FIRST AMS RADIOCARBON DIRECT DATES ON BONES FROM EXTINCT MEGAFAUNA IN CAMET NORTE (SANTA CLARA DEL MAR, BUENOS AIRES PROVINCE, ARGENTINA) MaRTIN COTTE1 FRaNCISCO J. PREVOSTI2 IRKa HaJDaS3 PaBLO STRaCCIa4,5 DaNIEL SCIaN4 LEOPOLDO SOIBELZON6 HERVÉ BOCHERENS1,7
Department of Geosciences, Biogeology, University of Tübingen, Hölderlinstrasse 12, 72070 Tübingen, Germany. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR), Provincia de La Rioja, UNLaR, SEGEMAR, UNCa, CONICET, Entre Ríos y Mendoza s/n, 5301 - Anillaco, La Rioja, Argentina. 3 Laboratory of Ion Beam Physics, ETH, Otto-Stern-Weg 5, 8093 Zurich, Switzerland. 4 Museo Municipal de Ciencias Naturales Pachamama, Santa Clara del Mar, Argentina. 5 Universidad Nacional de Mar del Plata, Argentina. 6 Division Paleontología Vertebrados, Museo de La Plata (UNLP), Paseo del Bosque, 1900 La Plata, Argentina. 7 Senckenberg Research Center for Human Evolution and Paleoenvironment, University of Tübingen, Hölderlinstrasse 12, 72074 Tübingen, Germany. 1 2
Submitted: November 23rd, 2016 - Accepted: March 31st, 2017 - Published online: april 10th, 2017
To cite this article: Martin Cotte, Francisco J. Prevosti, Irka Hajdas, Pablo Straccia, Daniel Scian, Leopoldo Soibelzon, and Hervé Bocherens (2018). First aMS radiocarbon direct dates on bones from extinct megafauna in Camet Norte (Santa Clara del Mar, Buenos aires Province, argentina). Ameghiniana 55: 126–133. To link to this article: http://dx.doi.org/10.5710/aMGH.31.03.2017.3072
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PALEONTOLOGICAL NOTES
AMEGHINIANA - 2018 - Volume 55 (1): 126 – 133 ISSN 0002-7014
FIRST aMS RaDIOCaRBON DIRECT DaTES ON BONES FROM EXTINCT MEGaFauNa IN CaMET NORTE (SaNTa CLaRa DEL MaR, BuENOS aIRES PROVINCE, aRGENTINa) MARTIN COTTE1, FRANCISCO J. PREVOSTI2, IRKA HAJDAS3, PABLO STRACCIA4,5, DANIEL SCIAN4, LEOPOLDO SOIBELZON6, AND HERVÉ BOCHERENS1,7 1 2
Department of Geosciences, Biogeology, University of Tübingen, Hölderlinstrasse 12, 72070 Tübingen, Germany.
[email protected]
Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR), Provincia de La Rioja, UNLaR, SEGEMAR, UNCa, CONICET,
Entre Ríos y Mendoza s/n, 5301 - Anillaco, La Rioja, Argentina.
[email protected]
3 4 5 6 7
Laboratory of Ion Beam Physics, ETH, Otto-Stern-Weg 5, 8093 Zurich, Switzerland.
[email protected] Museo Municipal de Ciencias Naturales Pachamama, Santa Clara del Mar, Argentina. Universidad Nacional de Mar del Plata, Argentina.
[email protected]
Division Paleontología Vertebrados, Museo de La Plata (UNLP), Paseo del Bosque, 1900 La Plata, Argentina.
[email protected]
Senckenberg Research Center for Human Evolution and Paleoenvironment, University of Tübingen, Hölderlinstrasse 12, 72074 Tübingen, Germany.
[email protected]
Key words. AMS radiocarbon dates. Late Pleistocene. Pre-LGM. South America.
Palabras clave. Fechados radiocarbónicos AMS. Pleistoceno tardío. Pre-LGM. América del Sur.
SOuTH america is the continent most affected by the
megafauna extinction around the Pleistocene/Holocene
transition (Stuart, 2015). The province of Buenos aires,
Prado et al., 2015). The number of taxon dates is very limited
even in comparison with that of other parts of South ame-
rica such as southern Patagonia (e.g., Metcalf et al., 2016).
argentina, has one of the most informative Pleistocene
The low number of taxon dates limits the possibility of
large bodied mammals at the beginning of the Holocene,
tinction of these mammals. Increasing the number of direct
fossil records of the continent; it recorded the demise of when all the mega mammals and about 80% of the large
mammals became extinct (e.g., Politis and Messineo, 2008; Cione et al., 2009; Steele and Politis, 2009; Prevosti and Schubert, 2013; Politis and Steele, 2014; Prado et al., 2015).
