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Asociación Paleontológica Argentina. Publicación Especial 5
Paleógeno de América del Sur y de la Península Antártica: 35-40.
Buenos Aires, 30-12-1998
ISSN 0328-347X
A NEW PALEOCENE ARMADILLO (MAMMALIA, DASYPODOIDEA)
FROM THE ITABORAÍ BASIN, BRAZIL
Édison Vicente OLIVElRA' and Lilian Paglarelli BERGQVISP
ABSTRACT.Riostegotherium yanei is a new genus and species described on the basis of isolated osteoderms from Itaboraí Basin
(Brazil) of Itaboraian land-mammal age (middle Paleocene). The osteoderms of this armadillo have unique features distinguishing it
from members of the early Tertiary Patagonian Astegotheriini. Among these are the presence of a subcircular main field, many pits
in the grooves around this field, a better-developed central keel, and the absence of foramina on the posterior border. It is difficult to
precise the affinities of the astegotheriines among the Dasypodoidea. Astegotheriines differ from other dasypodoids in having a
moderate number of pits in the grooves limiting the main field, pelvic osteoderms with straight anterior and posterior borders, smooth
lateral borders (indicating little articulation between osteoderms), and reduced number of piliferous foramina. The occurrence of at
least two families of dasypodoids in the Itaboraian of Brazil, together with the presence of Peltephilidae and Astegotheriini in the
Riochican of Patagonia, suggests that cingulates (or xenarthrans) were present at least since the early Paleocene in South America.
RESUMEN.UN NUEVO ARMADILLO (MAMMALIA, DASYPODOIDEA) PALEOCENO DE LA CUENCA DE ITABORAÍ,
BRASIL. Riostegotherium yanei es un nuevo género y especie de armadillo de la cuenca de Itaboraí, de edad mamífero Itaboraiense
(Paleoceno medio) propuesto sobre osteodermos aislados. Los mismos presentan rasgos singulares que los diferencian de los
Astegotheriini del Terciario temprano de la Patagonia, entre ellos: figura principal subcircular con muchas per.foraciones en el surco
que la rodea, carena central más desarrollada y ausencia de per.foraciones en el borde posterior. Es difícil precisar las afinidades de
los Astegotheriini dentro de los Dasypodoidea. Los Astegotheriini difieren de otros dasypodoideos por la presencia de moderado
número de perforaciones en el surco que rodea la figura principal, borde anterior y posterior de los osteodermos pélvicos recto,
bordes laterales lisos (indicando poca articulación entre los osteodermos), y número reducido de forámenes pilíferos. La presencia
de distintas familias (dos por lo menos) de dasypodoideos en el Itaboraiense de Brasil, conjuntamente con la presencia de peltefilinos
y astegoterinos en el Riochiquense de Patagonia, sugiere una mayor antigüedad (Paleoceno temprano por lo menos) de los cingulados
(o xenartros) en América del Sur.
KEY
WORDS.Riostegotherium yanei. Xenarthra. Cingulata. Itaboraian land-mammal age. Itaboraí Basin. Brazil.
INTRODUCTION
PALABRASCLAVE.Riostegotherium yanei. Xenarthra. Cingulata. Edad mamífero Itaboraiense. Cuenca de Itaboraí. Brazil.
Ci ngulate xenarthran remains are frequent in
Cenozoic South American mammal-bearing beds,
especially in post-Paleocene deposits (Scillato- Yané,
1986). By contrast, in older deposits, xenarthrans are
recorded only in the upper Paleocene of Patagonia
(Riochican land-mammal age), and Itaboraí Basin, Brazil
(middle Paleocene, Itaboraian land-mammal age). The
relative scarcity of xenarthran remains in comparison to
the well-represented ungulate and marsupial specimens
in these deposits is remarkable.
'Museu de Ciencias Naturais, Fundacáo Zoobotánica do Rio
Grande do Sul; Rua Salvador Franca, 1427; CEP 90 690-000,
POltO Alegre, RS, Brasil.
'Depto de Geologia. Av. Brigadeiro Trompowski
sIno.
Cidade
Universitária, I1ha do
Fundáo,
CEP 21949-900, Rio de Janeiro,
RJ, Brasil.
©Asociación Paleontológica Argentina
The discovery of osteoderms in the Itaboraí fauna
was reported nearly 30 year ago (Paula Couto, 1949), but
they were not described and illustrated until 1976
(Scillato- Yané). The description was based on two
isolated osteoderms assigned to Prostegotherium aff. P.
astrifer Ameghino, 1902. Later, Ciffeli (1983) referred
two astragali to Dasypodidae and ?Glyptodontidae indet.
