Sayimys, WOOD, 1937

Hartman, Julian, Van De Weerd, Andrew A., Bruijn, Hans De & Wessels, Wilma, 2019, An Exceptional Large Sample Of The Early Miocene Ctenodactyline Rodent Sayimys Giganteus, Specific Variation And Taxonomic Implications, Fossil Imprint 75 (3 - 4), pp. 359-382 : 372

Sayimys obliquidens BOHLIN, 1946

H o l o t y p e. A part of a mandible with damaged and worn cheek teeth, no 268.

Ty p e l o c a l i t y. The bad-lands near Taben-Buluk, Gansu Province, China; age of the site: middle (13 Ma?) Miocene. Taben-Buluk is now known as the Danghe area. The fossils described are surface finds from several locations in a tectonized area. Bohlin himself was unsure if all his material belonged to the same species, for a discussion, see Wang (1997), who concluded that all material can be included in the same species.

P a r a t y p e s. If all material described by Bohlin is included: Tb 254 right upper tooth row, Tb 261 right upper tooth row, Tb 279a partial skull, Tb 279b lower tooth row, TB 268 a left mandible with damaged molars.

D i s c u s s i o n. The geology of the Taben-Buluk (Danghe) area was studied by Wang et al. (2003), who were unable to fit Bohlin’s Sayimys locations precisely into their sections, which span an age from 24 to 10 Ma. They state that three of the Bohlin localities are close to their fossil site Dh199913, correlated to the geomagnetic polarity timescale at 13 Ma, making the Taben-Buluk Sayimys obliquidens some 5 Ma younger than previously assumed. The material described and measured by Bohlin is of large size, in the lower-end of the range of S. giganteus, however, the m3 is in the high-end part of the range ( Text-fig. 13 ). Considering the doubts about the homogeneity of the collection, and the exact location(s) and age of the type locality S. obliquidens is a nomen dubium, we therefore ring-fence the species name, that is, restrict it to its holotype.

The early Miocene material from Aktau ( Kazakhstan) described by Kordikova and de Bruijn (2001) as Sayimys aff. obliquidens is much smaller. It shows a long mesolophid in the m2, but not in the m1, like in the holotype from Taben- Buluk. A more appropriate classification for the material from Aktau is S. aff. minor .

Figures

Text-fig. 13. Ranges of the length of the m3 based on data from the literature, see Text-fig. 12 for explanation.