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Greater variations existed within braincases of tyrannosaurs, study finds

The differences cited by the study shakes notions that little variation existed in dinosaurs that are closely related and that shared similar skeletons.

(CN) — Researchers now believe that closely related species of dinosaurs could exhibit greater variations in their brains and skulls than previously thought.

The results of a new study were published Thursday in the Canadian Journal of Earth Sciences, and challenge previous notions that the brains and surrounding bones of dinosaurs showed little differences within related species.

Researchers examined the bones of a late Cretaceous period tyrannosaur named Daspletosaurus, which lived roughly 75 million years ago and about 10 million years before its relative the Tyrannosaurus rex.

It was previously believed that even among related species of dinosaurs, that little variation would be present within their brains and surrounding area.

“Our study with the two Daspletosaurus specimens suggests otherwise,” said Tetsuto Miyashita, paleontologist with the Canadian Museum of Nature and senior author of the study. “It was surprising to see so many variations in the braincases even though the skeletons are similar.” 

The researchers believe these differences point to the fact that the two specimens, while both being daspletosaurs, are actually different species.

“We know that tyrannosaurs had relatively good-sized brains for a dinosaur, and this study shows that this pattern holds for Daspletosaurus. Furthermore, based on the shapes of the brain, ear structure and braincase, we suggest that these two specimens represent distinct species of daspletosaurs,” said Miyashita.

Scientists in both Canada and Argentina used CT scans on two well kept Daspletosaurus specimens to map and digitally recreate the brain, inner ear and braincase of the massive dinosaur.

The mapping of this area is important to researchers because it provides details on one of the more complex areas of a dinosaur’s body, and gives scientists information about the brain structure, cranial nerves, and sensory biology of the massive animal.

While this type of research can provide valuable information, it takes a tremendous effort to complete, with scientists investing hundreds of hours of work to recreate the brain and other parts piece by piece.

Due to the extensive amount of work required to do this type of research, similar studies have generally focused on only one specimen from a specific dinosaur species.

“Researchers have looked inside so few braincases in dinosaurs, typically one each for whatever species they studied, that this reinforced the assumption that these structures don’t change much within and among species. We just haven’t looked inside enough skulls to document variation,” said Miyashita.

One of the study’s co-authors, Ariana Paulina Carabajal, a dinosaur braincase expert in Argentina at the Instituto de Investigaciones en Biodiversidad y Medioambiente, provided the models of the brain and surrounding areas.

Within those models was evidence of the presence of large air sacs that would have filled up most of the braincase bones, and bony canals and thick nerve bundles that would have moved the dinosaur’s eyes.

“These cavities within the bones not only make the huge skull lighter, but also are related to the middle region of the ear,” said Paulina Carabajal. “The cavities probably helped to amplify sound and assist the system that communicates to the left and right ears, allowing the brain to determine where a sound is coming from.”

The international research was made possible because of the well-preserved specimens of the two daspletosaurs. The first of the skeletons was discovered in 1921 in Alberta near the banks of the Red Deer River and is on display at the Canadian Museum of Nature in Ottawa.

The more recently discovered second specimen was found in 2001 and is housed at the Royal Tyrrell Museum of Paleontology in Alberta. Miyashita will continue to study it alongside another author of the study, Philip Currie of the University of Alberta for use in a different study.

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