CSG Species Accounts: Iriomote cat (Prionailurus bengalensis iriomotensis/Incertae sedis)

Description and Behavior
The Iriomote cat was first described for science in the late 1960s, when Imaizumi (1967) labelled it "probably one of the most primitive species among the Asiatic Felidae". It is found only on Iriomote island, an island of 293 km² at the southernmost tip of the Ryuku chain, located about 200 km east of Taiwan. Imaizumi (1967) considered the Iriomote cat to be a highly differentiated form based upon the following principal characters: the ventral border of the paraoccipital process separated from the auditory bulla; an oval disc on each side of the basisphenoid and basioccipital region; P3 with postero-external corner evenly rounded, without a cingulum cusp; and auditory bullae unusually small. These characters, however, are polymorphic in the leopard cat (Petzsch 1970, Corbett and Hill 1993), and karyotypic studies (Wurster-Hill et al. 1987) also indicate a close relationship to the leopard and fishing cats.
The Iriomote cat has variously been considered a monotypic species (Mayailurus iriomotensis: Imaizumi 1967), a species closely related to the leopard cat (Prionailurus iriomotensis: Hemmer 1978a, Leyhausen 1979, Corbett and Hill 1993), and a subspecies of the leopard cat (P. bengalensis iriomotensis: Wozencraft 1993, Yu and Wozencraft in press), “subjected to extreme selective pressures with the attendant possibility of genetic drift” (Glass and Todd 1977). Moreover, Groves (1982) has noted cranial characters which indicate a close relationship to Catopuma (Asian golden cat and Bornean bay cat), and Wurster-Hill et al. (1987) found that the karyotype of the Iriomote cat is not only identical to that of the leopard and fishing cats (Prionailurus spp.), but also the puma. Genetic analysis of the Iriomote cat as well as other island populations of “leopard cats” (particularly those of the eastern Philippines) needs to be carried out in order to reach a consensus on whether the Iriomote cat is the world’s rarest felid, or a rare subspecies of one of the world’s common cats. According to Leyhausen and Pfleiderer (in press), skull characters of the Iriomote cat have more in common with those of the Asian golden cat and the marbled cat than with those of leopard cat populations of east and south-east Asia. They also state that the Iriomote cat has incompletely sheathed and semi-retractile claws, resembling the fishing and flat-headed cats. They conclude that the Iriomote cat is an ancient species, linking together the three genera, Prionailurus, Profelis and Pardofelis and still being close to their common root. They consider it most properly classified as Prionailurus iriomotensis, while noting that further investigation might show that elevation to the original genus Mayailurus is indeed warranted. However, molecular investigations by two Japanese teams (Masuda et al. 1994 and Suzuki et al. 1994) led to the conclusion that the Iriomote cat is related to the leopard cat and that separation occured less than 200,000 years ago, which coincides with the geological isolation of the Ryuku archipelago. Both teams agree that the Iriomote cat has evolved to some extent and has some unique morphological characteristics compared with the mainland leopard cat.
The Iriomote cat has a dusky brown pelt with rather long hair, patterned with horizontal rows of darker spots which tend to form indistinct bands. It has a relatively elongate and low-slung build, with short legs and tail (TL=19 cm, 32% of head-body length [n=3]: Imaizumi 1967). Average weight is 4.2±0.5 kg for males (n=15), and 3.2±0.3 kg for females (n=10) (Izawa et al. 1989). The diet of the Iriomote cat has been studied in detail (Yasuma 1981, 1984, 1988): 95 prey species were identified from 849 scats. Major prey species include the common rat (36%), Ryuku flying fox (16.5%), birds (brown-eared bulbul and banded crake - 7.4%), and Kishinoue skink (18.6%). A variety of insects is frequently eaten (including 39 species of beetle), but they contribute little to the diet by weight (Yamaya and Yasuma 1986). Amphibians, crabs, and fish are occasionally taken. The Iriomote cat is primarily nocturnal, partially arboreal, and swims well (Yasuma 1981).