Introduction
Isotopes studies in Argentina
Stable isotopes (δ13C and δ15N) measurements obtained from bone collagen have been used in the South America Southern Cone for reconstructing vegetation, diets, prey preferences and also for estimating paleoenvironmental conditions, such as moisture, temperature or annual precipitation (Bocherens et al., 2016; González-Guarda et al., 2017; López-Mendoza et al., 2016; Tessone, 2022a). For this reason, they are useful for deciphering faunal paleoecology and/or climate changes. In Argentina, in the field of archaeology most isotopic studies have been performed for understanding Holocene human diets and on analyzing the isotopic variability of the zooarchaeological record (Barberena et al., 2009, 2011; Loponte & Corriale, 2020; Panarello et al., 2021; Politis et al., 2009; Tessone et al., 2020). Also, the guild structure and the paleoautoecology of extinct species was examined, mostly focusing in δ18O and δ13C stable isotopes from the bioapatite fraction (Bellinzoni et al., 2023; Bocherens et al., 2016; Domingo et al., 2020; Fernández et al., 1991; MacFadden, 2005; Panarello et al., 2021; Prado et al., 2011; Sánchez et al., 2006; Sanz-Pérez et al., 2022). Extinct carnivores (Bocherens et al., 2016; Prevosti & Martin, 2013; Prevosti & Schubert, 2013), equids (Prado et al., 2011; Sánchez et al., 2006) and toxodons (MacFadden, 2005) were the most important studied groups. In turn, Xenarthra order, including giant ground sloths, have fewer isotopic information (Bellinzoni et al., 2023; Bocherens et al., 2016; Domingo et al., 2020; Pradeiro et al., 2012; Prevosti & Martin, 2013; Sanz-Pérez et al., 2022; Steele & Politis, 2009). Recently, stable isotope studies are starting to integrate records of the last 12,000 years for characterizing the isotopic variability of extinct and extant species, as well as for understanding the changing scenarios of human occupations, especially for South Patagonia (Paunero et al., 2017; Tessone et al., 2020; Tessone, 2022b). In this work, we expand these analyses for the last ca. 20,000 cal BP, when South America Southern Cone suffered drastic climatic and biotic events that shaped its current landscape and faunal communities: Last Glacial Maximum (ca. 23,000–19,000 cal BP), Pleistocene-Holocene transition (ca. 15,000–10,000 cal BP) and Holocene warming (Early Holocene, ca. 10,000 to 5,000 cal BP and Late Holocene, 5,000 cal BP to present) (chronology based on Iglesias et al., 2014 and Tammone et al., 2014). This time interval encompasses the climatic fluctuations from the last part of the Late Pleistocene period, the megamammals extinction, and the first arrival and expansion of Homo sapiens (Iglesias et al., 2014; Rabassa, 2008).
This is the case for the Nahuel Huapi Region (North West Patagonia, Argentina) where extinct giant ground sloths (Megatherium americanum, Mylodontinae), indeterminate species (Cervidae indet., Canidae indet. and Hippocamelus sp.) and extant species (Hippocamelus bisulcus and Lama guanicoe), from the last ca. 20,000 cal BP were detected in archaeological and paleontological sites, located to the West and East sides of the Nahuel Huapi lake (Arias Cabal et al., 2013; Buckley et al., 2015; Hajduk et al., 2007, 2008, 2012; Lezcano et al., 2010) (Fig. 1): the shore of the lake (Buckley et al., 2015; Presslee et al., 2019) and El Trébol to the West (Hajduk et al., 2007, 2008, 2012; Lezcano et al., 2010), and Arroyo Corral I and II to the East (Arias Cabal et al., 2013; Hajduk et al., 2007). Most of the paleoenvironmental studies in this region have been performed in pollen, charcoal and tephra records (Bianchi, 2007; Bianchi et al., 1999; Iglesias et al., 2014, 2017; Lirio, 2011; Whitlock et al., 2006). Takenaka et al. (2020) focused on the δ18O and δ13C values of rodents for reconstructing Holocene and historical periods. Faunal remains of these sites have been analyzed in proteomic, micromammal and zooarchaeological studies (Buckley et al., 2015; Lezcano et al., 2010; Presslee et al., 2019; Tammone et al., 2014, 2018).
[See PDF for image]
Fig. 1
Study area. ACO, Arroyo Corral; NHL, Nahuel Huapi lake; ET, El Trébol
Stable isotopes values of the extinct and extant species can also reflect different paleoenvironmental conditions of lake Nahuel Huapi. Consequently, our main objective in this study is to contribute new δ13C and δ15N measurements on bone collagen for characterizing landscape evolution of the last 20,000 cal BP in the Nahuel Huapi Region. The particular paleontological and archaeological record found here allows to expand the range of isotopic studies in Patagonia and South America Southern Cone for this crucial period, thus providing new information for the study region. We also present new AMS dates of giant grounds sloths and their first Last Glacial Maximum isotopes measurements from North West Patagonia. These values are compared regionally, due to the scarcity on this type of information from these extinct species.
Paleoenvironment of the Nahuel Huapi Region
The Nahuel Huapi Region is located in the eastern flank of the Andes and has a well-marked West-to-East climatic gradient, as reflected in vegetation changes along less than 50 km: the Western humid forest is replaced by the Patagonian steppe located to the East (Bianchi, 2007; Bianchi et al., 1999; Iglesias et al., 2014, 2017; Lirio, 2011; Tammone et al., 2018; Whitlock et al., 2006). This gradient reflects the ecotone between forest and steppe, which is dominated by a mosaic of different vegetation patches (Bianchi, 2007; Bianchi et al., 1999; Iglesias et al., 2014, 2017; Lezcano et al., 2010; Tammone et al., 2018). Consequently, small environmental changes in precipitation and humidity (Bianchi, 2007; Bianchi et al., 1999; Iglesias et al., 2014, 2017) influence the distribution of the flora and fauna (Tammone et al., 2018).
