Potwarmus, 2009

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 : 665-668

POTWARMUS FLYNNI SP. NOV. ( FIG. 3 )

Etymology: In honour of Lawrence J. Flynn (Peabody Museum of Archaeology and Ethnology, Harvard University) in recognition for his important contributions to palaeomammalogy.

Holotype: AJ 13 ( Fig. 3A ), right m1 .

Paratypes: AJ 7 ( Fig. 3B ), left M 1; AJ 11 ( Fig. 3C ), left M 2; AJ 12 ( Fig. 3D ), left M 2. All material is housed in the collections of the MNHN.

Type locality: Al Jadidah area (~ 25° 41′ N; 49° 29′ E), Saudi Arabia.

Horizon: Hofuf Formation.

Age: Middle Miocene, MN6?

Diagnosis: Species of Potwarmus with relictual or absent ‘normal’ longitudinal crest; m1 with main cusps arranged in rows, having anterior part very reduced, and posterior cingulum well developed, but lacking hypoconulid; upper molars with posterior main cusps higher than anterior ones; M1 having bilobed anterocone, main cusp-pairs slightly alternating, strong ledge on anterior face of anterocone, and well-developed lingual cingulum bearing enterostyle; M2 having main cusps arranged in rows, prominent anterolabial and lingual cingula, the latter with an enterostyle.

Differential diagnosis: Differing from Potwarmus primitivus in having the anterior side of m1 much more reduced, the protoconid more anteriorly located, on M1 the enterostyle less prominent, and in lacking metaloph on the M2; distinct from Potwarmus thailandicus in having the anterior part of m1 more reduced and in having a prominent crest located anterior to the anterocone, a less broader valley between the middle and last row of cusps on the M1, and in lacking metaloph on the M2; differing from Potwarmus sp. nov. from Jebel Zelten in having the anterior part strongly reduced and a posterior cingulum without hypoconulid on m1, and a more anteriorly situated enterostyle on M1; distinct from Dakkamys zaiani in lacking a new longitudinal crest, in having an isolated and smaller enterostyle on the upper molars, and the anterior part of the m1 reduced; differing from ‘ Dakkamys ’ asiaticus and ‘ Dakkamys ’ barryi in lacking anterior arms of lingual and labial cusps on the upper and lower molars, respectively, in having an isolated and small enterostyle on the upper molars, and in having the anterior part of the m1 reduced; distinct from Paradakkamys chinjiensis in having much less prominent and isolated enterostyle on the upper molars, and the anterior part of the m1 reduced; distinct from ‘ Paradakkamys ’ ouaichi in having the cusps less alternating and a well-developed longitudinal crest on the M1; differing from ‘ Paradakkamys ’ seboui in lacking longitudinal crest, in having the enterostyle isolated on the M1-M2, and the anterior part of the m1 very reduced; distinct from Myocricetodon afoudensis in lacking a new longitudinal crest, a mesoloph, and alternating cusps, and in having an isolated enterostyle; distinct from ‘ Myocricetodon ’ sivalensis in lacking the anteroconid and longitudinal crest, and in having the anterior part of the m1 reduced; differing from Myocricetodon eskihisarensis in having a smaller and isolated enterostyle, lacking a paracone spur and longitudinal crest on the upper molars, and in having the anterior part of m1 reduced; distinct from ‘ Myocricetodon ’ liui in having a smaller enterostyle on M1, absent metaloph on M2, and the anterior part of the m1 reduced; differing from Vallaris zappai in lacking longitudinal crest, mesoloph, mesolophid, hypoconule, and hypoconulid on the cheek teeth; distinct from Antemus chinjiensis and Progonomys debruijni in lacking the basic murine pattern of three chevrons.

Description

m1: The occlusal outline of this tooth is subrectangular, longer than wide, with its anterior part somewhat rounded and slightly narrower than the posterior one. The longitudinal crest is absent; the main cusps are arranged in rows, forming two rather elevated, oblique, and nearly parallel ridges, which are separated by a transverse valley. These cusps are higher posteriorly. The posterior cusps (entoconid– hypoconid) are larger than the anterior ones (metaconid–protoconid). The anterior part of this tooth is strongly reduced, having the anteroconid fused with the low anterior cingulum. The anterior cingulum is long and well developed: its labial branch connects to the anterolabial side of the protoconid, whereas the lingual one reaches the lingual side of the tooth. This tooth has a minute ectostylid as well as an incipient mesostylid. The posterior cingulum is well developed but lacks the hypoconulid; it reaches the posterolingual side of the entoconid, enclosing a rather shallow, but large, posterolingual valley. Its labial branch reaches the base of the hypoconid. Two roots are present. The absolute as well as relative size (LM1/Lm1 ratio) of this tooth is well within the range shown by all the species of Potwarmus known so far ( Jaeger, Tong & Buffetaut, 1985; Lindsay, 1988; Wessels et al., 2003).

M1: On this tooth the posterior cusps are higher than the anterior ones (the metacone–hypocone are higher than the paracone–protocone and the latter are, in turn, higher than the anterocone). The occlusal outline is longer than wide with the greatest width near the mid-length. The large anterocone is clearly divided into two asymmetric lobes: the labial one is larger than the lingual one. They are separated by a relatively deep groove. There is a prominent ridge anterior to the anterocone. The anterolophule is lacking and there is a deep transversal valley separating the anterocone from the paracone–protocone. The anterior cingulum is swollen lingually as an incipient anterostyle: it descends lingually, joining with the strong lingual cingulum. This cingulum is continuous around the protocone to connect to the small enterostyle near the base of the hypocone. The enterostyle is isolated from both lingual cusps. This tooth has an incipient cusp close to the anterolabial base of the paracone. The short protoloph is narrow and joins the paracone with the posterior part of the protocone. The hypocone is fused with the metacone and with the posterior cingulum, an enamel funnel remaining in the centre. The lingual main cusps (protocone and hypocone) are situated slightly anteriorly with respect to the labial ones, and the protocone is slightly more lingually located than the hypocone. The separation between the protocone and the hypocone is less marked than between the paracone and the metacone: this manifests itself as a relict of the longitudinal crest. Posterior sulcus and posterosinus are lacking. This tooth has three roots.

M2: These teeth have the occlusal outline subrectangular, longer than wide, with the posterior part rounded. The posterior main cusps are higher than the anterior ones. The anterior cingulum is low and strong, with both branches well developed. The labial branch is longer than the lingual one, and reaches the anterolabial base of the paracone, enclosing a low anterolabial valley. The lingual branch is interrupted before reaching the anterolingual base of the protocone. The weak anterolophule connects the anterior cingulum with the protocone. These teeth lack the longitudinal crest (AJ11) or show a relict of it (AJ12). The anterior cusps are separated from the posterior ones by a narrow and relatively deep transversal valley. This valley has its labial part shallower than the lingual side. The paracone is fused with the anterior part of the protocone. The metacone joins with the posterior cingulum, but not with the hypocone, from which it is isolated. These teeth lack a labial cingulum, and have a very short lingual cingulum that bears a small and isolated enterostyle. They have three roots.

Figures

Figure 3. Potwarmus flynni sp. nov. A, right m1 (AJ13, holotype, occlusal view); B, left M1 (AJ7, occlusal view); C, left M2 (AJ11, occlusal view); D, left M2 (AJ12, occlusal view). Scale bar = 1 mm.