Convergent Evolution Led To Similar Bone Structure Between Ancient Beasts And Dinosaurs
The ancient wildebeest-like animal, Rusingoryx atopocranion, had an extraordinary trumpet-like nasal passage that has been viewed in other nasal crests of lambeosaurine hadrosaur dinosaurs. Fossilized skulls were found on Kenya's Rusinga Island, which led to the study. It is a good example of "convergent evolution", in which distantly related species evolve similar characteristics even as they adapt 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."
They also examined the anatomy of the Rusingoryx through six skulls of juveniles as well as adults with the help of CT scans. They showed a sudden 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.
The examinations, along with acoustical modeling made the team believe that the trumpet-like nasal passage permitted Rusingoryx to enhance its standard vocalizations, touching infrasound, making other animals unable to hear the herds communicating. The Rusingoryx and hadrosaur dinsosaurs were social species, so they communicated only over large distances, which indicates "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 its 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 study was published in Feb. 4,2016 issue of Current Biology.