Parapodemus badgleyae, 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 : 205-206

Parapodemus badgleyae sp. nov.

H o l o t y p e.YGSP 33936, left M1, Text-fig. 9a (length × width = 1.79 × 1.14 mm).

E t y m o l o g y. For Dr. Catherine Badgley, vertebrate paleobiologist and paleoecologist, pioneer in Siwalik research, well known for her syntheses of disparate paleobiological data in interpreting the fossil record.

Ty p e l o c a l i t y. Y 259, upper part of the Nagri Formation, Siwalik Group, Potwar Plateau, northern Pakistan, age 10.5 Ma.

R e f e r r e d m a t e r i a l. One additional left M1 from locality Y 259 (YGSP 33939, 1.84 × 1.09 mm), two M2 from Y 259 (YGSP 34206 [1.25 × 1.17] and 34233 [1.2 × 1.13]), and two M1 from Y 311, YGSP 34542 (right, 2.05 × 1.19 mm) and 34543 (left, 1.95 × 1.19 mm) ( Text-fig. 9 ).

D i a g n o s i s. Smaller than Parapodemus hariensis , molar lengths about 10% less, and relatively more slender, widths about 15% less; size falls at the lower end of the range for P. gaudryi . Stephanodonty moderately developed; thin paracone-metacone (t6-t9) connection; a low crest leads from the enterostyle to the hypocone (weak t4-t8 connection in late wear).

D e s c r i p t i o n. Four M1 are illustrated in Textfig. 7a–d. The first chevron is not as asymmetrical as in Progonomys . The labial anterocone is smaller than the lingual anterocone, which has a weak connection to the anterostyle until moderate wear. The anterostyle is conical to oval and is not as posterior in position as in Progonomys . The enterostyle is large and includes a posteriorly projecting spur with connection low on the hypocone. More prominent is the buccal connection between paracone and metacone (t6-t9), evident even in early wear. Hence, stephanodonty is moderate. The posterior cingulum is strong and there is a shelf-like precingulum. Three roots are present, a large oval lingual root that is anteroposteriorly elongated, a large anterior root, and a posterior root; no rootlet is evident.

The robust M2 is slightly longer than wide, with large anterostyle extending the tooth outline anterolingually. The labial anterocone is small, but distinct and shows wear from an early stage. The posterior spur from the enterostyle abuts the hypocone. The most prominent feature of M2 is that the paracone and metacone are closely positioned and connected early in wear. Roots are broken.

D i s c u s s i o n. For the validity of Parapodemus , we follow de Bruijn et al. (1999) and Sen (2003), and recognize four species from Europe: P. gaudryi (DAMES, 1833) , P. lugdunensis SCHAUB, 1938 , P. barbarae VAN DE WEERD, 1976 , P. meini MARTÍN SUÁREZ et FREUDENTHAL, 1993 as well as Siwalik forms (below). Martín Suárez and Mein (1998) had a different viewpoint and transferred most species previously considered under Parapodemus to the genus Apodemus KAUP, 1829 ; they retained the type species P. gaudryi in Parapodemus . Parapodemus is similar in morphology to Apodemus but lacks t7 as the major difference in M1 (de Bruijn et al. 1999). None of the Siwalik Parapodemus specimens have a swollen structure in the crest connecting the enterostyle to the hypocone. De Bruijn (1976) elucidated the morphological variation of the type species, P. gaudryi , including size, and its advanced stephanodonty. This species as well as P. barbarae and P. meini are not only larger and more stephanodont than P. badgleyae , but are considerably younger. The remaining species, Parapodemus lugdunensis , was until now the earliest record of the genus and has been considered to be the most basal ( Van de Weerd 1976, Martín Suárez and Mein 1998). Based on comparison with SEM images in Martín Suárez and Freudenthal (1993), stephanodonty of the species is slightly more advanced than that of the Siwalik Parapodemus badgleyae in that the inclination of the metacone (t9) toward the paracone (t6) is greater. The Siwalik species is older and appears to be more plesiomorphic than any known species of Parapodemus .

Jacobs (1978) noted the presence of Parapodemus in the Dhok Pathan Formation at locality Y 182A, 9.2 Ma, contemporary with Karnimata darwini and Progonomys debruijni . It was described but not named, its large size distinctive. Working in the Haritalyangar region of India, Vasishat (1985) found a similar large murid and named it Parapodemus hariensis . Despite unclear illustrations, his jaw fragments from east of Haritalyangar village include lower molars comparable in size to specimens from site Y 182A ( Jacobs 1978). We accept provisionally the species name as applicable to the Y 182A Potwar sample. Our new Parapodemus fossils from the older Nagri Formation in the Potwar region are smaller. We recognize their distinction from the younger material as Parapodemus badgleyae sp. nov.

Mein et al. (1993) considered Parapodemus from locality Y 182A to express morphological variation within Karnimata darwini , a view followed by other scholars. The discovery of Parapodemus specimens from older localities is important because these specimens show that moderate stephanodonty (weak t6-t9 and t4-t8 connections without t7) was already present by 10.5 Ma. At these localities (Y 259, Y 311), the morphological difference regarding stephanodonty is distinct between Parapodemys badgleyae and coexisting Karnimata fejfari . The M 1 specimens that are assigned to P. badgleyae should not be considered morphological variants of K. fejfari .

Freudenthal and Martín Suárez (1999) discuss further the validity of P. gaudryi and point out the separate and ancient radiation of the Apodemus group. They argue that the origin of Apodemus , and we would add Parapodemus , should be sought among earlier murines, such as the early late Miocene “ Progonomys ” of the Siwaliks. We note here that in our interpretation, the Parapodemus lineage extends in the Siwaliks from 10.5 Ma to 9 Ma or younger.

Figures

Text-fig. 9. First upper molars of Parapodemus badgleyae sp. nov. (a–d) and Muridae, gen. et sp. indet. (e). a) YGSP 33936, holotype, locality Y 259, b) 33939 from Y 259, c) 34542 from Y 311, d) 34543 from Y 311, e) 34559 from Y 311. All molars but c are left molars, all figured with buccal side upward and at the same scale.