The extraordinary K-T extinction and the earliest known history of the South American land mammals

PASCUAL, ROSENDO; ORTIZ JAUREGUIZAR, EDGARDO

Origins and Evolution of South American Mammals

Springer

Año: 2010;

This chapter can be divided into four sections: (1) A brief account on what was known about the history of South American mammals until 1983, when Bonaparte and staff found the first reliable Mesozoic land mammals in Late Cretaceous beds of northern Patagonia. According to this record the mammal remains only represent endemic non- and pre-tribosphenic Gondwanan taxa. These endemic taxa lived as advanced relicts of pangeic lineages, showing varying endemic features: some with few advanced features (e.g., ?Eutriconodonta and “Symmetrodonta”); some others with more advanced features, although preserving some primitive ones to be regarded as vicariant types of well known Laurasian Mesozoic lineages (e.g., Gondwanatheria as vicariant of Multituberculata).  The worldwide K-T mass extinction led to the whole extinction of all the Gondwanan lineages of mammals, with only two lineages living just up to the beginning  of the Paleocene, closing up then what we have nominated Gondwanan Period and, in turn, opening the  South American Period  characterized by the immigration of Laurasian  therians  from the incipient North American continent. Just during the earliest Paleocene these therian immigrants lived together with the few last survivors of the Gondwanan Period; (2) an analysis of the evolutionary pattern of land mammal faunas during the Late Cretaceous-Paleocene span in South America and compare it with the coetaneous North America pattern; (3) a discussion of the  complete extinction of the Gondwanan non-Therian mammals, and their replacement by the exclusively  therian mammals of Laurasian origin. This analysis includes the regional and astronomical processes among which –isolated or in association–  directly or even indirectly, contributed to the unique whole extinction of the Gondwanan mammals on the South American continent, and apparently somewhat later also on the Antarctic Peninsula; and, finally, (4) a review of eight  probable long-term and short-term extinction factors that,  in our opinion, likely contributed to the K-T extinction: (a) Rifting and drifting of the South American Plate from the African one; (b) Drifting west-southward of the South American Plate; (c) Beginning of the eruption of the wide-ranged “flood basalt” in the proto-Caribbean region; (d) Geological steps leading to the differentiation of Central America and its connection to the South American Plate; (e) Short-term effect by impact of an extraterrestrial body; (f) Marine regression of the Late Cretaceous-Danian seaway; (g) Transient global cooling climatic event in the latest Paleocene time; and h)  Competitive displacement and/or opportunistic replacement of the non-tribosphenic and pre-tribosphenic Gondwanan mammals  by  the therians (marsupials and placentals) arrived from North America.