Palaeoecological implications of the mid-Pliocene faunal turnover in the Pampean Region (Argentina)

Abstract

Known since Darwin's time, the Plio-Pleistocene succession exposed at the Chapadmalal sea cliffs have provided abundant mammal remains even though palaeobiological studies are scarce. Different authors have identified several assemblages in this stratigraphic interval of homogeneous lithology, which records an important mid-Pliocene faunal turnover dated at ca. 3.3 Ma. This paper examines the palaeoecological characteristics and the regional importance of this faunal turnover: 37% of all genera and 53% of all species became extinct between the older Chapadmalalan and the younger Barrancalobian chronostratigraphic units, a level that is actually higher than the percentage of genera extinct at the global-scaled Cretaceous - Tertiary extinction. The palaeoecological analysis permits to infer that the species-rich Chapadmalalan fauna seems to have been very balanced from the trophic - energetic point of view. On the other hand, the succeeding and less-explored Barrancalobian represents a relatively poorer environment, highly unbalanced in terms of the herbivore - carnivore relationships, due mainly to the absence of medium to large mammal and bird carnivores. The cause of the mid-Pliocene faunal turnover is still debatable. Climatic change has been traditionally related to this faunal turnover. Stratigraphically, an impact event dated at ca. 3.3 Ma is recorded in the succession. This event coincides with a change in the deep-sea stable isotopic record, reflecting a sudden change in climate and ocean circulation. This suggests that the impact might have induced regional faunal extinctions. Correlation with other areas different from the coast of Buenos Aires Province is needed to establish the geographic scale of the extinction. New fossils will provide a more complete and accurate picture of this remarkable faunal turnover.