A new giraffid (Mammalia, Ruminantia, Pecora) from the late Miocene of Spain, and the evolution of the sivathere-samothere lineage

Giraffe relatives with four horns once lived near Madrid. The animal had a moderately long neck, strong limbs and two small horns in front of two much larger, backward-curving ones. Named Decennatherium rex, it lived about nine million years ago, when the giraffe family included shapes very different from the tall, slender animals alive today.

María Ríos, Israel Sánchez and Jorge Morales examined a rich collection from Batallones-10 in Spain, including skulls, jawbones, limb bones and an articulated skeleton. They described the skin-covered bony headgear, called ossicones, and compared 111 anatomical features across 31 living and extinct animal groups to work out where the new species belonged in the giraffe family tree.

Their analysis placed Decennatherium near the base of a branch containing other four-horned giraffe relatives, extending that branch's known history back to the late Miocene in western Europe. The skulls also fell into two horn-size patterns, which the authors interpreted as probable differences between males and females. Fossils cannot reveal the animals' sex directly, and several relationships in the family tree had weak statistical support. What the bones establish is a much broader giraffe family: not simply modern giraffes with shorter necks, but animals with strikingly different bodies and headgear.