A prehistoric animal similar in appearance to a modern wildebeest had a "trumpet-like nasal passage" that enabled it to produce a unique array of calls, a new study has found.
The animal's internal trumpet nasal passage has only been seen once before, in another beast that would seem to have little in common with this now-extinct hoofed mammal, Rusingoryx atopocranion.
"The nasal dome is a completely new structure for mammals - it doesn't look like anything you could see in an animal that's alive today," co-author Haley O'Brien of Ohio University, Athens, said in a press release. "The closest example would be hadrosaur dinosaurs with half-circle shaped crests that enclose the nasal passages themselves."
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For the study, O'Brien, co-author Tyler Faith of the University of Queensland and colleagues analyzed the remains of Rusingoryx. The fossils were unearthed on Kenya's Rusinga Island and date to the Late Pleistocene.
Faith explained that their curiosity was piqued in 2009, after they were told about a site called Bovid Hill. The hill had been so named because of an abundance of fossil Bovidae, the group including antelopes and buffaloes, eroding from its surface.
"After several years of collecting fossils from Bovid Hill, it became very clear that most of the fossils belonged to the poorly known species Rusingoryx atopocranion, described from the same site in 1983, and that we may be dealing with an entire herd that was somehow wiped out and buried at the site," Faith said.
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The researchers also uncovered stone tools and butchered bone, strongly raising the possibility that early modern humans were responsible for the concentration of Rusingoryx skeletons. In 2011, study co-author Kirsten Jenkins of the University of Minnesota took charge of excavations, hoping to find more complete fossils and to establish why so many skeletons had ended up in that spot. Along the way, she found several intact skulls.
"I was astonished to see that [the skulls] looked unlike any antelope that I had ever seen–the only thing more surprising would have been fossil zebras with horns growing from their heads!" Faith said. "The anatomy was clearly remarkable."
Faith and O'Brien CT-scanned the remains, which revealed their inner structures. They immediately noticed the similarity to hadrosaur anatomy around the nose area.
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The little-known hoofed mammals turned out to have a very unusual, trumpet-like nasal passage similar only to the nasal crests of lambeosaurine hadrosaur dinosaurs. These were duck-billed dinos that sported such prominent crests.
At first the scientists thought the hollow nasal dome might have had something to do with thermoregulation. After anatomical investigations and acoustical modeling, however, they now think the trumpet-like nasal tube may have allowed Rusingoryx to deepen its normal vocal calls.
Their calculations even suggest that the animals might have been able to call at levels very close to infrasound, such that other animals may not have been able to hear individuals in the herd calling back and forth to each other.
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Explaining why the wildebeest-like animal would have shared this trait with hadrosaurs, O'Brien shared that both types of animals were thought to have been highly social. Both animals are also believed to have communicated with each other across fairly large distances.
"Vocalizations can alert predators, and moving their calls into a new frequency could have made communication safer," she continued. "On top of this, we know that Rusingoryx and hadrosaurs were consummate herbivores, each having their own highly specialized teeth. Their respective, remarkable dental specializations may have initiated changes in the lower jaw and cheek bones that ultimately led to the type of modification we see in the derived, crest-bearing forms."
Next the researchers hope to learn more about how such unusual anatomy evolved. They also hope to determine what exactly caused the once-thriving Rusingoryx to disappear.