By ca. 20,000 cal BP ago, the Andean flanks in Patagonia were covered by several glacial ice sheets (Rabassa, 2008), which shaped the current geomorphology, excavated valleys and locating moraines that were afterwards covered by glacial lakes, as happened in the Nahuel Huapi Region (Bianchi et al., 1999; Iglesias et al., 2014; Lirio, 2011; Rabassa, 2008; Tammone et al., 2014). In the East, the glacial ice field extended during Last Glacial Maximum times eastward almost to the Limay river mouth, where free-ice and free-forest conditions dominated (Tammone et al., 2014). By ca. 20,000 cal BP ago, micromammals and pollen data from Arroyo Corral reflect an open grassland in a cold environment (Iglesias et al., 2014; Tammone et al., 2014). In the West, the Elpalafquen paleolake (sensu del Valle et al., 2007) started to form with the first deglaciation (19,200–18,800 cal BP). This deglaciation event was fast, contributing with a high level of water to the Nahuel Huapi basin. These conditions continued until 16,840 ± 250 cal BP, when its disintegration started (Lirio, 2011). One of the first sectors to emerge was El Trébol lagoon and its surroundings, thanks to its higher altitude. Thus, El Trébol rock shelter was habitable since 14,680 ± 261 cal BP (ca. 14,500 cal BP) (Lirio, 2011). Palynological and charcoal studies indicate for > 15,000 cal BP drier and colder climatic conditions than today, with steppe vegetation (Bianchi et al., 1999; Iglesias et al., 2014, 2017; Whitlock et al., 2006). Afterwards an increase of water input took place, leading to wetter conditions. This increase in moisture allowed the fast development of a population of pioneers’ arboreal taxa (Bianchi et al., 1999; Iglesias et al., 2014; Lirio, 2011; Whitlock et al., 2006). Between 11,400 and 10,200 14C (ca. 13,300–11,870 cal BP) the Huelmo-Mascardi cold reversal event was detected (Iglesias et al., 2014), with presence of open forest and an increase in fires (Bianchi, 2007; Bianchi et al., 1999).
In Arroyo Corral, the warming of the Pleistocene-Holocene transition allowed the colonization of small patches of forest (Tammone et al., 2014). The increase of precipitation through the Holocene allowed an expansion of the forest habitats, as seen today (Tammone et al., 2018). Meanwhile, seismic and volcanic events were registered in El Trébol near the Pleistocene-Holocene transition, which led to the fall of the roof in several caves (Hajduk et al., 2012). The Early Holocene was characterized by arid and dry conditions, which might have displaced further West (in relation with its current position) the forest-steppe ecotone (Bianchi, 2007). Open forest with patches of shrubland/steppe and evidence of fires were detected near El Trébol lagoon (Bianchi, 2007; Iglesias et al., 2014; Whitlock et al., 2006). Finally, in the Late Holocene forest taxa developed and expanded to the East, thanks to an increase in precipitation (Bianchi, 2007; Iglesias et al., 2014, 2017; Whitlock et al., 2006).
Stable isotope basis
Stable isotopes (δ13C and δ15N) from bone collagen represent a highly valuable proxy for estimating the dietary preferences of ancient species and, indirectly, for providing inferences on the paleoenvironment (Coltrain et al., 2004; Domingo et al., 2020; Drucker et al., 2003; Fox-Dobbs et al., 2008; France et al., 2007; Palmqvist et al., 2008; Rabanus-Wallace et al., 2017; Sanz-Pérez et al., 2022; Stevens & Hedges, 2004). Several studies describe how plants fix stable isotopes of carbon and nitrogen, how they are transferred by isotopic discrimination to herbivorous, carnivorous and omnivorous organisms, as well as their relationship with environmental variables such as average annual precipitation, temperature or altitude (Ambrose, 1991; Gröcke et al., 1997; Hartman, 2011; Murphy & Bowman, 2006; Palmqvist et al., 2008). Plants with a C3 photosynthesis include all trees and shrubs, as well as herbaceous plants adapted to cold areas with high altitude and/or high latitude conditions (Heaton, 1999; Kohn, 2010). Water stress, canopy effect, precipitation, humidity, temperature, and altitude can all have an impact on plant δ13C variability (Heaton, 1999; Kohn, 2010). In Patagonia, the modern vegetation is composed of C3 plants, with δ13C values between −33.4 ‰ in forest and −20.9 ‰ in open habitats conditions (Tessone et al., 2023).
On the other hand, δ15N is generally used as an indicator of the trophic position of the species, since each level tends to increase between 3 ‰ to 5 ‰ over the previous one (Bocherens & Drucker, 2003). However, δ15N is also inversely related with the mean annual precipitation of the region, higher δ15N values are associated with more open and arid environments (Ambrose & DeNiro, 1986; Hartman & Danin, 2010; Heaton et al., 1986; Murphy & Bowman, 2009). The modern vegetation’s δ15N values in Patagonia range from –11.8 ‰ to 7.4 ‰ in forests and open areas respectively (Tessone et al., 2023).
Material and methods
Materials
The sample set analyzed is composed of 17 different bones samples from paleontological and archaeological sites spanning the last ca. 20,000 cal BP (Table 1; Online Resources 1 and 2): the shore of the Nahuel Huapi lake and El Trébol, located to the West of the Nahuel Huapi Region, and Arroyo Corral I and II to the East (Fig. 1; Table 2).
