Episodes in South American land-mammal evolution and sedimentation: Testing their apparent concomitance in a Paleocene sequence in Central Patagonia

BOND, MARIANO; CARLINI, ALFREDO A.; GOIN, FRANCISCO J.; LEGARRETA, LEONARDO; ORTIZ JAUREGUIZAR, EDGARDO; PASCUAL, ROSENDO; PRADO, JOSÉ LUIS; ULIANA, MIGUEL

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Congreso; VI Congreso Argentino de Paleontología y Bioestratigrafía; 1994

Museo Paleontológico "Egidio Feruglio"

  The relationships between sequence stratigraphy and evolutionary succession on land mammal communities of Paleocene beds in coastal Patagonia (45º S) are analyzed. We found that there exists a harmonic correspondence between the discontinuities in strata and mammal sequences. More specifically, we conclude that : (1) each of the Patagonian Paleocene "fauna! zones" recognized by Simpson represent discrete episodes in South American mammal evolution ; (2) those mammals recently recovered from the "Banco Negro Inferior" of the Salamanca Group at Punta Peligro represent fourth, older, and more distinct Paleocene episode than assemblages previously described from this area; (3) the mammals characterizing each of the theses episodes were recovered from discrete strata packages bounded by complex surfaces irregularly shaped after subaerial incisions, coastal abrasion and marine scouring; (4) we think that the implicit discontinuities that separate both the mammals evolutionary episodes (turnovers) and the sedimentary sequences (unconformities) were developed concurrently, and both consequently may have been linked to global eustatic changes; (5) three of the four episodes previously had been considered to characterize discrete SALMAs, from older to younger, Tiupampian (Peligran?), Itaboraian (" Kibenikhoria fauna! zone"), and Riochican (" Ernestokokenia fauna! zone"). The fourth episode ("Carodnia fauna! zone"), between Tiupampian and Itaboraian, have not been distinguished previously as a SALMA, and although it seems to characterize a discrete one, the present evidence is not sufficient to warrant building a new SALMA; (6) as for other SALMAs based on Patagonian faunas, it could be difficult to distinguish these SALMAs in areas outside this region. During the Cenozoic Patagonia acted as a distinct paleogeographic region (particularly during the Paleogene) and it is difficult to assert if all the determinants evolutionary processes affecting these faunas occurred just in Patagonia; and (7) the high endemic diversity of marsupials during the Tiupampian SALMA, when the endemic radiation of placentals showed only their first steps, supports the hypothesis of a previous immigration of marsupials to South America.