Novttates PUBLISHED by the AMERICAN MUSEUM of NATURAL HISTORY CENTRAL PARK WEST at 79TH STREET, NEW YORK, N.Y
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AMERICAN MUSEUM Novttates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 3098, 31 pp., 4 figures, 3 tables May 20, 1994 Paleogene Mammals from the Andes of Central Chile: A Preliminary Taxonomic, Biostratigraphic, and Geochronologic Assessment A. R. WYSS,1 J. J. FLYNN,2 M. A. NORELL,3 C. C. SWISHER III,4 M. J. NOVACEK,5 M. C. MCKENNA,5 AND R. CHARRIER6 ABSTRACT Two highly unexpected and diverse fossil mam- appearances ofat least seven subfamilial or higher- mal assemblages have been discovered in the up- level taxa. This co-occurrence of formerly tem- per Rio Tinguiririca valley in the Andes Main porally disjunct taxa identifies the fauna as rep- Range of central Chile. This work brings to light resenting a new interval of South American land the first Paleogene mammal faunas from Chile, as mammal evolution. This fauna (here termed the well as the first fossil mammals from the central Tinguiririca Fauna) represents the youngest di- Andean Main Range. The younger fauna presently versely sampled pre-Deseadan fauna from South includes representatives of at least three higher- America, and records the earliest occurrence of level groups ofmarsupials, five notoungulate fam- rodents on the continent. Radioisotopic dates from ilies, two groups of edentates, a rodent, plus a volcanic units containing and associated with the probable litoptern, and represents the first well- Tinguiririca Fauna are the first available for the known transitional Eocene-Oligocene fauna from Eocene through early Oligocene South American South America. It documents the first or last mammal record, and thus represent a critical cal- ' Assistant Professor, Department of Geological Sciences, University of California, Santa Barbara, CA 93106.. 2 Curator, Department ofGeology, Field Museum ofNatural History, Roosevelt Rd. @ Lake Shore Drive, Chicago, IL 60605. 3Assistant Curator, Department of Vertebrate Paleontology, American Museum of Natural History. 4Geochronology Center, Institute of Human Origins, 2453 Ridge Rd., Berkeley, California 94709. 5 Curator, Department of Vertebrate Paleontology, American Museum of Natural History. 6 Professor, Departamento de Geologia, Universidad de Chile, Casilla 13518 Correo 21, Santiago, Chile. Copyright K) American Museum of Natural History 1994 ISSN 0003-0082 / Price $4.70 2 AMERICAN MUSEUM NOVITATES NO. 3098 ibration point for mammalian biogeochronology. tory. Likewise they shed light on crucial and here- The second fauna (here termed the Tapado Fauna) tofore poorly understood phases of South Amer- is presently less completely known than the first, ican mammal evolution, and establish an im- but is clearly significantly older. Both faunas are portant new source ofgeochronologic information of demonstrated importance to the interpretation for this Andean region. of central Andean stratigraphy and tectonic his- INTRODUCTION Prior to its Late Pliocene connection with migrant taxa stems from the length of the North America, South America was isolated faunal hiatus preceding the Deseadan and lack from other continents for a span of some 60 of radioisotopic control for Mustersan and million years. This long period of insularity Casamayoran sediments. and the peculiar biota it engendered have We have recovered two new fossil mam- captured the attention of evolutionary biol- mal faunas of transitional Eo-Oligocene and ogists and paleontologists for more than a probable early Eocene age from volcaniclas- century (Simpson, 1984). The best known, tic sediments assigned to the Abanico (= and perhaps most unusual, element of South Coya-Machali) Formation near the axis of America's endemic biotic history is its Ce- the Andean Main Range in the valley of the nozoic mammals, the succession of which is Tinguiririca River in central Chile (fig. 1). generally divided into a sequence of 13 dis- The first discovered (Novacek et al., 1989) tinct South American Land Mammal Ages and younger ofthese faunas is from exposures (SALMAs). Some of these (particularly Pa- near the town of Termas del Flaco (34°59'S, leogene) faunas remain very incompletely 70'26'W). This fauna, hereafter referred to as known, however, and decades of intensive the Tinguiririca Fauna, represents South investigation have failed to close several im- America's first diversely sampled pre-Desea- portant gaps. Among these, an approximately dan, post-Mustersan mammal assemblage. 