Endemism and migration in the Kochkor Basin? Identification and description of Adcrocuta eximia (Mammalia: Carnivora: Hyaenidae) and c.f. Paramachaerodus (Mammalia: Carnivora: Felidae) fossils at the Miocene locality of Ortok, Kyrgyzstan

摘要

Dentition from a Miocene hyaenid and a saber-toothed fetid are described from the Chu Formation of Kyrgyzstan. Identified as Adcrocuta eximia (UOMNH F-70508) and c.f. Paramachaerodus (UOMNH F-70509), these represent one of the only formalized descriptions of fossil taxa from the Miocene in Kyrgyzstan. These specimens were recovered from the Ortok locality at the northwestern corner of the Kochkor Basin, the youngest of the known bone-bed localities in the Chu Formation. Using bio- and magnetostratigraphy, the Chu Formation is attributed to the late Miocene to Pliocene, deposited approximately at 8 to 4 Ma. The Adcrocuta specimen consists of a partial dentary with condylar and angular processes, one upper, five lower teeth, and the partial root and alveoli of a fifth mandibular tooth. The c.f. Paramachaerodus specimen includes a partial M1, P4, and C1, and exhibits the features of the "scimitar-toothed" machairodontines. Preserved diagnostic characters place the Kyrgyz specimen closest to P. ogygia, although with certain features similar to that of P. transasiaticus, such as incipient crenulations on the canine. However, the age of the Kyrgyz specimen, approximately 6 Ma, is substantially younger than what is known for either of these taxa. We therefore hypothesize this Paramachaerodus specimen could be evidence of an endemic taxon in Kyrgyzstan from earlier migrating Asian species, potentially due to geological uplift with the Tien Shan Mountains. Both these fossils bring new evidence of the ecology and biodiversity of Chu fauna during the Late Miocene/Early Pliocene in Kyrgyzstan.