Progonomys hussaini CHEEMA et al., 2000

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 : 199-200

Progonomys hussaini CHEEMA et al., 2000

H o l o t y p e. PMNH 5062, left M1.

Ty p e l o c a l i t y. JAL-101, Jalalpur area, District Chakwal, early late Miocene Nagri Formation, no nearby dated section.

R e f e r r e d m a t e r i a l. 68 molars from Y 311, 12 from Y 450, 160 from Y 259.

D e s c r i p t i o n a n d a d d i t i o n a l n o t e s. This species is already described ( Cheema et al. 2000), but we illustrate 12 molars ( Text-fig. 2 ) to show observed variation in M1. These molars display apparent variation due to wear, and true minor differences in cusp position and proportions. M1 are generally narrow, although a few, such as Text-fig. 2b are relatively broader. In all, the anterostyle touches, but is generally posterior to the double anterocone. The labial anterocone is distinctly smaller than its lingual pair, and the anterior part of the molar is quite asymmetrical, with a deep inflection of the first chevron at the anterostyle. The precingulum is weakly developed in some teeth, and bears no cuspule. The enterostyle is posterior in position, weakly connected to the protocone (isolated in Text-fig. 2f ). There is no stephanodonty (paracone-metacone, t6-t9, connection undeveloped). The posterior cingulum is usually prominent. These molars are larger than the younger Siwalik Progonomys debruijni JACOBS, 1978 (~9 Ma), and with less inclined cusps. Molars of Text-fig. 2 exhibit variable cusp inclination, a feature difficult to assess in late wear, and the chevrons are positioned closely (limited antero-posterior distance between them).

D i s c u s s i o n. This species is adequately described and illustrated by Cheema et al. (2000), with the caveat that their sample includes several specimens that we would now identify as Karnimata (differentiation of the taxa developed below). Cheema et al. (2000: 73) suspected that a second species might be present in the hypodigm, but the total sample size was too small to defend this position at the time. For example, PMNH 5063 and 5085 figured by Cheema et al. (2000: fig. 5b, e) would be classified now as Karnimata (see below). Other tooth positions show variation that we can now defend as evidence of two species: gracile m2 (PMNH 5096) and m3 (PMNH 5115) represent Progonomys hussaini and contrast with their more robust counterparts. Cheema et al. (2000) used biochronological arguments to date JAL-101 to about 11 to 10 Ma. Identity of the species in sites of 10.5 to 10.1 Ma in Potwar paleomagnetic sections confirms this age.

In some past publications beginning with Jacobs and Flynn (2005) and continuing in Kimura et al. (2013a, b, 2015, 2016), we applied the name Progonomys hussaini to older samples from low in the Nagri Formation and top of the Chinji Formation (approximately 11.5 to 11 Ma). We now realize that murids of that age are distinctly more primitive and should be excluded from P. hussaini .

Progonomys sinensis QIU et al., 2004 from Lantian, Shanxi Province, China, is a larger species of about the same age ( Kaakinen 2005) as Y 311. It shows a similar conservative stage of evolution as P. hussaini . All early Progonomys across Eurasia show similar molar structures despite some variation in size, and relative sizes of cusps (see Mein et al. 1993). Reasonable conclusions on dental morphology and metrics led Wessels (2009) to consider P. hussaini and P. sinensis as junior synonyms of the somewhat younger P. cathalai SCHAUB, 1938 , type locality of which is Montredon in southern France. Yet, given the straight-line distance from the Potwar to the Mediterranean of> 3000 km, and the much farther distance from China to Spain, species identity on such a scale seems unlikely. We argue that population variation can be used to defend recognition of separate species. We do think that the similarity of distant populations reflects close relationship; minor local differentiation followed after dispersal from the Indian subcontinent between 11 and 10 Ma, with westward spread to the Mediterranean area and then northeastward dispersion to Shanxi, as hypothesized by Flynn and Wessels (2013). It is likely that the populations over this vast area were distinct, if difficult to define morphologically.

Current age estimates for Progonomys place its dispersal to Europe ( Mein et al. 1993) in late mammal zone MN 9, around 10 Ma. Our geohistorical view of Siwalik murine evolution sees P. hussaini as the Potwar successor of a somewhat older successful disperser that was the progenitor of P. cathalai and P. sinensis . Samples of Siwalik Progonomys older than 10.5 Ma ( Jacobs and Flynn 2005) remain to be studied in a future publication.

Figures

Text-fig. 2. First upper molar variation in Progonomys husssaini from three localities in the upper part of the Nagri Formation, Potwar Plateau, Pakistan. The 12 molars are oriented with buccal side upward, each at the same 1 mm scale, making size variation apparent. a) YGSP 33187 from locality Y 450; b) 34556, c) 54131, d) 54143, e) 54151, f) 54152, all from Y 311; g) 33937, h) 33947, i) 33957, j) 33959, k) 33963, l) 33976 all from Y 259. Figures a, c, e, f, h, k are all right M1; the others are left M1.