Flood-induced catastrophic mortality of a fossorial rodent of Western Pampean Region (Argentina) during historical times: Taphonomy, taxonomy and conservation issues

Abstract

We present a taxonomic, taphonomic, and paleobiological study of a historical assemblage composed of skeletal remains of the Argentine endemic fossorial rodent Ctenomys mendocinus (Rodentia, Ctenomyidae), recovered from a small area along the banks of the ephemeral Arroyo El Surgente in Western Pampean Region (centraleastern La Pampa Province, Argentina). Studied remains are referred to Ctenomys mendocinus based on com­ parisons with specimens of this species and samples identified as C. azarae (a nominal form now included withinthe synonymy of C. mendocinus) from central La Pampa; a restriction on the type locality of this latter is proposed. The assemblage is widely dominated by skulls and hemimandibles that show no evidence of rounding, weath­ ering, or corrosive digestion, suggesting negligible transport, limited or null exposure to atmospheric agents, and no involvement of predators/scavengers. The skeletal elements were exhumed but scarcely moved from their original depositional context. Taxonomic and ethological evidence (overwhelming dominance of a fossorial and gregarious rodent), taphonomic assessment (age profile consistent with living populations, absence of predationmarks and weathering, and diagenetic processes), and contextual setting (presence of several modern burrows on the creek terrace and sedimentological signs) suggest that the bone accumulation is compatible with a cata­ strophic mortality event caused by flooding. Subsequently, impregnation with manganese oxide/hydroxide and encrustations of salts and gypsum are interpreted as diagenetic processes requiring time to develop and supporting a low-energy depositional setting.