Gigarton louisi, Hooker & Russell, 2012

Hooker, Jerry J. & Russell, Donald E., 2012, Early Palaeogene Louisinidae (Macroscelidea, Mammalia), their relationships and north European diversity, Zoological Journal of the Linnean Society 164 (4), pp. 856-936 : 896-897

GIGARTON LOUISI SP. NOV. ( FIGS 18 , 19L–N, P)

Etymology: After the late Monsieur Pierre Louis, for his exceptional knowledge of the mammals and stratigraphy of the Champagne region, his discoveries, and his collaboration over many decades.

Holotype: LM 2, MNHN.F.CR-93-L, Cernay.

Paratypes: LM 1, MNHN.F.CR-291-L; four RM 1 s, MNHN.F.CR-435, CR-289-L, CR-8-MD, CR-1447-Pn; RM 2 , MNHN .F.CR-45- MD; LM 3 , MNHN .F.CR-129-Pn; LDP 4 , MNHN .F.CR-290-L; all Cernay.

Cast in MNHN.F: RDP 4, CR-72-Ro, Cernay.

Age and distribution: Sables de Châlons-sur-Vesle supérieurs, late Thanetian, Late Palaeocene, Cernay, France.

Diagnosis: Small species of Gigarton , mean length of M 2 2.24 mm. Upper molar main cusps semibulbous and distinctly crested; enamel not thickened. M 1–2 with small hypocone; buccal and lingual cusps not occlusally convergent. (Lower teeth and premolars unknown.)

Description

M 1: Outline shape is similar to that of G. sigogneauae and the metacone is larger than the paracone, but the cusps are taller and more gracile (Fig. 19L). It lacks the bunodonty of the other two species. The main crests, the premetaconule crista (in two specimens), and the metaconule are well marked. There is variation in development of the paraconule, however. Cingula are absent only lingually. The parastyle projects mesially slightly less than in G. sigogneauae . One specimen has an entostyle. The centrocrista is weak in one specimen. There is a tendency for development of a very small cingular mesostyle (Fig. 19L1).

M 2: The two specimens differ from M 1 in the outline, which is more triangular, tapering lingually, with a much smaller hypocone (Fig. 19M). In only one of the two is the metacone substantially larger than the paracone. Both have a very weak paraconule. Cingular development is as on M 1. The parastyle is weak and low.

M 3: The single specimen is 1.42 mm long by 1.92 mm wide. It is similar to that of B. pellouini in size and outline proportions, but it is like the M 3 of G. sigogneauae in having a very weak postcingulum and a weak parastyle (Fig. 19N). Like M 1–2 of B. pellouini , it differs from G. sigogneauae in lacking the bulbous shape of the paracone.

DP 4: One specimen is nearly unworn, but damaged along the preprotocrista (Fig. 19P). It is similar to M 1, but slightly smaller, lower crowned, and with a larger parastyle. The postprotocrista joins the metaconule and there is a premetaconule crista. Another has a different outline, narrower proportions, a more mesially projecting parastyle, and no premetaconule crista.

Discussion

Despite no knowledge of lower teeth or permanent premolars, the morphology and distinctly smaller size ( Fig. 18A ) distinguish it from its two relatives.

Figures

Figure 18. Scatter diagrams of Ln length vs. Ln width of species of Gigarton. For explanation of symbols see Figure 8. A, M1–2; B, P. 4