A middle Miocene mandible of Stegolophodon (Proboscidea, Mammalia) discovered in Katsura Village, Ibaraki Prefecture, eastern Japan

Abstract

A fossil elephantoid mandible was found in a mudstone boulder on the riverbed of the Nakagawa river at Katsura village, Ibaraki Prefecture, eastern Japan. This specimen (Katsura specimen) is assigned to a left mandible of the genus Stegolophodon. It is made of broken ramus with three molars in situ. The first molar is only represented by a tip of tooth-root, and the second one is severely abraded, but the last one is rather well preserved. The mandible is presumed to be derived from the lower part of the Asakawa Formation distributed around the fossil site. The geological age of the fossil is assigned to the earliest middle Miocene based on fission track dating and chronostratigraphic data.