Table 1. Detail of samples analyzed in this study
Nomeclature | Site | Specie | Element | Chronology | References |
|---|
MAPB 3965 | L. Nahuel Huapi | M. americanum | Rib | 19,050 ± 80 | Presslee et al., (2019) |
93886 | ET | Mylodontinae | Osteoderm | older than 10,600 | – |
93095 | ET | Mylodontinae | Osteoderm | 11,120 ± 50 | This paper |
93923 | ET | Mylodontinae | Osteoderm | 11,675 ± 45 | This paper |
93048 | ET | Mylodontinae | Osteoderm | 10,570 ± 130 | Hajduk et al., (2006), Lezcano et al., (2010) |
93014 | ET | Hippocamelus sp. | Phalanx distal | 10,570 ± 130 | Hajduk et al., (2006), Lezcano et al., (2010) |
ET52* | ET | H. bisulcus | Phalanx distal | 5,620 ± 80 | Hajduk et al., (2006), Lezcano et al., (2010) |
ET54* | ET | L. guanicoe | Carpal | 5,620 ± 80 | Hajduk et al., (2006), Lezcano et al., (2010) |
ET53* | ET | H. bisulcus | Phalanx | ca. 1,500-300 BP (ceramic) | Lezcano et al., (2010) |
ET55* | ET | L. guanicoe | Metapodial distal | ca. 1,500-300 BP (ceramic) | Lezcano et al., (2010) |
1442/1443 | ACO I | Mylodontinae | Osteoderm | 18,920 ± 60 | This paper |
2636/2648 | ACO I | Mylodontinae | Osteoderm | 18.620 ± 75 | This paper |
90662 | ACO I | L. guanicoe | Metapodial diaphysis | 6,100 ± 65 | Arias Cabal et al., (2013) |
90195 | ACO I | L. guanicoe | Femur proximal | 4,384 ± 64 | Arias Cabal et al., (2013) |
1789 | ACO II | L. guanicoe | Tibia proximal | 7,117 ± 72 | Tammone et al., (2018) |
L. guanicoe | 7,179 ± 75 | Tammone et al., (2018) |
1682 | ACO II | L. guanicoe | Metatarsal diaphysis | 5,056 ± 62 | Tammone et al., (2018) |
1634 | ACO II | L. guanicoe | Metapodial distal | 2,100 ± 80 | Tammone et al., (2018) |
Abbreviations: ET, El Trébol; ACO I, Arroyo Corral I; ACO II, Arroyo Corral II; BP, Before Present. *Provisory nomenclature
Table 2. General characteristics of the species
Species | Chronology | Area | Nº Samples | Site |
|---|
M. americanum | LGM | W | 1 | NHL |
Mylodontinae | PHT | W | 4 | ET |
Mylodontinae | LGM | E | 2 | ACO |
Hippocamelus sp. | PHT | W | 1 | ET |
Hippocamelus bisculus | H | W | 2 | ET |
Lama guanicoe | H | W | 2 | ET |
Lama guanicoe | H | E | 5 | ACO |
Abbreviations: LGM, Last Glacial Maximum; PHT, Pleistocene-Holocene transition; H, Holocene; W, West; E, East; NHL, Nahuel Huapi lake; ET, El Trébol; ACO, Arroyo Corral
Sites
Nahuel Huapi lake shore (41º6′12.15″ S-71º12′6.72″ W)
An individual of M. americanum was found on the shore of the Nahuel Huapi lake. The bones were located in clay sediments of glacial till, in a sector seasonally underwater. The specimen was collected by Walter Cardenas and is currently housed in the Museo Arqueológico y Paleontológico de Bariloche (MAPB) (Iglesias, 2023 pers. comm.). This individual was dated to 19,050 ± 80 (UCIAMS-209020, Presslee et al., 2019, Supplementary Information Table 2). A 2-sigma (95% confidence interval) offers an age confidence interval of 23,093 to 22,630 cal BP, and a median of 22,956 cal BP (Online Resource 2).
El Trébol (41º04′35″ S-71º29′25″ W; ca. 780 m.a.s.l.)
El Trébol is a rock shelter located at 200 m from El Trébol lagoon in a forest-like environment (Hajduk et al., 2008, 2012). It is 5 km southeast distant from the transitional forest-steppe ecotone and 19 km from the steppe (Hajduk et al., 2008; Lezcano et al., 2010). Excavations performed in 2002, 2004 and 2006 (Hajduk et al., 2008, 2012) revealed several paleontological and archaeological levels, separated by seismic activity that produced the fall of rocks from the cave roof. Paleontological levels were located up to 4.9 m deep (Hajduk et al., 2008, 2012). Mylodontinae osteoderms, Cervidae, Canidae and Rodentia bones were found in them. Volcanic ashes associated to seismic activities were deposited in the interstices between these rocks, sealing the lower levels (Hajduk et al., 2012). In these interstices (located to 3.5 m deep) the first signs of human occupation in association with cut and burned osteoderms of Mylodontinae were dated to 10,570 ± 130 BP (AA65707) (Hajduk et al., 2006). Considering a 2-sigma (95% confidence interval) of 12,738 to 12,000 cal BP, and a median of 12,463 cal BP, this archaeological level dates to ca. 12,500 cal BP. Other AMS dates confirmed a first human occupation in the Pleistocene-Holocene transition (Online Resource 1). Apart from Mylodontinae, bone remains with cut marks of an indeterminate cervid larger than the current huemul, of Hippocamelus bisulcus and of a canid were found (Hajduk et al., 2006; Lezcano et al., 2010). The one sampled for this work is probably H. bisulcus (Hajduk et al., 2006), but for this paper we identify it as Hippocamelus sp. After the first human occupation of the cave, human settlements continued during the Holocene. These hunter gatherers exploited forest and steppe resources, as reflected by the remains of huemul and guanaco, respectively (Lezcano et al., 2010).
Arroyo Corral (40°55′52″S -71°03′19″W; 844 m.a.s.l.)
Arroyo Corral I and II locate near the Limay river, Neuquén Province at the East stepped region of Nahuel Huapi lake. They have been excavated by national and international teams since the eighties of the twentieth century (Arias Cabal et al., 2013; Hajduk et al., 2007; Tammone et al., 2014). Both rock shelters have been occupied by humans since the Pleistocene-Holocene transition (Arias Cabal et al., 2013; Tammone et al., 2014). Arroyo Corral I also preserves paleontological levels that contain remains of L. guanicoe, osteoderms of Mylodontinae and micromammal bones (Arias Cabal et al., 2013; Hajduk et al., 2007; Tammone et al., 2014). L. guanicoe was the main species exploited by humans (Hajduk et al., 2008).
El Trébol and Arroyo Corral were occupied several times by humans and both represent the earliest human signal in the region (Arias Cabal et al., 2013; Hajduk et al., 2007, 2008, 2012; Lezcano et al., 2010).
Samples and time-periods
Material was analyzed considering three main climatic periods of the last ca. 20,000 cal BP (based in Iglesias et al., 2014; Tammone et al., 2014) and according to AMS dates and stratigraphic position of the material (Tables 1 and 2). Special attention was paid to selecting osteoderms of ground sloths, as they can move across stratigraphy (López-Mendoza & Mena-Larraín, 2011).
Last Glacial Maximum (23,000–19,000 cal BP). Three samples were considered for this period: MAPB 3965 M. americanum found in the Nahuel Huapi lake shore from the West, and 1442 and 2636 from the East (Mylodontinae from Arroyo Corral I).
Late Pleistocene-Holocene transition (15,000 to 10,000 cal BP). Five samples from the West (El Trébol site) were selected for this period. These include at least one osteoderm of Mylodontinae (93048) and one Hippocamelus sp. phalanx (93014) from the earliest archaeological level, while the rest of the material was from paleontological levels (93886, 93923 and 93095).
