Feeding ecology of pleistocene herbivorous megamammals from southern Brazilian Amazon revealed by stable isotopes and stereoscopic microwear

Megamammal fossils from Quaternary deposits of rivers and tributaries of the Brazilian Amazon basin have been reported for over a century. Although these fossil assemblages can shed light on the paleoenvironmental history of the Amazon region, their paleoecological aspects have been poorly explored. In this study, we conduct new 14 C (AMS) dating and a multiproxy approach using stable isotopes (carbon, δ 13 C; oxygen, δ 18 O) and stereoscopic microwear to suggest the feeding ecology and habitats of the Pleistocene megamammals Notiomastodon platensis , cf. Eremotherium, and Toxodon platensis from the Teles Pires basin, Mato Grosso state, southern Brazilian Amazon. Radiocarbon dating performed in the N. platensis specimen (M398) reveals a Late Pleistocene age (30 ka BP), extending the previously estimated age range for this species in the region. Our δ 13 C results suggest heterogeneous habitats, ranging from woodlands to C 3 /C 4 landscapes ( δ 13 C VPDB = −14.0 to −4.8 ‰). T. platensis and cf. Eremotherium were likely browsers living in woodland habitats. Nonetheless, N. platensis exhibited distinct feeding behaviors, with a Middle Pleistocene individual displaying a browsing diet from woodland habitats, and generalist individuals - including a specimen from the Late Pleistocene - that could have foraged savanna-like landscapes. All taxa presented low δ 18 O VSMOW values (+22.3 to +25.5 ‰), although generalist N. platensis specimens showed higher values that may be suggestive of slightly drier conditions. A consistent browsing diet, similar to that of African forest elephants, was estimated for N. platensis from the Brazilian Amazon through stereoscopic microwear analysis. The browsing diet estimated for the last meals of these generalist individuals indicates seasonal influences in the diet composition. The C 3 -dominant diet found in our study is in agreement with paleoecological data of megafauna taxa from other Amazonian localities. Our study corroborates the integrity of forest phytodomains during the Pleistocene in the studied Amazonian regions, although marginal regions of the biome could be more sensitive to cold and dry climatic conditions during glacial periods, when savannas could have expanded. Further investigations into the paleoenvironmental and paleoecological aspects of the southern Amazon megafauna during the Pleistocene are encouraged to deepen current knowledge on this topic. • AMS 14 C dating support a Late Pleistocene age for N. platensis from the Teles Pires basin. • T. platensis and cf. Eremotherium were browsers in woodland habitats. • N. platensis varied from browser in woodland to mixed feeders in savanna landscapes. • The browsing diet estimated for the last meals of the generalists indicates seasonal influences in the diet. • The C 3 -dominant diet is in agreement with previous paleoecological data from other Amazonian localities.