How Species Change: Bizarre Ancient Giraffe Had Four Horns and a Short Neck

Decennatherium rex is an extinct animal in the ancient giraffe lineage. Ríos et al (2017)

With their comically long necks, horn-like head ornaments and lengthy strides, giraffes are some of the most bizarre creatures alive. But if you think they're weird, wait until you see their dead ancestors. Newly discovered fossils in Spain reveal that ancient giraffes were quite different from their modern counterparts—but just as interesting.

A nearly-complete fossil animal, found outside Madrid, is described in a paper published today in PLOS One. Decennatherium rex,as it's named, was a comparatively short-necked giraffe ancestor, with proportions more like a moose or a horse. It had four "ossicones," or horn-like bony projections on its forehead, two small ones in front and big ones pointing backward above the eyes. Modern giraffes, even females, have two ossicones per head.

Extinct (and modern) giraffids are notoriously bizarre. Sivatherium—with a neck that was longer than that of Decennatherium but shorter than that of a modern giraffe—had wide, palmated ossicones, which looked more like moose antlers. Bramatherium had a strange, four-pointed head ornament, and prolibytherium had large, flat, wing-like growths, like shields on its head. Scientists have discovered the ancient remains of countless weird giraffids with bizarre head ornaments and sloping backs that led to the narrow creature we have today.

This newly discovered ancient animal is an evolutionary offshoot of the "Sivathere" clade of animals, which includes Sivatherium and Samotherium, a similar-looking giraffid. As a "basal offshoot," that means that the animal was closely related to the common ancestor of sivatherium and samotherium, but it evolved in another direction. The discovery helps scientists understand the evolutionary timeline of giraffe ancestors and how they became the otherworldly mammals that they are today.

Many other extinct relatives of giraffes were equally bizarre. This image shows the African Miocene giraffids Palaeotragus primeavus (center left), P. germaini (center right), Climacoceras africanus (far left) and C. gentryi (far right). P. germaini stands about 3 meters from hoof to shoulder. Apokryltaros on Wikipedia

This discovery also influences our knowledge of how wide the Sivathere clade range was—it extended all the way from North America and Asia to at least the Iberian peninsula. Because we know that this animal lived roughly 9 million years ago, we know that the group was generally successful and lived on earth for a long time.

While Decennatherium might look goofy to some, it is actually a modest creature in comparison to modern giraffids. There are arguably four species of giraffes (and subspecies grouped within those species), including Masai, northern, southern and reticulated giraffes, and they are the tallest animals in the world. The only living non-giraffes in the giraffid group are okapis, which are brown and have zebra-striped legs and butts.

Giraffids represent a group of animals that was once shockingly diverse, successful and widespread. Now, the only animals that we have left are giraffes and okapis. Modern giraffes, which have a population only one-quarter the size of the African elephant population, are quietly going extinct as well. Without giraffes or okapis, the entire giraffid family might go the way of Decennatherium.