Cite this article: Farin
˜a RA, Tambusso PS, Varela
L, Czerwonogora A, Di Giacomo M, Musso M
Bracco R, Gascue A. 2014 Arroyo del Vizcaı
Uruguay: a fossil-rich 30-ka-old megafaunal
locality with cut-marked bones. Proc. R. Soc. B
Received: 23 August 2013
Accepted: 25 October 2013
megafauna, South America, Quaternary,
taphonomy, bonebed, peopling
Author for correspondence:
Richard A. Farin
Electronic supplementary material is available
at http://dx.doi.org/10.1098/rspb.2013.2211 or
Arroyo del Vizcaı
´no, Uruguay: a fossil-rich
30-ka-old megafaunal locality with
Richard A. Farin
˜a1, P. Sebastia
´n Tambusso1, Luciano Varela1,
Ada Czerwonogora1, Mariana Di Giacomo1, Marcos Musso2,
Roberto Bracco3and Andre
´a, Facultad de Ciencias, Universidad de la Repu
´4225, 11400 Montevideo, Uruguay
´cnica, Facultad de Ingenierı
´a, Universidad de la Repu
´blica, Julio Herrera y Reissig 565,
11300 Montevideo, Uruguay
´n Nacional de Arqueologı
´tedra de Radioquı
´mica, Facultad de Quı
Universidad de la Repu
´blica, Gral. Flores 2124, 11200 Montevideo, Uruguay
Centro Universitario Regional Este, Universidad de la Repu
´blica, Burnett casi M. Chiossi (Campus Municipal ),
20000 Maldonado, Uruguay
Human–megafauna interaction in the Americas has great scientific and ethi-
cal interest because of its implications on Pleistocene extinction. The Arroyo
´no site near Sauce, Uruguay has already yielded over 1000 bones
belonging to at least 27 individuals, mostly of the giant sloth Lestodon. The
assemblage shows some taphonomic features suggestive of human presence,
such as a mortality profile dominated by prime adults and little evidence of
major fluvial transport. In addition, several bones present deep, asymmetri-
cal, microstriated, sharp and shouldered marks similar to those produced by
human stone tools. A few possible lithic elements have also been collected,
one of which has the shape of a scraper and micropolish consistent with
usage on dry hide. However, the radiocarbon age of the site is unexpectedly
old (between 27 and 30 thousand years ago), and thus may be important for
understanding the timing of the peopling of America.
The South American Pleistocene megafauna  includes spectacular, taxonomi-
cally unique assemblages of many giant-sized species whose extinction has been
attributed to human arrival in the past millennia of the Pleistocene . Here, we
account for the megafaunal site of Arroyo del Vizcaı
´no, which had been prelimina-
rily dated to about 30 thousand years ago (hereafter, ka) . Some fossils were
collected when the site was first discovered during a severe drought in January
1997. More rigorous excavations had to wait until permission was obtained from
´n del Patrimonio Cultural de la Nacio
´n and the weather conditions
became favourable. The results of two field seasons, undertaken in late March
2011 and in late January to early February 2012, are also reported here.
(b) Geological setting
The site (figure 1a) is formed by a streambed in a place where the stream becomes
deeper, forming a natural pond on a substrate of a Cretaceous silicified sandstone
(Mercedes Fm.) . The sediments were exposed in an area of about 30 m
basin delimited by the Mercedes Fm. (figure 1b). Three beds were identified. Bed 1
is a greenish muddy sand bed that is more than 0.60 m thick and lies unconform-
ably upon the Mercedes Fm. in the central, deeper part of the basin. Bed 2 is a richly
fossiliferous layer that is 0.60– 0.80 m thick, conformably overlying bed 1 and
fining upwards (see electronic supplementary material, figure S3) from a greenish
muddy sandy gravel (facies a) to a brownish muddy sand (facies b), with
&2013 The Author(s) Published by the Royal Society. All rights reserved.
polymictic (K-feldspar-quartz pegmatite, quartz, reworked
sandstones) clasts. Igneous clasts are angular to subangular
and reworked sandstone clasts are angular to rounded. Two
facies can be observed in bed 2, related with an upward shift
in coloration from green (facies a) to brown (facies b), which
may be due to slightly different sedimentary conditions or per-
haps differential postdepositional oxidation events. The
morphology of bed 2 is compatible with a fluvial system deposit
. Finally, bed 3, which unconformably overlies bed 2, shows
variable thickness (0.20– 1 m) and is composed of reworked bed
2 sediments mixed with modern stream alluvium, mainly fine
sand and clayey silt.
