Then they somehow have to mate with only each other, rather than with either parental species, "hence allowing them to spin off onto their own, independent evolutionary trajectory and become a species of their own," Willis added. "Both of these conditions are hard to meet."
Scientists had thought hybrid speciation was exceptionally rare in mammals. "Mammals generally are less capable than other types of animals to produce healthy, fertile hybrids," Willis said.
Still, hybrids were not unheard of in cetaceans such as whales and dolphins—both in captivity and in the wild. Since cetaceans have very similar numbers of chromosomes across species, researchers had speculated they could produce viable hybrids more easily than other mammals.
"Ironically, one translation of clymene can mean notorious or infamous, and now this dolphin turns out it's living up to its name by being the first marine mammal known to arise through hybrid speciation," said study co-author Howard Rosenbaum, a marine biologist at the Wildlife Conservation Society and American Museum of Natural History in New York.