Perhaps the most remarkable feature of the living tapirs is their short, fleshy, prehensile trunk. The presence of this trunk is reflected in the shape of their facial skeleton. Examples of these skeletal indicators of a trunk include such things as: a loss of the bony wall of the nasal chamber; indications of areas where the muscles of the trunk might have attached; and a posterior displacement of the upper bones of the face relative to the bones surrounding the brain and the bones of the lower face. This displacement of bones of the face is called ‘telescoping.’ The evolution of the tapir’s trunk through time can be investigated by studying the shape of the skull of fossil tapirs, and by comparing the differences in the conformation of the features with the skulls of recent tapirs mentioned above.

This paper describes two skulls from a fossil tapir called Colodon from the early Oligocene epoch of South Dakota (about 30 Ma). The description of these skulls uses high-resolution X-ray CT technology to nondestructively explore the shape of the interior of the skulls. The skulls are surprisingly modern in their overall appearance, although they are not as modified in features related to having a trunk as the living tapirs. Nonetheless, based on their facial skeleton, these specimens almost certainly had a trunk similar to those seen in modern tapirs. This not only documents the antiquity of the trunk in fossil and recent tapirs, but also indicates that Colodon is more closely related to the living tapirs than had previously been recognized.