The last surviving member of a successful subfamily known as the Protoceratidae, a purely north American group  whose remains are known from the middle Oligocene to the lower Pliocene. 

Synthetoceras, whose remains were discovered in Pliocene deposits of Texas, was the largest genus of the protoceratidae presently known. These animals had hypsodont (tall) grinding teeth, showing that they were grazing animals. The horn cores of the skull were of solid bone, most likely covered with tough skin in life, rather than keratin, like that found in modern day cattle. The males were endowed with large canine teeth and the most spectacular of the horn sizes. The feet were four- toed in the front and two in the back.

Although the protoceratinae are well represented over millions of years, their fossilized remains are not numerous.