Potwarmus primitivus, (WESSELS ET AL., 1982)

Antoñanzas, Raquel López, 2009, First Potwarmus from the Miocene of Saudi Arabia and the early phylogeny of murines (Rodentia: Muroidea), Zoological Journal of the Linnean Society 156 (3), pp. 664-679 : 668

POTWARMUS PRIMITIVUS (WESSELS ET AL., 1982)

Synonym: Potwarmus minimus Lindsay, 1988 .

Wessels et al. (1982) erected the new species Antemus primitivus on the basis of eight complete and seven incomplete isolated cheek teeth from the Chinji Formation (near Banda Daud Shah), Pakistan. They assigned this taxon to the genus Antemus . Later, Jacobs et al. (1989) excluded this species from the genus Antemus because it has a single lingual cusp on the M1 (the enterostyle), whereas A. chinjiensis (type species of the genus) has two (an isolated enterostyle and an anterostyle, t1, connected to the lingual anterocone, t2). The reassessment conducted by Jacobs et al. (1989), then in press, together with the study of additional material from the Middle Miocene Pakistani localities YGSP 589, YGSP 709 (Chinji Formation) and YGSP 591 and YGSP 592 (Kamlial Formation), motivated Lindsay (1988) to re-allocate A. primitivus to the new genus Potwarmus , an action with which I agree. Lindsay (1988) also erected a new species of Potwarmus , P. minimus , the holotype being an isolated left m1 (YGSP 19555) from the Middle Miocene locality YGSP 589 (Chinji Formation, Potwar Plateau, Pakistan) ( Lindsay, 1988: pl. 10, fig. l). This species was said to be also recorded in Pakistan, in the Middle Miocene locality YGSP 642 in the Kamlial Formation and, possibly, in some HGSP localities in the Chinji Formation at Banda Daud Shah ( Lindsay, 1988). However, based on analysis of a larger sample from a single locality, Lindsay (1994) synonymized P. primitivus and P. minimus . Incidentally, Lindsay (1994: table 1) listed P. primitivus in the Kamlial Formation of Pakistan, but also in the Manchar Formation and not in the Chinji Formation.

The holotype of this species (H-GSP 5521) is a right M1 from Chinji locality H-GSP 107, which is possibly Middle Miocene in age ( Wessels et al., 1982). The morphology of the first lower molar of Potwarmus primitivus is very distinct from P. flynni sp. nov. The m1s of P. primitivus have an unreduced anterior portion: they have a distinct single anteroconid and a metaconid, which are not distinct in P. flynni sp. nov. Potwarmus primitivus has a larger enterostyle and a better developed longitudinal crest on the M1s than AJ7. On the M2s of P. primitivus , the longitudinal crest is also better developed than in the Arabian specimens and, the strong, long lingual branch of the anterior cingulum descends lingually continuing posteriorly as a prominent lingual cingulum. In contrast, these cingula are less prominent, much shorter and not in continuity both in AJ11 and AJ12. In addition, the hypocone joins with the metacone more anteriorly on the M2 of P. primitivus than in P. flynni sp. nov.