Abstract
Numerous fossils belonging to the genus Cervus were collected from Yoshinoda, Sodegaura City, Chiba Prefecture. The fossil-bearing horizon is part of the Kiyokawa Formation, Shimosa Group. It is interpreted as a fluvial deposit which is assigned to the middle Middle Pleistocene (MIS7.4—7.2). Eighty-five specimens were identified based on their proportions and taxonomy. Of them, CBM-PV803 is identified as the left antler of Cervus (Sika) nippon Temminck (Japanese sika deer) based on the existence of three branches with four tines, the low position of the first fork (40mm from the lower border of the burr), the acute angle of the first fork (60 degree), the short length of the first tine (84mm) and the short distance between the first fork and the second fork (139mm). Metacarpal and metatarsal bones are identified as Cervus (Sika) sp. by their slenderer proportions than Cervus (Nipponicervus) spp. Other specimens, including postcranial bones (vertebrae, ribs, and limb bones), mandibles, skull fragments and teeth, are identified as Cervus sp. indet..
The existence of the sika deer suggests that the vicinity of Yoshinoda was part of a Temperate Zone with open forest in MIS7. CBM-PV803 marks the fifth record of Japanese sika deer with a highly accurate age, and it becomes one of the oldest (MIS7) records of the sika deer in Japan. This does not correspond to the previous scenarios of sika deer in Japan based on paleontological view, but matches the estimated divergence time of the West Japan group in the scenario based on molecular genetics.
