New remains of caviomorph rodents from the Paleogene of the Juanjui area (Peruvian Amazonia): systematics, macroevolutionary implications and biostratigraphy

ASSEMAT, A.; BOIVIN, M.; MARIVAUX, L.; PUJOS, F.; BENITES PALOMINO, A.; SALAS-GISMONDI, R.; TEJADA-LARA, J. V.; VARAS-MALCA, R. M.; NEGRI, F. R.; RIBEIRO, A. M.; ANTOINE, P.-O.

GEODIVERSITAS

PUBLICATIONS SCIENTIFIQUES DU MUSEUM

Lugar: Paris; Año: 2019 vol. 41 p. 699 - 730

1280-9659

Paleogene deposits of Peruvian Amazonia have yielded the oldest caviomorph rodent communities from South America, and the clues that their early diversification had occurred in this area. Here we report fossil dental remains of rodents from two new sections located in the vicinity of Juanjui and Balsayacu (San Martín Department, Peruvian Amazonia). Analyses of occlusal morphology of cheek teeth and of incisor enamel microstructure indicate the occurrence of basal caviomorphs (such as Cachiyacuy, Antoine et al., 2012, Canaanimys, Antoine et al., 2012, and Eoespina, Frailey & Campbell, 2004, genera so far restricted to late middle Eocene deposits of Contamana, Peruvian Amazonia) in levels situated in the lower part of the studied stratigraphic section. More derived taxa (such as Eoincamys, Frailey & Campbell, 2004), known from early Oligocene deposits of Tarapoto/Shapaja and Santa Rosa, Peruvian Amazonia) occur only in upper levels of the section. Based on these considerations, the rodent-bearing localities of the Juanjui/Balsayacu area seem to be intermediate in age between the Contamana Eocene localities and the Tarapoto/Shapaja Oligocene ones and the Santa Rosa ?Eocene/Oligocene one. These new data document a poorly known period in Western Amazonia, in providing a sedimentological record most likely documenting the late middle Eocene, the late Eocene and the earliest Oligocene interval. Furthermore, the existence of a long temporal hiatus between Canaanimys?Cachiyacuy?Potamotrygon ucayalensis assemblages (Contamana, Pozo Formation; Balsayacu; lower levels at Juanjui) and Eoincamys-yielding faunas (Santa Rosa; Tarapoto/Shapaja; uppermost levels at Juanjui) is demonstrated in a single continuous and long-ranging stratigraphic section at Juanjui.