MMCO (Henrot et al. 2010). Proxy-based studies suggest a warming at mid-latitudes of about +6 C° and a weak equator-to-pole latitudinal temperature gradient (Bruch et al. 2007; Henrot et al. 2010). This MMCO was followed by a drastic temperature drop starting at 13.9 Ma and was followed by strong alternating changes (Billups and Schrag 2003; Majewski and Bohaty 2009). Moreover, the disap- pearance of warm climatic taxa can be observed in the oceanic and continental areas during Serravallian (13.5– 11.5 Ma), including the sudden decrease in abundance of Steneofiber in Europe (Lauriat-Rage et al. 1993). In contrast, fossils of Steneofiber appear in tropical areas such as Southeast Asia, during late middle Miocene. This discovery represents the first presence of tropical castorids that have ever been recorded in Southeast Asia and therefore the southernmost record of Steneofiber.
Here we describe a new species of Steneofiber recorded from two localities in Thailand, Mae Moh and Chiang Muan coal mines of Northern Thailand (Fig. 1), in levels dated of about 12.4–11.6 Ma (Coster et al. 2009).