Bed 2 is the main source of the remains studied here,
although some reworked elements are found in bed 3.
2. Material and methods
(a) Geology and age
Standard descriptive methods were followed for the geological
setting . Seven additional samples , including purified and
non-purified bone collagen and wood , were radiocarbon
dated. See the electronic supplementary material for further details.
All the specimens were identified and counted. The biostrati-
nomical characterization of the vertebrate assemblage follows .
The number of specimens (NISP), minimum number of anatomical
units (MAU), minimum number of individuals (MNI) and mini-
mum number of elements (MNE) were calculated. Weathering
and evidence for transport of the bones were assessed through
macroscopical analyses.Unless otherwise stated, counts and percen-
tages refer to a total with glyptodont scutes excluded. Bones were
cleaned following the usual procedures . Statistics follow
Sokal & Rohlf .
(c) Surface modifications of bones
Bones were examined under low magnification using a hand
lens to determine the presence of surface modifications and were
preliminarily classified to distinguish trampling from possible
anthropogenic marks . Further analysis of selected marks was
carried out with light microscopy under magnifications of 20,
30and 45. Several pictures of the marks at different focal
depths were taken and a complete in-focus image was made. A
three-dimensional model of each mark accurately representing the
micromorphology of the modifications was constructed. At least
four perpendicular sections of the grooves were obtained for each
mark. The cross-sectional profiles were then digitized and measured
[12,13]. Five morphological attributes were measured , includ-
ing opening angle, angle of the tool impact index, shoulder height
index, depth of cut and floor radius. Other, larger bone modifi-
cations were macroscopically analysed through digital and plastic
models. Lithic material was analysed with the usual techniques
. See the electronic supplementary material for further details.
3. Results and discussion
Based on nine samples of bone collagen and wood from bed
2b, the site age is between 27 +0.45 and 30.1 +0.6
bed 3, modern debris
bones in bed 2b
bones in bed 2a
bed 2b, fine facies
bed 2a, coarse facies
libertad Fm dolores Fm
Figure 1. Arroyo del Vizcaı
´no site: (a) geographical location near Sauce, Departamento de Canelones, Uruguay (34837030S, 56820330W); (b) geological setting.
(Online version in colour.)
rspb.royalsocietypublishing.org Proc. R. Soc. B 281: 20132211
(see electronic supplementary material, table S1). Except for
the rib URU 0496, the other eight dates obtained are statisti-
cally the same ( p.0.05) and their pooled average is 29 +
C ka, between 32.298 and 31.219 cal ka (0.941).
(b) Assemblage characterization
The site is a bonebed with numerous, mostly megafaunal,
fossil remains. Only a small portion has yet been collected,
resulting in 1145 catalogue entries, with NISP ¼1095, or
779 excluding glyptodont scutes. Unless otherwise stated,
this number (779) will be used hereafter to make appropriate
comparisons and calculate percentages. The giant ground
sloth Lestodon armatus is the most abundant of the taxa rep-
resented (94% of the identifiable specimens, NISP ¼732,
MNI ¼17). A small number of elements of two other extinct
giant sloths (Glossotherium robustum and Mylodon darwinii),
three glyptodonts (Glyptodon cf. clavipes,Panochthus tubercula-
tus and Doedicurus clavicaudatus),one notoungulate (Toxodon
platensis), one fossil horse (Hippidion principale), one probosci-
dean (the gomphothere Stegomastodon sp.), one adult deer
(Cervidae indet.) and one sabretoothed felid (Smilodon
populator) were also collected.