15 million year interval between post-Mus- In addition to illuminating a crucial phase of tersan (?middle Eocene) and pre-Deseadan mammalian evolution, this fauna represents (late Oligocene-?early Miocene) horizons has the first chronologically significant paleon- previously represented the most poorly tological find for a major group of central known span ofthe South American Cenozoic Andean rock units, and is of broad signifi- mammal record (Marshall, 1985). Apart from cance for the interpretation of regional geo- its length (encompassing up to a third of Ce- logic history. Radioisotopic dates associated nozoic time), additional factors compound with the Tinguiririca Fauna are key calibra- the difficulties posed by this faunal hiatus. tion points for early Cenozoic South Amer- First, the faunas generally accepted as brack- ican biochronology, they aid in constraining eting this hiatus, the ?middle Eocene Mus- the timing of the immigration of rodents to tersan and ?Eo-Oligocene Divisaderan SAL- South America, and they help to date an im- MAs, (the latter sometimes being considered portant middle Cenozoic faunal turnover early Deseadan in age) are the two most poor- event. The bulk of the present contribution ly known of the entire South American Ce- represents a preliminary description of the nozoic mammal record. Second, this span co- Tinguiririca Fauna. incides with a crucial faunal transition, from A second fauna, here designated the Ta- mammal communities dominated by archaic pado Fauna (after Quebrada El Tapado which lineages to communities characterized by is near the principal locality), has been re- mammals of a markedly more "modern" covered from exposures approximately 12 km stamp (Pascual et al., 1985). And third, this NW of Termas del Flaco (Flynn et al., 1991; post-Mustersan pre-Deseadan hiatus encom- Wyss et al., 1992a, 1992b). As material from passes the inadequately dated first appear- this area is in preliminary preparation stages, ance ofprimates and rodents in South Amer- we make only cursory reference to the Ta- ica, two lineages ofmajor importance in later pado Fauna in this report. To clear up pos- Cenozoic and Recent faunas. Uncertainty sible confusion stemming from our expressed over the timing of arrival of these two im- earlier views (ibid.), it is necessary to mention 1 994 WYSS ET AL.: PALEOGENE MAMMALS FROM CENTRAL CHILE 3 that the Tapado Fauna is assuredly not youn- new mammal faunas) (Domeyko, 1862, ger than the Tinguiririca Fauna. Accepted Burckhardt, 1897, 1900; Philippi, 1899; stratigraphic interpretations of the region, Gerth, 1931; Groeber, 1947a, 1947b). These which place sediments producing the former led ultimately to the abandonment of Dar- fauna some 2000 m higher in the local strati- win's Porfiritica designation in favor of graphic section than those producing the lat- Klohn's (1957, 1960) finer stratigraphic sub- ter, had led us to expect a younger Tapado. divisions, which are still employed (table 1). Rather, the few specimens that have been Important, more recent, refinements of this prepared to date suggest that the Tapado Fau- sequence include: Arcos (1987); Charrier na is subtantially older than the Tinguiririca (1973,198 1b); Davidson and Vicente (1973); Fauna; subject to revision by ongoing prep- Gonzalez and Vergara (1962); and Charrier aration, preliminary comparisons indicate a et al. (submitted). Casamayoran age. This establishes that the The Porfiritica sequence is exposed over a much older Tapado Fauna has been tecton- 400 km north-south long, 50 km east-west ically superposed over the Tinguiririca Fauna wide, swath along this segment ofthe Andean via post-Oligo-Miocene thrust faulting, dem- Main Range and measures roughly 10,000 onstrating much greater tectonic complexity meters in stratigraphic thickness. Its lower than had been previously appreciated for this half (the Nacientes del Teno, Rio Damas, region of the Andes. Bafios del Flaco, and Colimapu Formations) In sum, the new faunas and associated geo- (table 1) consists of interbedded, sedimen- chronometric data are of demonstrated im- tary, marine and terrestrial formations re- portance in elucidating the tectonic history cording a series of transgressive and regres- of the rock units hosting them, the ages and sive phases of detrital back arc deposition. history of several related formations in the Marine levels contain abundant invertebrate region, and the ages of several related South fossils, firmly establishing these lower de- American faunas and faunal events. posits to be medial Jurassic through Late Cre- taceous in age (Klohn, 1960; Gonz'alez and ABBREVIATIONS Vergara, 1962; Charrier, 1981a, 1981b). Such clarity does not extend, unfortunate- AMNH American Museum ofNatural History BRCU Brownish Red Clastic Unit ly, to age determinations for the upper units LBLC Lomas Blancas (or La Curandera) of the Porfiritica assemblage (approximately MLP Museo de La Plata 5 km thick), ofwhich the Abanico Formation PU Princeton University forms an important component. These for- SGOPV Museo Nacional de Historia Natural, mations