Holocene (10,000 cal BP to present). Only extant species were present in the last 10,000 years at West and East sides of the Nahuel Huapi lake. Four bones were selected from the West: two of H. bisulcus (ET52 and ET53) (El Trébol) and other two of L. guanicoe (ET54 and ET55). Five L. guanicoe bones were selected from the East (Arroyo Corral I and II) (90662, 90195, 1789, 1682 and 1634).
Thus, we sampled M. americanum from the West in the Last Glacial Maximum, Mylodontinae and Hippocamelus sp. in the Pleistocene-Holocene transition, and H. bisulcus and L. guanicoe in the Holocene. The East had a sparse faunal community, with only Mylodontindae by the Last Glacial Maximum and L. guanicoe during Holocene times.
In general terms, extinct and extant species cover an ample dietary gradient: from mostly browsers, such as H. bisulcus and probably Hippocamelus sp. (Barberena et al., 2011), generalized selective feeder and partially browser (M. americanum), mixed or selective-feeders (Mylodontinae) (Bargo, 2003; but see Chichkoyan et al., 2022, for an update discussion regarding M. americanum diet) to predominantly grazers (L. guanicoe) (Lezcano et al., 2010).
Methods
Stable isotopes
The 17 bone samples were treated at Instituto de Geocronología e Isotopía Geológica (INGEIS) (CONICET-Universidad de Buenos Aires) as follows. Extraction of collagen for isotope analyses was performed following the methodological guidelines proposed by Waters-Rist et al. (2011). First, bones were cut and cleaned with a Dremel rotary tool. Between 300 to 600 mg of the obtained fragments were subject to an ultrasonic bath with distilled water by about 15 min at least two times. Samples were soaked with HCl (0.5%) at room temperature. The acid was changed every 24–48 h with an average duration of 7 days. Once demineralized, samples were rinsed with deionized water and treated with a solution of 0.125% NaOH for 20 h (Waters-Rist et al., 2011). Finally, the samples were rinsed with deionized water and dried in an oven at 40 °C.
The measurement of δ13C and δ15N values were performed with a Carlo Erba EA1108 Elemental Analyzer (CHN), connected to a continuous flow Thermo Scientific Delta V Advantage mass spectrometer through a Thermo Scientific ConFlo IV interface. 13C/12C and 15N/14N ratios were expressed as the relative per mil (‰) difference between the samples and international standards where: δ13C or δ15N = (Rsample/Rstandard−1) X 1000 (‰) (R = 13C/12C or 15N/14N, respectively). At INGEIS stable carbon isotopic composition was expressed relative to the VPDB scales using L-SVEC, NBS-19 and NBS-22. Stable nitrogen isotopic composition was expressed relative to AIR scales with IAEA N1 and IAEA N2. Measurement uncertainty was monitored using three in-house standards: cafeine (δ13C: −39.3 ‰, δ15N: 7.0 ‰), sugar (δ13C: −11.4 ‰) and collagen TRACE (δ13C: −18.2 ‰, δ15N: 6.1 ‰). Analytical error was ± 0.2 ‰ for both δ13C and δ15N.
AMS dating
The collagen extraction for AMS dating was made at INGEIS as follows. Bones were cut and cleaned with a Dremel rotary tool. Fragments were subject to an ultrasonic bath with distilled water by about 15 min at least three times, in order to extract the possible contamination. Bone samples (300 to 500 mg) were transferred to a tube with 10 ml of 1.0 M HCl for 48 h at room temperature. Subsequently, the reagent was replaced by one at 0.5 M HCl at 4 °C. The acid was changed every 48 h. The decalcification process took approximately between 10 and 20 days. Once demineralized, samples were rinsed with deionized water. Gelatinization of the sample was carried out with deionized water and three drops of 0.5 M HCl (pH 3) at a temperature of 70 °C for 48 h. The samples were filtered to remove any insoluble residues. Finally, the samples were dried in an oven at 40 °C.
Collagen extracted in osteoderms 1443 from level 6 (same one of 1442), 2648 from level 5 (same one of 2636) from Arroyo Corral I, and 93093 and 93095 from El Trébol were sent for AMS dating at Beta-Analytics in the case of the first one, and to University of Groningen in the case of the other three. These laboratories also provided IRMS δ13C and δ15N.
Published AMS dates and those obtained in this study were calibrated in https://c14.arch.ox.ac.uk/oxcal/OxCal.html, using Southern Hemisphere curve SHCal20 (Bronk Ramsey, 2009; Hogg et al., 2020) and their media was used for comparison issues (see Online Resource 2). Samples ET53 and ET55 were dated by association with ceramic between 1,500 to 300 BP. (Lezcano et al., 2010) and a media of 600 BP was calculated for its general analyses. For regional comparison of M. americanum and Mylodontinae δ13C and δ15N values, we calculated the median of the published dates (see Online Resource 2). Due to the scarce information, we review the bibliography of the South American Southern Cone (Argentina, Chile and Uruguay) (Bocherens et al., 2016; Pradeiro et al., 2012; Prevosti & Martin, 2013; Steele & Politis, 2009; Tessone, 2022b; Todisco et al., 2018; Varela et al., 2023).
Results and discussion
Stable isotopes
δ13C and δ15N isotopic values were obtained in 15 of the 17 processed samples (Table 3). Two samples from El Trébol could not be measured due to lack of collagen: an osteoderm of Mylodontinae from the paleontological level (93095) and a metapodial of L. guanicoe (ET55).
