A Blancan (Pliocene) short-faced bear from El Salvador and its implications for Tremarctines in South America

Abstract

We present here a deciduous tooth recovered from the Blancan (Pliocene) Río Tomayate locality (Republic of El Salvador) and assign it to cf. Arctotherium (South American short-faced bears) based on its morphology and size. Carnivores, like many other taxa, entered South America from North America during the “Great American Biotic Interchange” (GABI). We think that this individual was part of the stock that entered South America and may have been ancestral to later Arctotherium species. It has been postulated that Arctodus and Arctotherium are sister groups that make up the “short-faced bears clade”. Until now, Arctotherium had only been recorded in South America; the oldest record corresponds to Arctotherium angustidens from the Ensenadan (Early to Middle Pleistocene) of the Pampean Region of Argentina; 5200 km from the Panamian Isthmus. Among Ensenadan sediments the oldest ones are those of “las toscas del Río de La Plata” locality (Pampean Region). The age of these sediments is 1Ma and they correspond to Chron C1r2r. In the northern portion of South America (Venezuela) Arctotherium specimens are only recorded from the Late Pleistocene. Thus, the new specimen provides the earliest record of Arctotherium, extends the distribution of this taxon to Central America and may represent the basal stock for short-faced bears in South America.

Full text

DOI: 10.1127/0077-7749/2008/0250-0001 0077-7749/08/0250-0001 $ 2.00
© 2008 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart
N. Jb. Geol. Paläont. Abh.
2008, vol. 250/1, p. 1–8, Stuttgart, October 2008, published online 2008
A Blancan (Pliocene) short-faced bear from El Salvador
and its implications for Tremarctines in South America
Leopoldo H. Soibelzon, La Plata, M. R. Romero, D. Huziel Aguilar, San Salvador,
and V. B. Tartarini, La Plata
With 3 figures and 1 table
S
OIBELZON
, L. H., R
OMERO
, M. R., H
UZIEL
A
GUILAR
, D. & T
ARTARINI
, V. B. (2008): A Blancan
(Pliocene) short-faced bear from El Salvador and its implications for Tremarctines in South America.
– N. Jb. Geol. Paläont. Abh., 250:1–8; Stuttgart.
Abstract: We present here a deciduous tooth recovered from the Blancan (Pliocene) Río Tomayate
locality (Republic of El Salvador) and assign it to cf. Arctotherium (South American short-faced
bears) based on its morphology and size. Carnivores, like many other taxa, entered South America
from North America during the “Great American Biotic Interchange” (GABI). We think that this
individual was part of the stock that entered South America and may have been ancestral to later
Arctotherium species. It has been postulated that Arctodus and Arctotherium are sister groups that
make up the “short-faced bears clade”. Until now, Arctotherium had only been recorded in South
America; the oldest record corresponds to Arctotherium angustidens from the Ensenadan (Early to
Middle Pleistocene) of the Pampean Region of Argentina; 5200 km from the Panamian Isthmus.
Among Ensenadan sediments the oldest ones are those of “las toscas del Río de La Plata” locality
(Pampean Region). The age of these sediments is 1Ma and they correspond to Chron C1r2r. In the
northern portion of South America (Venezuela) Arctotherium specimens are only recorded from the
Late Pleistocene. Thus, the new specimen provides the earliest record of Arctotherium, extends
the distribution of this taxon to Central America and may represent the basal stock for short-faced
bears in South America.
Key words: Ursidae, Tremarctinae, Arctotherium, Central America, Blancan, Pliocene.
1. Introduction
The bear genera that constitute the subfamily Tre-
marctinae (Carnivora: Ursidae) are distributed ex-
clusively in America. Of these, Plionarctos is re-
corded from the Late Miocene to the Early Pliocene
of North America with two species (T
EDFORD
&
M
ARTIN
2001). Arctodus contains two North Ameri-
can Late Pliocene and Pleistocene species: A. pristinus
and A. simus. The oldest record for Arctodus is
Blancan IV (Late Pliocene), and the youngest is
Rancholabrean (K
URTÉN
1967; R
ICHARDS
et al. 1996).