Recently, the discovery of astragali and other postcranial
elements, confirmed the presence of dasypodoids in
Itaboraí (Bergqvist and Oliveira, 1995a). Reexamination
of Cifelli's (1983) glyptodontid specimen revealed that it
was identified on presumed plesiomorphic characters for
cingulates, and that it shares no derived characters with
glyptodonts (Bergqvist and Oliveira, 1995b). Thus, the
specimen was thought to be a dasypodoid.
The Itaboraian land mammal age was based on a
faunal assemblage from the Itaboraí Basin, and from
levels bellows Riochican deposits in Patagonia. This
0328-347X198$00.OO+.50
36 E.V. OLIVEIRA and L.P. BERGQVIST
fauna represents an intermediate interval between the
Riochican and older as emblages (Marshall, 1985). This
scheme generated contraversy as to the validity of this
age and the time interval represented (see Pascual and
Ortiz-Jaureguizar, 1991; Bonaparte et al., 1993). Recent
advances in the knowledge of the Paleocene land
rnammal-bearing deposits of central Patagonia show that
the Itaboraian interval corresponds to rniddle Paleocene
(Bond et al., 1995).
Herein, we describe a new genus and species of
armadillo and discuss the róle of early Tertiary
dasypodoids in the understanding of the early history of
South American xenarthrans.
ABBREVIATIONS.MCN-PV, Museu de Ciencias Naturais,
Fundacáo Zoobotánica do Rio Grande do Sul, Porto
Alegre, RS, Brazil; MCT-M (ex-DGM), Museu de
Ciencias da Terra, Departamento Nacional de Producáo
Mineral, Rio de Janeiro, RJ, Brazil; MLP, Museo de La
Plata, La Plata, Argentina; AP, maximum antera-
posterior length; W, maximum width.
SYSTEMATICS
Superorder XENARTHRACope, 1889
Order CINGULATAlJIiger, 1811
Superfamily DASYPODOIDEASimpson, 1931
Tribe ASTEGOTHERIlNI(Ameghino, 1902)
Riostegotherium gen. nov.
TYPE SPECIES.Riostegotherium yanei sp. nov.
ETYMOLOGY.Rio, of Rio de Janeira, in reference to
the state where the specimens were found; stego (Latin),
meaning covering; therium (a latinized Greek word),
meaning beast, a comrnonly-used suffix for mammalian
genera.
DIAGNOSIS.As for the type and only species.
Riostegotherium yanei sp. nov.
Figures 2A-H
1976. Prostegotherium aff. astrifer, Scillato-Yané, p. 527.
HOLOTYPE.MCN-PV 1774, pelvic osteoderm.
HYPODIGM.The type, and MCN-PV 1775: pelvic
osteoderms; MCN-PV 1776,1778,1779, MCT 2081 M,
MLP 75-XII-26-1 and MLP 75-XII-26-2: isolated
moveable osteoderms; and MCN-PV 1777: caudal
osteoderm.
ETYMOLOGY.yanei, for Dr. Gustavo J. Scillato-Yané,
fram the Museo de La Plata, Argentina, in recognition of
his contributions to knowledge of Itaborian cingulates
and of xenarthran systematics and evolution.
DIAGNOSIS.Differs frorn all known early Tertiary
astegotheriins in having a better-developed central keel,
subcircular main field, many pits in graove araund field,
ranging frorn seven to twelve in moveable osteoderms,
and fram eighteen to twenty-five in pelvic osteoderms;
slightly wrinkled external surface, presence of at least
A.P.A. Publicación Especial 5, 1998
two pits in graove surrounding anteralateral fields, and
complete absence of piliferous foramina on posterior
border.
HORIZONAND LOCALITY.Itaboraí Formation, near
Itaboraí, Rio de Janeira (figure 1), Brazil (22
0
44'51
"S,
42
0
51 '21
"W);
Itaboraian land-rnamrnal age; middle
Paleocene (61.8 to 58.5 Ma, Pascual and Ortiz-
J
aureguizar, 1991).
