Microhyus sp.

Tabuce, Rodolphe, Antunes, Miguel Telles, Smith, Richard & Smith, Thierry, 2006, Dental and tarsal morphology of the European Paleocene / Eocene “ condylarth ” mammal Microhyus, Acta Palaeontologica Polonica 51 (1), pp. 37-52 : 38-39

cf. Microhyus sp.

Locality: Berru, France.

Age : MP6a (Thanetian, Paleocene).

Material and measurements.—MNHN L−3−BR right M1, L = 2.8, W = 3.2.

Description ( Fig. 1A).—This upper molar is sub−square in outline. The four main cusps are bunodont, very close to the center of the crown and they are separated by shallow valleys. The paracone is larger than the metacone and the protocone is lower than the hypocone. The hypocone and the protocone are very labially situated and their lingual walls are sloping toward the base of the crown. The paraconule and metaconule are small and twinned with the protocone and hypocone respectively. A short postprotocrista is directed toward the metaconule. Both the mesial and distal cingula are thick and bear a blunt ectocone and an incipient hypostyle respectively. There is no salient parastyle on the mesial aspect of the tooth. A cingulum can be detected on the damaged labial part of the crown.

Comparisons.—The morphology of MNHN L−3−BR is similar to that of other louisinines in exhibiting the following traits: the outline is sub−square, the four main cusps are low and bunodont, the paracone is larger than the metacone, the parastyle is reduced, the metastyle is absent and a robust cingulum runs around the mesial, labial and distal sides of the tooth. The development and the position of the hypocone indicate possible affinities with the species Monshyus praevius and Louisina mirabilis as well as with the genus Microhyus . Monshyus praevius from the early Paleocene of Hainin, Belgium (reference level MP1−5) is the earliest representative of the louisinines and has been interpreted as being the most derived species of the subfamily ( Sudre and Russell 1982); it is documented by only one tooth, an M1(or M2) that recalls the specimen from Berru by the labial position of both the protocone and the hypocone. Monshyus differs, however, in lacking conules, and in having a longer preprotocrista, a hypocone connected with the distal cingulum, a salient parastyle, and a less robust mesial cingulum. Upper molars of Louisina mirabilis from Cernay, France (reference level MP6a; Russell 1964) also differ from MNHN L−3−BR by several characters: the cusps are less bulbous; the pre− and postprotocrista are long and linked with more prominent paraconules and metaconules; and the hypocone is smaller and connected with the distal cingulum. On the basis of all these characters, MNHN L−3−BR is similar to first upper molars of Microhyus . However, M. musculus and M. reisi are notably smaller, the outline of their M1s is relatively labio−lingually shorter, the four main cusps are less closely positioned in the center of the crown, the valleys are deeper, the hypocone is larger and the mesial cingulum is weaker. The species from Berru thus appears to be less derived than the

TABUCE ET AL.—DENTAL AND TARSAL MORPHOLOGY OF MICROHYUS 39

1 mm labial cingulum paracone parastyle metacone mesial metaconule cingulum paraconule hypocone protocone hypoconid protoconid hypoconulid paraconid mesial cingulid entoconid metaconid

two known species belonging to Microhyus by the slight transverse development of the crown and the relative small size of the hypocone; but it is more derived in being larger with centrally positioned, more bulbous cusps. MNHN L−3− BR certainly represents a new taxon, likely a new species of Microhyus ; this form is, however, still insufficiently documented to be formally defined.