Sensitive T-Rex Relative Might Have Evolved In A Different Way

Artist's impression of Daspletosaurus horneri. Illustration is used courtesy of © Dino Pulerà.

Researchers from several American universities have finally given a name to a species of tyrannosaur dinosaur that was unearthed 25 years ago, helping build a clearer understanding of the T-rex family tree. The new species, called Daspletosaurus horneri, was found in Montana and might have had sensitive facial skin.

The announcement, published in Scientific Reports, is based on the presence and distribution of foramina, small holes in the bones where blood vessels and nerves connect with the skin. Nowadays, this is seen in crocodiles and alligators, which gave the researchers the idea that D. horneri might have had a sensitive snout too. The sensitivity might have been useful in catching prey and even in object identification and manipulation.

The discovery included the skeleton and skull of an adult and teenage D. horneri, as well as several fragments of other individuals of all ages. This gave researchers a good sense of the growth changes in the species. The fossils, which date from around 74 to 75 million years ago, are in excellent condition and reveal an intriguing face.

The face of D. horneri was covered in flat scales with sheaths of horn and smaller patches of armor-like skin. This species is smaller than its more famous relative, the T-rex. An adult could reach 9 meters (30 feet) in length – about three-quarters the size of a full-size T-rex.

“In terms of facial sensitivity, we would see that in all tyrannosaurs. The foramina and the texture, it’s in T-rex, DaspletosaurusAlbertosaurus, etc. That’s ancestral for the big tyrannosaurus,” lead author Professor Thomas Carr told IFLScience. “Tyrannosaurus provide an extreme case of having numerous foramina that penetrate the entire snout.”

When D. horneri was first discovered in 1992, researchers believed the T.rex to be the direct descendent of another Daspletosaurus, known as Daspletosaurus torosus. This is known as anagenesis, a gradual accumulation of changes over millions of years until a species is different, rather than a species splitting into two different ones with a common ancestor. Paleontologists believe that the diversity seen in dinosaurs is due to the latter.

“We are only at the very beginning of understanding how pervasive anagenesis might be," added Carr. "It could be that this is the process that produced diversity in other tyrannosaurus and possibly in other dinosaurs."

The new study shows that the Daspletosaurus were the grand-aunts of the T-rex, rather than the grandmothers, as well as highlights that the D. horneri directly evolved from the Daspletosaurus torosus.

The fossil record is not complete, but every new finding brings us closer to a clearer picture of how the dinosaurs evolved.



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