Arctotherium comprises five South American Pleisto-
cene species: A. angustidens,A. vetustum,A. bonari-
ense,A. wingei and A. tarijense (see S
OIBELZON
2004a; S
OIBELZON
et al. 2005). Tremarctos includes
two species, T. floridanus from the Late Pliocene and
Pleistocene of North America and the only living
Tremarctinae, T. ornatus of South America, which has
not been recorded as a fossil (see Fig. 1).
The short-faced bear clade (S
OIBELZON
2002a,
2002b, 2004b), composed of Arctotherium (in South
America, and after the present contribution in Central
America) and Arctodus (in North America), was a

2L. H. Soibelzon et al.
group of gigantic to medium sized bears that were
endemic to the Americas.
Short-faced bears (Arctotherium) arrived in South
America from North America, through the Panamian
Isthmus, as part of the “Great American Biotic Inter-
change” (GABI, M
ARSHALL
et al. 1982). The oldest
reported record of a tremarctine bear in South
America corresponds to Arctotherium angustidens
which is first recorded in the Ensenadan of the
Pampean Region of Argentina (S
OIBELZON
2004a,
S
OIBELZON
et al. 2005). Among Ensenadan (Early to
Middle Pleistocene) sediments the oldest ones are
those of “las toscas del Río de La Plata” (Pampean
Region). The age of these sediments is 1Ma and they
correspond to Chron C1r 2r. In the northern portion
of South America Arctotherium (A. wingei) is re-
corded only in the Late Pleistocene (S
OIBELZON
&
R
INCÓN
2007; see Fig. 1).
The aim of this work is to describe a fourth lower
deciduous premolar (dp4, Fig. 2A, B) that was re-
covered from the Late Pliocene of Río Tomayate,
El Salvador (Fig. 3) and analyze the biogeographic
significance of the discovery. After this study we
assigned this deciduous tooth to cf. Arctotherium.
Deciduous premolars of short-faced bears are scarce
in the fossil record, they are only known from one
South American species: Arctotherium tarijense
(see S
OIBELZON
& C
ARLINI
2004). The present con-
Fig. 1. Chronological chart of the late Cenozoic in North and South America showing the biochrons and geographic
distribution of all Tremarctinae taxa and cf. Arctotherium MUHNES-UDP 1-ss-ap-24-120 (modified from S
OIBELZON
et al. 2005, chronostratigraphic units according to W
OODBURNE
et al. 2006).

A Blancan short-faced bear from El Salvador 3
tribution establishes a more precise date for the
potential immigration of short-faced bears into South
America and extends the distribution of Arctotherium
to Central America. Here we present the oldest and
northern most record of Arctotherium.
2. Material and methods
Morphological terms and measurement definitions
follow K
OBY
(1952) and T
ORRES
(1988) but we
numbered the deciduous premolars mesiodistally as
T
ERZEA
(1969) and S
OIBELZON
& C
ARLINI
(2004)
(i. e. the last deciduous premolar is dp4) to facilitate
comparisons. The meaning of the chronostratigraphic/
geochronologic units used is that expressed in W
OOD
-
BURNE
et al. (2006). Measurements were taken with
dial calipers to the nearest mm.
Abbr e v i ati o n s. – AMNH: Vertebrate Paleontology
Collection, American Museum of Natural History, USA.
CM: Carnegie Museum, USA. LACM: Los Angeles County
Museum, USA. MACN-pv: Colección del Departemento
Paleontología de Vertebrados, Museo Argentino de Ciencas
Naturales “Bernardino Rivadavia”, Argentina. MLP: Colec-
ción del Departemento Paleontología de Vertebrados, Museo
de La Plata, Argentina. MNHN AC: Muséum National
d’Histoire Naturelle, Anatomie Comparée, Paris, France.
