Potwarmus thailandicus (Jaeger, 1985)

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, pp. 664-679 : 668-669

POTWARMUS THAILANDICUS (JAEGER ET AL., 1985)

This species was originally erected as Antemus thailandicus on the basis of five cheek teeth. The holotype of this species is a left first upper molar (L84-6, housed in DMRB) from the Middle Miocene ( Chaimanee et al., 2007) Li vertebrate locality of the Mae Long Sub-Basin, Li Basin, northern Thailand ( Jaeger et al., 1985: pl I, fig. b). Lindsay (1988) pointed out that ‘ A. ’ thailandicus is closely related to Potwarmus primitivus and, for this reason, he transferred it to the genus Potwarmus . As for ‘ A. ’ primitivus (see above), Jacobs et al. (1989) excluded this species from the genus Antemus based on the presence of two lingual cusps on the M1s of A. chinjiensis and the absence of one of them (the anterostyle) in ‘ A. ’ thailandicus .

From the Li basin, about 300 additional specimens of this taxon have been reported by Mein & Ginsburg (1985), but unfortunately no description of this material is available. However, the BSPG houses casts of numerous specimens, which allows comparison of the new Arabian species with Potwarmus thailandicus .

The M1s of Potwarmus thailandicus differ from AJ 7 in being higher crowned, in lacking a prominent crest located anterior to the anterocone, in having more prominent lingual cingula, a larger enterostyle, and the protoloph joining with the posterior part of the protocone (it joins the posterior arm of the protocone in AJ7). With regard to the M2s, those of P. thailandicus have a very strong anterior cingulum, which is in continuity with the prominent lingual cingulum whereas in the Arabian specimens the anterior cingulum is less strong and it is not in connection with the lingual cingulum, which is very short. In addition, the M2s of P. thailandicus have a quite large enterostyle, a rather deep posterior valley, and a posterior cingulum that bears a hypoconule. In P. flynni sp. nov., the enterostyle is smaller, and there is neither a posterior valley nor a hypoconule. The m1s of P. thailandicus are distinct from that of P. flynni sp. nov., in being higher crowned, in having the anterior part of the teeth less reduced, in having strong anterior and labial cingula that are in continuity, and a posterior cingulum bearing an hypoconulid. AJ13 has a very weak labial cingulum that is not continuous with the labial branch of the anterior cingulum.

de Bruijn & Hussain (1984) reported a primitive species of Antemus from locality 81.14 (Lower Manchar Formation, Sehwan Sharif, Pakistan). According to them, this species would be more archaic than ‘ A. ’ primitivus from the Chinji Formation near Banda Daud Shah. Mein & Ginsburg (1985) pointed out that the description of this material could correspond to ‘ A. ’ thailandicus . However, according to the description provided by de Bruijn & Hussain (1984), the four known M2s of this species of Antemus lack the enterostyle (t4). As the latter is present in most M2s of ‘ A. ’ thailandicus , the species reported by de Bruijn & Hussain (1984) is unlikely to be ‘ A. ’ thailandicus .

POTWARMUS SP. NOV. FROM JEBEL ZELTEN WESSELS, FEJFAR, PELÁEZ- CAMPOMANES, VAN DER MEULEN & DE BRUIJN, 2003

This species was described, but not named, by Wessels et al. (2003) on the basis of five cheek teeth (3M1s, 1M2, and 1m 1) and three incisors (2i, and 1I) from the early Middle Miocene localities of ‘Measured Section 2’ (MS2) and Wádí Shatirát (WS), Mardah Formation, Jebel Zelten, Libya.

The morphology of this species is close to that of the Arabian species, but it differs in some characters. For instance, the M1s of Potwarmus sp. nov. from Jebel Zelten have a stronger lingual cingulum, a larger enterostyle, a less prominent precingulum (sensu Jacobs et al., 1989), and less alternate cusps than AJ7. The M2 of Potwarmus sp. nov. from Jebel Zelten has a very long and strong lingual cingulum, whereas it is short and less prominent in AJ11 and AJ12. With regard to the m1, although the Libyan specimen is damaged and worn on its anterior part, it is less reduced than AJ13.