The study of a tyrannosaurid reveals its face features and some relationships

Daspletosaurus horneri skull
Daspletosaurus horneri skull

An article published in the journal “Scientific Reports” describes the discovery of a new tyrannosaurid, a group of carnivorous theropod dinosaurs that included the famous T. rex. Called Daspletosaurus horneri (photo ©James St. John), it was discovered in Montana and has an age of about 75 million years. The fossils’ excellent state of preservation allowed an analysis that suggests that it had sense organs on its snout similar to those of crocodiles and was a descendant of Daspletosaurus torosus.

The discovery of many fossils of tyrannosaurids over the last few years showed the diversity in this group of dinosaurs. The excellent state of preservation of many of those fossils are allowing to reconstruct their relationships and also to better understand their biomechanical characteristics, their development, their anatomy, their evolution and more.

The Daspletosaurus genus was created in 1970 following the study of a partial skeleton discovered decades ago in Alberta, Canada, belonging to what was called Daspletosaurus torosus. Over the years a number of new species discovered were initially assigned to the genus Daspletosaurus but after a proper analysis were reassigned to other genera. This time, the scientists are not only convinced that the new species studied is part of that genus and called it Daspletosaurus horneri but also that it descended from Daspletosaurus torosus.

Fossils of Daspletosaurus horneri were mentioned for the first time in 1992 after the discovery of the first specimen in 1989 but there wasn’t a thorough study. However, it was suggested that the area between today’s Montana and Alberta tyrannosaurids had evolved from one to another with no other ramifications, which in evolutionary jargon is called anagenesis.

In 2007 Thomas Carr, a paleontologist at Carthage College, became interested in the dinosaur later called Daspletosaurus horneri and spoke with his colleague Jack Horner, the author of the first article on these fossils. After several years, eventually Carr was able to direct the team that studied them in depth giving this species a name and a lot more.

The isotopic analysis of sedimentary deposits in the area where Daspletosaurus horneri was found shows that it didn’t live in the same time as Daspletosaurus torosus. That helped to better define the timeline and the environmental and ecological changes that occurred in that area, known as the Two Medicine Formation. There is a geographical proximity and a sequentiality in the fossil presence, together with the similarities between the two species, suggest that Daspletosaurus torosus evolved into Daspletosaurus horneri.

The excellent preservation of the Daspletosaurus horneri fossils allowed to perform a reconstruction of its subcutaneous tissues. This type of work is done based on the traces that muscles, nerves and blood vessels leave on bones. It’s already been done in the past for many different animals and in 2009 even for a dinosaur called Pachyrhinosaurus.

In the reconstruction of those facial tissues, the researchers noted that Daspletosaurus horneri had more similarities with crocodiles than with birds. For this reason, their hypothesis is that its snout and perhaps that of other tyrannosaurids was covered with large and flat scales and had various sensory organs.

According to this reconstruction, Daspletosaurus horneri had no lips but this feature is a subject of discussion in particular about its cousin T. rex. Probably further research on the various species of tyrannosaurids will be needed to better understand certain details of their snouts and the similarities or differences between different species.

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