Sayimys hintoni, Hartman & Van De Weerd & Bruijn & Wessels, 2019

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 : 373-374

Sayimys hintoni n. sp.

Text-figs 14 , 15

H o l o t y p e. An isolated dp4 no H.- GSP82.14 a no 3001, Text-fig. 14 ; shown by de Bruijn et al. (1989) on pl. II, fig.10. Temporarily housed in Faculty of Earth Sciences, University Utrecht, the Netherlands .

D e r i v a t i o n o m i n i s. Named after M. A. C. Hinton who described Pectinator sivalensis.

Ty p e l o c a l i t y. H.- GSP81.14 a, lower Manchar Formation , Sind, Pakistan; early Miocene, age approximately 18 Ma ( Wessels 2009) .

O c c u r r e n c e s. H.-GSP82.06, H.-GSP82.07 and H.-

GSP82.14 . Lower Manchar Formation , Sind, Pakistan; early

Miocene (approximate range 19.5–16.3 Ma; Wessels 2009). Assemblages from Z120 and Z122 ( Baskin 1996).

M a t e r i a l a n d m e a s u r e m e n t s. See Tab. 5 for type locality H.-GSP81.14a, Tab. 6 for locality H.-GSP81.07, Tab. 7 for locality H.-GSP81.06. See the table in de Bruijn et al. (1989: 196). Text-fig. 16 shows length-width scatter diagrams of the molars of Sayimys hintoni and S. cf. minor.

D i a g n o s i s. Sayimys hintoni is relatively small. The anteroconid of the dp4 is elongate, ovoid in shape, and tends to form low ridges to metaconid and protoconid, anterolophid absent. A long confluent diagonal ridge is formed by the protoconid, ectolophid, hypolophid and entoconid. The metalophulid of most m1–3 has a narrowconstricted connection to the protoconid (arrow in Text-fig. 14 ). In upper molars the para- and metaflexus are short and poorly developed.

D i f f e r e n t i a l d i a g n o s i s. Sayimys hintoni is larger than S. flynni and S. intermedius , roughly similar S. minor and S. baskini, but smaller than S. obliquidens and S. giganteus; it is slightly smaller and partially overlapping in size with S. chinjiensis. It differs from S. flynni, S. minor, S. obliquidens and S. intermedius in the absence of a mesolophid. Its dp4 is different from S. flynni, S. minor, S. obliquidens and S. intermedius in the long, smooth and confluent diagonal lophid formed by protoconid, ectolophid, hypolophid and entoconid, and in the narrow connection between protoconid and metaconid. It differs from S. intermedius and S. chinjiensis in the shape of the anteroconid. Assemblages of S. chinjiensis tend to have dp4 and lower molars with more oblique lophids, whereas para- and metaflexus in the upper molars are more reduced, or absent. In contrast to S. hintoni , almost all dp4 of S. chinjiensis have a well-developed anterolophulid.

D i s c u s s i o n. In the Sayimys assemblage of H.- GSP81.14a, type locality of S. hintoni , the two smallest lower molars are subject to discussion. The outline of the teeth suggests that they could be m1 or m3. The lack of a posterior interdental facet indicates m3; if so, these m3 are too small to fit the assemblage of S. hintoni n. sp. Text-fig. 16 compares the Sayimys molars of locality H.-SGP14a with the outline of the size clouds of m1 and m2–3 from the large sample of S. chinjiensis from H.-SGP82.24. The two sizecloud outlines are indicative of the size and variation of m1 and m2–3, and demonstrate that the two m3 identified as Sayimys cf. minor are much smaller than those of S. hintoni n. sp. The molars are the smallest m3 of Sayimys known ( Text-fig. 13 ); these differ in morphology from S. hintoni in their short V-shaped mesoflexid and a triangular metalophid ( Text-fig. 14 ). We have also identified a small unworn M3 that could be included in S. cf. minor ( Text-figs 15 , 16 ). The M3 of Sayimys species have the same length and width as the M2 ( Text-figs 5 , 17 ), therefore this small M3 does not fit in with the group of probable M3 of S. hintoni in Text-fig. 16 .

Baskin (1996) compared 34 isolated cheek teeth from five sites, two in the Zinda Pir area (Z120 and Z122) and three on the Potwar Plateau (Y591, Y592 and Y802), to Sayimys intermedius . The measurements of these are not presented for each location separately, but have been lumped into one table ( Baskin 1996: tab. 4). The anteroconid of the four dp 4 in this collection is ovoid in shape ( Baskin 1996: fig. 5h); the entoconid is cuspate with a narrow connection to the protoconid ( Baskin 1996: fig. 5i, j, k) and the mesoflexid is long and forward directed, the paraflexus and metaflexus of M1–2 are short, with wear the paraflexus persists longer than the metaflexus. These teeth are morphologically and in size like Sayimys hintoni , and are labelled S. hintoni in Text-figs 12 , 13 .

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. 16. Length-width scatter diagram of isolated molars of Sayimys hintoni n. sp. and S. cf. minor from sites H.-SGP 81.14a (lower Manchar Formation, Sind, Pakistan) with the size-cloud outlines of molars of the large sample of S. chinjiensis from H.-GSP.24 shown in Text-fig. 17.

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

Text-fig. 5. Length-width scatter diagrams of upper molars of Sayimys giganteus from Keseköy.

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).

Text-fig. 12. Ranges of the length of the dp4 based on data from the literature. Vertical scale in Ma, the samples are from the Siwaliks (black) and Turkey, Greece and Arabia (red). Type localities of species are indicated with an asterisk. The Y and Z sites are from Baskin (1996), its size ranges are composed of data from several localities and the vertical arrowed broken line indicates the age range of these sites.