MUHNES-UDP: Depósito de paleontología de Vertebrados
de La Unidad de Paleontología; Museo de Historia Natural
de El Salvador, El Salvador. UF: Vertebrate Paleontology
Collection, Florida University, USA. dp 4: fourth lower
deciduous premolar, m1: first lower molar, mm: millimeters.
Spec i men s us ed fo r comp a r iso n . – Definitive teeth:
Arctodus pristinus – UF 97258, UF 81692, UF 81693,
UF 81694, UF 64300, UF19397, AMNH 95696, AMNH
95696, AMNH 22578. Arctodus simus – AMNH 25531,
AMNH 25531, AMNH 127691, AMNH 98969, AMNH
98969, CM 38359, LACM 122434, UF 170690 (cast).
Tremarctos floridanus – UF10333, UF3566, UF7454
and those published by K
URTÉN
(1966). The specimens
of Arctotherium used for comparison are those listed in
S
OIBELZON
(2004a).
Deciduous teeth: A. tarijense MACN-pv 8582 (described
in S
OIBELZON
& C
ARLINI
2004). Melursus ursinus MNHN
AC 10998 Ursus arctos MNHN AC 1896-346 and those
described in K
OBY
(1952), T
ERZEA
(1969) and T
ORRES
(1988).
3. Systematic paleontology
Class Mammalia L
INNAEUS
, 1758
Order Carnivora B
OWDICH
, 1821
Family Ursidae G
RAY
, 1857
Subfamily Tremarctinae M
ERRIAM
& S
TOCK
, 1925
cf. Arctotherium B
URMEISTER
, 1879
Fig. 2A, B
Fig. 2.A, B – dp4 of cf. Arctotherium sp. (MUHNES-UDP
1-ss-ap-24-120), A: occlusal view, B: labial view;
C, D – dp4 of A. tarijense (MACN 8582) C: occlusal view,
D: labial view; E– m1 of A. angustidens (MMPH 18);
F– m1 of A. tarijense (MACN 2667); G– m1 of Arctodus
pristinus (UF 81694); H– m1 of A. simus (UF 57550).
Scale bars equal 1 cm.

4L. H. Soibelzon et al.
Refe r re d spec i men : MUHNES-UDP 1-ss-ap-24-120,
left fourth lower deciduous premolar (Fig. 2A, B).
L oc al i ty a nd a g e: Río Tomayate (13º 49’ 06’’ N, 89 º 11’
26’’ W), República de El Salvador (Fig. 3). C1 Member of
Cuscatlán Formation, Blancan (Late Pliocene, Fig. 1). The
C1 member corresponds to the uppermost Pliocene and is
composed of fluvial and lacustrine detritus. A partial skull
of Borophagus hilli was found in this member, this species
is recorded only in Blancan sediments.
Desc r ipt i o n: The crown of the dp4 (MUHNES-UDP
1-ss-ap-24-120) is slightly compressed labiolingually, the
labial margin is almost straight, the lingual margin is
slightly convex and the mesial and distal margins are
rounded (Fig. 2A, B). The trigonid shows three main cusps,
paraconid, protoconid and metaconid, and an accessory
small cusp (always present in Tremarctinae) on the postero-
labial side of the protoconid near its base (S
OIBELZON
2002 a, 2004 b, S
OIBELZON
& C
ARLINI
2004). The dp4 para-
conid lies on the mesial margin of the crown and is rounded
and relatively smaller than in m1. The protoconid is the
most conspicuous cusp; it occupies all the width of the
crown and completely separates the paraconid from the
metaconid, as in m1. Three ridges descend from the apex of
the protoconid, one on the antero-labial side toward the
paraconid, another on the postero-labial side toward a small
accessory cusp, and the third on the postero-lingual side
extending toward the metaconid. The metaconid is placed
on the lingual side of the crown just behind the protoconid
and its size is similar to that of the metaconid of the m1.
