The “Diahot Tooth” is a Miocene rhinocerotid fossil brought by humans to New Caledonia

The “Diahot Tooth” is an isolated postcanine tooth of a large herbivorous mammal, discovered in the Diahot region of northern New Caledonia in 1875. Most authors have identified it as an upper premolar of a rhinocerotid, but an alternative proposal is that it belongs to a diprotodontoid marsupial that has been named Zygomaturus diahotensis. Either possibility raises biogeographical difficulties, because New Caledonia has been isolated from other major landmasses for 80 million years, and neither rhinocerotids nor diprodotontoids appear to be good candidates for such a long-distance overwater dispersal event. Here, we present a novel interpretation of the affinities and origin of the Diahot Tooth, based on qualitative study of its preserved morphology and quantitative phylogenetic analyses that include both rhinocerotids and diprotodontoids. We show that the Diahot Tooth most closely resembles the first deciduous premolar of Western Eurasian Miocene teleoceratine rhinocerotid Brachypotherium brachypus, with the few discrepancies relating to traits that are known to be variable in B. brachypus. Our phylogenetic analyses also support this relationship. The preservation of the Diahot Tooth closely resembles that of B. brachypus teeth from the “Faluns Sea” of the Loire basin, and we propose that the New Caledonian specimen originated there and was taken to New Caledonia by a European colonist during the mid-19th century, where it was lost, rediscovered, and incorrectly assumed to be autochthonous.