Chronostratigraphy of the mammal-bearing Paleocene of South America

The origin and evolution of mammals

“…In China, Early Palaeocene mammals of the Shanghuan Formation include both endemic forms, and primitive members of groups that appear later in North America, such as the herbivorous pantodonts and tillodonts Lucas 2001). In South America, Palaeocene faunas containing diverse marsupials, and indigenous placental groups leave wide open the question of where and when they originated, and how they relate to the North American extinction (Marshall et al 1997). As to what happened to mammals at the K/T boundary of Australia, Africa, and Antarctica, there is simply no evidence at all.…”

“…For a long time it was believed to be Late Cretaceous in age, but this is disputed and it is more probably Early Palaeocene (Marshall et al 1997). In any event, the fossils themselves are sparse and fragmentary, there being a possible tooth of the didelphid Peradectes and a possible member of the Pediomyidae (Sigé 1972).…”

“…Far the richest Palaeocene localities on the continent occur in the Santa Lucia Formation at Tiu Pampa in Bolivia, which is either Early (Muizon 1998) or possibly early Late (Marshall et al 1997) Palaeocene in age, and at Itaboraí in Brazil, where the fissure-fill fauna is slightly younger. Both sites have yielded abundant and diverse marsupial faunas, including six or seven indigenous South American families between them.…”

“…There are also representatives of the modern marsupial family Didelphidae, and the genus Khasia which is a member of the biogeographically challenging Microbiotheria to which the modern Dromiciops belongs. Other, less-rich Palaeocene mammal localities occur in the San Jorge Basin of Patagonia, some of which are Early Palaeocene (Marshall et al 1997).…”

“…The dentition exhibits the characteristics of the family Didelphidae, including a fully expressed V-shaped centrocrista. Pucadelphys was part of an extensive radiation of small didelphid opossums well under way during the Palaeocene; there are four or five Tiupampan genera, and Itaboraí has yielded nine (Marshall et al 1997). During the Eocene and Oligocene there was a marked decline in didelphid diversity although this is due at least in part to the relatively few fossil-bearing localities yet unearthed for this period of time (Flynn and Wyss 1998).…”