Masillamys TOBIEN , 1954

Vianey-Liaud, Monique, Marivaux, Laurent & Lehmann, Thomas, 2019, A Reevaluation Of The Taxonomic Status Of The Rodent Masillamys Tobien, 1954 From Messel (Germany, Late Early To Early Middle Eocene, 48 - 47 M. Y.), Fossil Imprint 75 (3 - 4), pp. 454-483 : 457-458

Genus Masillamys TOBIEN, 1954

Ty p e s p e c i e s. Masillamys beegeri TOBIEN, 1954.

S p e c i e s i n c l u d e d. M. beegeri TOBIEN, 1954, M. krugi TOBIEN, 1954, M. mattaueri ( HARTENBERGER, 1975) and M. parvus TOBIEN, 1954.

O r i g i n a l d i a g n o s i s.DentalformulaP3–P4–M1–3 /

p4–m1–3, sciuromorph rodent from the Pseudosciuridae family; hypocone present on upper molars; metaconule aligned between metacone and protocone. Mesostyle, crestlike and elongated present, aligned between the paracone and the metacone. Lower p4 shorter than molars with only one mesial cuspid. Molars without individualized ‘paraconid’ (= anteroconid), merged in the anteroloph; metalophid wholly or only partially present, whereas the entolophid is always present, albeit more or less pronounced; ectolophid developed, with weak mesoconid; hypoconulid weak to absent; occlusal surface of the upper and lower cheek teeth with relatively coarse wrinkles and furrow. On the dentary, front edge of the masseter pit reaching the mesial end of m2. ( Tobien 1954, translation adapted from German).

P r e v i o u s e m e n d e d d i a g n o s i s. Thaler (1966, translation from French): ‘ Pseudosciuridae with imperfectly quadrangular upper molars: protocone and hypocone close together, sinus incompletely developed, metaconule aligned between protocone and metacone.’

Escarguel (1999, translation from French): ‘Large sized Microparamyini ; P3 present and occlusal surface of enamel strongly wrinkled; low-crowned jugal teeth. Anterior edge of the masseteric fossa reaches the mesial edge of m2. Mesial part of P4 reduced. M1–2 with massive conules and mesostyle; the hypocone tends to be as large as the protocone; metaconule weakly or not linked at all to the protocone, to the hypocone or to the lingual margin (= endoloph?); metacone significantly more lingual than the paracone. Strong metaconule, on M3. p4 stocky; ectolophid and posterior cingulid well-developed. On m1–2, the postprotocristid stops shortly before reaching the mesoconid; it is prolonged in a well-developed but rarely complete hypolophid [= entolophid]; massive posterior cingulid, with a well-marked interruption between hypoconulid and entoconid. m3 with trigonid basin widely open distally, and a usually well-developed hypoconulid.’

N e w e m e n d e d d i a g n o s i s. Basal Theridomorpha. Enamel rough to strongly wrinkled on the outskirts of the crown; wrinkles and granules numerous in the mesoflexus. Preparacrista absent on M1–M2; parastyle moderate on M2; ectocingulum variably present on M1–M2; one to two mesolophs on M1–M2; one to two mesostyles on M3; metalophule II variably connected to the posteroloph; posthypocrista variably present on M1–M2; paracone strongly higher than the protocone on M3. On m2, trigonid only slightly higher than the talonid; buccal mesolophid distinct from a postmesoconid ridge; more than three mesiodistal extra-ridges along the distal slope of the trigonid on molars; ectomesolophid present on dp4 and p4; buccal entolophid connected/directed to the postmesoconid ridge; buccal anterolophulid absent on molars; entoconulid variably present.

D i f f e r e n t i a l d i a g n o s i s. The genus Masillamys differs from:

– Pantrogna and Hartenbergeromys in its less reduced p4, its metaconid less high than the other cuspids, the hypocone larger compared to the protocone, although remaining smaller.

– Protadelomys in the occurrence of an ectolophid bearing a mesoconid (cf. original diagnosis of Stehlin and Schaub 1951), the lingual metalophule (or metaconule lingual connection) lower and more mesial (to the postprotocrista or the endoloph, exceptionnally to the hypocone).