Table 3. δ13C and δ15N values of 15 samples and %C, %N and C/N ratio
Nomeclature | Lab. code | Period/region | Specie | %N | %C | C/N | Collagen yield | δ13C ‰ | δ15N ‰ |
|---|
MAPB 3965 | 42230 | LGMW | M. americanum | 14 | 39.8 | 3.3 | 12.48 | −18.9 | 5.3 |
93886 | 45091 | PHTW | Mylodontinae | 9.2 | 25.1 | 3.2 | 5.67 | −22.1 | 3.4 |
93095 | – | PHTW | Mylodontinae | N/C | N/C | N/C | N/C | N/C | N/C |
93923 | 42223 | PHTW | Mylodontinae | 14.5 | 40.8 | 3.3 | 3.16 | −22.1 | 2.2 |
93048 | 42224 | PHTW | Mylodontinae | 14.9 | 41.7 | 3.3 | 6.87 | −22.4 | 3.9 |
93014 | 42226 | PHTW | Hippocamelus sp. | 9.8 | 28.4 | 3.4 | 6.22 | −21.9 | 4.3 |
ET52 | 42227 | HW | H. bisulcus | 14.1 | 39.6 | 3.3 | 17.92 | −21 | −0.1 |
ET54 | 42229 | HW | L. guanicoe | 14 | 39.3 | 3.3 | 19.12 | −20.3 | 3.1 |
ET53 | 42228 | HW | H. bisulcus | 14.1 | 39.7 | 3.3 | 19.75 | −20.9 | −1.6 |
ET55 | – | HW | L. guanicoe | N/C | N/C | N/C | N/C | N/C | N/C |
1442 | 42217 | LGME | Mylodontinae | 15.2 | 43.1 | 3.3 | 5.70 | −20.4 | 5.9 |
2636 | 42202 | LGME | Mylodontinae | 13.9 | 41.8 | 3.5 | 0.52 | −21.2 | 6.3 |
90662 | 42218 | HE | L. guanicoe | 13.4 | 37.6 | 3.3 | 11.94 | −20.1 | 4.5 |
90195 | 42219 | HE | L. guanicoe | 11.2 | 31.4 | 3.3 | 12.64 | −20.5 | 3.9 |
1789 | 42220 | HE | L. guanicoe | 14.9 | 41.6 | 3.3 | 11.01 | −20.1 | 4.2 |
1682 | 42221 | HE | L. guanicoe | 14.6 | 41.2 | 3.3 | 4.79 | −20.3 | 5.2 |
1634 | 42222 | HE | L. guanicoe | 12.9 | 36.3 | 3.3 | 12.14 | −20.1 | 1.7 |
Abbreviations: LGMW, Last Glacial Maximum West; LGME, Last Glacial Maximum East; PHTW, Pleistocene-Holocene transition West; HW, Holocene West; HE, Holocene East; N/C no collagen
The range of C: N ratios of the 15 samples was 3.2 to 3.5. Consequently, all they fall within the 2.9–3.6 range stablished by DeNiro (1985). %C ranges from 25.1% to 43.1%, falling into the range of 22.6% to 47% for modern bones (Ambrose, 1990). %N ranges from 9.2% to 15.2%, also into the proportion of modern bones (5.5% to 17.3%) (Ambrose (1990). In addition, all samples yielded more than the cut-off of 1% of extraction (Van Klinken, 1999) with the exception of 2636 that yielded 0.5%. (Table 3). Nevertheless, this sample was included in the analysis, as the rest of the parameters (%N, %C and C: N) were correct.
In the Last Glacial Maximun, the values of δ13C and δ15N were −18.9 ‰ and 5.3 ‰ in the West and −20.8 ‰ and 6.1 ‰ in the East respectively. For the Pleistocene-Holocene transition West (N: 4) the means value were −22.1 ‰ ± 0.2 ‰ and 3.4 ‰ ± 0.9 ‰, respectively. In the case of the Holocene, the mean values were δ13C −20.7 ‰ ± 0.3 ‰ and δ15N 0.4 ‰ ± 2.4 ‰ for the Holocene West (N: 3), and δ13C −20.2 ‰ ± 0.1 ‰ and δ15N 3.9 ‰ ± 1.3 ‰ for the Holocene East (N: 5), respectively (Table 4).
Table 4. Statistics per time-period and region
Statistic | LGMW | LGME | PHTW | HW | HE |
|---|
δ13C ‰ | δ15N ‰ | δ13C ‰ | δ15N ‰ | δ13C ‰ | δ15N ‰ | δ13C ‰ | δ15N ‰ | δ13C ‰ | δ15N‰ |
|---|
N | 1 | 1 | 2 | 2 | 4 | 4 | 3 | 3 | 5 | 5 |
Mean | −18.9 | 5.3 | −20.8 | 6.1 | −22.1 | 3.4 | −20.7 | 0.4 | −20.2 | 3.9 |
St. dev. | 0 | 0 | 0.5 | 0.2 | 0.2 | 0.9 | 0.3 | 2.4 | 0.1 | 1.3 |
Min | −18.9 | 5.3 | −21.2 | 5.9 | −22.4 | 2.2 | −21 | −1.6 | −20.5 | 1.7 |
Max | −18.9 | 5.3 | −20.4 | 6.3 | −21.9 | 4.3 | −20.3 | 3.1 | −20.1 | 5.2 |
Abbreviations: LGMW, Last Glacial Maximum West; LGME, Last Glacial Maximum East; PHTW, Pleistocene-Holocene transition West; HW, Holocene West; HE, Holocene East
AMS dating
Table 5 (and also Online Resource 2) depicts four new AMS dates, their calibration range and the median. Samples from Arroyo Corral I were dated in: Beta-641499 18,920 ± 60 years (2-sigma confidence interval from 22,980 to 22,571 cal BP and a median of 22,811 cal BP) and GrM-31626 18,620 ± 45 years (2-sigma confidence interval from 22,797 to 22,332 cal BP, with a median of 22,480 cal BP). Their confidence interval superposes in 226 years and their means are separated by 331 years. Previous dates performed over other osteoderms in this site are in the same range, especially the sample AA 75674 18,700 ± 260 (Arias Cabal et al., 2013). Consequently, osteoderms found in levels 5 and 6 of Arroyo Corral I were deposit between 22,811 and 22,480 cal BP.
Table 5. AMS new dates and isotopic values of Beta-Analytics and U. of Groningen
Nomeclature | Site | Specie | Lab code | 14c date BP | Sigma | δ13C ‰ | δ15N ‰ | Calibration Cal yrs BP %95.4 |
|---|
From | To | Median |
|---|
93095 | ET | Mylodontinae | GrM-31109 | 11,120 | 50 | −21.3 | – | 13,154 | 12,898 | 13,017 |
93923 | ET | Mylodontinae | GrM-31629 | 11,675 | 45 | −21.7 | 3.4 | 13,599 | 13,362 | 13,499 |
1443 | ACO I | Mylodontinae | Beta-641499 | 18,920 | 60 | −19.8 | – | 22,980 | 22,571 | 22,811 |
2648 | ACO I | Mylodontinae | GrM-31626 | 18,620 | 75 | −21.2 | 7.2 | 22,797 | 22,332 | 22,480 |
Abbreviations: ET, El Trébol; ACO I, Arroyo Corral I
Isotopic measurements obtained at Beta-Analytics and U. of Groningen (Table 5) are also very similar to the values from INGEIS (Table 3). For example, sample 2648 measured at U. of Groningen (δ13C = −21.2 ‰ and δ15N = 7.2 ‰) has similar values with 1442 measured at INGEIS (−20.4 ‰ and 5.9 ‰, respectively).