Nearly all of them were adapted to the predominant open
areas related to the dry and cold climates of the late Qua-
testing competing or alternative hypotheses about the exradiocarbon dates for the late Quaternary megafauna fossils
from South america is crucial to advance the debate on
climate versus humans as main actors in the Pleistocene extinction (Barnosky et al., 2004; Cione et al., 2009).
The chronological context of most megafaunal bones
from the latest Pleistocene is established through indirect
ternary (Cione et al., 2009).
methods. Therefore, the chronology of Quaternary paleon-
change and human colonization of South america had on
through biostratigraphic studies; many of the available ra-
However, understanding the relative impact that climate
tological sites in the Pampean region is mainly constructed
extinction is difficult. a low number of reliable direct ra-
diocarbon dates were obtained from organic matter and
corresponding to strong climatic oscillations and human
the rich fossil mammal site of Camet Norte. It has been ten-
diocarbon dates for megafaunal bones during the period
immigrations, from around 30,000 to 10,000 years ago,
poses a problem even if some progress has been made
during the last decade (e.g., Barnosky and Lindsey, 2010;
126
molluscan shells (Scanferla et al., 2013). This is the case of tatively dated to the time around the Last Glacial Maximum (approximately 29,000–15,000 14C BP; Denton et al., 1999;
Clark et al., 2009) with Pardiñas et al. (1998) reporting a date aMGHB2-0002-7014/12$00.00+.50
COTTE ET AL.: RaDIOCaRBON aMS DaTES FROM CaMET NORTE
of 24,550 ± 600 years 14C BP produced from herbivore dung
was originally interpreted as a freshwater paleo-lagoon
± 60 14C BP years for the tooth enamel of a Stegomastodon.
et al. (1984), all bones come from level B of the site, which
and alberdi and Prado (2008) giving an aMS date of 17,880 Therefore, the Camet Norte site is of special interest for the discussion about the possible impact of climate change
on Megafauna in South america. Here, we present the first aMS dates on bone collagen from the late Pleistocene
near the coastline (Fasano et al., 1984). according to Fasano
is a clayey silt and clay deposit of greenish color with a thin and convolute lamination. The sampled specimens were
eroded out of the cliff comprising level B and can be associated with this level. However, a clear ascription to any
fossil site of Camet Norte.
position within level B is impossible. Level B of Fasano et al.
MATERIALS
meters 0.25 to 1.45 in the profile (Fig. 1).
Twenty-two bones from the Camet Norte site were
sampled. The bones are part of the collection of Museo Mu-
(1984) corresponds approximately to the height between Collagen preservation was expected to be good as her-
bivore dung was well preserved. The dung was successfully
nicipal de Ciencias Naturales Pachamama (Santa Clara del
radiocarbon dated at 24,550 ± 600 BP by Pardiñas et al.
Camet Norte is located in the community of Santa Clara
were used in a paleo-ecological investigation with stable
Mar, Buenos aires Province, argentina). The fossil site of del Mar, approximately 20 km north of Mar del Plata in the
Province of Buenos aires in argentina. Previous publications
(1998). Of the 22 sampled bones, ten yielded collagen and isotope tracking (Bocherens et al., 2016) and, among those, four were used for dating. The dated samples encompass
described the stratigraphy and the fauna found in this site
various bones from taxa that became extinct at the end of
(Pardiñas et al., 1998; alberdi and Prado, 2008). The lithos-
al., 2009): they include a vertebra from the sabre-toothed
(e.g. Fasano et al., 1984) and included some dating attempts
the Pleistocene or the beginning of the Holocene (Cione et
tratigraphy and sedimentary structures of the site were
cat Smilodon populator, two specimens from large bodied
diñas et al. (1998), and are associated with finely laminated,
and a Toxodon humerus, and a pelvic bone from the large
described in some detail by Fasano et al. (1984) and Pargreenish sediments exposed in the local sea cliffs. The site
and endemic ungulates, specifically a Macrauchenia fibula armoured armadillo relative Glyptodon.
Figure 1. Location map showing the Camet Norte locality and a stratigraphic profile of the coastal cliffs at the site.
