Friday, February 5, 2016

[PaleoMammalogy • 2016] Unexpected Convergent Evolution of Nasal Domes between Pleistocene Bovids, Rusingoryx atopocranion, and Cretaceous Hadrosaur Dinosaurs

• Pleistocene Rusingoryx atopocranion are first known mammals with hollow nasal crests
Rusingoryx ontogeny and evolution are broadly similar to lambeosaurine hadrosaurs
• The best-supported nasal crest function is phonic modification
• Combination of convergent ontogeny, evolution, and function may explain crest rarity

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.

An artist's interpretation of Rusingoryx atopocranion on the Late Pleistocene plains of what is now Rusinga Island, Lake Victoria. Scientists have found many links between Rusingoryx and hadrosaur dinosaurs -- particularly the large, hollow dome that makes a crest on top of the animal's skull.
illustration: Todd S. Marshall

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 and Christian A. Tryon. 2016. Unexpected Convergent Evolution of Nasal Domes between Pleistocene Bovids and Cretaceous Hadrosaur Dinosaurs. Current Biology. DOI: 10.1016/j.cub.2015.12.050

Ancient wildebeest-like animal shared 'bizarre' feature with dinosaur via  @physorg_com
Ancient wildebeest-like animal had bizarre nose like dinosaur via @ABCNews

J. Tyler Faith, Jonah N. Choiniere, Christian A. Tryon, Daniel J. Peppe and David L. Fox. 2010. Taxonomic status and paleoecology of Rusingoryx atopocranion (Mammalia, Artiodactyla), an extinct Pleistocene bovid from Rusinga Island, Kenya. Quaternary Research. 75(3); 697–707. DOI: 10.1016/j.yqres.2010.11.006