Two new dates were also obtained for the paleontological levels of El Trébol: 11,120 ± 50 (2-sigma confidence interval from 13,154 to 12,898 cal BP and a median of 13,017 cal BP) for GrM-31109 and 11,675 ± 45 (2-sigma confidence interval from 13,599 to 13,362 cal BP and a median of 13,499 cal BP) for GrM-31629 (Table 5, Online Resource 2). The first, osteoderm 93095 (GrM-31109), is from level 6 and the second, 93923 (GrM-31629), is from a stratum near the cultural level dated in ca. 12,500 cal BP. The confidence interval of both osteoderms do not overlap by ca. 200 years, being 93923 older than 93095. Isotopic values of 93923 from INGEIS are −22.1 ‰ for δ13C and 2.2 ‰ for δ15N, while the estimates from Groningen are −21,7 ‰ and 3.4 ‰, respectively. 93095 could not be measured at INGEIS and in Groningen, only the δ13C value was obtained: −21.3 ‰. Overall these osteoderms, as also 93886 (with similar isotopic results to those of sample 93923, which was measured at INGEIS and Groningen, Tables 1 and 5) were excavated from a layer between and below the rock fall, that according to the new dates might have been deposited between 13,017 and 13,499 cal BP (or ca. 13,000–13,500 cal BP) (Table 5). Considering the new dates and the isotopic information, these osteoderms might differentiate from the ones dated at ca. 12,500 cal BP (Hajduk et al., 2006), regardless the mentioned migration trend of them (López-Mendoza & Mena-Larraín, 2011). The presence of Mylodontinae osteoderms by ca. 13,000–13,500 cal BP shows the colonization of El Trébol at least one millennia after its emersion by ca. 14,500 cal BP (Lirio, 2011), in coincidence with pollen, micromammals and sediment proxies (Bianchi et al., 1999; Iglesias et al., 2014; Lirio, 2011; Whitlock et al., 2006) and before or just at the beginning of the Huelmo-Mascardi cold reversal at ca. 13,300 cal BP (Iglesias et al., 2014).
Considering the new AMS dates the presence of Mylodontinae in the last part of the Late Pleistocene of the Nahuel Huapi Region is best depicted. At least three individuals were differentiated between ca. 22,000 to 12,500 cal BP: one inhabiting Arroyo Corral I at the Last Glacial Maximum, at least another one, almost a millennium after the emersion of El Trébol, and a third one exploited by humans another millennium latter, ca. 12,500 cal BP.
Time and space variability
Isotopic values obtained at INGEIS were divided by the three time-period as proposed in Sect. 2.1.2. Figures 2 and 3 represents separately the values of δ13C and δ15N for each time-period and region at the Nahuel Huapi Region. Figure 4 represents δ13C and δ15N of the 15 samples, showing the values obtained for each species. δ13C values, at around −20 ‰ (Fig. 2), reflects a C3 dominant vegetation during the last ca. 20,000 cal BP. Figure 3 portrays a high variation of δ15N values across time and space. δ15N values decrease from almost 6 ‰ in the Last Glacial Maximum to nearly 0 ‰ in recent Holocene times. Figure 4 shows the species with highest and lowest values in δ13C and δ15N, extinct species of the Last Glacial Maximun and H. bisulcus from the Holocene West respectively. Intermediate values correspond to Lamas and species of the Late Pleistocene-Holocene transition.
[See PDF for image]
Fig. 2
Scatterplot of δ13C values from the Nahuel Huapi Region with indication of the three main climatic periods and paleoenviromental information based in pollen, charcoal and micromammals proxies mentioned in the text. LGMW, Last Glacial Maximum West; LGME, Last Glacial Maximum East; LGM, Last Glacial Maximum; PHTW, Pleistocene-Holocene transition West; PHT, Pleistocene-Holocene transition; HW, Holocene West; HE, Holocene East
[See PDF for image]
Fig. 3
Scatterplot of δ15N from the Nahuel Huapi Region with indication of the three main climatic periods and paleoenviromental information based in pollen, charcoal and micromammals proxies mentioned in the text. LGMW, Last Glacial Maximum West; LGME, Last Glacial Maximum East; LGM, Last Glacial Maximum; PHTW, Pleistocene-Holocene transition West; PHT, Pleistocene-Holocene transition; HW, Holocene West; HE, Holocene East
[See PDF for image]
Fig. 4
Scatterplot of δ13C and δ15N values of the 15 samples. LGMW, Last Glacial Maximum West; PHTW, Pleistocene-Holocene transition West; HW, Holocene West; LGME, Last Glacial Maximum East; HE, Holocene East
Last glacial maximum (23,000–19,000 cal BP)
By Last Glacial Maximum only the West has the highest value of δ13C (−18.9 ‰) corresponding to M. americanum (Fig. 2). This value can be related with the ingestion of C3 plants in arid environments. The δ13C of these plants are higher in these environments, as indicated by the measurements of this species in the Pampean region (Bocherens et al., 2016), where it was mostly identified. In Fig. 5a the sample form Nahuel Huapi fits into the range of the measured species between 28,478 to 13,997 cal bp. (N: 9, −18.2 ‰ ± 1.3 ‰, Online Resource 2). In these cases, C3 input was consider (Bocherens et al., 2016) with the exception of the region located to the Central West of Argentina (Manqui-Malal, COA region, Online Resource 2) where a diet of C3-C4 plants was inferred (Pradeiro et al., 2012). This region is in the phytogeographic province of Monte characterized as arid to semiarid which influence in the presence of C4 plants (Pradeiro et al., 2012). Isotopic measurements on the bioapatite also support the preference of C3 plants of this species (Bellinzoni et al., 2023; Domingo et al., 2020; Sanz-Pérez et al., 2022).
[See PDF for image]
Fig. 5
a Scatterplot of δ13C values from M. americanum. b Scatterplot of δ15N values from M. americanum. LGMW, Last Glacial Maximum West; COA, Centro-Oeste Argentina
Last Glacial Maximum East values are in the same range of Holocene West and Holocene East (Fig. 2; Table 4). Consequently, the similarities among the Mylodontinae individual living during Last Glacial Maximum and Lamas from the Holocene, points to a constancy of C3 vegetation at the East side of Nahuel Huapi Region during the last ca. 20,000 cal BP, regardless the dietary preferences of both species.
