Proremiculus lagnauxi, Bast & Sigé & Smith, 2012

Bast, Eric De, Sigé, Bernard & Smith, Thierry, 2012, Diversity of the adapisoriculid mammals from the early Palaeocene of Hainin, Belgium, Acta Palaeontologica Polonica 57 (1), pp. 35-52 : 45-46

Proremiculus lagnauxi sp. nov.

Fig. 7 ; Table 4.

Etymology: In honour of Hector Lagnaux, for his efforts in manually sinking the Hainin well reaching a depth of 27 metres, with a diameter of one metre.

Type material: Holotype: IRSNB M2006 ( R1−46 ): left M2 . Paratypes: IRSNB M2005 (Q2−44), left M1 ; IRSNB M2007 ( R1−38 ), right m1 ; IRSNB M2008 ( R1−74 ), left m1 or m2 .

Type locality: Hainin , Hainaut province, Belgium .

Type horizon: Early Palaeocene, Hainin Formation, Mons Basin.

Referred material.—N2−43, talonid of left m1 or m2.

Diagnosis.—General morphology of upper molars similar to that of Afrodon , with only two stylar cusps (parastyle and stylocone), marked internal crests of the conules, and a typically “predilambdodont” morphology with a rectilinear centrocrista. Differs from all species of Afrodon in the presence of a lower paracone and metacone, the presence of pre− and postcingula, and a less asymmetrical hypoflexus on the upper molars, as well as more massive cusps and a wider talonid on the lower molars. Differs from all species of Remiculus in the presence of a rectilinear centrocrista, the absence of a mesostyle, and a less developed lingual cingulum on the upper molars, as well as a slightly less strongly developed hypoconid and a medial hypoconulid on the lower molars. Measurements.—See Table 4.

Description.—The M1 ( Fig. 7A ) described here is incomplete, lacking the metacone, the metastylar lobe and part of the postcingulum. The stylar shelf is relatively short and bears two well−defined cusps (parastyle and stylocone). The preparacrista is short and almost parallel to the labiolingual axis of the tooth. The paracone and metacone are well individualised and the postparacrista is oriented anteroposteriorly, indicating that the entire centrocrista was rectilinear. The paracingulum is very narrow. The lingual part of the tooth is more developed than the labial part. The paraconule is well defined, while the postparaconule crista is marked but not very visible owing to poor preservation of the tooth. The precingulum and the partially broken postcingulum are long and almost join on the lingual side of the protocone.

The M2 ( Fig. 7B ) is the only complete upper tooth. The relatively short stylar shelf bears two marked cusps (parastyle and stylocone). The preparacrista and postmetacrista are long, the latter being more oblique with respect to the labiolingual axis of the tooth. The ectoflexus is moderately deep and slightly asymmetrical. The parastylar lobe has about the same

http://dx.doi.org/10.4202/app.2010.0115

size as the metastylar lobe, but is oriented more labially. The paracone and metacone are well separated down to their bases and linked by a rectilinear centrocrista. The paracone is higher and situated slightly more labially than the metacone. The lingual part of the tooth is much more transversely developed than the labial part. The protofossa is moderately developed, and the paraconule is better individualised than the metaconule. The internal crests are well marked, with the postparaconule crista extending on to the lingual face of the paracone. The protocone is the largest cusp of the tooth and has a massive and slightly procline aspect. The presence of a very small precingulum and large postcingulum enlarges the base of the protocone anteroposteriorly. There is no hypocone on the postcingulum.

The m1 ( Fig. 7C ) is massive, with strong and low cusps. There is little difference in height between the trigonid and the talonid, with the latter being slightly wider than the former. The precingulid is moderately developed. The paraconid, though relatively large, is the smallest trigonid cusp, points anteriorly, and is located slightly labial to the metaconid. The metaconid has the same height as the protoconid and is situated more posteriorly than the latter, resulting in the posterior wall of the trigonid being oblique to the anteroposterior axis of the tooth. The posterior wall of the trigonid is not very steep anteroposteriorly. The three talonid cusps are equidistant, with the hypoconid being slightly larger than the two other cusps, and projecting labially. The talonid basin is relatively deep. The crista obliqua reaches the posterior wall of the trigonid halfway between the protoconid and metaconid, and extends up towards the metaconid. The hypoflexid is wide and shallow.

Specimen IRSNB M2008 ( Fig. 7D ) represents either m1 or m2, and is the only other known lower tooth. It is very similar to m 1 in its size and morphology, with a slightly smaller and more posteriorly situated paraconid. However, the somewhat shorter trigonid could be a reason to consider this tooth an m2, rather than m1.

Discussion.—The morphology of Proremiculus lagnauxi resembles that of Afrodon , showing marked internal crests, a rectilinear centrocrista, only two stylar cusps on the upper molars, and a small hypoconid on the lower molars. However, its lower paracone and metacone, anteroposteriorly longer protocone, small precingulum and postcingulum, relatively square upper molars and relatively shallow talonid basin, as well as the bulbous cusps of its lower molars resemble the genus Remiculus , although these derived features are not as well developed as in R. deutschi or R. delsatei . The presence of such derived characters excludes this species from the genus Afrodon . At the same time, the absence of other derived characters such as a mesostyle, D cusp, and dilambdodont centrocrista excludes it from the genus Remiculus , thus justifying its inclusion in the new genus Proremiculus .

Stratigraphic and geographic range.—Known only from the early Palaeocene of the Mons Basin, Belgium.

Figures

Fig. 7. SEM pictures of the adapisoriculid mammal Proremiculus lagnauxi sp. nov. from the early Palaeocene of Hainin (Belgium). A. Left M1, IRSNB M2005 (Q2−44), in labial (A1) and occlusal (A2) views. B. Holotype: left M2, IRSNB M2006 (R1−46), in labial (B1) and occlusal (B2) views. C. Right m1, IRSNB M2007 (R1−38), in labial (C1), occlusal (C2), and lingual (C3) views. D. Left m1,2, IRSNB M2008 (R1−74), in labial (D1), occlusal (D2), and lingual (D3) views.