An Ohio University study revealed that the ancient wildebeest-like animals Rusingoryx atopocranion possessed an unusual trumpet-like nasal passage that has only been seen elsewhere in the nasal crests of lambeosaurine hadrosaur dinosaurs. The findings were made after the analysis of fossilized skulls that were unearthed on Kenya's Rusinga Island and are a perfect example of convergent evolution, a process whereby two distantly related species develop similar characteristics due to the adaptation to similar environments or ecological niches.
"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," said Haley O'Brien, co-author of the study, in a press release. "The closest example would be hadrosaur dinosaurs with half-circle shaped crests that enclose the nasal passages themselves."
"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!" said Tyler Faith, another co-author of the study. "The anatomy was clearly remarkable."
Faith and O'Brien further explored the anatomy of the Rusingoryx through the examination of six skulls from both juveniles and adults using CT scans, revealing an immediate similarity to hadrosaurs.
"We were expecting the inside of the dome to have something closer to normal mammalian anatomy, but once we took a look at the CT scans, we were pretty shocked," said O'Brien.
After anatomical investigations along with acoustical modeling, the team believes that the trumpet-like nasal passage likely allowed Rusingoryx to deepen its standard vocalizations, reaching levels close to infrasound so that other animals would be unable to hear the herds communicating with each other. Due to both the Rusingoryx and hadrosaur dinsosaurs being very social species, they likely communicated with each other over large distances, which is the probable explanation for the convergent evolution of this shared adaptation.
"Vocalizations can alert predators, and moving their calls into a new frequency could have made communication safer," said O'Brien. "On top of this, we know that [both] 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 findings were published in the Feb. 4 issue of Current Biology.
