Tapiroidea: The first tapiroids, which appear in the fossil record around 50 MYA, show modifications in their skulls, including a retracted nasal bone, which indicate that a proboscis, like that of modern tapirs, had begun to evolve. The proboscis is a muscular structure, similar to that of an elephant's trunk but shorter, which is formed from the nose and upper lip. Even though the proboscis does not fossilize, we can trace the evolution of the structure in fossil tapirs by studying the shape of their skulls, and in particular the retraction of the nasal bone over the course of the group’s history. Many early tapiroids did not have severely retracted nasal bones, although their skulls all had enlarged nasal spaces, suggesting that enlarged specialized noses and upper lips were present.
Left: Skull of the early tapiroid Hyrachyus (AMNH 12364) from the Eocene of North America. Nasal bones show minimal retraction. Victoria Healy/AMNH. Right: Skull of the Miocene tapir Tapirus johnsoni (AMNH 37302) from Cherry County, Nebraska. Arrow shows position of greatly retracted nasal bone. Victoria Healy/AMNH.