Tens of thousands of years ago, a weird wildebeest-like creature, unlike any other mammal seen before or after its time, roamed the savanna. Known as Rusingoryx atopocranion, the little-known hoofed animal probably looked somewhat like modern wildebeest, except for one thing: it possessed a peculiar nasal structure more befitting of a dinosaur than a mammal.
“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,” explains Haley O'Brien, who coauthored the paper describing the dome's structure in Current Biology. “The closest example would be hadrosaur dinosaurs with half-circle shaped crests that enclose the nasal passages themselves.”
The bizarre beast has been known since the 1980s, from a site rich in both adult and juvenile Rusingoryx fossils, but the team behind this study was only directed to the site in 2009, and eventually noticed the odd structure on the complete skulls. After performing CT scans on them the researchers realized truly how remarkable the animals were. They discovered that the crests on their heads contained a winding nasal tube, which would have sat on top of enlarged sinuses. This would have allowed the Rusingoryx to completely alter their calls by deepening their normal voice.
The CT scan revealed that the nasal passage passes through the crest, and would have altered the creatures' vocalizations. O'Brien et al. 2016
But rather than bellowing across the savanna to other members of their herd, the researchers think that the crest and the sounds it produced might have been used, paradoxically, to avoid predators. The calculations suggest that the noises being produced were actually infrasonic, or of such a low frequency that it would have been outside of the hearing range of their predators, allowing them to communicate over vast distances without being heard. This is not unlike modern elephants, which use infrasonic communication, sometimes over hundreds of kilometers.
The only other animals known to have had such strange structures on their heads were dinosaurs called hadrosaurs, which lived tens of millions of years earlier. The researchers therefore suspect that this is a prime example of convergent evolution, in which two completely separate groups of animals independently evolve similar traits to adapt to similar environments.
“Vocalizations can alert predators, and moving their calls into a new frequency could have made communication safer,” says O’Brien. “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.”
The fossil site also hints at why so many of the Rusingoryx ending up preserved at the same site. Among the bones they found stone tools no doubt created by our ancestors, as well as cut marks on some of the fossils, indicating that they were hunted. This, mixed with a changing climate, is probably what led to the bizarre crested creatures dying out around 50,000 years ago.