Paleontology and Geochronology of the Deseadan (Late Oligocene) of Moquegua, Peru´
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PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3668, 24 pp., 8 figures, 5 tables November 30, 2009 Paleontology and Geochronology of the Deseadan (late Oligocene) of Moquegua, Peru´ BRUCE J. SHOCKEY,1 RODOLFO SALAS GISMONDI,2 PHILLIP GANS,3 ANNIE JEONG,4 AND JOHN J. FLYNN5 ABSTRACT Subsequent to our initial reports of the discovery of Deseadan fossils in southern Peru´, we have obtained new data regarding the paleontology and geology of the upper member of the Moquegua Formation. These data include newly recovered fossil specimens and further analyses of those collected in our earlier field seasons. We have also obtained an ash directly from within the fossil- bearing units near the summit of Cerro Pan de Azu´car. Biotites from this Sugarloaf ash give an age estimate of 26.25 6 0.10 Ma, thus supporting our previous suggestion that these fossil-bearing horizons are of late Oligocene age (Deseadan South American Land Mammal ‘‘Age’’) and removing our query regarding a possible early Miocene age. Most of the fossils are of notoungulates and most of these are trachytheriine mesotheriids. Remarkably, three distinct mesotheriid taxa appear to have been present in the Moquegua fauna, none of which are referable to the common Trachytherus alloxus of the nearby and at least partly contemporaneous Salla beds of Bolivia. Other fossils documented here include postcranial elements of the notohippid notoungulate, Moqueguahippus, a macraucheniid litoptern (cf. Coniopternium), an osteoderm of an unnamed species of armadillo (Dasypodidae, cf. Dasypodinae), and a claw of a phorusrhacid bird. We also describe a diminutive new hystricognath rodent, Sallamys quispea, sp. nov. It is similar to, but distinct from, S. pascuali of Salla. Indeed, despite the temporal and geographic proximity of Moquegua to Salla, none of the taxa from Moquegua that can be identified to species are known from Salla. Likewise, we have failed to find any dasypodids from Salla that have osteoderms like that described in this work. Thus, it is appears that distinctive paleogeographic and 1 Department of Biology, Manhattan College, New York, NY 10463. Research Associate, Division of Paleontology, American Museum of Natural History ([email protected]). 2 Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima, Peru´ ([email protected]). 3 Department of Geological Sciences, University of California at Santa Barbara ([email protected]). 4 Biology Department, Barnard College, New York ([email protected]). 5 Division of Paleontology and Richard Gilder Graduate School, American Museum of Natural History (jflynn@ amnh.org). Copyright E American Museum of Natural History 2009 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3668 paleoenvironmental conditions in the late Oligocene led to a regional biotic differentiation for the Moquegua area of coastal Peru´. INTRODUCTION regarding the paleontology and geology of these localities in the upper member of the Upper regions of peaks west of the Rı´o Moquegua Formation. The new data include Moquegua, near the city of Moquegua (fig. 1), additional specimens collected in subsequent have yielded the first known fossils of the fieldwork, further analyses of previously Deseadan South American Land Mammal collected material, and 40Ar-39Ar geochrono- ‘‘Age’’ in Peru´ (Shockey et al., 2006). Since logical analyses of an ash collected from preparation of the initial report of this directly within the fossil-bearing horizons near discovery, additional data have been gathered the summit of Cerro Pan de Azu´car (fig. 2). Fig. 1. Geologic map of the fossil localities of the upper Moquegua Formation. Based on: Bellido, E. and C. Guevara. 1961 (Mapa Geolo´gico del Cuadra´ngulo de Clemensı´, Carta Geolo´gica Nacional y Instituto Geogra´fico Militar); Shockey et al., 2006: fig 1; and satellite images from Google Earth. Trachytheriine localities of Bolivia are indicated in insert map at upper right: Salla (Trachytherus alloxus); A, Lacayani (T. spegazzinianus); and B, Rı´o Iru Pluma (T. subandinus). 