Abderitidae Ameghino, 1889

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 : 469

Family Abderitidae Ameghino, 1889 Abderitidae indet.

Fig. 8C, D.

Material.— UFAC-CS 101, right M2; UFAC-CS 109, left?m2; from the locality PRJ 33 , stratified conglomerate level, Juruá River , State of Acre, Brazil; Solimões Formation , Acre Basin, Middle Miocene .

Measurements.— UFAC-CS 101, L = 1.58 mm, W = 1.9 mm; UFAC-CS 109, W = 1.41 mm, L = 1.08 mm.

Description.— UFAC-CS 101 ( Fig. 8C) is a small upper molar, quadrangular in occlusal view, strongly recalling the morphology and outline of an M2. It is wide at its base, especially labio-lingually, with a conspicuous labial slope at the base of the StB. The protocone is robust but relatively short. The metaconule is smaller than the protocone. The postprotocrista meets a crest that runs anterolingually to the metaconule, lingually delimitating a small trigon basin, which is separated from the talon basin. There is a wide anterior cingulum, with a conspicuous parastylar cusp sensu Abello and Rubilar-Rogers (2012) present at its labial margin, which possesses a small projection/style at its labial base. The StB is large and high, being the tallest cusp of the molar. The posterior StB crest presents a small cusp-like structure. This crest and the anterior StC+D crest do not form a V-shaped sulcus but run more parallel to the anteroposterior molar axis. The StC+D is small and is placed quite posteriorly. Posterolingual to the StC+D, there is a short wide basin formed by the postmetaconular crest. Crest-like structures run from the stylar cusps towards the protocone and metaconule.

The UFAC-CS 109 specimen ( Fig. 8D) is a fragment of a lower molar, with only the talonid preserved. None of the trigonid cuspids are preserved, and the talonid displays two lingual cuspids and one labial. The two lingual ones correspond to an anterior cuspid-like entocristid, which has a blunt tip, and a posterior entoconid, both labio-lingually compressed. The hypoconid occupies a posterior position, with a cristid-like structure running antero-lingually from its tip to the talonid basin. The talonid basin is relatively narrow. Posteriorly to the entoconid, a postentocristid runs almost perpendicular to the anteroposterior molar axis, joining a postcristid towards the molar midline. Basal to them there is a small hypoconulid. The cristid obliqua is slightly oblique and has a sharp occlusal margin.

Remarks.—The presence of lophodont molars is considered a diagnostic characteristic of the family Abderitidae . Besides, the presence of a parastylar cusp on the M2 is also common among abderitids ( Abello 2007). The latter and the absence of both paracone and metacone on this tooth, as well as a cristid obliqua with sharp occlusal margin on the m2–m3, and a hypoconid not anteroposteriorly compressed are characteristics present in UFAC-CS 101 and UFAC-CS 109 which are diagnostic of the genus Abderites Ameghino, 1887 , according to Abello and Rubilar-Rogers (2012). Three species of Abderites are currently recognized, Abderites meridionalis Ameghino, 1887 , Abderites crispus Ameghino, 1902 , and Abderites aisenense Abello and Rubilar-Rogers, 2012 . The size of UFAC-CS 101 and UFAC-CS 109 is much smaller than the specimens assigned to any known species of Abderites , the closer of them in size being A. crispus ( Abello and Rubilar-Rogers 2012) . Several of the characteristics that define each of the species of Abderites are located on other molar loci or regions not preserved in the specimens from Acre. Several synonymies were already considered among the referred species, the differences among them being somewhat subtle ( Abello and Rubilar-Rogers 2012). The labial slope seen in UFAC-CS 101 is a peculiar characteristic not found in none of the previously known species of Abderites , which have a sub-vertical labial wall on M1–M3. Besides, compared to another abderitid, Pitheculites Ameghino, 1902 , the specimens from Acre are slightly larger than Pitheculites minimus Ameghino, 1902 , slightly smaller than Pitheculites rothi Marshall, 1990 , and Pitheculites ipururensis Stutz, Abello, Marivaux, Boivin, Pujos, Benites-Palomino, Salas-Gismondi, Tejada-Lara, Custódio, Roddaz, Ventura Santos, Ribeiro, and Antoine, 2022 , and much smaller than Pitheculites chenche (Dumont and Bown, 1997) ( Marshall 1976b; Suárez Gómez, 2019; Stutz et al. 2022). Furthermore, Pitheculites is characterized by a metacone on M2 and a short cristid obliqua with a rounded occlusal margin ( Abello 2007).

Therefore, due to their scarcity and fragmentary state, the open taxonomic assignation Abderitidae indet. is considered more conservative for the specimens UFAC-CS 101 and UFAC-CS 109.