127
aMEGHINIaNa - 2018 - Volume 55 (1): 126 – 133
METHODS
quent reliability of dates were verified by using the bone
previously used for the paleo-ecological investigation of
(%C), nitrogen (%N) content and their resulting elemental
The collagen used for this study is the same that was
powder nitrogen (Nt) content as well as the collagen carbon
Bocherens et al. (2016). The sampling was conducted using
ratios C/N. The ratios were calculated as atomic ratios.
pieces of bone, all of which range between 0.4 and 1.9
analyzer NC 2500 at the Isotopic Geochemistry unit of the
a rotary tool with a circular diamond-coated blade. Small
grams, were sawn out. The bone fragments were treated using the protocol described in Bocherens et al. (1997a).
To clean the pieces from remaining soil, they were washed
These measurements were conducted with an elemental
Department of Geosciences at the university of Tübingen (Germany).
Four of the ten samples that yielded collagen were
with acetone in an ultrasonic bath and then rinsed and
dated using an aMS radiocarbon dating. The radiocarbon
temperature and then crushed and sieved using a 0.7 mm
at Eidgenössische Technische Hochschule—ETH in Zurich
washed with distilled water. The bones were dried at room
mesh (Bocherens et al., 1997a). To assess the degree of
dating was performed by the Labor für Ionenstrahlphysik (Switzerland). The obtained radiocarbon ages were cali-
collagen preservation, a subsample of each specimen was
brated using the OxCal v4.2.4 software with the atmos-
done using a Vario EL III elemental analyzer with Sulfanilic
were modelled in a sequence model including existing
analyzed for its nitrogen content (%N). The analysis was
acid from Merck as an internal standard. The mean standard
errors for %N were better than 0.05%. The elemental analysis was performed at the Laboratory for Soil Science and
Geoecology of the Department of Geosciences at the uni-
pheric curve ShCal13 (Hogg et al., 2013). These results
dates for the site, and a combination model was done for
the new aMS dates to test the contemporaneousness hypothesis.
versity of Tübingen (Germany).
RESULTS
those with a nitrogen content of between 0.4% and 4%
dating, as well as the calibration, were summed up in Table
Samples that promised good collagen preservation—
The elemental analysis results and the radiocarbon
(Bocherens et al., 2005)—underwent collagen purification.
1. all radiocarbon dated collagen exhibited an excellent
the protocol described in Bocherens et al. (1997a). The bone
%C and %N ranged from 38.9% to 45.0% and from 13.5% to
The collagen was extracted from the samples following
powder obtained from crushing the bones was decalcified
preservation. as measured by the elemental analysis, the 14.9%, respectively (Tab. 1). all the C/N ratios are within the
in approximately 40 ml of 1 M HCl at room temperature.
normal range and the amount of dated carbon is of at least
and the residue was soaked for 20 hours in approximately
ages can be considered reliable. The aMS radiocarbon
were filtered again using a 5 µm millipore filter. For gela-
to 24,730 ± 110
tubes with a 0.01 M HCl (pH 2) solution and cooked at
from 27,936–27,561 cal. BP to 28,988–28,440 cal. BP
using a 5 µm millipore filter and then collected in closed
The combination model for the four new aMS samples
Next, the samples were filtered using a 5 µm millipore filter 40 ml of 0.125 M NaOH at room temperature. The samples
tinization, the remaining residue was collected in closed
100°C for 17 h. The sample solution was filtered again
1 mg for each collagen (Tab. 1). Therefore, all radiocarbon
dates obtained narrowly ranged from 23,690 ± 100 14C BP 14
C BP. The calibration was performed
with two standard deviations. The calibrated ages ranged (Fig. 2).
glass vials. The filtrate was freeze-dried. In their studies,
yielded a modelled age of 28,718 cal. BP to 28,391 cal. BP.
1999) showed that elemental carbon/nitrogen ratios (C/N)
ETH-57490 (27,936 cal. BP to 27,561 cal. BP) failed a X²
DeNiro (1985) and others (e.g., ambrose, 1990; van Klinken,
lower than 2.9 or higher than 3.6 are indicative of alterations
and contamination in the collagen. Similarly, bones with a
nitrogen content of less than 0.7% were shown to not yield
sufficient collagen for a C aMS dating (Brock et al., 2012). 14
Thus, the quality of the extracted collagen and the conse-
128
The model detected an outlier though. The Toxodon sample test (p
