Excerpted from Colbert, M. W. 2005. The facial skeleton of the early Oligocene Colodon (Perissodactyla, Tapiroidea). Paleontologia Electronica 8:12A:27p
Two skulls of the early Oligocene Colodon from the White River Group in South Dakota are much more derived than previously reported. In particular, morphologies of the facial skeleton and narial region are surprisingly modern, including a deeply retracted nasoincisive incisure, and other indicators of prehensile proboscis development. High resolution X-ray computed tomography (HRXCT) is used to explore the internal anatomy of these tapiroids, and reveals frontal sinuses, and an internal facial skeletal anatomy approaching that of modern tapirs. This not only records an earlier origin for these anatomical conditions than than previously indicated, but in a phylogenetic context indicates that Colodon is more closely related to Tapirus than is Protapirus.
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Colbert, M. W. 2005. The facial skeleton of the early Oligocene Colodon (Perissodactyla, Tapiroidea). Paleontologia Electronica 8:12A:27p