Only a small number of bones have juvenile features: two
differently sized right femora, one left femur, a fragmentary
hyoid, two mandibular fragments, a rib, a sacrum, two ver-
tebrae, two tibiae, two caniniforms assigned to L. armatus,
one femur of a glyptodont, an incompletely worn deciduous
tooth of the gomphothere and the four horse bones, which
amounts to 20 identified specimens (2.6%) belonging to at
least five (mostly subadult) juvenile individuals. Owing to
the presence of osteoarthritis, 58 bones (7.4%) have been
identified as belonging to at least two old individuals. The
remaining 90% of the elements belong to adult, prime
individuals, yielding a prime-dominated mortality profile.
This profile is unlike those found in either attritionally, cata-
strophically or accidentally accumulated assemblages . By
contrast, the age profile is similar to that seen in kill sites, in
which a selection of the strongest individuals by human hun-
ters with appropriate technology (long-distance weaponry)
and cooperative ambush strategies is implied.
Among the identified specimens, limb bones and girdles
(35.7%) predominate, followed by vertebrae (33.9%), rib por-
tions (15.7%), cranial fragments (9.2%), and bones of manus
and pes (5.3%). The proportions found resemble those of
the surface assemblage in Amboseli , African hominid
sites , carnivore dens  and San hunter–gatherer
camps  (figure 3a). The representation of all anatomical
regions despite their hydraulic transportability potential
 suggests the accumulation being mostly autochthonous,
with little evidence for major hydraulic transport, although
slight outgoing hydraulic transport might have removed
some of the lighter elements. Limb and elongated bones are
randomly oriented (figure 2), compatible with no major
sorting of the bones owing to fluvial transport  and
suggesting biogenic agency . This, in turn, is congruent
with the sedimentological evidence of low current speed.
The teeth : vertebrae ratio of the sloth elements (as corrected
for making allowance of the appropriate numbers in the indi-
viduals of the clade, 18 and 34, respectively) is 0.76. This
resembles a trampled surface accumulation and is unlike a
sorting by transport, in which heavier, durable elements are
over-represented . However, one-fifth of the bones show
some signs of transport and must have had a different tapho-
nomic history. In addition, between one-fifth and one-quarter
of the bones collected exhibit several features indicative of
transport, and are slightly more weathered  and trampled
than the majority of the recovered sample (see electronic
bones lacking a long axis
long + elongated bones
long and elongated bones
Figure 2. Panoramic view and orientation of the bones: (a) the bonebed showing the 1 m grid used to reference collected elements: (b) schematic of the bones to
show their orientation; (c) rose diagrams showing orientation of the bones. (Online version in colour.)
rspb.royalsocietypublishing.org Proc. R. Soc. B 281: 20132211
supplementary material, figure S6). Those specimens show
an orangish colour when wet and tend to come from the
lower part of bed 2 (facies a). The representation of the ana-
tomical units (%MAU) of L. armatus (figure 3b) resembles
those in kill sites associated with gourmet consumption .
In summary, fluvial agency can be ruled out as the main
source of the accumulation. This conclusion is also supported
by the general state of preservation of the bones, which mostly
display little abrasion and only a slight polish. However, the
existence of more than one population of bones cannot be dis-
carded or corroborated with the data currently available and
will require finer stratigraphic control in future excavations. In
any case, physical preservation is rather homogeneous in the
vast majority of the elements, indicating fast burial, perhaps as
a single event , which is congruent with the obtained dates.
Because major long-distance fluvial transport can be
excluded as the main origin of the accumulation, the fossil
association must have involved external factors. Among
such processes, natural trap or other catastrophic sources
can also be excluded , as they do not show the inverted
U-shaped age distribution found here (figure 3c).
(c) Surface modification of bones
No carnivore tooth marks were identified. Nearly 59% of the
bones collected show modifications with features identifiable
as trampling marks , with over one-third of the bones
exhibiting trampling abrasion on more than 25% of their sur-
face area (see electronic supplementary material, figure S7).
