Progonomys morganae, Kimura & Flynn & Jacobs, 2017

Kimura, Yuri, Flynn, Lawrence J. & Jacobs, Louis L., 2017, Early Late Miocene Murine Rodents From The Upper Part Of The Nagri Formation, Siwalik Group, Pakistan, With A New Fossil Calibration Point For The Tribe Apodemurini (Apodemus / Tokudaia), Fossil Imprint 73 (1 - 2), pp. 197-212 : 200-201

Progonomys morganae sp. nov.

H o l o t y p e. YGSP 33180, left M1, Text-fig. 3a.

E t y m o l o g y. Named in honor of Dr. Michèle E. Morgan in recognition of her extensive contributions to research on the Siwalik mammalian faunas of Pakistan, in particular meticulous field work and ongoing data analysis, and perpetual optimism in interpreting the fossil record.

Ty p e l o c a l i t y. Y 450, Hasnot area, early late

Miocene Nagri Formation, 10.2 Ma.

R e f e r r e d m a t e r i a l. From Y 450, YGSP 54091, left M1 and 33202, broken left M1. From Y 311, six molars: left M2, YGSP 34563, left m1 54160, three right m1 34523, 36167, 36168, worn right m2 54180. From Y 259, three molars, left m1 YGSP 34159, right M2 34238, left M3 34033. Also from older locality Y 797, 11.2 Ma: YGSP 36837, right M2.

M e a s u r e m e n t s. See Table 1.

D i a g n o s i s. Small size, similar to that of Progonomys shalaensis QIU et LI, 2016 and P. minus SEN, 2003 ; molars are narrower than either, particularly than P. minus . Dimensions of P. morganae lie at the small periphery of the size range for P. cathalai SCHAUB, 1938 , and its M1 length is about 15% less than that of P. hussaini . Progonomys morganae sp. nov. has an elongated M1 (high L/W ratio) and a narrow m1 with small, closely appressed anteroconid cusps.

D e s c r i p t i o n. The few teeth that can be attributed to this species share small size. M1 and M2 show the low degree of cusp inclination comparable to Progonomys hussaini . The anterior lobe of M1 is dominated by the large, lingual anterocone of the first chevron, located near the midline of the tooth. The small labial anterocone is lateral to it; the anterostyle is posterior in position, connected to the posterolingual corner of the large lingual anterocone. The holotype M1 has only a shallow, marginal anterolingual indentation, no deep inflection at the anterostyle, unlike Progonomys hussaini . YGSP 54091 ( Text-fig. 3b ) does have an anterolingual inflection. In both, the chevrons are well-separated, anteroposteriorly. The anterostyle is laterally compressed. M1 lacks a precingulum. The second chevron is nearly symmetrical, the enterostyle being somewhat posterior in position; it weakly joins the large hypocone. There is no stephanodonty and the posterior cingulum is thin. M1 is slender, elongated relative to width (L/W ratio of holotype = 1.76; for YGSP 54091 = 1.68); this is apparent in greater distances between chevrons relative to P. hussaini .

M2 has a near-symmetrical major chevron, and the enterostyle turns posteriorly toward the hypocone. The anterostyle is small but shows wear from an early stage; the minute labial anterocone shows no wear. The posterior cingulum is present. M3 is quite small ( Tab. 1) and has a minute anterostyle; there is only a bead of enamel at the position of the labial anterocone.

The slender m1 shows the murid double anteroconid as twinned cusps at the midline of the tooth, closely appressed, and much smaller than the protoconid and metaconid ( Text-fig. 3c, d ). There is no room for a medial anteroconid and the labial cingulum is weak, bearing a c1, variable in size, and minute c3 or c4. The m2 is represented only by one well-worn specimen.

D i s c u s s i o n. This uncommon small Progonomys is a contemporary of abundant P. hussaini and early Karnimata . Its size does not overlap that of P. hussaini . It is somewhat smaller than the mean size of P. debruijni , and has less strongly inclined cusps and less anteriorly expanded base of the anterocones than the latter. Individuals in some populations of P. cathalai ( Wessels 2009) are near the size observed for the small Siwalik Progonomys morganae . Progonomys morganae is conservative in most features, except for the slender molars and strongly appressed anteroconids of m1; P. morganae has a thinner posterior cingulum than other species of the genus.

Very close in molar length to P. shalaensis and P. minus , Progonomys morganae differs in having a narrower M1, that is, a higher L/W ratio. The L/W ratio of P. shalaensis is 1.65 ( Qiu and Li 2016), and that of P. minus is 1.5 ( Sen 2003).

Figures

Text-fig. 3. Progonomys morganae molars from the upper part of the Nagri Formation. a) YGSP 33180, holotype, from Y 450 and b) 54091 from Y 450; both left M1 with buccal side upward. c) 34159 from Y259; and d) 36168 from Y 311, left and right m1, respectively, with lingual side upward. Scale for all is 1 mm.