2009 SHOCKEY ET AL.: THE DESEADAN OF MOQUEGUA, PERU´ 3 Fig. 2. Photo of the north face of the summit of Cerro Pan de Azu´car illustrating the lower region of the upper Moquegua Formation, including the Sugarloaf ash. (The boundary between the lower and upper Moquegua Formation is covered at this locale.) Note crew members hiking up the slopes for an impression of scale. Most of the fossils recovered are of no- removing prior uncertainty regarding a possi- toungulates. The present work describes post- ble early Miocene age for the fossil-bearing cranial remains from three species of me- units (Shockey et al., 2006). sotheriid notoungulates, including the nearly complete pes of the largest of the three (cf., T. BACKGROUND spegazzinianus). This represents the first such description of any mesotheriid pes. Also, we The Tertiary sediments in the Moquegua/ describe additional material of the notohip- Tacna Basin traditionally have been referred pid notoungulate, Moqueguahippus glycisma to as the Moquegua Formation (Bellido and Shockey et al., 2006, and we expand the faunal Guerra, 1963) or Moquegua Group (Tosdal list by reporting the remains of the only et al., 1981; Acosta et al., 2002), composed of xenarthran (Dasypodidae, cf. Dasypodinae), the ‘‘formacio´n Moquegua inferior’’ and and a diminutive new species of rodent, the ‘‘formacio´n Moquegua superior’’ (see Sallamys quispea, closely related to but dis- Sempere et al., 2004, for discussion of tinct from the Deseadan species S. pascuali nomenclature problems). These are separated from Salla, Bolivia. by an angular unconformity (Acosta et al., As detailed below, the geochronological 2002; Sempere et al., 2004); in addition, the analysis provides a date of 26.25 6 0.10 Ma ‘‘lower Moquegua Formation’’ consists of for the ash that lies in the lower part of the finer sediments than the upper. fossil-bearing sequence. This date strongly Work in progress (see Sempere et al., 2004) supports the initial conclusion that the fauna may clarify the complex depositional history collected is late Oligocene in age, thus of the Tertiary deposits of southern Peru´and 4 AMERICAN MUSEUM NOVITATES NO. 3668 the resulting unstable geological nomencla- their 40K-40Ar geochronological analysis (see ture. The strata of interest for our study 40Ar-39Ar Geochronology below). involve the upper unit of the Moquegua The Moquegua Formation has generally Formation (sensu Bellido and Guevara, been considered ‘‘nonfossiliferous’’ (Tosdal et 1963; Bellido and Landa, 1965; Tosdal et al., al., 1981). However, in 2002, Rossana Quispe 1981; equivalent to: ‘‘Formacio´n Moquegua and her classmates and instructor (Jorge Superior’’ of the Moquegua Group [Acosta et Acosta) from the Universidad Nacional al., 2002]; ‘‘Formacio´n Moquegua superior’’ ‘‘Jorge Basadre Grohmann,’’ Tacna, Peru´, [Flores et al., 2004] or ‘‘Upper Moquegua found fossils in the upper Moquegua Formation’’ [Shockey et al., 2006]; ‘‘Mo- Formation, at and just below the summit of quegua C’’ [Sempere et al., 2004]; Moquegua Cerro Pan de Azu´car (Shockey et al., 2003, Formation [Sa´nchez Fernandez et al., 2000]), 2006). This initial discovery motivated our underlain by the lower unit of the Moquegua more intensive National Geographic–spon- Formation (equivalent to: ‘‘Formacio´n Mo- sored fieldwork in the austral winters of 2002 quegua Inferior’’ of the Moquegua Group to 2004, with results detailed here. [Acosta et al., 2002]; ‘‘Formacio´n Moquegua inferior’’ [Flores et al., 2004]; ‘‘Moquegua B’’ MATERIALS,ABBREVIATIONS,METHODS [Sempere et al., 2004]; Sotillo Formation [Sa´nchez Fernandez et al., 2000]). For conve- Specimens collected from the Deseadan nience, given this conflict among various aged localities of the upper Moquegua For- stratigraphic assignments, we will refer to mation are curated in the MUSM (Depart- the upper part of the Moquegua Formation amento de Paleontologı´a de Vertebrados, as the ‘‘upper Moquegua Formation’’ and Museo de Historia Natural, Universidad the lower part as the ‘‘lower Moquegua Mayor de San Marcos, Lima, Peru´). Other Formation.’’ institutional abbreviations used in the text Bellido and colleagues (Bellido and Landa, include: UF (vertebrate paleontology collec- 1965; Bellido and Guevara, 1963) character- tions, Florida Museum of Natural History, ized the Moquegua Formation as continental University of Florida, Gainesville, FL, siltstones, sandstones, and conglomerates. U.S.A.); AMNH (American Museum of Conglomerates form the base of the upper Natural History, New York, NY, U.S.A.). Moquegua Formation (fig. 2) with overlying Additional abbreviations used in this study finer-grained lagoonal facies (Tosdal et al., include SALMA, South American Land 1981; Acosta et al., 2002). These are composed Mammal ‘‘Age’’; I, C, P, and M for upper of clayey and fine-grained sandstones and incisors, canines, premolars, and molars, mudstones, with pink ignimbrite intercalations respectively (lowercase notation for lower (Acosta et al., 2002). The regionally extensive teeth). lower Moquegua Formation locally uncon- The 40Ar-39Ar ages were obtained at the formably overlies the late Cretaceous to early argon geochronology laboratory in the Tertiary Toquepala Group (Tosdal et al., Department of Earth Sciences at the 1981; Marocco and Noblet, 1990; Acosta et University of California, Santa Barbara. al., 2002; and fig. 1). Conventional stepwise-heating and plateau- Tosdal et al (1981)