Furthermore, 40 elements (nearly 5% of the identified speci-
mens, a percentage similar to the proportion in human sites
) show marks that have macroscopical features consistent
with human agency (figure 4; electronic supplementary
material, figures S8– S13). Ten of the bones that showed
little or no trampling abrasion in the studied area of the
anthropogenic-style marks were examined under greater
magnifications. A total of 15 marks were analysed from the
selected bones. Congruent with previous preliminary find-
ings , most of these marks show microscopical features
described in cuts made by human stone tools, such as
shoulder effects, Herzian cones and even microstriations
 (figure 4a–e; electronic supplementary material, table
S6), the latter being very rarely preserved in prehistoric
material [11,26]. The mean value of the opening angle was
112.5 +12.18. For the angle of tool impact (ATI) index, the
mean value was 0.089 +0.058, indicating that the object
that made the mark was on average oriented at a consistent
angle relative to the bone surface and not perpendicular to it.
The shoulders are 42 mm high on average (higher than in
many experimental marks ), with mean shoulder height
(SH) index value of 0.256 +0.251, similar to the published
values for a tool held at 458in regard to the bone surface .
The mean value for the depth of cut was 0.191+0.070 mm.
The floor radius shows a mean value of 0.161+0.073 mm
(figure 4a–d). These features and values resemble those found
in fossil bones cut with flint tools [13,28,29], including in
Most marks are observed in the anatomical regions that
would be expected to have been produced by humans, for
instance in the proximal portions of three ribs, trochlear
notch of an ulna, hyoid, lingual side of the lower jaw, etc.
[11,31]. Remarkably, at least one of the bones has marks
located in a very concave surface, the groove on the distal
epiphysis of a tibia (where the tendon of the flexor hallucis
longus muscle runs), which renders it nearly impossible
to have been caused by trampling . Indentations are
discussed in the electronic supplementary material.
All individuals with body masses not much above one
tonne ( juvenile L. armatus, other ground sloths, adult and juven-
ile glyptodont, toxodont, juvenile gomphothere, juvenile horse,
deer, sabretooth) are represented by few bones (61, or 8%),
whereas the four-tonne adult individuals of L. armatus consti-
tute over 92% (718 specimens) of the identified specimens.
San hunter–gatherers have been reported  to schlep entire
carcasses with masses in excess of several hundred kilograms
to more permanent camps, whereas the largest individuals are
processed in situ. A similar pattern has been observed in archae-
ological kill sites . Stalking by human hunters is performed
archaeological cave sites Amboseli
Olduvai’s bed 1 frida
Leakey Korongo (FLK)
FxJj50 Koobi Fora Site
FLKN level 6
Arroyo del Vizcaíno
o del Vizcaíno
brown and spotted hyaenas:
hyaena dens, Namib desert, Namibia
modern human sites
010 20 30 40 50 60 70 80 90 100
0–15 15–30 30–50
vertebrae + ribs
limbs + girdles
Figure 3. Frequency of the bones collected in Arroyo del Vizcaı
of anatomical regions found in biogenic sites with detail of the ternary diagram
near the position of the Arroyo del Vizcaı
´no (AdV) site recalculated and redrawn
after ; (b) percentage of minimum anatomical units of ground sloth bones;
(c) proportion of bones and individuals in the mortality profile.
rspb.royalsocietypublishing.org Proc. R. Soc. B 281: 20132211
in places in which the animalstransit frequently , such as on
the way to a body of water, which might help explain the
observed extent of the trampling.
(d) Lithic material
Although during the fieldwork no systematic effort was made
to collect lithic material and only a part of this site has been
exhaustively explored, a few lithic elements were found to
have seemingly anthropogenic features, although such elements
are scarce, as is usual in South American Pleistocene archaeolo-
gical sites . These include flakes made of silicified sandstone
(see the electronic supplementary material), but their grain size
prevented further microscopical analysis. However, a small
piece of translucid silcrete has features compatible with a scra-
per (figure 4f,g) . This piece was found in bed 2 in very
close association with several bones (figure 2b). It is a pseudo-
pyramidal nucleus with dimensions 29.6 14.5 15.5 mm.