When comparing the samples from Last Glacial Maximum with the available information from the South American Southern Cone, Arroyo Corral samples fits with Patagonian sites dated between 18,774 and 14,186 cal BP (Fig. 6a, Online Resource 2). The mean is −20.8 ‰ ± 1 ‰ (Online Resource 2) which reflects the consumption of C3 plants, as observed in other Patagonian regions (Paunero et al., 2017; Prevosti & Martin, 2013; Tessone et al., 2020; Tessone, 2022b).
[See PDF for image]
Fig. 6
a Scatterplot of δ13C values from Mylodontinae. b Scatterplot of δ15N values from Mylodontinae. LGME, Last Glacial Maximum East; PHTW, Pleistocene-Holocene transition West
Figures 3 and 4 show that the Last Glacial Maximum has the highest δ15N values, 5.3 ‰ in Last Glacial Maximum West and a mean of 6.1 ‰ in Last Glacial Maximum East (Table 4), represented by M. americanum and Mylodontinae, respectively. As proposed in Sect. 1.3, this isotope can reflect the position of the species within the trophic chain, but also the prevailing environmental conditions. Due to the lack of information from other species, the δ15N measurements obtained here probably show arid conditions at both sides of the Nahuel Huapi Region ca. 20,000 cal BP, as indicated by other proxies. Pollen and charcoal studies from the West side of Nahuel Huapi Region describe a cold, dry and windy Last Glacial Maximum, with a high development of steppe and herbaceous taxa as Poaceae and Asteraceae (Bianchi, 2007; Bianchi et al., 1999; Iglesias et al., 2014; Whitlock et al., 2006). Micromammals analyses in Arroyo Corral I point to the presence of Euneomys chinchilloides and Phyllotis xantophygus as indicators of barren rocky and grassland habitats, respectively. The less common occurrence of Ctenomys sociabilis and Chelemys macronyx could reflect the existence of patches of mesic areas, associated with some type of glacial runoff (Tammone et al., 2014). Consequently, M. americanum in the West and Mylodontinae in the East were living in the cold temperatures typical of the Last Glacial Maximum, with glacial water inputs that supported specially stepped and herbaceous taxa with a C3 photosynthetic way and low precipitation rates. Figure 3 also shows that drier conditions continued in the Holocene East, due to the similar δ15N values of Lamas (excepting sample 1634, Table 3).
When cautiously compared δ15N values, with the few other Argentinean samples, M. americanum from Nahuel Huapi coast is among the lowest, along with the values of Arroyo Seco 2 dated ca. 14,000 cal BP (Fig. 5b, Online Resource 2) (Steele & Politis, 2009). The standard deviation is high, N: 9, mean 8.6 ‰ ± 3 ‰ (Online Resource 2) revealing a high variability of this isotope. It is still not clear the causes of this variability on this species (Bocherens et al., 2016), whose feeding has been characterized from herbivore to carnivore and it is still very much discussed (Bargo, 2003; Bocherens et al., 2016; Chichkoyan et al., 2022).
δ15N of Mylodontinae at a South American Southern Cone level also presents a high variation from the sparse available samples (N: 9, mean 5.3 ‰ ± 2.2 ‰, Online Resource 2). The highest value is recorded in Arroyo del Vizcaíno at ca. 32,0000 cal BP (9.8 ‰) (Varela et al., 2023) and the lowest one presented in this study (2.2 ‰) (Online Resource 2). Also, the values from Arroyo Corral I during Last Glacial Maximum are higher than other Patagonian sites, contrastingly to was observed with δ13C (Fig. 6a–b).
Late Pleistocene-Holocene Transition (15,000 to 10,000 cal BP)
Only samples from El Trébol are present for the Pleistocene-Holocene transition. As seen in Sects. 1.2, 2.1.1.2 and 2.2.2, this time-period evidenced several environmental and biological events. El Trébol emerged at ca. 14,500 cal BP, thanks to the retraction of the Elpalafquen paleolake. The new dates presented in 3.2, confirms the fast recolonization of the region (Bianchi et al., 1999), between ca. 13,000 to 13,500 cal BP. Afterwards, the Huelmo-Mascardi cold pulse occurred at 13,300–11,870 cal BP, with seismic events. By that time, also human presence exploiting Mylodontinae and Hippocamelus sp. was detected (ca. 12,500 cal BP). This date also indicates the last appearance of megafauna in the region.
The lower values of δ13C, with a mean of −22.1 ‰, are located in this time-period (Figs. 2, 4), with a difference of 2 ‰ with the rest of the periods from the Nahuel Huapi Region (Table 4). Nevertheless, this value is still reflecting a C3 vegetation diet for both Mylodontinae and Hippocamelus sp. An outlier of −22 ‰ is observed in Cueva Chica, Southern Chile, dated in 12,723 cal BP. (Fig. 6a, Online Resource 2) (Prevosti & Martin, 2013).
δ15N isotopic values drops from 5.3 ‰ in the Last Glacial Maximum to a mean of 3.4 ‰ ± 0.9 ‰ in the transition into the West side of the lake (Fig. 3; Table 4). The lower values of δ15N might be related with moister habitats and with tree and/or shrubs vegetation. In this sense, a humid trend started just after the emersion of the El Trébol lagoon, being fast colonized by pioneers of forest and shrubland/grassy taxa indicating an open forest (Bianchi et al., 1999; Iglesias et al., 2014, 2017; Whitlock et al., 2006). An increase in Nothofagus dombei-type pollen, as well as Myrtaceae, Drymys and Podocarpus as indicators of a rainy forest were favoured by moister conditions (Bianchi, 2007; Bianchi et al., 1999).
Nevertheless, the almost coeval Huelmo-Mascardi cold reversal might be also influencing δ15N values, as the mean value from Pleistocene-Holocene transition West is similar to Lama of Holocene East (δ15N mean of 3.4 ‰ and 3.9 ‰, respectively; Table 4), which is described as dryer (see Sect. 3.3.3). This tendency between both sides of the Nahuel Huapi region is also observed in Fig. 3, where values from El Trébol of the Late Pleistocene-Holocene transition are closer to the values from Arroyo Corral from the Holocene (including sample 1634, Table 3). Other proxies, such as the presence of fires due to shrub combustion (Iglesias et al., 2014) and Poaceae increment (Bianchi et al., 1999) have detected the influence of the Huelmo-Mascardi cold reversal in the region.
