Presentation Information
[O12-P21]Identification of two types of rhinoceros fossils from the Mizunami Formation and determination of the shape of the mandible.
*momoha kano1, *yuna kawamori1, nanaki kuwashita1, eito kuwashita1, subaru emi1, ryouma funahashi1 (1. Gifu Prefectural Kamo High School)
Keywords:
Rhinoceros fossils,lower jaw,eating habits,habitat,tooth size
The rhinoceros fossils unearthed from the Mizunami Formation in Gifu Prefecture include two species: the large Brachypoterium? pugnator and the smaller Plesiaceratherium sp. In 2006, a specimen of the left lower jaw of a rhinoceros discovered in Minokamo City was examined and found to be consistent with the characteristics of the smaller P. sp. Furthermore, severe wear on the premolars and the presence of two unerupted premolars on X-ray CT images led to the estimation that it was a juvenile P. sp. Considering that the reason two rhinoceros species could coexist in the same area was due to differences in diet and habitat, the shape of the lower jaw was estimated by comparing the tooth size with that of extant rhinoceroses. The mesiodistal length ratio of P. sp. was close to that of the black rhinoceros, and the buccolingual width ratio was close to that of the Indian rhinoceros. P3-M2 of B.? pugnator were close to those of the white rhinoceros and Indian rhinoceros. Therefore, it was concluded that P. sp. had a short lower jaw and a narrow snout, similar to the black rhinoceros, while B.? pugnator had a long lower jaw and a broad snout, like the white rhinoceros. The difference in jaw shape is thought to be due to differences in diet, and this difference in diet may be the reason why the two species of rhinoceroses were able to coexist in the same area.