Journal of Biogeography (J. Biogeogr.) (2007) 34, 1642–1646
CORRESPONDENCE
Early Holocene survival of
megafauna in South America
Comments on Steadman, D.W., Martin, P.S.,
MacPhee, R.D.E., Jull, A.J.T., McDonald,
H.G., Woods, C.A., Iturralde-Vinent, M. &
Hodgins, G.W.L. (2005) Asynchronous extinction of late Quaternary sloths on continents and islands. Proceedings of the
National Academy of Sciences USA, 102,
11763–11768.
The debate over the causes of the Pleistocene megafaunal extinction dates back to
the early 19th century (Grayson, 1984),
and continues to generate considerable
controversy (e.g. Grayson & Meltzer,
2003; Araujo et al., 2004; De Vivo &
Carmignotto, 2004; Fiedel & Haynes,
2004; Burney & Flannery, 2005; Wroe
et al., 2006). Typically, protagonists in
this debate can be classified into two
groups. One group argues that Late
Pleistocene megafaunal extinctions were
primarily caused by direct and indirect
human action through hunting, habitat
modification or introduction of new
predators (Burney & Flannery, 2005,
2006; Barnosky et al., 2004; Fiedel &
Haynes, 2004). The other interpretation
is that humans had at most a minor role
in the megafaunal extinction, and that the
loss was attributable principally to a climatic cause (Ficcarelli et al., 2003; Grayson & Meltzer, 2003, 2004; Barnosky
et al., 2004; De Vivo & Carmignotto,
2004; Boeskorov, 2006; Guthrie, 2006;
Wroe et al., 2006; Wroe & Field, 2006).
Here we contest the position of Steadman et al. (2005), who favour the overkill
hypothesis to explain the ground sloth
extinction in the Americas. Although
making an important contribution to the
debate on extinction of the New World
megafauna, Steadman et al. (2005) make
some important assumptions in their
analysis.
Steadman et al. (2005) argue that the
extinction of ground sloths in the New
1642
World was concomitant with, and a
consequence of, the human occupation of
the Americas. Their argument is twofold. First, the radiocarbon dates (14C)
accepted by them for the last appearance
dates (LADs) of these animals roughly correspond to megafaunal extinction dates in
South and North America and the West
Indies. These dates coincide with the human
colonization of these regions and they argue
that this supports the thesis that human
arrival caused extinction of the ground
sloth. Second, according to Steadman et al.,
extinctions caused by climatic fluctuation
would result in concomitant LADs across
the entire continent and associated islands,
as they viewed these fluctuations as being
widespread and uniform, whilst they found
that the LADs for the West Indies, around
4400 14C yr BP [c. 4800–5050 calibrated
years before present (cal. BP); dates calibrated with CALIB 5.0, Stuiver et al., 2005],
are much younger than those found in the
continent (c. 11,000 14C yr BP; c. 12,880–
12,950 cal. BP for North America and
c. 10,500 14C yr BP; c. 12,390–12,640 cal. BP
for South America).
We contend that the chronological data
presented by Steadman et al. (2005) are
incomplete, especially when considering
South America. While Steadman et al.
(2005) suggest that there are no acceptable Holocene LADs for ground sloths, a
large number of Holocene dates generated through direct dating of bone and
dung remains are indeed available in the
literature. Barnosky et al. (2004; supporting material) revised the radiocarbon
dates available for megafaunal remains
throughout the world. In South America,
they listed four articles with remains of
megafauna dated within the Holocene,
based both on direct and indirect dates.
Even when considering only the results
based on direct dates of bone remains,
sufficient evidence still supports Holocene
LADs for subequatorial ground sloths.
For instance, from Argentina, Borrero
et al. (1998) presented a total of seven 14C
dates consistent with a Holocene survival of
www.blackwellpublishing.com/jbi
doi:10.1111/j.1365-2699.2007.01744.x
megafauna, albeit two of these ages are
potentially unreliable, and four were
obtained from one single specimen (indeed,
one of the unreliable dates comes from this
specimen; Table 1). Other reports not
included in Barnosky et al. (2004) provide
two direct radiocarbon ages of megafaunal bone remains from central Brazil at
the
Pleistocene⁄Holocene
boundary
(Table 1; Neves & Piló, 2003; Araujo
et al., 2004). Politis et al. (2004; also not
included in Barnosky et al., 2004) presented two additional Holocene direct
radiocarbon ages of Megatherium americanum (Blumenbach) specimens (Table 1)
and a third one from the Holocene⁄Pleistocene boundary (10,190 120 14C yr BP;
c. 11,820–12,020 cal. BP; Table 1), all in
Argentina; and Marshall et al. (1984; also
not included in Barnosky et al., 2004)
reported a single Holocene age of
8910 200 14C yr BP (c. 9780–10,150 cal.