Both proximal and distal borders are short and convex. They
are unifacially retouched and asymmetrically bevelled at inter-
mediate angles (708in the proximal border and 608in the
distal one). The proximal border presents marginal semicircular
retouching, and the distal border shows deep retouching of
irregularly parallel morphology. Using a scanning electron
microscope (SEM) at 700– 4300, an area was identified (aster-
isk in figure 4f) extending along a large portion of the distal edge
of the largest face that reflectsthe incidental electrons differently
from the central parts of that face. That area is rather dull and
coarse, with circular microdepressions that are darker than the
rest of the surface (see the electronic supplementary material,
figure S15), covering the high zones as well as the low ones,
and is accompanied by noteworthy edge rounding. These fea-
tures are consistent with those observed in a second-stage
micropolish, as produced by working on dry hide . Micro-
polish is the only feature observable with optical microscopy
that is produced by the use of a tool and not by natural or acci-
dental causes, and thus it is a diagnostic indicator of human
agency even in the absence of any other kind of evidence .
Both retouched edges show a nearly continuous pattern of
microflaking of different size and morphology.
4. Final remarks
The taphonomy of the site, intrinsically important as a large
bonebed, is suggestive as having accumulated as the result of
biogenic (particularly human) agency. The presence of sur-
face modifications on the bones and the possible scraper are
consistent with this interpretation. However, besides some
rather controversial claims in both South [34 – 36] and North
[37–41] America, current evidence for humans arriving in
the New World (excluding Beringia) before the Last Glacial
Maximum (as indicated by the dates at Arroyo del Vizcaı
is equivocal. Thus, the age of the site and the scarcity of
formal tools urge caution in interpretation. In any case, we
argue that the Arroyo del Vizcaı
´no site deserves to be
included in the agenda of early American peopling, either
as a not foreseeable discovery  or as an example of natural
processes mimicking human presence. As such, further
detailed study of the site is warranted to resolve these issues.
Figure 4. Bone surface modifications: (a) rib CAV 451; (b) detail of the proximal region; (c) detail of the cut marks: (d) three-dimensional reconstruction of the
boxed mark indicated in (c), indicating where sections (i), (ii) and (iii) were taken (section profiles show the two slopes and unaffected bone surface); (e) portion of
that cut mark displaying microstriations (arrow) preserved at the base of the groove (right), and parallel set of microstriations (arrow) preserved on a cut mark in CAV
453 showing a V-shaped section (left); (f) lithic element with features characteristic of a scraper, showing an area (*) that differentially reflects the incidental light;
(g) SEM photography showing micropolish in area *.
rspb.royalsocietypublishing.org Proc. R. Soc. B 281: 20132211
Acknowledgements. We are indebted to the following people and insti-
tutions for their help: Eileen Armstrong, Alfonso Arribas, Anna
K. Behrensmeyer, Martı
´s, Silvia Bello, Batallo
´n 14, Cristina
Bertoni, Karen Borrazzo, Luis Borrero, Juan Cabrera, Reynaldo
Castilla, Gabriela Costoya, Comisio
´n Sectorial de Investigacio
´fica (CSIC) of the Universidad de la Repu
´blica, Eva Farin
´lez family, Signe Haakonsson, IMFIA, Intendencia de Cane-
lones, Emily Lindsey, Dimila Mothe
´, Gustavo Politis, Ximena
´nez Blanco, Rubens Ottonello and Municipio de Sauce,
Elena Pareja, Santiago Patin
˜o, William Rey, Jorge and Elena Rizzo,
´guez, Raymond R. Rogers, Ana Elisa Ro
´nchez, Montevideo, Uruguay: Valetto family, Jorge
Wagensberg, Marcelo Arı
´rate and two anonymous
reviewers. R.A.F. wishes to acknowledge the indirect encouragement
by Beatriz Aguirre-Urreta, Ana Ba
´ez, Ismar Carvalho and Rodolfo
˜ido, who regarded this project as too ‘ambitious’.
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