of Steneofiber have been well studied in Europe since Stirton (1935), but are less so for those more recently described from Asia. Two species have been erected from the late Oligocene of Kazakhstan in Central Asia, Steneofiber kumbulakensis and Steneofiber schokensis (Lopatin 2003). These two species of Steneofiber from Altyn Schokysu locality of Kazakhstan have been initially assigned to Propalaeocastor kumbulaken- sis and Propalaeocastor schokensis by Bendukidze et al. (2009), according to their irregular enamel crenulations of slightly worn teeth. Additional remains of Steneofiber sp. were found in the late Oligocene Sasebo Group, Kyushu, west Japan (Kato and Otsuka 1995) and Steneofiber hesperus was described from early to middle Miocene, Inner Mongolia and Zhangbei, Hebei Province of China (Xu 1994). However, Steneofiber sp. from Japan is only represented by a fragmentary tooth, probably M1or M2.
Most Tertiary castorids were temperate mammalian herbivores and successful at high latitudes like modern Castor. Only Steneofiber seems to have been subtropical to tropical according to its abundant appearance in Europe during the Miocene period (Lauriat-Rage et al. 1993). Occurring during a long-term climatic cooling trend, the late middle Miocene was one of the coolest periods of the Neogene, following the middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Various proxy data support a warmer and more humid climate during the