­Trained Pronghorn - though I suppose antelope and giraffe are equally distant in their relation to pronghorns, it looks closer to the already established Antelope.

The pronghorn's closest living relative is the giraffe. That being said, giraffes have yet to appear in Magic, so who knows what creature type they'd receive.

From my understanding, among the ruminant branches, the pecora infraorder splits into two brances, one branch having giraffidae and the pronghorn, with the other branch having deer and another branch that splits into bovidae (which would include animals called antelope) and a branch for musk deer.