Choerolophodon (Proboscidea, Mammalia) from a new upper Miocene locality: Kivi-1 (Iran)

摘要

In this article, we report on two proboscidean upper tusks from a new locality in Iran, Kivi-1 (KIV). The tusks are oval to circular in cross-section, lack an enamel band, are strongly curved and double-twisted, and turn inwards at the tip. This morphology permits the attribution to Choerolophodon, an elephantimorph proboscidean well distributed during the Miocene in the Old World and already known from the late Miocene of Iran. Although the known upper tusks of Choerolophodon are few, the current data indicate that the curvature of the upper tusks may have biostratigraphic significance: in earlier and more primitive representatives from the early and middle Miocene of Eurasia, the curvature is less pronounced, whereas in the later and more derived ones from the late Miocene, it is strong. Based on this feature, we propose that the horizons from which these tusks derive date to the upper Miocene. During this epoch, two choerolophodont species were present in the Greco-Iranian palaeobiogeographic province, C. anatolicus and C. pentelici, the latter one well represented in the nearby Maragheh faunas. Because more diagnostic specimens are so far lacking, we attribute the KIV specimens to Choerolophodon sp. indet. "derived morph". Based on the presence of either C. anatolicus or C. pentelici in KIV, a relatively open palaeoenvironment is assumed, in agreement with previous palaeoecological reconstructions from the wider region during this period.