Abstract
To date, fossil deer (Ryukyu jika) Cervus astylodon (Matsumoto, 1926) occurs abundantly from Late Pleistocene fissure and cave deposits in four islands of the Ryukyu Islands : Tokunoshima, Okinawa, Kume, and Ishigaki. This study on Cervus astylodon from the comparative morphological viewpoint reveals that each of the four islands of the Ryukyu Islands yields a characteristic endemic morphotype.
Furthermore, on the island of Kume, several morphotypes can be distinguished. The four Kume morphotypes are characterized by different body-sizes and proportions of teeth and limb bones. These four morphotypes share characteristic metacarpal features, and demonstrate four phases in the dwarfing process. In the process of miniaturization, limb segments distal to the elbow and knee, exhibited a greater degree of dwarfing than did the humerus, femur, and mandibular teeth.
This process also indicates that dwarfism of Cervus astylodon in the Ryukyu Islands occurred bycontinuous morphological change in a relatively short period.
Consequently, morphotypes occur with higher frequency in insular than mainland environments. It is suggested that variation in size and form in deer is more likely to occur in limb bones, especially in metacarpal and metatarsal bones.
