Pseudopotamarchus, Kerber, Negri, Ribeiro, Vucetich & Souza-Filho, 2016

Kerber, Leonardo, Negri, Francisco Ricardo, Ribeiro, Ana Maria, Vucetich, Maria Guiomar & Souza-Filho, Jonas Pereira De, 2016, Late Miocene potamarchine rodents from southwestern Amazonia, Brazil-with description of new taxa, Acta Palaeontologica Polonica 61 (1), pp. 191-203 : 197-199

Genus Pseudopotamarchus nov.

Etymology: Meaning false Potamarchus , regarding to the similarity to the latter genus.

Type species: Pseudopotamarchus villanuevai sp. nov., monotypic; see below.

Diagnosis.—Small-sized potamarchine, protohypsodont, with check teeth composed of lophs, distinguished from Potamarchus by the presence of a notch on the anterior surface of the ventral zygomatic root.

Pseudopotamarchus villanuevai sp. nov.

Figs. 5–7 ; Tables 2 and 3; SOM 1: fig. S4, SOM 3.

Etymology: In honor of the palaeontologist Jean Bocquentin-Villanueva who has studied the fossil vertebrates from Amazonia.

Holotype: UFAC 4762 , incomplete right maxilla with P4–M1.

Type locality: Cachoeira do Bandeira locality (see Bocquentin and Melo 2006 for details), Acre River, Solimões Formation (Late Miocene), State of Acre, Brazil .

Type horizon: Solimões Formation, Late Miocene.

Diagnosis. —As for the genus; monotypic.

Description. —The cheek teeth are protohypsodont and show little wear ( Fig. 5 ). The P4 and M1 have two labial roots ( Fig. 6 ). The crown of the P4 is higher than the M1 (SOM 1: fig. S4), and its last loph shows little wear. The P4 has six lophs and it preserves (although almost closed) two labial and three lingual flexi. The lophs are quite oblique in comparison with the M1. The mesial face of the first loph is not as convex as in Potamarchus murinus . The first loph is shorter liguo-labially than the second, which is the largest one. Distally to the second one, the lophs decrease in size towards the last one, which is almost rudimentary. The M1 is rectangular and has six lophs (the last loph is fragmented). Labially, there is no open flexus, while lingually the first and second are open and the third is almost closed. The lophs have almost the same width. The lophs of both teeth are compressed, and the rectangular outline of the M1 is distinct from older specimens of P. murinus , in which the M1 is subquadrangular (but see Discussion). The lingual area of the lophs of the P4 and M1 are not bent as in Potamarchus . The ventral root of the zygomatic process of the maxilla is posteriorly oriented and its anterior area shows a notch not present in P. murinus ( Fig. 7 ). This notch is prolonged posteriorly up to the fourth loph of the P4.

Stratigraphic and geographic range.—Late Miocene of southwestern Amazonia, Brazil.

Figures

Fig. 5. Sequence of tridimentional reconstructions of the maxilla of potamarchine rodent Pseudopotamarchus villanuevai gen. et sp. nov. (UFAC 4762) from Solimões Formation, Late Miocene, Brazil; from occlusal to medial view (A–D).

Fig.6. CT-scan slices of the maxilla of potamarchine rodent Pseudopotamarchus villanuevai gen. et sp.nov.(UFAC 4762) from Solimões Formation, Late Miocene, Brazil; in longitudinal (A), horizontal (B), and transverse (C) planes, showing the labial roots of the cheek teeth (arrows).

Fig. 7. Maxilla of potamarchine rodent Pseudopotamarchus villanuevai gen. et sp. nov. (A, UFAC 4762) from Solimões Formation, Late Miocene, Brazil; in occlusal (A1), anterior (A2), and lateral (A3) views, in comparison with Potamarchus murinus (B, MACN-Pv 3500, inverted) from Ituzaingó Formation, Late Miocene, Argentina; showing the notch (arrows) on the anterior face of the ventral root of the zygomatic process of the maxilla.