An Attempt at Age Estimation of the Ryukyu Long-Furred Rat (Diplothrix legata) Using Tooth Wear Analysis: First Report on the Difference in Molar Wear Patterns between Rats in Okinawajima and Amami-Oshima Islands

Nozomi Nakanishi, Yuzuha Tsubasaka, Ibuki Sawanaka, Kei Kondo, Shun Kobayashi, Masako Izawa, Shoji Hayashi

Age estimation of the Ryukyu long-furred rat Diplothrix legata, which inhabits only three islands in Central Ryukyus, was conducted by analyzing molar wear. We measured the skulls and examined the molar wear condition of 87 and 19 individuals from Okinawajima and Amami-Oshima Islands, respectively. The molar wear was divided into seven stages. Stage I individuals whose third molars were in the process of eruption were considered juveniles emerging from nests and their skull lengths were < 50 mm. On Okinawajima, Stage I individuals were found only from November to January, and Stage II individuals (yearings) were found only from March to August. In contrast, the relationship between skull growth and molar wear was unclear on Amami-Oshima because individuals with skull lengths < 50 mm were included in Stage II and later. The skull length of Stage VII was significantly larger on Okinawajima than on Amami-Oshima. Furthermore, growth stage discrimination based on coat appearance did not coincide with the molar wear on Amami-Oshima. These results indicate that estimating the age of this species on Amami-Oshima using molar wear as on Okinawajima is difficult and that the relationship between age and molar wear should be examined on each island.

Mammal Study