BP; GIF-4116) of a Scelidodon chiliensis
(Lydekker) in Peru (Marshall et al., 1984;
Pujos & Salas, 2004).
Four of the sites where these dates were
obtained are located in Argentina, while two
are located in central Brazil and the last in
Peru (Fig. 1). All the Argentinean sites
(Arroyo Seco 2, La Moderna, Campo
Laborde and Paso Otero 5) are open-air
archaeological sites, i.e. the megafaunal
remains are associated with prehistoric
human occupations (see Borrero et al.,
1998; Politis et al., 2004 for detailed
descriptions). Arroyo Seco 2 is interpreted as a base camp where a large
variety of activities were undertaken
(Politis et al., 2004), including the
exploitation of ground sloths and other
megafauna by humans. However, Borrero et al. (1998) and Politis et al. (2004)
do not state clearly if the two specimens
(M. americanum and Equus neogeus Lund)
that dated to the Holocene (Table 1)
showed marks of human manipulation.
The remaining open-air sites are believed
to be sites used for specific activities
(Politis et al., 2004): La Moderna is
interpreted as an occasional megafaunal
ª 2007 The Authors
Journal compilation ª 2007 Blackwell Publishing Ltd
Journal of Biogeography 34, 1642–1646
ª 2007 The Authors. Journal compilation ª 2007 Blackwell Publishing Ltd
*Dates obtained from one single specimen. Considered problematic by Politis et al. (2004) due to the difference observed between the dates obtained.
Dates obtained from one single specimen.
àConsidered problematic by Borrero et al. (1998).
Marshall et al. (1984)
Neves & Piló (2003)
Neves & Piló (2003)
Borrero et al. (1998)
Borrero et al. (1998)
Borrero et al. (1998)
Politis et al. (2004)
Borrero et al. (1998)
Borrero et al. (1998)
Borrero et al. (1998)
Borrero et al. (1998)
Politis et al. (2004)
Politis et al. (2004)
Garcia (2003)
Long et al. (1998)
Politis et al. (2004)
?
AMS
AMS
AMS
Standart
AMS
AMS
Standart
AMS
AMS
AMS
AMS
AMS
?
Standart
AMS
c. 9780–10,150
c. 10,260–10,480
c. 11,320–11,600
c. 9740–10,150
c. 9290–9440
c. 8020–8160
c. 13,980–14,140
c. 7330–7470
c. 7700–7840
c. 8200–8340
c. 8180–8320
c. 8780–9010
c. 8420–8540
c. 9920–10,190
c. 10,680–10,860
c. 11,820–12,020
8910 200
9260 150
9990 40
8890 90
8390 240
7320 50*
12,200 170*
6555 160 à
7010 100 7510 370 7460 80 8080 200
7750 250
8990 90
9560 90
10,190 120
GIF-4116
BETA-174722
BETA-165398
TO-1504
LP-53
TO-1506
CAMS-58182
BETA-7824
TO-1507-1
TO-1507-2
TO-2610
AA-55118
AA-55117
LP-925
GrN-5772
AA-19291
Pampa de los Fósiles
Escrivânia 5
Gruta Cuvieri
Arroyo Seco 2
Arroyo Seco 2
Arroyo Seco 2
Arroyo Seco 2
La Moderna
La Moderna
La Moderna
La Moderna
Campo Laborde
Campo Laborde
Gruta del Indio
Gruta del Indio
Paso Otero 5
Bone
Bone
Bone
Bone
Bone
Bone
Bone
Bone
Bone
Bone
Bone
Bone
Bone
Dung
Bone
Bone
Scelidodon chiliensis
Smilodon populator (Lund)
Catonyx cuvieri
Equus neogeus
Megatherium americanum
Megatherium americanum
Megatherium americanum
Doedicurus clavicaudatus
Doedicurus clavicaudatus
Doedicurus clavicaudatus
Doedicurus clavicaudatus
Megatherium americanum
Megatherium americanum
Sloth
Sloth
Megafauna
Peru
Brazil
Brazil
Argentina
Argentina
Argentina
Argentina
Argentina
Argentina
Argentina
Argentina
Argentina
Argentina
Argentina
Argentina
Argentina
Age (yr
Site
Sample
Taxa
Country
Laboratory
number
Table 1 Late Pleistocene⁄Early Holocene radiocarbon dates obtained for South American megafaunal specimens.
BP)
Two sigma
calibration
(cal. BP)
Technique
References
Correspondence
processing site, where the remains of a
single glyptodont (Doedicurus clavicaudatus Owen) dated to the Holocene (Table 1)
were recovered; Campo Laborde presents
evidence that it was used as a hunting and
processing site for ground sloths
(M. americanum; Table 1); and Paso
Otero 5, was also identified as a hunting
and processing site for local megafauna.
