The discovery of a unique nasal adaptation in the skulls of extinct wildebeest-like creatures on Kenya's Rusinga Island provides insight into how different species adapt and evolve similar features, even when those species are not closely related.
Dr. Daniel Peppe, associate professor in Baylor's Department of Geosciences, co-directed the research team that uncovered nearly intact skeletons of Rusingoryx atopocranian, a wildebeest-like creature that has been extinct for more than 40,000 years. While scanning the skulls, they found something unexpected--a long, curved nasal tract that resembled nasal passages found only in dinosaurs.
"Rusingoryx atopocranian had a strange bump on it's head. Atopocranian translates to 'strange skull.' Initially, people interpreted the bump to mean it had a long, fleshy nose like a trunk," Peppe said. "We later suggested that was unlikely, but didn't know what the strange skull shape was for. We CT scanned some skulls and the scans revealed a really long nasal tract that we've only seen in one other type of animal, a lambeosaurine hadrosaur."
The discovery of the similar nasal tract in two disparate animals is an example of convergent evolution, which is when different species develop the same features independently of one other.
"These are two animals that are not closely related. They are from very different animal groups and they lived in very different times--
hadrosaurs lived 66-85 million years ago, and the Rusingoryx lived from 100,000 to 40,000 years ago. But when you closely examine the skulls of closely related species of hadrosaurs, you see how their nasal pathways evolved. They elongated and developed more twists. We see the same progression in Rusingoryx and species related to it. So they essentially evolved the same features in their nasal passageways in the same way," Peppe said.
The reason the hadrosaur and Rusingoryx probably evolved the similar features, Peppe and his team hypothesize, is vocalization. Similarities between the two species' social habits provide insight into why that might have been necessary. Both species were migratory and traveled in herds, meaning there was a need to communicate and warn other herd members of incoming threats.
"Based on the nasal passage itself, we think the noise would have sounded like a vuvuzela," Peppe said. "If you add any fleshy bits to the nose, we think its even possible that their vocalization level was low enough that carnivores might not have been able to hear it, allowing herds to communicate to avoid predators."
Peppe and his team's findings were published in Current Biology. They studied the paleoenvironment of equatorial Eastern Africa and how it might have influenced human behavioral evolution when they made their unexpected discovery. In addition to revealing more about convergent evolution, their findings provide more information about how humans and animals interacted on the ancient landscape. Several of the skeletons of Rusingoryx had cut marks left by humans. Peppe believes Lake Victoria was once grassland, which limited obstacles to animals migrating across Africa and the ways that humans could track and hunt them. Humans may have hunted the Rusingoryx and chased a herd into a river system, where they drowned.
"In the late Pleistocene about 50,000 to 100,000 years ago, when Rusingoryx was alive, Lake Victoria was either much smaller in size or had completely dried up and was replaced by a large grassland that probably expanded northward from the Serengeti," Peppe said. "The removal of the geographic barrier allowed large mammals, like Rusingoryx to migrate across the region and also allowed a mixture of animals that now live far to the north of the equator to mix with animals that today live only south of the equator. Early modern humans were likely following the migrating animals, which may have allowed them to disperse across and out of Africa."
Going forward, Peppe's team will study further factors that led to these animals evolving their "strange skull" adaptation and examine how the once common Rusingoryx became extinct.