Paleoecology and diversity of Pliocene to Pleistocene fossorial mammals in the Pampean region of Argentina based on a quantitative analysis of fossil burrows

Abstract

Pliocene and Pleistocene sedimentary successions in the Pampean region of Argentina contain abundant and diverse fossil mammalian burrows. In this paper, we report fossil burrows from eight localities from near Mir-amar to the northern area of Mar del Plata, spanning the Early Pliocene to the Late Pleistocene, and analyze burrow size patterns. The minimum width of each fossil burrow was measured as an indicator of its diameter. Available allometric equations for extant burrowing vertebrates were used to estimate the body size of potential producers based on burrow diameter. Size distribution patterns indicate that, in the Early Pliocene to Early Pleistocene levels, small burrows (attributed to rodents, typotheres, and small armadillos) were abundant, while medium- to large-sized burrows (attributed to large cingulates) were less common. In the Middle to Late Pleistocene levels, small burrows are very scarce, and medium-sized burrows are most abundant, together with giant burrows (attributed to ground sloths). Our findings indicate a significant size diversity for Pliocene – -Pleistocene burrowing mammals in the studied area, from small rodents to giant ground sloths. Although present in Pliocene to Early Pleistocene times, the largest ground sloths began to build subterranean galleries only later in the Middle to Late Pleistocene. Small burrowers were comparatively less active during that time. These patterns are discussed in the light of paleoclimate and paleoecology of the putative guild of extinct burrowers, to develop working hypotheses for future studies. A paleoclimatic shift from Pliocene Climate Optimum to more arid and colder conditions from the Late Pliocene to Late Pleistocene, and the incursion of large predators to the region, are proposed as major factors promoting large ground sloths to adopt a fossorial lifestyle.