Elsevier

Quaternary Science Reviews

Volume 242, 15 August 2020, 106428
Quaternary Science Reviews

The extinction of the Pleistocene megafauna in the Pampa of southern Brazil

https://doi.org/10.1016/j.quascirev.2020.106428Get rights and content

Highlights

  • The late Pleistocene-Holocene extinction in the Brazilian Pampa is investigated.

  • All megamammals and several large mammals disappeared from the Brazilian Pampa.

  • The extinction occurred in two phases, one around 30 ka and the other after 12.7 ka.

  • The onset of the extinction predates the known human arrival to the Pampa.

  • Climate-driven environmental changes seem to have driven the extinction.

Abstract

The Late Pleistocene-early Holocene faunal turnover in South America was characterized by the extinction of all mammals with body mass >300 kg and several smaller taxa, but the driving mechanisms behind it are still poorly understood. Here is presented an analysis of the extinction in the Pampa of southern Brazil (Rio Grande do Sul state), based on fossil assemblages found in the coastal plain (CPRS) and western area of the state (WRS). The comparison between fossil and extant mastofaunas show that 90% of the mammals represented in fossil assemblages went extinct, and allowed distinguishing three groups: 1) taxa that underwent local extinction, i.e., disappeared locally but survived in other regions until becoming extinct later (including all megamammals); 2) pseudoextinct taxa that disappeared locally but survive until today in other areas, and 3) taxa that disappeared locally but returned during the Holocene. The faunal changes recorded along stratigraphic successions and available numerical ages indicate two phases of extinction, the first around 30 ka b2k in the CPRS (apparently also recorded in Argentina and Uruguay) would have been related to the onset of the cold and dry conditions of the stadial MIS 2, predating the arrival of humans to the region by about 25 kyrs. The second phase eliminated taxa that survived until about 12.7 ka BP in WRS in reduced suitable environments (‘refugia’) associated with perennial rivers; it coincides with the transition from glacial to interglacial conditions, but pollen data suggest that humans may have contributed for environmental modifications through fire. The results show that the Pleistocene xenarthran-dominated mastofauna was replaced by a Holocene fauna dominated by small rodents and carnivores, and indicate that climate-driven environmental changes, also influenced by sea-level oscillations, were a major agent in the Late Pleistocene mammalian extinctions in the Brazilian Pampa.

Introduction

The Late Quaternary Extinction (LQE) in the Americas has been a subject of discussion among scientists of different fields in the last decades (Martin and Klein, 1984; Koch and Barnosky, 2006; Haynes, 2009), focusing mainly on the cause(s) of extinction, with climate change or overhunting by humans being advocated as the most probable agents. Although the extinction is regarded as having occurred during the Pleistocene-Holocene transition (∼12.4–7.8 ka BP), relatively little is known about the exact timing of the process. Some models advocate a relatively sudden extinction, occurring shortly after the arrival of humans (Martin, 1973; Brook and Bowman, 2002; Steadman et al., 2005), whereas models based on absolute ages show thousands of years of coexistence between humans and megamammals prior to the extinction (Barnosky and Lindsey, 2010). The question of the timing is of major importance, because it could indicate whether the extinction was sudden or protracted, or if it was synchronous or occurred at different times in different areas across the continent. It could also help assessing the mechanism(s) of extinction by allowing correlation with environmental changes or human occupation obtained from other paleo-records.

This extinction was responsible for a dramatic change in the composition of mammalian communities (faunal turnover) and has received much attention not only because it potentially could have been linked to human dispersal or to climate change, but also because it wiped away mostly large mammals, thus deeply influencing the character of the modern ecosystems and terrestrial communities. The turnover was particularly striking in South America, where some 80% of the large-bodied mammals (body mass ≥ 44 kg) and 100% of the megamammals (body mass ≥ 1,000 kg) disappeared (Cione et al., 2009).

In Brazil, little is known so far about the LQE, mostly because researches have historically focused on systematics. Moreover, the lack of good stratigraphic records with associated numerical ages in several Quaternary deposits makes difficult to assess faunal dynamics and correlate extinctions with specific environmental changes that could be inferred from sedimentary records. Because of these deficiencies, it has been difficult to establish the temporal range represented by most of the Pleistocene-Holocene fossil assemblages, which were regarded as ‘pontual’ in time (Cartelle, 1999), but now recognized as representing longer intervals (Auler et al., 2006).

