Umayodus raimondi, Gelfo & Sigé, 2011

Gelfo, Javier N. & Sigé, Bernard, 2011, A new didolodontid mammal from the late Paleocene-earliest Eocene of Laguna Umayo, Peru, Acta Palaeontologica Polonica 56 (4), pp. 665-678 : 667-668

Umayodus raimondi sp. nov.

Figs. 1 , 2 .

Etymology: In honor of the Italian geographer and scientist, Antonio Raimondi (1824–1890) who dedicated most of his life to study of Peruvian nature.

Holotype: LU3−801 isolated right m3 ( Figs. 1 , 2 ).

Type locality: Laguna Umayo, Puno department, southern Peru.

Type horizon: Lower Muñani Formation (Puno Group) .

Material.—Only the type.

Diagnosis.—The same as the genus, by monotypy.

Description.—The only known specimen of the hypodigm is a right m3 (LU3−801), partially broken in the lingual and mesial side of the trigonid and with the distal portion of hypoconulid enamel missing. Its minimum size is 5.4 mm labiolingually (width) and 8.95 mm mesiodistally (length), so it is larger than any Kollpaniinae and is comparable in size to the lesser didolodontids ( Fig. 3 ). The crown is low and bunodont, and the talonid bears numerous small cuspules. The trigonid is higher and mesiodistally shorter than the talonid. Between the trigonid and the talonid, there is a narrow labiolingual fracture, which ends distal to the ectostylid and does not affect the morphological interpretation ( Figs. 1 , 2 ). Even though it is partially broken, the presence of a continuous cingulid surrounding the base of the trigonid may be inferred from the remnant of cingulid, mesial to the protoconid and lingual to the metaconid. The cingulid projects from the low ectostylid on the distolabial base of the protoconid, up to the distolingual side of the metaconid. The cingulid is absent labial to the hypoconid, but, distal to it, a weak labial rim runs over the preserved portion of the talonid.

The metaconid is the highest cusp, followed by the lower and rounded protoconid. The paraconid is small, placed mesiolabial to the metaconid. In the trigonid, wear only appears at the top of the metaconid and protoconid, where the dentine is exposed. The paracristid is only partially preserved, labially at its contact with the protoconid basis, and lingually near the paraconid. A short and low metacristid runs mesiolabially from the metaconid to the paraconid. The oblique distal wall of the trigonid (or postvallid) is vertical, particularly distal to the metaconid, which does not invade the talonid basin as in Kollpaniinae or in Escribania chubutensis . The metastylid is strong and located distolingual to the metaconid. A short and smooth crest descends from the apex of the metaconid, up to the transverse furrow that separates it from the metastylid.

The talonid is almost twice the mesiodistal length of the trigonid but somewhat narrower. The bases of the talonid cusps are not in contact, so the talonid basin is relatively wide and lingually open. The walls of the cusps delimit a sloped talonid basin, with its deeper portion located mesial to the entoconid. The hypoconid, the only talonid cusp with significant evidence of wear, is the largest talonid cusp, followed in size by the hypoconulid and the entoconid. The base of the hypoconid is connected by projections of its base to several small protuberances, placed in the central part of the talonid basin ( Figs. 1 , 2 ).

The cristid obliqua is strongly arcuate, extending a short distance mesially from the hypoconid before curving lingually about 90 ° and pointing distolingually at its ending. The base of the cristid obliqua is bulky and the surface of the cristid very irregular. No evident centroconid is present, but a small cusp is located at the end of the cristid ( Figs. 1 , 2 ). The trajectory of the cristid obliqua does not contact either the protoconid or the metaconid distal walls, but surrounds the base of the postvallid, distal to the above cited fracture between trigonid and talonid. Several bulges lie distal to the postvallid and on its lingual base. Most of them are placed distal to the metastylid and metaconid, and lingual to the

http://dx.doi.org/10.4202/app.2010.0067

cristid obliqua, except for one located over the postvallid, distal to the protocristid and mesial to the cristid obliqua.

The mesial base of the hypoconulid bears two small protuberances. Labially, the hypoconulid looks taller than the hypoconid, partly due to the wear encompassed ( Fig. 1 ). The hypocristid descends from the hypoconulid, delimiting the labial side of the talonid up to the contact with the hypoconid. A massive accessory cusp (ac 1) lies over the mesial side of the hypocristid, close to the hypoconulid base but separated from it by a conspicuous furrow. The postcristid gradually descends from the hypoconulid, first lingually and then turning mesially up to the entoconid. A second accessory cusp of the talonid (ac 2) is associated with the postcristid and is twinned to the lingual side of the hypoconulid. The postcristid is interrupted by a postentoconulid, which has a low and rounded projection through the talonid basin. This projection separates the distolabial base of the entoconid from the mesiolingual side of the hypoconulid, ending in a small and rounded protuberance. The entoconid is a large cusp though smaller than the hypoconid. It occupies almost all of the lingual side of the talonid. The lingual flank of the entoconid forms a vertical plane. The labial side is bulbous and its base expands within the talonid basin. The mesial portion of the entoconid could be interpreted as having a smooth entocristid, which descends to the distal wall of the trigonid without contacting it, thus leaving the talonid basin open lingually. A small?entoconulid lies mesial to the entoconid as a protuberance of the entocristid.

Figures

Fig. 1. Didolodontid mammal Umayodus raimondi gen. et sp. nov. from the Muñani Formation (late Paleocene– earliest Eocene) of Laguna Umayo, Peru; LU3−801 (holotype), in occlusal (A) and labial (B) views.

Fig. 2. Didolodontid mammal Umayodus raimondi gen. et sp. nov. from the Muñani Formation (late Paleocene–earliest Eocene) of Laguna Umayo, Peru; LU3−801 (holotype) in occlusal view. A. Jean R. Remy's artistic drawing. B. Diagram of LU3−801 specimen showing the nomenclature of cusp mentioned in the text. Abbreviation: ac 1, accesory cusp 1; ac 2, accesory cusp 2.

Fig. 3. Plot of the maximum length and width relationship of the last lower molars in Kollpaniinae (white circles) and Didolodontidae (black circles). Umayodus raimondi gen. et sp. nov. (star). Measurements of Kollpaniinae and Didolodontidae represent an average of several specimens and were taken from the literature (Muizon and Cifelli 2000; Gelfo 2006, 2007a).