Classification and Genealogy
In 1967, Dr. Yoshinori Imaizumi (今泉吉典, Imaizumi Yoshinori) announced the Iriomote cat to the scientific community as a new species of feline in its own genus. It was labeled Mayailurus iriomotensis. Dr. Yoshinori Imaizumi pointed out that compared to other leopard cats, the Iriomote cat retained some especially primitive features. Judging from these characteristics, Yoshinori Imaizumi estimated that the Iriomote cat appeared as a species sometime between ten million years ago in the Miocene epoch and three million years ago during the Pliocene epoch. He also believed that they shared many primitive characteristics with fossils in the extinct Metailurus genus. He emphasized these points, stating that the Iriomote cat and Metailurus shared a common ancestor sometime between ten million and five million years ago, and from that he deducted that the Iriomote cat's ancestors must have widened its range from mainland Asia to Iriomote and other areas beginning three million years ago. It appears to be a very ancient species, a ‘missing link’, nearer to the common root of the cat tribe than any other extant species.
In contrast to Yoshinori Imaizumi's assertions about its unique characteristics, other researchers have strongly refuted the idea that the Iriomote cat is its own species ever since its discovery. Investigations involving skulls and teeth, samples and living animals, and genetic research were conducted to determine whether it is its own species or a subspecies of leopard cat. Because of these studies, it has been subordinated under the genus Prionailurus as Prionailurus iriomotensis.
The Iriomote cat's karyotype, the restriction fragment length of the ribosomal RNA (rRNA), and molecular phylogenetic analyses of the mitochondrial 12S rRNA and cytochrome b have proven to be identical, or nearly so, to the leopard cat's. The two cats are assumed to be extremely closely related, their differences being categorized as either intraspecies variations or individual mutations. Also, from the speed of cytochrome b's base-pair substitution and its diversity, it is estimated that the Iriomote cat diverged from the leopard cat around 180,000-200,000 years ago. According to marine geologists, the Ryukyu Islands were connected to mainland Asia via a land bridge from about 20,000 years ago to 240,000 years ago. Scientists believe that the Iriomote cat moved its range to the islands during this period. Because of this, it is assumed that there is little genetic variety within the species.
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