In southern Brazil, the Pleistocene fossiliferous sites better characterized in terms of stratigraphy and chronology are found across the Pampa landscape, in the state of Rio Grande do Sul (Fig. 1), where two fossiliferous units have been studiedwere described. In the western part of the state (WRS), the Touro Passo Formation (TPF) outcrops along the Touro Passo Creek (Bombin, 1976; Oliveira and Kerber, 2009; Kerber et al., 2014), whereas the Santa Vitória Formation (SVF) outcrops along Chuy Creek in the coastal plain (CPRS) to the east (Soliani, 1973; Soliani and Jost, 1975). The mammalian fossil record of the CPRS also includes specimens found on the continental shelf (CS) and modern beaches, but these lack defined stratigraphic setting (Lopes and Buchmann, 2010; Aires and Lopes, 2012; Cruz et al., 2017).

The aim of this paper is to describe the Late Pleistocene-Early Holocene mammalian turnover recorded in the Pampa of southern Brazil, based on an integrative approach that included a survey of the fossil mammalian assemblages of the CPRS and WRS, analysis of the stratigraphic distribution and age of the deposits and associated fossils, comparison between the extinct and extant mastofauna, and assessment of pattern of faunal changes recorded in those units within a chronostratigraphic framework. A comparison of the pattern of faunal turnover and its chronostratigraphic setting with the available archaeological and paleoclimatic records is also presented, in order to identify possible mechanisms that could have driven the Late Pleistocene extinction in the Brazilian Pampa.

Section snippets

Methods

Traditionally, the main focus of studies about the Pleistocene fauna of southern Brazil has been systematics (e.g. Paula Couto, 1953; Souza Cunha, 1959; Oliveira, 1992). The research program focused on Quaternary deposits of Rio Grande do Sul that has been developed for the last ten years broadened the spectrum of disciplines and methods employed, including stratigraphy, chronology, taphonomy and paleoecology (Da Rosa, 2009; Kerber et al., 2011; Lopes, 2013; Lopes et al., 2010, 2013; 2014a,

Regional setting

The Pampa landscape of South America is a low relief area with altitudes between 0 and 1,300 m stretching across Rio Grande do Sul state in Brazil, Uruguay and Argentina (Fig. 1A). The Pampa encompasses an area of some 178,000 km2 across the southern half of Rio Grande do Sul state (IBGE, 2019), bordered to the north by the Araucárias Plateau (Fig. 1B). The Pampa is occupied by a grassland biome with herbaceous and shrubby formations, and sparse arboreal vegetation concentrated mostly along

Ages and biostratigraphy of the fossil assemblages and fossil-bearing units

The fossil teeth from the CS dated by ESR exhibit a wide age range (Fig. 2C). Some specimens are chronocorrelated to those of the SVF (207 ± 28, 165 ± 28 and 146 ± 9 ka), whereas others are much older (650 ± 100, 464 ± 65 and 428 ± 30 ka), and one tooth of a mastodont is much younger, being dated as of 18 ± 3 ka (Lopes et al., 2010). These ages correspond to late interglacial or glacial epochs, when sea-level was much lower (up to about −130 m) than the present one (Rohling et al., 1998).

The

Discussion

The diverse Chuy Creek local fauna is the assemblage of Pleistocene mammals in southern Brazil better known so far in terms of stratigraphic resolution and chronology. Despite the diversity of the assemblages from the continental shelf and Touro Passo Creek, these lack stratigraphic resolution to allow recognizing faunal changes through time. Nevertheless, the available absolute ages from these deposits allow establishing chronostratigraphic comparisons with the fossils from the SVF.

Faunal

Conclusions

The fossil assemblages of mammals within defined stratigraphic successions, temporally calibrated by numerical ages, allows assessing the faunal turnover caused by the extinction of the megafauna between the Late Pleistocene and Early Holocene across the Pampa of southern Brazil. This extinction was characterized by the disappearance of all megamammals and several large taxa, comprising 90% of the paleomastofauna, whereas small taxa (mostly rodents) were less affected. It dramatically changed

Declaration of competing interest

The authors declare no conflict interest.

Acknowledgments

The authors would like to thank Dr. Jairo Savian (Universidade Federal do Rio Grande do Sul) for providing two of the OSL datings mentioned in the text. This research was funded by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) through the Postdoctoral Research Grant no. 150153/2014-7 to R.P. Lopes, and Research Fellowship no. 305393/2017-0 to S.R. Dillenburg.

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