Marvelous connections: The Paleocene-Eocene Record of South American and Antartic Ungulates

LOPEZ G. M.; GELFO J. N.; BOND, M.; LORENTE, M.; REGUERO, M.

Origins and Evolution of Cenozoic South American Mammals

SPRINGER

Año: 2017;

The biological history of South America is characterized by the strong endemicity of its taxa. This was a direct consequence of geographic isolation, since South America was an island during most of the Cenozoic (Simpson, 1980; Marshall et al., 1983). The origin, evolution, and later extinction of the so-called South American native ungulates (SANU) were tightly related to this geographic context. It has been argued that Notoungulata, Litopterna (including Notopoterna, see below), Astrapotheria (including Trigonostylopoidea, see below), Pyrotheria and Xenungulata evolved in situ from a Laurasian ancestor, widely supposed to have arrived during the Late Cretaceous or earliest Paleocene (Simpson, 1948; Cifelli, 1983b, 1993; Muizon and Cifelli, 2000). This immigration may have been facilitated by dry-land connections that existed between Laurasia and Gondwana in the present day Caribbean region (Iturralde-Vinent and Macphee, 1999; Case et al., 2004). However, Notoungulata and Astrapotheria have been closely related to Afrotheria, a clade that includes the African taxa Proboscidea, Hyracoidea, Sirenia, Tubulidentata, Tenrecoidea and Macroscelidea (Agnolin and Chimento, 2011). The SANU first appear in the fossil record during the early Paleocene in Bolivia (Muizon and Cifelli, 2000; Gelfo, 2006), while the geologically youngest representatives occur in association with humans, 8,500 years ago (i.e., Toxodon sp. Tonni et al., 1992). The wide evolutionary radiation of the SANU during the Paleocene and earliest Eocene, led to a high pick in their taxonomic and morphological diversity in the Eocene-Oligocene span. Outcrops hosting Paleocene and Eocene mammals are concentrated in several localities of southern South America, particularly in Argentina. The main sites producing native ungulates in Argentina are in Patagonia, followed by other localities in the northwest, and isolated sites in the central Argentinean basin of great biogeographic significance. This record also extends to the Antarctic Peninsula, as well as to isolated sites in Chile, Bolivia, Brazil, Peru, and Colombia. The biotic history of South America Cenozoic mammals is described via a succession of biochronological units: the South American Land Mammal Ages (SALMAs) based mostly on the ?Etages? of Ameghino (Ameghino, 1906), which follow the North American Land Mammal Ages (NALMAs) concept (Pascual et al., 1965). Here we review the relationships between several South American and Antarctic Paleocene-Eocene localities with SANU fossils and, also, we integrate their record for this span. The significance of these mammals in the establishment of a biostratigraphical and biochronological framework is enhanced by the cluster analysis performed here. The relationships of SANU to each other, and their inclusion in a new phylogenetic framework for the living placental mammals are also discussed.