Arquivos do Museu Nacional, Rio de Janeiro, v.66, n.l, p. 161-178, jan./mar.2008 ISSN 0365-4508 MAMMALS FROM THE LATE PLEISTOCENE/ EARLY HOLOCENE OF SAN LUIS PROVINCE (ARGENTINA) AND PALAEOENVIRONMENTAL INFERENCES 1 (With 15 figures) JORGE ORLANDO CHIESA 2 ABSTRACT: This report informs about the findings of extinct mega-mammals of the Late Quaternary in San Luis Province, produced between 1993 and 2003. They constitute the first descriptions with geographic and stratigraphic references correctly identifiable. The remains are dominated by Equus (Amerhippus) neogeus, Stegomastodon platensis, Sclerocalyptus omatus, Megatherium americanum, and Scelidotherium leptocephalum. This association establishes its link to the Lujanense Mammalian Age recognized in the Pampean region; it also suggests a strong similarity with the climatic conditions prevailing during the Late Maximum Glacial Ice. The relatively scarce and partially fractured presence of fóssil mammals as well as some stratigraphic evidences suggests a larger severity in the environment taking into account its closeness to the area of contribution of arenas and Patagonian slimes and the Andean glacial fronts. Key words: Megafauna. Late Quaternary. San Luis Province. Climatic conditions. RESÚMEN: Los mamíferos fósiles dei Pleistoceno Tardío-Holoceno temprano en la Província de San Luis (Argentina). Inferências paleoambientales. Se dan a conocer los hallazgos de megamamíferos extintos dei Cuaternario Tardio de la província de San Luis, producidos por el autor y colaboradores entre 1993 y 2003, los que constituyen las primeras descripciones con referencias geográficas y estratigráficas correctamente identificables. Los restos están dominados por Equus (Amerhippus) neogeus, Stegomastodon platensis, Sclerocalyptus omatus, Megatherium americanumy Scelidotherium leptocephalum. Dicha asociación establece su vinculación con la Edad Mamífero Lujanense reconocida en la región pampeana, a la vez que sugiere una fuerte similitud con las condiciones climáticas dominantes durante el Ultimo Máximo Glacial. La relativamente escasay parcialmente fracturada presencia de los restos fósiles, sumada algunas las evidencias estratigráficas, sugiere una mayor rigurosidad en el ambiente, considerando su cercania al área de aporte de arenas y limos patagónicos y los frentes glaciares andinos. Palabras claves: Argentina. San Luis. Cenozoico. Mamíferos. Paleoambiente. INTRODUCTION cataloguing of the remains was produced at the end of the last century (Tognelli etal, 1993). Additionally, San Luis Province is located in the center-west of radio carbon dating of those remains improved the Argentina between 31°50’ and 36°00’S and 64°69’ quality of these records (Chiesa, 2005). and 67°22W. It is 700km west of the Atlantic Ocean The objective of this contribution is to submit a and 250km east of the Andes Mountains. The present-day condition about the knowledge of the largest area of the relief is a plain with a height presence of Quaternary fóssil mammals in San Luis between 600 and 700m above sea levei, whereas Province as well as producing a general in the highland zone there are 2,200m above sea characterization of bearing sediments and levei. The fóssil remains recognized in this report paleoenvironmental conditions prevailing during were exhumed at Depresión Oriental, Planicie the Late Pleistocene and Recent Holocene. Medanosa Austral and Sierra de San Luis (Fig.l). Field references and comparative quotations about the Antecedents presence of Quaternary fossils in isolated areas of this region are known since the end of the XIX centuiy. The major stratigraphic and paleontological However, the first work of description, illustration, and contributions related to the Upper Quaternary of 1 Submitted on September 14, 2006. Accepted on February 22, 2008. 2 Universidad Nacional de San Luis, Departamento de Geologia, 950 Ejército de los Andes, Postcode: 5700, San Luis, Argentina. E-mail: [email protected]. 162 J.O.CHIESA San Luis have been produced in the last 30 years. of the area. Several other published and In this context, the most significant antecedents unpublished studies at a zonal range generated referring to the stratigraphy of Quaternary significant advance in the knowledge of deposits of San Luis Province is attributed to Santa sedimentary characteristics of the main Cruz (1979) whose proposal was debated by geomorphologic units. Their most highlighting Latrubesse & Ramonell (1990) who put forward a contribution was the Progressive clarification new lithostratigraphy. Pascual & Bondesio (1981) about the space and/or temporal distribution with and Costa et dl. (1997/2002) published important the detailed descriptions of the outcrops, sometimes compilations on the sediments and scarce fossils associated with microflora and megafauna. Fig.l- Map of the location of the main quaternary fossiliferous localities (*) of San Luis Province. Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p.161-178, jan./mar.2008 MAMMALS FROM THE LATE PLEISTOCENE/EARLY HOLOCENE OF SAN LUIS PROVINCE (ARGENTINA) 163 Finally, Costa et al. (1997/2002) presented study of them. Those fossils were assigned to contributions with a detailed compilation and Scleroclyptus, Glyptodon, Megatherium, Mylodon, description of stratigraphic profiles representative of Panochtus, Toxodon, and Equus argentinus remains. the Quaternary of the central and northern region. Finally, during the last decade studies such as those From the paleontological point of view, the first of Chiesa et al. (1999) and Tognelli et al. (2000) historical and synthetic review linking geology and provided a significant advance in the description, Quaternary fossils from San Luis corresponds to illustration, and chronostratigraphy of Quaternary the study of Strasser et al. (1992). In this respect, fóssil remains from peripheral basins of the province the oldest citations belongs to De Moussy (1860) highland region. who mentioned, “it is told that in some plains of Sierra de San Luis there are very voluminous fóssil Geology skeletons. All our searches have been fruitless and we have not been able to gather evidences”. A The Quaternary sediments take up the largest area similar situation was commented by Ave Lallemant of the province, approximately 85%, distributed in (1875) in Canada de Zavala. Although he pointed the plains. They overlie without agreeing with the out having found “a rib”, it is not presented a rocks of the basement, Neopaleozoic, Cretaceous, further description of the fragment. and Neogene continental sedimentary rocks. Adaro (1917) was the first researcher that presented Although units assigned to the Lower to Middle descriptions and illustrations of the Pleistocene Pleistocene are proposed in some sections taking xenarthra and ungulates of San Luis remains. The into account the fóssil findings and radio carbon author referred at the point 1 (:4) “the first fóssil that datings, the most ancient ones involve the carne to our hands was a Megatherium dorsal vertebra Lujanense Mammalian Age or the Late Pleistocene. found on the left shore of Rio Quinto” without From the geomorphologic point of view, San Luis providing the date of such finding, whereas in the Province presents two contrasting environments: the point 2 (:7) he mentioned that “later, in 1901, we highland one and the plain one (González Díaz, 1981). received another bone that was better fossilized, The highland environment is located in the northern colored in black as if it were coai and found by our half like stretched strips in north-south direction friend Antenor Orueta on the left shore of Rio Conlara and is distributed from east to west in Sierra de and on the alley that departs from San Pablo to La Comechingones, Sierra de San Luis, and Serranias Riojita. It is the ileum of a Megatherium”. Adaro went Occidentales; whereas the plains take up the Planicie on describing the finding of fóssil remains in the Austral and the inter-highland northern depressions Quaternary successions of different spots close to known as Depresión Oriental with the Valle dei Rio Sierra de San Luis supplied by villagers from 1910 Conlara, Depresión Central, and Depresión until 1926. The finding of a Megatherium vertebra in Occidental with the Valle dei Rio Desaguadero. the zone of El Morro was presented by Pastore (1915). In the geomorphologic units mentioned above, the A very important reference for the time is Frenguelli Quaternary sediments present peculiar (1931). The author registered the occurrence of characteristics for the region and contrast with those Megatherium americanum greslebini, Scelidotherium that are close to them including the “high pampas” sp., Lestodon sp., “Eumylodon” sp. (Mylodon sp.), where the evolution of paleosoils highlights. In Panochtus sp., “Auchenia” sp. (Lama sp.), general, the Planicie Austral is a stretched and Macrauchenia sp., Equus sp., and “Arctotherium” monotonous sandy unit, softly wavy with dunes (Arctodus; Arctotherium sp.). New quotations referred associated with trays of deflation sometimes to Quaternaiy fossils correspond to Gez (1938), who occupied by bodies of water and bordered on the pointed out to remains assigned to “Panochtus, north by the basin of the Rio Quinto. Sclerocaliptus, Toxodon, Equus argentinus, Pachyrucos, Megatherium americanum (the big one) The Depresión Oriental is a loessoid plain with and M. lundi(the small one), Scelidothoerium, Lycodon, outcrops isolated of the basement and bordered Lama and Paraclotherium parodf, found in several on the east by the softly tilted basement of Sierra zones of the province isolated among them. de San Luis, the Valle dei Rio Conlara on which Subsequently, different geologic analyses in San Luis basin it is possible to identify fluvial psephites and Province (Tapia 85 Rigal, 1933; Pastore & Ruiz Huidobro, psammites. On the eastern side it developed alluvial 1952; Pastore & González, 1954) mentioned the fans beginning from the steep piedmont of the presence of Quaternary fossils without producing a Sierra de Comechingones. Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p. 161-178, jan./mar.2008 164 J.O.CHIESA The Depresión Central is a sandy loessoid semidry acknowledgement of La Chumbiada Member and unit with two saline trays as depositional centers to Lobos Member as part of Luján Formation. the north (Pampa de las Salinas) and to the south In San Luis, a stratigraphic scheme of the (Salinas dei Bebedero), and which draining is Quaternary was recently proposed by Chiesa (2005) organized by a dorsal at the center of the depression. (Fig.2). The geographic position of the actual area of Finally, the Depresión Occidental is a wide area with study justifies in part the sedimentary differences a sandy cover; its fluvial-lacustrine evolution with respect to the wide Pampean region, but with associated to Rio Desaguadero is linked to the stratigraphic units more spatially enclosed probably glaciers of Rio Mendoza and Rio San Juan of the as a response to the prevailing geomorphologic Andes Mountains. environments linking the relations proposed by Latrubesse & Ramonell (1990), Tognelli et al. (1993), Regional Stratigraphic Setting Strasser et al (1996), and Chiesa et al (1999). During the last 15 years, there have been MATERIAL AND METHODS contributions referred to the paleontology and the stratigraphy of the Quaternary in different areas of the provinces bordering on San Luis, fundamental The fóssil material presented here is deposited in to generate a paleoenvironmental model. This model the Museo de Historia Natural of the Universidad allows us to come up with a biostratigraphic scheme Nacional de San Luis and registered under the relatively coherent for the center-west of Argentina reference ‘MHN-UNSL-V’ plus the accession number. because of its similarities and differences with other The data about the findings of extinct mega- regions that have been further studied. Some mammals of the Late Quaternary in San Luis contributions are related to the Córdoba region such Province, here described and discussed, were as those of Cantú (1992), Tauber (1997), and produced by the author and associates between Carignano (1999), whereas Rodríguez & Barton (1993) 1993 and 2003. and Zárate (2002) produced significant advances in the description of the Quaternary of Mendoza. RESULTS AND DISCUSSION Up to the present, the general biostratigraphic scheme for the Quaternary of Argentina corresponds to the Pampean region, especially Paleontology Buenos Aires Province (Zanchetta, 1995; Cione & Among the mammal megafauna remains of the Late Tonni, 1995). In general, that scheme foresees that Quaternary in San Luis Province, we recovered the identified units correspond to different elements of Sclerocalyptus omatus (Owen, 1845) depositional environments where the fóssil remains (Figs.3-4), Scelidotherium leptocephalum Owen, exhumed enable a chronology based in part on the 1840 (Figs.5-8), Megatherium americanum Cuvier, extinct megafauna. Thus, in the alluvial 1796 (Figs.9-10), Stegomastodon platensis environment Luján Formation, the lower unit (Ameghino, 1888) (Figs.11-14) and Equus denominated Guerrero Member is assigned to the (Amerhippus) neogeus Lund, 1840 (Fig.15). Late Pleistocene and characterized by the exclusive presence of Megatherium americanum and Equus Class MAMMALIA Linnaeus, 1758 (Amerhippus) neogeus, whereas the upper unit or Super-order XENARTHRA Illiger, 1811 Rio Salado Member belongs to the Holocene and is Order CINGULATA Illiger, 1811 linked to the presence of Lagostomus maximus. Family Glyptodontidae Burmeister, 1879 The so-called Platense with lake characteristics and Subfamily Sclerocalyptinae Ameghino, 1895 the Aeolian deposits of La Postrera Formation also Tribe Sclerocalyptini Ameghino, 1895 correspond to the Holocene. It is possible to identify Genus Sclerocalyptus Ameghino, 1891 the presence of two paleosoils, Puesto Callejón Viejo Sclerocalyptus omatus (Owen, 1845) (Late Pleistocene) and Puesto Berrondo (Middle Holocene), both inserted among the successions Localities and descriptive aspects - Pasos Maios, El mentioned above in different areas. Tala, Arroyo Mundo Nuevo (La Carolina), and Cerro El Recently, Dangavs & Blasi (2003), based on their Morro. An almost complete shell with part of the caudal own researches and antecedents, hold the shield and the pélvis were exhumed in Pasos Maios. Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p. 161-178, jan./mar.2008 MAMMALS FROM THE LATE PLEISTOCENE/EARLY HOLOCENE OF SAN LUIS PROVINCE (ARGENTINA) 165 AUSTRAL SAN LUIS SIERRA ORIENTAL DEPRESSION DEPRESSION n i s TIME AREA West Region East Region South Region Plain RioB Qasuiinn to Conlara Bas omechingoneSierra El Morro Hill o C Ri Puerta Algarrobito San Algarrobito HOLOCENE Negra Luis / La Estanzuela Los Toldos Los Filtros Los Toldos Rio Barranquita San Luis Barranquita Conlara Alto Grande o Fraga Uspara La Unida E ng Renca Merlo N e PLEISTOCE Units III / IV El Pantano / Olguín Donovan / dei Potrero / Las Chacras El Chul La Petra FSelainpe Papagallos Los Pozos Fig.2- Stratigraphic correlation of the Late Pleistocene - Holocene units at San Luis province. Fig.3- Sclerocalyptus omatus - carapace. Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p.161-178, jan./mar.2008 166 J.O.CHIESA Fig. 4 - Sclerocalyptus omatus - carapace fragment. The finding in El Tala includes the complete shell, as to have been conserved: femurs, tibiae, fibulae, the skull, and the lower maxillary with the right scapula, humeri, ulna, right radius, carpal, dentition; the cephalic small shield, ribs, and metacarpal, tarsal, and metatarsal bones. The vertebrae belonging to different segments included shells assigned to Glyptodontidae recognized by the tail, articulate zone of the pelvic waist, the author in Arroyo Mundo Nuevo (high pampa extremities and plates of the movable rings of the of Sierra de San Luis) and Cerro El Morro have tail. The shell is oval and low, with a fractured not been studied. cupule and well-preserved anterior-lateral Stratigraphic and geographic distribution - It projections. The thin dorsal plates are hexagonally was frequently found in the deposits of the to subquadrangulary-shaped with well-defined Pleistocene (Ensenadense and Lujanense sutures and piliferous pores. The central figure is Mammalian Ages) of Buenos Aires, Córdoba, oval and a little depressed, surrounded by Corrientes and Entre Rios Provinces, in Argentina peripheral polygonal figures with variable and in Uruguay. numbers (predominantly 8 to 9) with pronounced, narrow, and barely deep wrinkles. The ventral Habitat - According to Fidalgo & Tonni (1983), this plates are smaller with rectangular shapes species lived in open areas of pastures and stretched in an anterior-posterior sense; the steppes. central figure occupies nearly all the space Pasos Maios - MHN-UNSL-V 198. surrounded by small peripheral or absent figures. With regard to the extremities it can be mentioned El Tala - MHN-UNSL-V 487 to MHN-UNSL-V 500. Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p.161-178, jan./mar.2008 MAMMALS FROM THE LATE PLEISTOCENE/EARLY HOLOCENE OF SAN LUIS PROVINCE (ARGENTINA) 167 Fig. 5 - Scelidotherium leptocephalum - mandible fragment. Fig. 6 - Scelidotherium leptocephalum - skull fragment 342. Fig. 7 - Scelidotherium leptocephalum - skull fragment 342. Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p. 161-178, jan./mar.2008 168 J.O.CHIESA Order TARDIGRADA Latham & Davies, 1795 calcaneus; four caudal vertebrae and an Family Mylodontidae Gill, 1872 incomplete pelvic waist. The remains of Villa Subfamily Scelidotheriinae Ameghino, 1889 Larca correspond to the mandibular branch Genus Scelidotherium Owen, 1840 (without the 4th molar), the left zygomatic arch, Scelidotherium leptocephalum Owen, 1840 and fragments belonging to the base of the skull with the complete left dentition and the right Localities and descriptive aspects - Pasos Maios dentition without crown. In the horizontal (Merlo), Villa Larca, and Valle de Pancanta. A mandibular branch, the part that stretches ahead complete skull was found in Pasos Maios. Upper of the molars is slightly curved, narrow, and and lower maxillaries with molars were found in extended twice the toothed region. They are Villa Larca. In Valle de Pancanta were found an molariform, prismatic, sub-triangular or sub- isolated tooth; right and left femur without elliptical; the disposition is highly obliqúe except proximal portions; right humerus; proximal end for the anterior-posterior stretching of the lst of the left humerus; left tibia; right tibia without upper molar with sub-equal size except for the the proximal portion; right and left astragali; left 5th upper molar that is smaller. Fig. 8 - Scelidotherium leptocephalum - lateral view of the skull. Fig. 9 - Megatherium americanum - fragment of a thoracic vertebra. Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p.161-178, jan./mar.2008 MAMMALS FROM THE LATE PLEISTOCENE/EARLY HOLOCENE OF SAN LUIS PROYINCE (ARGENTINA) 169 Fig. 10 - Megatherium americanum - molar tooth. Fig. 11 - Stegomastodon platensis - first cervical vertebra (atlas). Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p. 161-178, jan./mar.2008 170 J.O.CHIESA Fig. 12 - Stegomastodon platensis - scapula (?). Fig. 13 - Stegomastodon platensis - manus. Arq. Mus. Nac., Rio de Janeiro, v.66, n.l, p.161-178, jan./mar.2008