7 Did Humans Cause the Late Pleistocene-Early Holocene Mammalian Extinctions in South America in a Context of Shrinking Open Areas? Alberto L. Cione,* Eduardo P. Tonni, and Leopoldo Soibelzon División Paleontología de Vertebrados Facultad de Ciencias Naturales y Museo Universidad Nacional de La Plata, Paseo del Bosque 1900 La Plata, Argentina [email protected], [email protected], [email protected] Keywords South America • mammals • extinction • pseu- Moreover, presently there are no megamammals in Europe and doextinction • human impacts Australia. In Asia today there are only two megamammals and in Africa four megamammal species and the giraffe, close to a ton in body mass. The largest terrestrial mammal in the Neotropics Introduction is the tapir Tapirus bairdii, some individuals of which slightly surpass 300 kg (Nowak and Paradiso, 1983). The last important – and possibly the most spectacular – turn- The large mammal extinction of the latest Cenozoic occurred over in South American mammal history occurred around the on different continents and islands at different times (Steadman Pleistocene-Holocene boundary, when 100% of megamam- et al., 2005). For explaining these extinctions several hypotheses mal species and about 80% of large mammal species became have been proposed, most related to cold climate, disease, or extinct. In this paper, we consider as “megamammals” those human activities. We agree with Barnosky et al. (2004) in that with body mass over 1,000 kg, and “large mammals” those the accumulated evidence suggests it is time to move beyond over 44 kg (Tables 7.1 and 7.2). With the exception of a few casting the Pleistocene extinction debate as a dichotomy of smaller mammals, no other animals or plants disappeared. climate versus humans. In this context, we have proposed what Consequently, this extinction event was distinct from mass we call the Broken Zig-Zag hypothesis (Cione et al., 2003). extinctions (see comments in Cione et al., 2003). During most of the middle and late Pleistocene, dry and cold South American communities had included at least some climate caused open areas to predominate in South America. megamammals since the latest Paleogene, but gigantism in Nearly all megamammals and large mammals that became mammals markedly emerged during the Ensenadan age (early extinct were adapted to this kind of environment. The periodic Pleistocene; Fig. 7.1) when many large mammal genera first though relatively short interglacial increases in temperature and appeared (Ameghino, 1889; Pascual et al., 1965; Cione and Tonni, humidity led to dramatic shrinking of open areas and extreme 2005). Most genera, with different species, survived during the reduction of the mammalian biomass (albeit not of species late Pleistocene when the remarkable figure of 37 megamammal richness) adapted to open habitats. However, during the longer species can be documented (Table 7.1). Many appear to have glacial periods, open-area mammal populations recovered. This persisted in the early Holocene. However, none is living today. alternation of low and high biomass of mammals from open and closed areas is what we refer to as the Zig-Zag. Remarkably, the extinction rate of large mammals and megamammals during * Address for correspondence: [email protected] more than a half million years was not high, until rising abruptly during the latest Pleistocene. G. Haynes (ed.), American Megafaunal Extinctions at the End of the Pleistocene, 125–144. In this paper, (1) we analyze the biostratigraphic and chrono- © Springer Science + Business Media B.V. 2009 logic pattern of the large continental mammals of South America 125 126 A.L. Cione et al. Table 7.1. Mammal taxa present in putative Lujanian (sensu Cione Table 7.2. Large mammals and megamammals in the Guerrero and Tonni, 1999) beds in South America and that became extinct Member of the Luján Formation and correlative units. (modified from Cione et al., 2003). Asterisks indicate taxa that occur Antifer neumeieri Megatherium americanum in archeological sites. Arctotherium bonariense Megatherium lundi Megamammals Large mammals Arctotherium tarijense Megatherium tarijense Ctenomys lujanensis Morenelaphus lujanensis Cuvieronius humboldti* Antifer niemeyeri Cuvieronius humboltii Mylodon darwinii Cuvieronius hyodon Arctotherium bonariense Dusicyon avus Mylodon listai Doedicurus clavicaudatus * Arctotherium brasiliense Doedicurus clavicaudatus Neochoerus aesopy Eremotherium carolinense Arctotherium tarijense Equus (A.) andium Neosclerocalyptus paskoensis Eremotherium laurillardi Brasiliochoerus stenocephalus Equus (A.) neogeus Neothoracophorus depressus Eremotherium mirabile Equus (A. merhippus) andium Eremotherium sp. Neuryurus n. sp. Eremotherium rusconii Equus (A.) insulatus Eulamaops paralellus Onohippidium salidiasi Glossotherium (Oreomylodon) Equus (A.) lasallei wagneri Eutatus seguini Palaeolama sp. Glossotherium lettsomi Equus (A.) neogeus* Eutatus punctatus Pampatherium typum Glossotherium (Pseudolestodon) Equus (A.) santa-elenae myloides Glossotherium lettsomi Panochthus morenoi Glossotherium robustum* Eulamaops paralellus Glossotherium myloides Panochthus tuberculatus Glossotherium tropicorum Eutatus seguini* Glossotherium robustum Paraceros fragilis Glyptodon clavipes Eutatus punctatus Glyptodon clavipes Plaxhaplous canaliculatus Glyptodon perforatus Glyptotherium sp. Glyptodon perforatus Propraopus grandis Glyptodon reticulatus Hippidion principale* Glyptodon reticulatus Scelidodon sp. Glyptotherium cf. cylindricum* Holmesina occidentalis Glyptotherium cylindricum Scelidotherium leptocephalum Hemiauchenia paradoxa * Holmesina paulacoutoi Hemiauchenia paradoxa Smilodon populator Lestodon armatus Hoplophorus euphractus Hippidion principale Stegomastodon platensis Lestodon trigonidens Lama gracilis Holmesina sp. Stegomastodon waringi Macrauchenia patachonica* Morenelaphus lujanensis Lama gracilis Toxodon burmeisteri Megalonyx sp. Mylodopsis ibseni Lestodon armatus Toxodon platensis Megatherium americanum* Neochoerus aesopy Lestodon trigonidens Megatherium medinae Neochoerus sirasakae Macrauchenia patachonica Mixotoxodon larensis Neosclerocalyptus paskoensis* Mylodon darwinii Neuryurus n. sp. Mylodon listai* Nothropus priscus Neothoracophorus depressus Nothrotherium roverei Panochthus frenzelianus Ocnopus gracilis Panochthus morenoi Ocnotherium giganteum during the late Pleistocene-earliest Holocene with new evidence, Panochthus tuberculatus Onohippidion saldiasi* (2) discuss why megamammals and large mammals were more Plaxhaplous canaliculatus Palaeolama niedae liable to become extinct than those that survived, (3) discuss the Stegomastodon platensis Palaeolama weddelli timing of human entry into South America, and (4) examine the Stegomastodon guayasensis Pampatherium humboldti Stegomastodon waringi Pampatherium typum possible role of humans in this extinction. Toxodon burmeisteri Paraceros fragilis Toxodon platensis* Parapanochthus jaguaribensis Xenorhinotherium bahiense Propraopus grandis The Broken Zig-Zag Hypothesis Propraopus humboldti Propraopus magnus We have proposed that megamammal and large mammal Scelidodon cuvieri Scelidodon chiliensis extinction in South America during the late Pleistocene- Scelidodon reyesi earliest Holocene was caused by human foragers (Cione Scelidotherium leptocephalum et al., 2003). However, we believe that this event would have Smilodon populator been favoured by a particular circumstance: total biomass (not Tapirus cristatellus diversity) and distribution of open-area-adapted mammals Trigonodops lopesi began to be extremely reduced in response to the periodic Medium sized mammals Small mammals shrinking of this kind of environments (the Zig-Zag) which Canis dirus Eligmodontia n. sp. was stimulated by the last (present) interglacial’s periodic Dusicyon avus* Microcavia robusta Protocyon orcesi Desmodus draculae rising temperature and humidity. Humans certainly did not Protocyon troglodytes exterminate all the extinct taxa (e.g., the large carnivores), Protopithecus brasiliensis but killed off many and provoked changes that occasioned the Valgipes deformis disappearance of the remaining ones (see also Kay, 2002). 7. Did Humans Cause the Late Pleistocene-Early Holocene Mammalian Extinctions in South America 127 Figure 7.1. Chronological chart of the middle Pleistocene-Recent in southern South America depicting mammal zones and South American ages (modified from Cione and Tonni, 2005) and the climatic oscilations represented by (1) 18O of Vostok, Antarctica (Petit et al., 1999) and (2) data from Dronning Maud Land, Antartica (Steig, 2006). The Zig-Zag struction of South America during the LGM, we calculated that open areas would have encompassed 31% of the terri- Studies based on geochemical proxies in glacial ice cores tory, medium areas 54%, and closed areas 15% (Cione et al., from Greenland, Antarctica, and South America show that 2003). Simberloff (1986 fide Raup, 1992: 136) had calculated temperatures strongly fluctuated during at least the last that areas of wet forests were reduced by 84% during this time. 400 ka and that the present interglacial is not substantially We understand that the most difficult definition is that of the different from the earlier ones, of which there were over 20 “medium vegetated areas.” In this term, cerrados, chaco, monte, during the middle-late Pleistocene (Fig. 7.1; McCulloch et al., and other relatively closed areas are included along with some 2000; Blunier