Two cusps are present on the talonid area, hypoconid and
entoconid, which are separated from the protoconid and
metaconid by a deep notch. The hypoconid, larger than the
entoconid, is placed on the labial margin. On the base of
the cusp, on the lingual-mesial angle of the crown, there is
a small amount of enamel thickening. Also on the postero-
lingual corner at the base of the hypoconid there is an
enamel shelf, which together with a thin enamel crest
running along the distal margin of the talonid toward the
entoconid, closes the distal margin of the talonid. The ento-
conid is relatively small, formed by a single cusp, and is
placed on the postero-lingual angle of the crown. A thin
cingulum runs along the labial side of the talonid at the level
of the hypoconid.
4. Comparisons
There are two previous studies on deciduous teeth of
tremarctine bears; S
APORITY
(1949) described the
order of eruption of milk teeth of Tremarctos ornatus
and S
OIBELZON
& C
ARLINI
(2004) described a deci-
duous incisor and some premolars (among them a
dp4) of Arctotherium tarijense. First we compare the
dp4 of cf. Arctotherium with that of Ursinae (the other
subfamily of Ursidae recorded in America), then we
contrast it with the dp4 of Arctotherium tarijense
(MACN-pv 8582) and finally with the m1 of Arctodus
(North American short-faced bears).
Here we compare the morphology of dp4 with
that of m1 based on the following information:
In most mammals the milk dentition is replaced once,
a condition called diphyodonty, the first set is called
Fig. 3. Map of El Salvador
showing the Río Tomayate
locality (San Salvador
department, El Salvador).

A Blancan short-faced bear from El Salvador 5
primary and the next set secondary (J
ERNVALL
1995).
As J
ERNVALL
(1995) pointed out, the last deciduous
premolars always resemble the first permanent
molars. In this sense, the crown morphology of
dP/dp 4 in ursids is quite similar to that of M/m1
respectively and, the dP4 occludes on dp4 in the
juvenile in much the same way as the M1 occludes
on the m1 in the adult. On the other hand, their cor-
responding permanent premolars (except for P4) are
simpler (S
OIBELZON
& C
ARLINI
2004).
In order to compare the dp4 of cf. Arctotherium with
other taxa we used morphology and size. Size is
a good character to compare deciduous and definitive
teeth since in all Ursidae definitive teeth are larger than
deciduous ones (L. S
OIBELZON
, pers. obs.). Among
South American short-faced bears this situation was
verified for A. tarijense by S
OIBELZON
& C
ARLINI
(2004) (see Table 1). The opposite situation (i.e. deci-
duous teeth bigger than definitive molars) was never
observed in bears (L. S
OIBELZON
, pers. obs.).
Com par iso ns b e twee n dp 4 o f cf . Arctothe-
ri u m and d p4 of U rs i na e . – The morphology of
cf. Arctotherium (MUHNES-UDP 1-ss-ap-24-120)
corresponds to Tremarctinae instead to Ursinae based
on its size (see Table 1), heavy build, the number of
apices that form the metaconid (one apex in MUH-
NES-UDP 1-ss-ap-24-120 and Tremarctinae; two
apices in Ursinae), and the comparative size of
the protoconid in relation with the paraconid and
metaconid (protoconid larger than paraconid
and metaconid in Tremarctinae and MUHNES-UDP
1-ss-ap-24-120; protoconid slightly larger than
paraconid and metaconid in Ursinae). In addition the
trigonid is very laterally compressed in Ursinae and
the talonid is projected labially in the area of the
hypoconid.
C om p ar i so n s b et we en d p 4 o f c f . Arctothe-
ri u m and d p4 of A. tarijense. – The dp 4 of cf.
Arctotherium (MUHNES-UDP 1-ss-ap-24-120) and
that of A. tarijense (MACN-pv 8582; Fig.2C,D,
Table 1, see S
OIBELZON
& C
ARLINI
2004 for more
details) exhibit the same fundamental morphology.