Consequently, the intermediate δ15N isotopic values between ca. 13,500 to 12,500 cal BP (Fig. 3) might be pointing that the Pleistocene-Holocene transition West might have had an open forest environment, moister than during the Last Glacial Maximum but drier than in Holocene times.
At a preliminar first regional comparison Mylodontinae δ15N values from El Trébol are among the lowest. Not only contrast with Arroyo Corral values, but also with the other Patagonian sites (Fig. 6b). As happens with M. americanum, the high variability in time and space of this isotope registered in Mylodontinae must be further analyzed.
Holocene (10,000 cal BP to present).
Holocene extant species from the West and East shows similar isotopic δ13C values (Fig. 2; Table 4). This confirms the presence of C3 plants, as in the previous time-periods. The correspondence is particular stronger for the Lama samples from both sides of the lake, due to their analogous measurements seen in Fig. 4.
The δ15N isotopic value drops from a mean of 3.4 ‰ in the Pleistocene-Holocene transition West to a mean 0.4 ‰ in the Holocene West given the presence of H. bisulcus, with negative values (Figs. 3, 4; Table 3) probably influenced by its browsing diet. Only the sample ET54 L. guanicoe, dated in 6,376 cal BP (Table 1) with a δ15N value of 3.1 ‰, is higher and is closer to the samples from Arroyo Corral in Fig. 4. Considering the grazing habits of this species (Lezcano et al., 2010), the value of ET54 tentatively suggests the presence of grassland patches into the West by Early Holocene times, as indicated by other proxies. For example, zooarchaeological studies have shown that almost all anatomical units are represented, including those of lesser economic use. This suggests that Lama might have been hunted near the site (Lezcano et al., 2010). Its presence could have been facilitated by the existence of an open forest, and in Late Holocene times, an increase in moisture led to the present-day mixed forest of Nothofagus and Austrocedrus (Iglesias et al., 2014; Whitlock et al., 2006). Consequently, during the Early Holocene, the West-to-East vegetation gradient developed and the steppe/shrubland herbs (Asteraceae, Tubuliflorae and Chenopodiineae) rose (Iglesias et al., 2014; Whitlock et al., 2006) allowing the occupation by humans, guanacos and huemuls.
In Arroyo Corral, the δ15N values fall from a mean of 6.1 ‰ in the Last Glacial Maximum to a mean of 3.9 ‰ after the beginning of the Holocene (Fig. 3; Table 4). The presence of new micromammals such as Irenomys tarsalis, Geoxus valdivianus and Oligoryzomys longicaudatus since Early Holocene is recorded. The first two are from forest habitats, while the third is from brushy areas. This suggests an expansion of tree and shrubland cover (Tammone et al., 2014). The decrease in the abundance of E. chinchilloides and C. sociabilis indicates the decline of open mesic areas (Tammone et al., 2014, 2018). Isotopic values of Ctenomys haigi also suggest the retreat of grasslands at the Late Holocene (Takenaka et al., 2020). Together, these proxies point that despite the ameliorated conditions of the Holocene, the East remained more arid than the West.
Pollen and micromammals proxies along with the isotopic results obtained in this work support a trend towards an increase in moisture and vegetational cover in the Nahuel Huapi Region, which led to the development of the current forested habitat in El Trébol (Bianchi et al., 1999; Iglesias et al., 2014; Whitlock et al., 2006) and to the mosaic grassland with patches of forest in Arroyo Corral I and II (Takenaka et al., 2020; Tammone et al., 2014, 2018).
Conclusions
Isotopic values from extinct and extant species from the Nahuel Huapi Region preliminarily underscore the evolution of the paleoenvironment of this region during the last ca. 20,000 cal BP. δ13C values reflect a coverage of C3 plants through the entire period for species with different dietary preferences, while δ15N values might be showing the changing conditions of the landscape. During Last Glacial Maximum, glacial and dry conditions were dominant. By these times, both M. americanum and Mylodontinae were present in the region, being adapted to low temperatures and a barren rocky and open herbaceous landscape. The presence of one individual of M. americanum in the shore of Nahuel Huapi lake at the time that the glacial tongue was present extends the paleoecological information of this species, which was mostly identified in the Quaternary of the Pampean region. After ca. 14,500 cal BP, moister conditions and the presence of Mylodontinae were registered in El Trébol. Almost two millennia latter, first humans signs exploiting Mylodontinae, Hippocamelus sp. and other species were registered in this rock shelter, during the Huelmo-Mascardi cold event. Mylodontinae individuals adapted to these changing conditions, in contrast with those living in the Last Glacial Maximum. The Mylodontinae community was present in the Nahuel Huapi Region during arid and cold/humid and warm phases, coexisting with M. americanum at Last Glacial Maximum and humans in the transition with the Holocene.
Through Holocene times, after an arid pulse, the current landscape developed in El Trébol. The humid trend that started with the transition also affected Arroyo Corral I and II, but the region maintained an open landscape. Humans dispersed also during this period and megafauna went extinct from the region. Results obtained coincide in general terms with other proxies from this region.
New AMS dates of paleontological levels from Arroyo Corral and El Trébol frame the chronology of the isotopic values, clearing the long-term occupations of extinct species during Late Pleistocene times. New dates from El Trébol also reflect the fast dispersal of Mylodontinae after the emersion of the cave, along with plant pioneers as suggested by other proxies.
This work expanded the isotopic information of the North Patagonian region for the last 20,000 cal BP, integrating paleontological and archaeological records along with other environmental information. Future works will deepen into the South American Southern cone information presented here, specially to understand the variability of δ15N stable isotope in giant ground sloths. At the end, regional isotopic studies will contribute to decipher long-term changes in environmental and biotic conditions that might have influenced the extinction of the large mammals and megafauna as well as the human dispersal into the South American southern cone.
Acknowledgements
Thanks to the Museo Arqueológico y Paleontológico de Bariloche (Dr. Ari Iglesias) for allowing access to the collection. To Sonia Lanzelotti, Gustavo Buzai and Eloy Montes Galbán for their comments on the map (Figure 1).
Funding
Partial financial support was received from the Sepkoski Grant 2020 (Paleontological Society International Research Program) and PICT PICT-2019-2019-02167/ PICT-2019-IV-A (FONCYT-MINCYT) for dating and isotopic analyses.
Declarations
Conflict of interest
The authors have no relevant financial or non-financial interests to disclose. They declare that they have no conflict of interest.
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