The two Brazilian sites, in contrast, are
exclusively palaeontological, i.e. they are not
associated with human occupations, and are
located in limestone caves in the karstic
region of Lagoa Santa. Gruta Cuvieri is a
cave where three vertical chambers functioned as natural traps for the now extinct
megafauna and other animals. The only
megafauna species found so far is Catonyx
cuvieri (Lund), a medium-sized ground
sloth. The Holocene date presented in
Table 1 was obtained from one of these
ground sloths, found at the surface of one
of the chambers. The other Brazilian site,
Escrivânia 5, is part of a complex of
caves, generically referred to as Escrivânia, representing one of the richest palaeontological limestone outcrops known
at Lagoa Santa. Together with tons of
animal fossil bones, in one of the chambers (Escrivânia 3) an almost complete
human skeleton was also recently recovered, dated to 7650 80 14C yr BP
(c. 8370–8420 cal. BP; Beta 174734).
The Peruvian site, Pampa de los Fósiles, is
also a palaeontological site located in the
Cupisnique Desert. Several archaeological
sites in the region have revealed no evidence
of human interaction with the megafauna in
the region (Pujos & Salas, 2004).
In addition to these reported dates,
Steadman et al. (2005; supporting material) disqualified two other Holocene dates
as unreliable (they also rejected a third
date, but it has a very large margin of
error). These were the only Holocene
dates found in their bibliographical revision and they Ôhave means that are up to
1000 years younger than means of any [of
the accepted LADs] [Supplementary online
material]Õ. As 10 reliable Holocene direct
radiocarbon dates for megafauna are described here, there is no further reason to
reject the dates of 8990 90 14C yr BP
(c. 9920–10,190 cal. BP; LP-925; Garcia,
2003) and 9560 90 14C yr BP (c. 10,680–
10,860 cal. BP; GrN-5772; Long et al.,
1998) as unacceptable outliers. These two
dates are from an Argentinean site, Gruta
del Indio (Fig. 1; see Long et al., 1998;
Garcia, 2003 for detailed descriptions).
This site is a rockshelter, and although it
1643
Correspondence
Figure 1 Archaeological and palaeontological sites in South America presenting
direct Late Pleistocene⁄Early Holocene radiocarbon (14C) dates for megafaunal remains.
Circles represent sites with no evidence of human exploitation of the megafaunal remains,
whereas triangles represent sites with evidence of human exploitation of megafauna. 1, Gruta
Cuvieri; 2, Escrivânia 5; 3, Gruta del Indio; 4, La Moderna; 5, Campo Laborde; 6, Arroyo
Seco 2; 7, Paso Otero 5; 8, Pampa de los Fósiles.
presents
chronological
information
placing humans together with megafauna
in time, there is no evidence of humans
exploiting the local megafauna (Long
et al., 1998; Garcia, 2003).
As presented in Table 1, from the 14
existing Holocene dates we found for
megafaunal remains in South America
eight are derived from ground sloths,
which severely weakens the position of
Steadman et al. (2005), that there are no
acceptable Holocene LADs for ground
sloths in the Americas. Assuming that
human groups already inhabited South
America around 12,500 14C yr BP
(c. 14,300–14,950 cal. BP; Dillehay, 2000),
the argument that the ground sloth LADs
were concomitant with the human arrival
in the New World can no longer be
accepted, at least not as an immediate
phenomenon.
The second argument presented by
Steadman et al. (2005) is that the apparent
1644
delay observed in the LADs of Central
America islands, when compared with the
continental ones, favours the overkill
hypothesis. Delayed LADs in insular
regions have been found in other parts
of the world, independent of human presence (Guthrie, 2004; Boeskorov, 2006).
Boeskorov (2006) showed that in northern
Eurasian islands, megafauna survived into
the Holocene, e.g. the mammoths of
Wrangel Island. Nonetheless, the extinction
of megafauna in Eurasia as a whole is
believed to be primarily due to climatic
changes (Barnosky et al., 2004; Boeskorov,
2006), particularly because no human
presence is found in the Wrangel Islands
until well after the extinction of the
megafauna (Boeskorov, 2006). Although
these data do not peremptorily disqualify
SteadmanÕs argument, they do bring into
question whether the overkill hypothesis
is the most parsimonious explanation for
megafaunal extinctions.
Finally, it must be emphasized that there
is a general lack of evidence of sloth remains
in archaeological contexts in the Americas as
a whole (but see Politis et al., 2004 for an
exception), which also speaks against the
overkill hypothesis. Specifically, in Lagoa
Santa, despite the excavation of dozens of
archaeological sites dated to the Pleistocene⁄Holocene transition (showing human
evidence as old as 11,000–11,500 14C yr BP;
c. 12,880–13,400 cal. BP; Neves et al.,
1999), evidence is lacking of megafaunal
use by humans, either as a source of food
or raw material (Kipnis, 1998; Prous &
Fogaça, 1999). In North America, a
similar situation is observed. According
to Grayson & Meltzer (2003), there are
only two genera of megafauna (Mammuthus Burnett, 1830 and Mammut Blumenbach, 1799) known to have been hunted
by humans during the Clovis period
(Grayson & Meltzer, 2003). This scenario is accepted even by Fiedel &
Haynes (2004), strong defenders of the
overkill hypothesis. Thus, at least in
South America (and most probably in
North and Central America as well), the
idea that ground sloths went extinct due
to overkill lacks archaeological support.
