AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2820, pp. 1-26, figs. 1-10, tables 1-9 June 26, 1985 Biostratigraphy of the Casamayoran, Early Eocene, of Patagonia RICHARD L. CIFELLII ABSTRACT The Casamayoran, presumed to pertain to the leontologic evidence suggests that these differences early Eocene, is the most diverse and best known are temporal and not ecological in nature. Faunal of South America's early to middle Tertiary land composition of the two localities is compared mammal ages. Because the composition of local qualitatively and statistically with respect to the faunas and the stratigraphic position of assem- magnitude ofdifference seen in preceding and suc- blages at any given locality have not been evalu- ceeding South American land mammal ages and ated, however, the Casamyoran has remained a to roughly equivalent North American land mam- dimensionless age, despite its seminal importance mal ages. Two new subdivisions of the Casama- to understanding the early radiations ofmammals yoran, the Barrancan and the Vacan, are defined on the South American continent. on this basis. In addition, a composite stratigraph- Preliminary analysis offield data and collections ic plot oftaxa from the younger ofthe two localities obtained by G. G. Simpson in 1930-1931 suggests (the Gran Barranca) produced a number of non- a faunal succession in the Casamayoran of Pata- overlapping range zones within the Barrancan; sta- gonia. Large, well documented samples are avail- tistical analysis indicates that the probability these able from two localities with relatively wide strati- observations are due to sampling error is small in graphic distributions of Casamayoran mammals: most, but not all, cases. The other Patagonian local Caniadon Vaca and the Gran Barranca south of faunas are briefly considered with respect to this Lago Colhue Huapi, central Chubut. The com- scheme, and an hypothesis oftheir relative ages is positions ofthese two local faunas differ markedly, presented. and lithostratigraphic, biostratigraphic, and pa- INTRODUCTION It is now widely accepted that South Amer- Tertiary-insular, or nearly so, with respect ica was an island continent for most of the to its biota. The Tertiary record of South 1 Curator of Paleontology, Department ofGeology, Museum ofNorthern Arizona, Flagstaff, Arizona 86001; Post- doctoral Fellow, Division of Mammals, National Museum ofNatural History, Smithsonian Institution, Washington, D.C. 20560. Copyright © American Museum of Natural History 1985 ISSN 0003-0082 / Price $1.70 America's mammalian faunas is fairly well local faunas or to the superposition of assem- known and, as a consequence, provides an blages from given localities, the Casa- ideal "natural experiment" for the study of mayoran has remained an age without tem- historical biogeography and evolutionary poral dimension. principles in general. Of particular interest The collections made in central Patagonia are the earliest faunas, those from the begin- by the Scamtt Patagonian Expeditions (1 930- ning of the Age of Mammals, because they 1931, 1933-1934), under the direction of are critical to understanding the phylogeny, George Gaylord Simpson, are of paramount adaptive radiations, and biogeographic de- importance in this regard. Today, more than ployment of mammals on the South Amer- 50 years later, they include the largest col- ican continent. Of these early assemblages, lections of Casamayoran mammals and are the Casamayoran is by far the most diverse the only ones for which precise stratigraphic and well known. provenience data are available. In the present The great Argentine paleontologist, Flo- paper I present the stratigraphic data for large, rentino Ameghino, who first described the well documented samples from two localities "Notostylops" (Casamayoran) fauna, be- with relatively wide stratigraphic distribu- lieved it to include dinosaurs and thus con- tions of Casamayoran mammals and consid- sidered it to be Late Cretaceous in age. This er the composition of other Patagonian local view has long since been shown to be incor- faunas of Casamayoran age. rect (Simpson, 1932) but, because the mam- malian fauna is so dissimilar to those from anywhere else in the world, the age of the Casamayoran is not well established in either I am deeply grateful to the late Dr. George Gaylord Simpson for his advice and for per- relative or radiometric terms. Simpson (1 940) considered the age of Patagonian marine for- mission to use his fieldnotes of the Scanitt Patagonian Expeditions. All original field ob- mations and placed the Casamayoran in the early Eo~ene.