By poring over the fossilized skulls of ancient wildebeest-like animals (Rusingoryx atopocranion) unearthed on Kenya’s Rusinga Island, researchers have discovered that the little-known hoofed mammals had a very unusual, trumpet-like nasal passage similar only to the nasal crests of lambeosaurine hadrosaur dinosaurs. The findings reported in the Cell Press journal Current Biology on February 4 offer “a spectacular example” of convergent evolution between two very distantly related taxa and across tens of millions of years, the researchers say.
“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,” says Haley O’Brien of Ohio University, Athens. “The closest example would be hadrosaur dinosaurs with half-circle shaped crests that enclose the nasal passages themselves.”
This evolutionary convergence may be explained by similarities in the way Rusingoryx and hadrosaurs lived. In fact, hadrosaurs are sometimes referred to as the “cows of the Cretaceous.”
At first, the researchers thought the hollow nasal dome might have had something to do with thermoregulation. Now, based on their anatomical investigations together with acoustical modeling, they think the trumpet-like nasal tube may have allowed Rusingoryx to deepen its normal vocal calls. In fact, their calculations 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.
Both Rusingoryx and hadrosaur dinosaurs are thought to have been highly social, O’Brien explains. They might have communicated with each other across fairly large distances.
The researchers say they will continue to explore the developmental shifts required to produce the animals’ bizarre morphology. They’d also like to understand what ultimately led the once-thriving Rusingoryx to disappear. More.
That’s an interesting question because Rusingoryx and the hadrosaur both had that “bizarre morphology” that enabled the crest in hadrosaurs.
Despite all the bloviating about “evolution,” we don’t know very much about the factors associated with: change in some life forms (evolution), extinction in others, and no change in a third group, despite vast environment upheavals (stasis)
See also: Evolution appears to converge on goals—but in Darwinian terms, is that possible?
Stasis: Life goes on but evolution does not happen
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Here’s the summary:
The fossil record provides tangible, historical evidence for the mode and operation of evolution across deep time. Striking patterns of convergence are some of the strongest examples of these operations, whereby, over time, similar environmental and/or behavioral pressures precipitate similarity in form and function between disparately related taxa. Here we present fossil evidence for an unexpected convergence between gregarious plant-eating mammals and dinosaurs. Recent excavations of Late Pleistocene deposits on Rusinga Island, Kenya, have uncovered a catastrophic assemblage of the wildebeest-like bovid Rusingoryx atopocranion. Previously known from fragmentary material, these new specimens reveal large, hollow, osseous nasal crests: a craniofacial novelty for mammals that is remarkably comparable to the nasal crests of lambeosaurine hadrosaur dinosaurs. Using adult and juvenile material from this assemblage, as well as computed tomographic imaging, we investigate this convergence from morphological, developmental, functional, and paleoenvironmental perspectives. Our detailed analyses reveal broad parallels between R. atopocranion and basal Lambeosaurinae, suggesting that osseous nasal crests may require a highly specific combination of ontogeny, evolution, and environmental pressures in order to develop. (Public access) – Haley D. O’Brien, J. Tyler Faith, Kirsten E. Jenkins, Daniel J. Peppe, Thomas W. Plummer, Zenobia L. Jacobs, Bo Li, Renaud Joannes-Boyau, Gilbert Price, Yue-xing Feng, Christian A. Tryon. Unexpected Convergent Evolution of Nasal Domes between Pleistocene Bovids and Cretaceous Hadrosaur Dinosaurs. Current Biology, 2016; DOI: 10.1016/j.cub.2015.12.050