In conclusion, the ground sloth overkill
hypothesis, as defended by Steadman et al.
(2005), is not sufficiently supported in the
empirical world. As we have briefly
pointed out: (1) a considerable number of
reliable Holocene dates for megafaunal
specimens in South America already exist,
including for ground sloths; (2) the
existence of late megafaunal LADs in
Central America islands can be equally
well explained through overkilling or
environmental changes; and (3) the general lack of megafaunal killing sites and
megafaunal remains in archaeological
contexts is inconsistent with the overkill
hypothesis. Nonetheless, it is important to
emphasize that the amount of information regarding the presence of megafauna
in archaeological sites is still too small to
be considered as strong evidence against
human predation of megafauna, and thus
this piece of information must be interpreted as complementary to the others.
Collectively, the data presented here are
more consistent with a model explaining
megafaunal extinction through climatic
fluctuations, although in South America the
poor chronological contextualization of the
megafaunal decline does not yet allow for a
percentage estimate of megafaunal genera
that survived until human arrival. In North
America (Grayson & Meltzer, 2002,
Journal of Biogeography 34, 1642–1646
ª 2007 The Authors. Journal compilation ª 2007 Blackwell Publishing Ltd
Correspondence
2003) and in Australia (Wroe et al., 2006;
Wroe & Field, 2006), this percentage
seems to have been small, suggesting that
the megafaunal extinction was a protracted process, beginning much earlier
than the human settlement of these continents. Such a decline may have been the
case in South America, as only a few
megafaunal genera apparently survived
until the Holocene. While a human presence could have accelerated the process
of extinction of the remaining megafaunal genera, climatic fluctuations could
also have been responsible. Araujo et al.
(2005) suggested a period of drought
during the mid-Holocene in central Brazil, based on a general abandonment of
the region by humans and also on palaeoenvironmental data. At least for central Brazil, megafaunal extinction could
thus be also explained by the dry period
that started between 8500 and 7500 14C
yr BP (c. 9520–8190 cal. BP). Furthermore,
according to Araujo et al. (2005) several
authors recognize the existence of dry
climatic periods during the early and midHolocene in South America. Bush et al.
(2005) also found evidence suggesting the
existence of this drier period in the Andes
region (between 0 and 24), although in
this case it was not a single or synchronous
event. Even if asynchronous, the important
point here is that this dry period seems to
have been a widespread phenomenon in
South America. Thus, we concur with
Borrero et al. (1998, p. 197) who propose
that Ôpeople played at most a secondary role
in the mega mammal extinctions, perhaps
accelerating a process already underway
before human arrival in South AmericaÕ.
ACKNOWLEDGEMENTS
We would like to thanks Rodolfo Salas for
his kindness in assisting us in determining
the Holocene date in Peru. Our long-term
research in Lagoa Santa is funded by FAPESP (grant 04⁄01321-6) and by scholarships
given to AH (FAPESP 04⁄11485-6), MH
(FAPESP 04⁄01253-0) and to WAN (CNPQ
305918⁄85-0).
A . H u b b e 1 * , M . H u b b e 2 and
W. Neves1
1
Laboratório de Estudos Evolutivos
Humanos, Departamento de Genética e
Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, Rua do
Matão, 277, 05508-090 São Paulo SP
Brazil
*
E-mail: [email protected]
2
Instituto de Investigaciones Arqueológicas y
Museo, Universidad Católica del Norte,
Calle Gustavo LePaige, 380, 141-0000
San Pedro de Atacama Chile
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BIOSKETCHES
Alex Hubbe is a graduate student at the Laboratory for Human Evolutionary Studies, Instituto de Biociências, Universidade de São Paulo.
His main interests are the palaeoecology and extinction of the South America megafauna.
Mark Hubbe is an investigator at the Instituto de Investigaciones Arqueológicas y Museo, Universidad Católica del Norte, Chile. His main
research interest is the origin and dispersion of the First Americans.
Walter Neves is the coordinator of the Laboratory for Human Evolutionary Studies, Instituto de Biociências, Universidade de São Paulo.
His main research interest is the origins and adaptations of the First Americans.
Editor: Mark Bush
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Journal of Biogeography 34, 1642–1646
ª 2007 The Authors. Journal compilation ª 2007 Blackwell Publishing Ltd