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 : 374-378

Sayimys chinjiensis BASKIN, 1996

H o l o t y p e. Left mandible fragment with p4–m1.

P a r a t y p e s. Two P4, one M1–2, one p4, one m3.

Ty p e l o c a l i t y. Site Y634, upper Chinji Formation,

Potwar Plateau, Pakistan; age of the site: 11.9 Ma.

O t h e r s i t e s. Eight sites in the upper Chinji and Nagri Formations (age range 12.1–9.1 Ma; see Baskin 1996), Daud Khel, upper Chinji Formation, age according to Jacobs et al. (1989) is 11–10 Ma (see Munthe 1980).

H.-GSP107, Chinji Formation near Banda Daud Shah ( Wessels et al. 1982), age ~14 Ma ( Jacobs et al. 1989, Wessels 2009).

H.-GSP82.24, lower Manchar Formation, age 13.5 Ma ( Wessels 2009).

O r i g i n a l d i a g n o s i s. “Moderately high crowned cheek teeth with relatively thick enamel base. The paraflexus is absent on the upper molars. A short metaflexus is present on the M1 and M2, it is usually absent on M3. On m3 the

metastriid [= metaflexid in lingual view] extends relatively deeply on the internal face” ( Baskin 1996).

E m e n d e d d i a g n o s i s. dp4 with rounded anteroconid and well-developed anterolophulid in medial position. In dp4 and molars, the mesolophid is absent, hypolophid is oblique, and the metalophulid-protoconid connection is narrow. A confluent, long diagonal lophid is formed by protoconid, ectolophid, hypolophid and entoconid in the dp4. Lophids of the lower molars are strongly diagonal. Upper molars have poorly developed paraflexus and metaflexus, disappearing early with wear; these flexids may be totally absent in molars of assemblages from the younger Nagri Formation.

D i s c u s s i o n. Unfortunately, the illustrations in Baskin (1996) are inadequate. Moreover, not all tooth positions are known from the type locality. In addition to the type locality, Baskin allocated 75 specimens from eight localities to this species. The eight assemblages are thus small; the largest has 17 teeth, the smallest two. The eight sites are in the upper Chinji Formation and overlying Nagri Formation, and range in age from 12.1 to 9.1 Ma. Baskin (1996) defined this species as having no paraflexus (and thus no anteroloph) in the upper molars, and in being more hypsodont than those of Sayimys sivalensis. It appears from the description that the paraflexus is absent in molars from the Nagri Formation. Baskin assigned the large collection from Daud Khel (described by Munthe 1980 as S. sivalensis) to S. chinjiensis.

Using measurements obtained from Baskin, López- Antoñanzas and Sen (2003) plotted the height of M1–2 and m3, and observed that the highest M1–2 are those classified in Sayimys chinjiensis, but the overlap with S. sivalensis is large; the m3 do not show a difference in height. The differences between the assemblages allocated to the two species are relatively small, and considering the large variability in Sayimys species , small samples are difficult to allocate. López-Antoñanzas and Sen (2003) therefore synonymized Sayinys chinjiensis with S. sivalensis. This decision is unfortunate, because S. chinjiensis has a clear type locality and S. sivalensis does not. Moreover, the holotype of S. sivalensis is not considered diagnostic. We therefore do not follow López-Antoñanzas and Sen, and maintain S. chinjiensis and restrict the name S. sivalensis to its holotype (see above). With the inclusion of the Daud Khel assemblage in Sayimys chinjiensis, this species is morphologically well defined. We also include the large assemblage from H.- GSP82.24 from the lower Manchar Formation (described by de Bruijn et al. 1989, illustrated here in Text-figs 14 , 15 ), and from site H.-GSP107 Banda Daud Shah ( Wessels et al. 1982) in Sayimys chinjiensis. Text-fig. 17 shows length- width scatter diagrams of S. chinjiensis from H.-GSP82.24, and Tab. 8 the measurements.

Our designation H.- GSP14 a in the lower Manchar Formation as the type locality of S. hintoni n. sp. is pragmatic. The material from this site is well described and figured ( de Bruijn et al. 1989), and the morphotypes are sufficiently different from the younger S. chinjiensis and the older S. baskini, S. minor to allow classification of all but the smallest assemblages .

Figures

Text-fig. 14. Cheek teeth of Sayimys hintoni n. sp. and S. cf. minor from H.-GSP81.14a, S. cf. giganteus from H.-GSP81.14 and S. chinjiensis from H.-GSP82.24.

Text-fig. 15. Lightly worn molars of Sayimys hintoni n. sp. (f, g, h) and S. cf. minor (e and i) from locality H.-GSP81.14a and S. chinjiensis from H.-GSP82.24 (a, b, c, d). Upper molars: occlusal surfaces and labial sides, lower molars occlusal surfaces and lingual sides. Side views horizontally-mirrored, anterior indicated by arrows.

Text-fig. 17. Length-width scatter diagram and histograms of isolated molars of Sayimys chinjiensis from locality H.-SGP82.24 in the lower Manchar Formation (Sind, Pakistan).