Other than cute horse-family hybrids, it's a much rarer occurrence.
Kristopher Helgen, the curator of mammals at the National Natural History Museum, recently identified a new mammal species in the cloud forests lining the Andes Mountains of South America. He has named it the olinguito and classified it in the procyonidae family, the same as raccoons.
The olinguito itself has been described by the Smithsonian Institution as "a cross between a house cat and a teddy bear."
During a news conference earlier today, Helgen said that the olinguitos suffered a long case of mistaken identity. "Anyone who has seen them for hundreds or even thousands of years thinks they might have seen an olingo or a kinkajou," he said.
Although olinguitos live in the same geographic region as its relatives, they live in different habitats. Olinguitos were found at higher elevations, 5,000 to 9,000 feet above sea level.
Hopi Hoekstra, the curator of mammals in the Museum of Comparative Zoology at Harvard University, said the differences in appearance and habitat are strong pieces of evidence for calling the olinguito a new species. "There are color and size differences, and the other key piece is that they are ecologically distinct," she told ABC News. "If [olingos and olinguitos] were interbreeding a lot, they wouldn't be as distinct in their appearance."
It turns out that olinguitos aren't just found in the wild. The diminutive mammal might be hiding in plain sight in museum collections and even zoos. When Helgen looked up a DNA sample from an olinguito, he was surprised to see that there was a match on GenBank, a public database filled with DNA sequences.
Helgen and his colleagues linked the GenBank entry back to an animal that traveled through several different city zoos in the 1970s, including Louisville, Tucson, Salt Lake City and Washington. It ultimately passed away in the Bronx Zoo in New York City.
Helgen got in touch with one of the zookeepers who looked after this animal. He said at today's news conference that the zookeeper always thought it was strange that the animal wouldn't breed with other olingos. "It would never breed," Helgen said. "They were entirely different species."
Hoekstra said that while she's not yet ready to call the olinguito a new species, most of the evidence is there. "The next step is to do a thorough genetic survey between olingos and olinguitos," she said. "But I'm convinced that they're onto something. Once they collect the genetic data, that seals the deal for me."
The discovery of a new species isn't complete without a Latin name, and Helgen decided on bassaricyon neblina. Bassaricyon is a logical step because it shares enough characteristics with the olingo that they would fall under the same genus. But neblina has a dual meaning for the curator.
"Neblina references mist and fog and evokes this fragile habitat that's [the olinguitos] only home," Helgen said. "But it can also mean obfuscation, like being lost in the mist. Our pleasure is to bring the olinguito out of the fog."