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 asRusingoryxatopocranion, the little-known hoofed animalprobably looked somewhat likemodern wildebeest, except forone 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,explainsHaley O’Brien, who coauthored the paper describing the dome’sstructure inCurrent Biology. The closest example would be hadrosaur dinosaurs with half-circle shaped crests that enclose the nasal passages themselves.
The bizarre beasthas been knownsince the 1980s, from asite rich in bothadultand juvenileRusingoryxfossils, but the team behind this study wasonly directed to the site in 2009, and eventuallynoticed the odd structure on the complete skulls. After performing CT scans on themthe researchersrealized 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 theRusingoryxto completely alter their callsby 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 savannato 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, orof 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 unlikemodern elephants, which use infrasonic communication, sometimes over hundreds of kilometers.
The only other animals known to have had such strange structures on their heads weredinosaurs 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 animalsindependently evolve similar traits to adapt tosimilar environments.
Vocalizations can alert predators, and moving their calls into a new frequency could have made communication safer,saysOBrien. On top of this, we know thatRusingoryxand 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 theRusingoryxending up preserved at the same site. Among the bonesthey found stone toolsno 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.