The dp4 of cf. Arctotherium is less laterally com-
pressed, the talonid is shorter and the distal margin is
very rounded. The main trigonid cusps (parconid, pro-
toconid and metaconid) of cf. Arctotherium and
A. tarijense show the same arrangement. In the talonid
area the entoconid is placed forwards in cf. Arctothe-
rium much closer to the metaconid and the hypoconid
Table 1. Measurements (mm) on the dp4 of cf. Arctotherium (MUHNES-UDP 1-ss-ap-24-120), Ursus and Arctotherium tarijense (MACN-pv 8582); and m1
of Arctotherium tarijense,A. angustidens,Arctodus pristinus,A. simus and Tremarctos floridanus. MDL: greatest mesiodistal length; BLW: greatest buccolingual
width; MDL and BLL measured between landmarks at the limit of the crown. M: mean; N: sample size; R: range; SD: standard deviation. 1Except U. spelaeus
because this species is not recorded in America; additional data taken from K
OBY
(1952). 2Additional data taken from K
URTÉN
(1966).

6L. H. Soibelzon et al.
is displaced towards the midline.These differences are
similar to the differences observed between the m1 of
Arctotherium angustidens (Fig. 2E), the oldest species
of Arctotherium (see above), and A. tarijense (Fig.
2H) the youngest species of this taxon (see Fig.1).
S
OIBELZON
(2002a, 2004b) suggested that A. tarijense
is the most specialized species of Arctotherium, well
differentiated from the ancestral stock that arrived in
South America.
Unfortunately, up to the present, there are no other
published descriptions of milk teeth in tremarctine
bears apart from those already noted (S
APORITI
1949;
S
OIBELZON
& C
ARLINI
2004) and, as far as we know,
there are not specimens in paleontological collections
in any other museum apart from those housed at
MACN-pv and MLP (Argentina) and described in
S
OIBELZON
& C
ARLINI
(2004). This implies that we
could not compare the dp4 presented here with those
of other taxa apart from A. tarijense.
Comparisons between dp4 of cf. A rc t ot h e-
ri u m and m1 of Arctodus. – The m1 of Arctodus
(Fig.2G,H) is differentiated from Arctotherium
(and MUHNES-UDP 1-ss-ap-24-120) based on the
occlusal shape of the crown; with Arctotherium
(Fig. 2E, F) having a more quadrate shape and the
preceding being more rectangular. This difference is
based on the fact that Arctodus has a compressed
trigonid, a well defined ectolofid, and a labially
projected talonid. In Arctotherium (and MUHNES-
UDP 1-ss-ap-24-120) the trigonid is laterally ex-
panded, the ectolofid is poorly defined and the
talonid is less projected labially. In addition the size
of MUHNES-UDP 1-ss-ap-24-120 (Table 1) is more
consistent with that of the m1 of Arctotherium
angustidens (the oldest species recorded in South
America, Fig. 1) than with the m1 size of Arctodus.
Comparisons between dp4 of cf. Arctothe-
ri u m and m1 of Tremarctos. – The same
morphological characters that distinguish cf. Arcto-
therium and Arctodus differentiates the dp4 of cf.
Arctotherium and m1 of Tremarctos. In addition
the m1 of Tremarctos is substantially smaller
than MUHNES-UDP 1-ss-ap-24-120 (see Table 1)
therefore it cannot have belonged to Tremarctos.
Finally, the morphology and size of dp4 from Río
Tomayate resembles that of m1 of the oldest species
of Arctotherium (A. angustidens). Unfortunately, this
species is known only from definitive teeth. Because
of this and the rarity of deciduous premolars of short-
faced bears, we could not make a definitive de-
termination.
5. Discussion and conclusions
Eutherian carnivores arrived in South America, like
many other taxa of holartic origin during the GABI.
This interchange occurred after the marine barrier
that separated South America and North America dis-
appeared in the Late Pliocene ca. 2.8 Ma (C
OATES
&
O
BANDO
1996).
Short-faced bears (Arctotherium) arrived in South
America within this context. The absence of T. ornatus
in the fossil record of either North or South America
may indicate that this species differentiated during
the Holocene from T. floridanus, its sister group
(S
OIBELZON
et al. 2005; see Fig.1). Consequently, a
subsequent second immigration event is needed to
explain the occurrence of the only recent South
American bear (T. ornatus, spectacled bear, see Fig.
