The facial skeleton of the early Oligocene Colodon shares several derived characters with both Tapirus and with other fossil tapirs from the late Oligocene to the Holocene (Colbert 1999). These characters involve morphological novelties, many of which are osteological correlates for a prehensile proboscis. These features are not known from other early Oligocene tapirs, or from geologically older tapirs. Protapirus simplex, which is roughly contemporaneous with Colodon, preserves less derived states for many of these same features. Thus, the evidence from the facial skeleton supports a phylogeny in which Colodon is more closely related to the crown-group Tapirus than is Protapirus. Because Protapirus has historically been considered the earliest tapirid, this also suggests that Colodon is a tapirid, and corroborates the assertion that the “Helaletidae,” to which Colodon had traditionally been referred, is not monophyletic (e.g., Colbert and Schoch 1998).
Regardless of the systematic significance of these specimens, they also serve as a foundation for interpreting the evolutionary modifications of the tapiroid facial skeleton. The two skulls illustrate a less derived state for tapiroids, that nonetheless have a number of osteological correlates for a prehensile proboscis, and that also show a telescoped condition. In many ways, the skull of Colodon represents an intermediate condition that bridges the morphological gap between the derived morphology of Tapirus and that of other Eocene and early Oligocene tapiroids which lack well-developed osteological indicators for a prehensile proboscis.