Marmosa sp.

Stutz, Narla S., Hadler, Patricia, Negri, Francisco R., Marivaux, Laurent, Antoine, Pierre-Olivier, Pujos, François, Jacó, Tiago R., Fontoura, Emmanuelle M., Kerber, Leonardo, Hsiou, Annie S., Santos, Roberto Ventura, Alvim, André M. V. & Ribeiro, Ana Maria, 2023, New records of marsupials from the Miocene of Western Amazonia, Acre, Brazil, Acta Palaeontologica Polonica 68 (3), pp. 457-475 : 462-464

? Marmosa sp.

Fig. 6A.

Material.— UFAC-CS 413, part of the stylar shelf (StC–E) of a right?M2 from the locality PRE 06 , sampling point C, Envira River , State of Acre, Brazil; Solimões Formation , Acre Basin, (?lower) Upper Miocene .

Measurements.—StE–ectoflexus = 1.8 mm; Metacone–labial margin = 2.36 mm; Metacone–StE = 2.68 mm.

Description.—The specimen is worn and broken at the level of the StC and the trigon basin. It includes part of the stylar shelf with the StC–E, and the metacone. The metacone is opposite to StD, relatively far from the latter, and lingually oriented. There is a subtle basin between the metacone and the StC and StD. The premetacrista is short and slightly labiolingually curved. The postmetacrista is longer, extending until the StE with an oblique orientation. There is a crest-like structure at the base of the posterior wall of the metacone, however, it is not possible to state to which crest it corresponds, it could also be a product of the fragmentary and worn state of the molar. There is a small crest-like structure lingually to the StC. The labial margin has a steep oblique orientation from the StC to the StE. The StC and StD are subequal in size; both poorly developed but still visible. The StC and StD are not twinned or close to each other. The StE is posteriorly broken, but it is still possible to observe a small and narrow cusp.

Remarks.—Morphological comparisons with similarly sized didelphids indicate that UFAC-CS 413 is smaller than species of Didelphis , the latter having more rounded stylar cusps. UFAC-CS 413 is approximately the same size as species of Lutreolina but has a smaller StC. In the species of Philander , the StC is more developed and morphologically different. UFAC-CS 413 shows closer affinities with the species of Marmosa in morphology, such as the presence of StE, StD and StC ( Rossi et al. 2010). UFAC-CS 413 is larger than the teeth of the recent species Marmosa demerarae (Thomas, 1905) . Fossil representatives of the genus include Marmosa laventica , the oldest record of Marmosa , which was described for the Middle Miocene deposits of La Venta, Colombia ( Marshall 1976a). Marmosa laventica is larger than the living species of Marmosa , among other diagnostic characteristics. However, it was described based only on lower dentition. Later, Goin (1997), when revisiting the diagnosis of M. laventica , assigned it to Micoureus laventicus and added upper molars in its hypodigm. However, recent molecular analyses considered Micoureus as a synonym of Marmosa , being now recognized as a subgenus of the latter ( Voss and Jansa 2009). UFAC-CS 413 is larger than the specimens reported by Goin (1997), and, because of its incomplete state, the diagnostic characteristics of M. laventica could not be observed on it. Marshall (1976a) also reported specimens of Marmosa sp. from La Venta, which are smaller than M. laventica , and thus not compatible in size with UFAC-CS 413. The size of UFAC-CS 413 also distinguishes it from Marmosa sp. 1 of Suárez Gómez (2019), which is reported as being ~40% smaller than M. laventica . Antoine et al. (2013) reported a partial M2 of Marmosa (Micoureus) cf. laventica for the lower Middle Miocene locality MD- 67 in Peru, which differs from UFAC-CS 413 in being smaller and not possessing StE. Yet, both specimens show a large stylar shelf and StC and StD. Compared to Hesperocynus , Sparassocynus , and Thylatheridium, UFAC-CS 413 does not possess a very long postmetacrista and the metacone does not seem to be a tall cusp, but the latter could be due to the great wear ( Goin et al. 2000; Forasiepi et al. 2009; Abello et al. 2015).

Therefore, UFAC-CS 413 was assigned to Marmosini ,? Marmosa sp. due to the morphological resemblance of it with Marmosa . Nevertheless, the incomplete state of the specimen hampers a more precise taxonomical identification.