~Welcome new evidence, in the servations and descriptions presented herein form of radiometric dates and a magnetic were made by him and are directly abstracted polarity sequence, is now at hand for part of from these notes, now deposited in the ar- the underlying Rio Chico Formation, fixing chives of the Department of Vertebrate Pa- its age as 6 1 to 56 million years (Marshall et leontology, American Museum of Natural al., 198 1). Such data are not yet available for History. This paper is therefore largely the rocks enclosing a Casamayoran fauna and the results of Simpson's efforts, although I of Riochican-Casamayoran boundary is placed, course assume full responsibility for any mis- interpretations I may have introduced. I ded- by convention, at the Paleocene boundary (Marshall, 1982). icate this paper to his memory. I thank Dr. Despite nearly a century of effort, South Malcolm C. McKenna of the Department of America's early land mammal history is so Vertebrate Paleontology for access to the col- lections and notes of the Scamtt Expeditions. inadequately documented that only very gen- Helpful review comments on an earlier draft eral observations can be made. A critical missing element is a precise chronology, either of this paper were provided by Drs. Mc- Kenna, L. G. Marshall, D. Savage, and R. H. absolute or relative. The stratigraphic rela- tionships of the faunas have not yet been Tedford, and their advice is warmly appre- ciated. Partial support for this research was evaluated and, because little attention has been provided by the Undergraduate-Graduate paid to variation between the composition of Research Program administered by the By suggesting that the arctostylopid Palaeostylops, American Museum of Natural History and of the Gashato fauna, Mongolia, was Paleocene in age supported by the Greenwall Foundation. and ancestral to both the Wasatchian Arctostylops and the notoungulatesof South America, Matthew and Gran- HISTORICAL AND GEOLOGICAL ger (1925) had already implied that the earliest Nearctic BACKGROUND forms (i.e., those of the Casamayor fauna; the Riochican was not then known) were of latest Paleocene or early The first mammals to be described from Eocene age. what is now known as the Casamayoran were 1985 CIFELLI: THE CASAMAYORAN 3 FIG. 1. Central Patagonia index map. Localities: 1, Gran Barranca south of Lago Colhue Huapi (black rectangular area; shown in greater detail on fig. 2); 2, Caniadon Vaca; 3, Caniado Hondo; 4, Caiiadon Lobo. Tapera de L6pez, not on the map, is approximately 30 km northeast ofLaguna Palacios; the exact location of several other (Ameghino) localities is uncertain. collected by Carlos Ameghino at the Gran three or even four distinct faunas were in- Barranca south of Lago Colhue Huapi, cen- cluded. The French collector Andre Tour- tral Chubut, in 1895-1896, and were pub- nouer, guided by Carlos Ameghino, made a lished by Florentino Ameghino (1897) in his small collection of Casamayoran mammals second work devoted to the Pyrotherium (De- at Cafnadon Lobo, near Punta Casamayor, seadan) fauna. Carlos later noted (Ameghino, and "Casamayoran" has since been adopted 1913-1936, vol. 21, p. 105) that the fossils as the geographic term for Ameghino's Noto- in question pertained to a much earlier, pre- stylops fauna (Simpson, 1933). Pyrotherium, fauna and, following Carlos' In addition to the Gran Barranca and suggestion, Florentino named this the No- Cafnadon Lobo, a number of other localities tostylops fauna after that characteristic and in Patagonia have yielded Casamayoran abundant genus (Ameghino, 1899). Floren- mammals; these have been reviewed by tino Ameghino subsequently (1902) distin- Simpson (1948, 1967a) and Marshall et al. guished two subdivisions of the Notostylops (1983). Some of the localities under consid- fauna and later (1903) added a "basal" part. eration here are shown in figure 1; these and In his great treatise of 1906, Ameghino aban- others for which data are available are in- doned these somewhat hypothetical subdi- cluded in the Casamayoran local fauna lists visions but noted that a large span of time of table 1. was probably represented and that perhaps Mammalian fossils ofCasamayoran age in 4 AMERICAN MUSEUM NOVITATES NO. 2820 TABLE 1 Composition of Casamayoran Local Faunasa Localitiesb Species 1 2 3 4 5 6 7 8 9 10 11 12 Coona pattersoni Simpson, 1938 - - X - - - - - - - - Coona gaudryi Simpson, 1964 X - - - - - - - - - Caroloameghinia mater Ameghino, 1901 X C. tenuis Amegbino, 1901 . ..X Arminiheringia auceta Ameghino, 1902 ?X - - ?X Patene coluapiensis Simpson, 1935 X Polydolops thomasi Ameghino, 1897 X X .X- - P. serra Ameghino, 1902 X P. princeps (Ameghino, 1902) X P. primulus (Ameghino, 1902) X P. borcurhor Simpson, 1948 - X Amphidolops serrula Ameghino, 1902 X - - - X Eudolops tetragonus Ameghino, 1897 X - - - X E. caroliameghinoi (Ameghino, 1903) - - X UtaetusbuccatusAmeghino, 1902 X - - - - ?X U. lenis (Ameghino, 1902) X U. deustus Ameghino, 1902 X "Pseudostegotherium" chubutanum Ameghino, 1902 X Prostegotherium notostylopianum Ameghino, 1902 X Adiantoides magnus Cifelli and Soria, 1983 X Sparnotheriodon epsilonoides Soria, 1980 X Didolodus multicuspis Ameghino, 1897 X D. latigonus (Ameghino, 1902) X D. minor Simpson, 1948 X Paulogervaisia inusta Ameghino, 1901 X P. porca (Ameghino, 1901) X P. mamma (Ameghino, 1901) X Proectocion argentinus Ameghino, 1904 X P. precisus Ameghino, 1904 X Enneoconus parvidens Ameghino, 1901 X Asmithwoodwardia subtrigona Ameghino, 1901 X Ernestokokenia nitida Ameghino, 1901 X E.