Daspletosaurus wilsoni exhibits a unique combination of features that indicate it represents a transitional stage in the line leading to Tyrannosaurus rex.

Tyrannosaurids are a family of large predatory theropods that include the famous T. rex. They were characterized by massive skulls, thick teeth and very short front legs. We are known to visit North America and Asia for a long time Much is still unknown about their evolutionary history.

This is especially true of the genus Daspletosaurus, which existed in western North America in Canada and the United States 77-74 million years ago. Lesser known than T. rex, these predators have yet to be measured eight nine meters long for almost three tons in scale.

Previously, two species were added to this genus: Daspletosaurus torosus and Daspletosaurus horneri. However, many paleontologists disagree on whether these tyrannosaurs belong to the same genus. Reconstruction of the evolutionary relationships of these predators has been hampered by the paucity of available specimens, hence the interest in this new discovery.

“Missing link” detection

Daspletosaurus wilsoni It roamed the Earth during the Upper Cretaceous period, about 76.5 million years ago. His fossilized remains, a left maxilla (upper jaw), were excavated in the Judith River Formation near Glasgow, Montana (USA).

The authors of the study in the journal Peerj note that Daspletosaurus wilsoni from older rocks shows a mixture of features found in more primitive tyrannosaurs, such as a prominent set of horns around the eyes, as well as features otherwise known from later members of this group (including tyrannosaurus rex), such as large eye sockets and enlarged air pockets in the skull.

In light of these analyses, it appears that this new species is “halfway” between older and younger tyrannosaur species. So it would be kind of missing link allows the species of the genus Daspletosaurus to be linked to the leading lineage tyrannosaurus rex.

Left upper jaw Daspletosaurus wilsoni shown in lateral (A) and medial (B) views. Credit: Warshaw & Fowler, doi: 10.7717/peerj.14461.
Daspletosaurus wilsonie tyrannosaurs
An illustration of what it might look like Daspletosaurus wilsoni. Credit: Andrey Atuchin / Badlands Dinosaur Museum.

What does the study of the evolution of dinosaurs tell us?

In the Upper Cretaceous of North America, many dinosaur families are represented by several closely related species. Previously, they were thought to represent some diversity (i.e. lived at the same time), which would be evidence of branching evolution. However, several new examples and a better understanding of their temporal placement have improved this view.

Now we can see that many of these species actually diverged very finely over time, forming successive stages within a single evolutionary line, with an ancestor species becoming a direct descendant species.

It is called evolutionary anagenesis method. This contrasts with cladogenesis, which involves successive branching events with the formation of many closely related species that are similar but only evolutionary cousins, but not direct ancestors and descendants.

We knew that other families of dinosaurs (including the horned or duck-billed ones) evolved according to this mode of anagenesis. This study suggests that linear evolution is more widespread than previously thought, arguing that tyrannosaurs were too.

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