1). F
LORENTINO
A
MEGHINO
(1885, 1906) suggested
a South American origin for the Tremarctinae sub-
family on the basis of the erroneous stratigraphic
provenance of the specimen MACN-pv 1277 (A.
vetustum), which he believed to be “Mesopotamian”
in age (Late Miocene). This hypothesis was accepted
by C
ARLOS
A
MEGHINO
(1916), but M
ERRIAM
et al.
(1916), M
ERRIAM
& S
TOCK
(1925), and K
RAGLIEVICH
(1926) placed the stratigraphic provenance of MACN-
pv 1277 in doubt and, in turn, questioned A
MEGHINO
’s
(1885, 1906) hypothesis.
S
OIBELZON
(2002a, 2004b) proposed that Arctodus
and Arctotherium are sister groups that together
make up the “short-faced bears” clade. In addition,
S
OIBELZON
(2002a) and S
OIBELZON
et al. (2005)
hypothesized that the time of divergence of these two
taxa was late Blancan on the basis of the oldest record
of a North American short-faced bear (Arctodus
pristinus, Blancan IV, Late Pliocene, Fig. 1) and a
South American short-faced bear (Arctotherium
angustidens, Ensenadan, Early Pleistocene, Fig.1).
However, there is no fossil record for short-faced
bears prior to the Ensenadan south of the Panamian
Isthmus.
According to W
EBB
(1991), the most successful
holartic families involved in the GABI diversified
north of the Panamian Isthmus before the interchange,
which suggests that the origin of Arctotherium must
be related to geodispersal (sensu L
IEBERMAN
2000).
The fossil record of Arctotherium in South America
also indicates that cladogenetic events occurred

A Blancan short-faced bear from El Salvador 7
in intertropical areas. For example, A.wingei (ex-
clusively), A.vetustum,A. angustidens, and A. tari-
jense have been recorded in those areas (S
OIBELZON
et al. 2005).
The specimen here described indicates that
Arctotherium was near the Panamian Isthmus by the
Late Pliocene and possibly migrating southwards.
In addition, this new finding may indicate that
Arctotherium did not first appear in South America,
as previously assumed (Ensenadan of the Pampean
Region of Argentina (S
OIBELZON
2004; S
OIBELZON
et
al. 2005)).
This new find may support the hypotheses of
W
EBB
(1991) and S
OIBELZON
(2002a) that in the
Blancan short-faced bears were moving from North
to South America. Almost one million year later
they were first recorded in the Pampean Region of
Argentina.
Acknowledgements
The reviewers, B
LAINE
S
CHUBERT
and M
ARTÍN
U
BILLA
,
provided useful comments on an earlier version of this
manuscript. The authors thank Dr. A
LEJANDRO
K
RAMARZ
(MACN-pv), Dr. W
EBB
(FMNH); Dr. T
EDFORD
(AMNH),
Dr. A
NDY
C
URRANT
(NHM, London), Drs. C
HRISTIAN
D
E
M
UIZZON
and F
RANCIS
R
ENAULT
(MNHNP AC) for
allowing us to study the material. The authors also thank
P
AULA
P
OSADAS
and L
UCAS
P
OMI
for their useful comments
and CONICET; ANPCyT PICT 38171/05; for financial
support.
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Addresses of the authors:
L. H. S
OIBELZON
, Departamento Científico Paleontología
de Vertebrados, Museo de La Plata, Paseo del Bosque, 1900
La Plata, Buenos Aires, Argentina;
e-mail: lsoibelzon@fcnym.unlp.edu.ar
M. R. R
OMERO
, D. H
UZIEL
A
GUILAR
, Unidad de Paleonto-
logía, Consejo Nacional Para La Cultura y El Arte (CON-
CULTURA), Final Calle Los Viveros, Colonia Nicaragua,
San Salvador, El Salvador.
V. B. T
ARTARINI
, Facultad de Ciencias Naturales y Museo,
Universidad Nacional de La Plata, 122 y 60 (1900) La Plata,
Buenos Aires, Argentina.