Say the word “dinosaur” to someone and chances are, the first image that pops up in their head will be that of the Tyrannosaurus Rex. But despite our long-standing fascination with the dinosaur species, scientists still know very little about its evolutionary history. But a new fossil discovered in the United States could give scientists important clues about the ancient predator’s ancestry.
In a study published in the journal Paleontology and Evolutionary science, researchers reported the discovery of a new species—Daspletosaurus wilsoni. It displays many of the features found in more primitive tyrannosaurs from older rocks, like a prominent set of horns around the eye.
At the same time, it also has many of the features found in later members of the group, like the T.rex, including a tall eye socket and expanded air pockets in the skull. The scientists propose that this makes D.wilsoni a missing link between older and younger tyrannosaurus species.
Many dinosaur families that existed in North America during the Late Cretaceous period are represented by multiple species that are closely related. Earlier, it was thought that they lived at the same time, providing evidence of branching evolution. But now, based on new evidence from the discovery of new specimens, many of these species seem to have existed during different times.
This seemingly ties into the “anagenesis” mode of evolution, where one member of a species evolves directly into a descendant species, forming a consecutive “ladder” of evolutionary lineage.
This new study on D.wilsoni suggests that tyrannosaurs should be added to a growing list of dinosaurs for which anagenesis, or linear evolution, has been proposed. Anagenesis is contrasted with “cladogenesis,” where new species “branch out” into many species that are closely related and therefore, are similar to each other. In cladogenesis, these different species are “cousins” rather than ancestors or descendants.
According to the Dickinson Museum Center, the dinosaur was discovered by museum crew member Jack Wilson in 2017. Wilson spotted a flat piece of bone projecting from the bottom of a cliff. This bone was the middle part of the nostril of a tyrannosaur. The researchers dug through more than eight metres of rock lying over the bones to retrieve them.
The fossil got nicknamed “Sisyphus” after a Greek mythological figure due to the seemingly endless task of removing rock and soil before retrieving the fossil. The species’ name Daspletosaurus wilsoni means “Wilson’s frightful reptile,” as it was named after Wilson.
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