MEASUREMETS. MCN-PV 1774: AP = 12.1 mm, W
= 9.7 mm; MCN-PV 1775: AP = 11.6 mm, W = 8.3 mm;
MCN-PV 1776: AP = 11.6 mm, W = 8.2; MCN-PV
1778: AP = 10.1 mm, W = 5.5 mm; MCN-PV 1779: AP
= 12.1 mm, W =9.8 mm; MCN-PV 1777: AP= 10.3 mm,
W= 7.1 mm; MCT 2081-M: AP = 10.7 mm, W= 5.4
mm.DESCRIPTION.The material does not include any
articulated osteoderms. The pelvic osteoderms are large
and subrectangular in shape. In comparison with
osteoderms of Dasypus hybridus, for example, those of
Riostegotherium yanei are relatively more rabust. The
lateral borders of the osteoderms in the Itaboraian species
are slightly concave and smooth. The anterior and
posterior borders are irregular; the posterior border has a
U-shaped concavity when viewed internally. The anterior
border has a small, weakly defined articulation zone. The
external surface is very punctate and bears fine
irregularities; in combination with the presence of small
depressions, these irregularities give the surface a slightly
wrinkled appearance. The main field has an inverted
U-
shape, with a subcircular anterior outline and occupies
almost the whole osteoderm surface. It is limited by a
shallow groove with eighteen to twenty-five pits.
Although the anterior shape of the main field varies
slightly, it never is triangular or lageniform. Two to four
small peripheral fields are present, limited by shallow
radial grao ves with at least two pits. A well-developed
central keel is present on the external surface of the main
field. The internal surface of the osteoderms is smooth
and slightly concave. No foramina of the piliferaus
system are observed in the posterior border.
The typical moveable osteoderms vary in shape,
ranging from subquadrangular to subrectangular. The
anterior articular surface is poorly developed, and the
external surface resembles that of the pelvic osteoderms.
The main field has a subcircular anterior outline, but with
a very reduced number of pits (seven to twelve). The
external surface bears a well-developed central keel. No
forarnina on the posterior border. The internal side of the
posterior border is moderately inclined toward the edge
of the osteoderm.
The shape of the osteoderm MCN-PV 1777 (figure
2G) resembles caudal osteoderms of the extant dasypodid
Dasypus. The most important differences in relation to
the typical moveable osteoderms are as follow:
articulation surface more developed laterally; smoother
external surface; pits more widely spaced in the graove
lirniting the main field and a sharp posterior border.
PALEOCENE ARMADILLO FROM BRAZIL
37
DISCUSSION.Vizcaíno (1994) included al! the oldest
known armadillos in a taxon that he considered a tribe
(Astegotheriini) of the Dasypodinae. However, some
characters used to define this tribe are thought to be
plesiomorphic (e. g., slender osteoderms, and presence of
central keel). We propose that the most important derived
characters supporting the assignment of Riostegotherium
yanei to the astegotheriines are the following: moderate
44' 42'
----+'--\:----
2
f
______+-~~--~~------r-----~22·
A N
A T L
o
e
E
o
Á
N T ,
eo
43
Figure 1.
Location map of Rio de Janeiro State detailing the region of Itaboraí Basin./Mapa de ubicacion del Estado de Rio de
Janeiro indicando la regián de la cuenca de
Itaborai.
A.P.A. Publicación Especial 5, 1998
38
s.v
OLIVEIRA and L.P. BERGQVIST
number of pits in the grooves limiting the main field;
pelvic osteoderm with straight posterior border; smooth
lateral border indicating little articulation between
osteoderms, and reduced number of piliferous foramina.
Compared to the other taxa referred to Astegotheriinae:
Prostegotherium, Astegotherium, P. seudostegotherium
and Stegosimpsonia, Riostegotherium seems to be more
related to Prostegotherium. However, Riostegotherium
yanei differs from these Patagonian astegotheriines in
A
e
F
having (1) a subcircular anterior outline of the main field,
(2) more pits in the grooves limiting this field, (3) a
better-developed central keel, (4) slightly wrinkled
external surface, (5) presence of at least two pits in the
groove surrounding anterolateral fields, and (6) absence
of foramina on the posterior border.
It is difficult, in view of the present state of
knowledge, to precise the affinities of astegotheriines
within Dasypodoidea. Ameghino (1902, 1906) grouped
B
o
1cm
H
~
n
3
Figure 2. Osteoderms of Riostegotherium yanei gen. et sp. nov.; A: holotype//¡olotipo (MCN-PV 1774); B: pelvic
osteoderm/osteodermo pélvico (MCN-PV 1775); C: moveable osteoderm/osteodermo móvil (MCN-PV 1776); D: moveable
osteoderm/osteodermo móvil (MCN-PV 1778); E: moveable osteodermlosteodermo móvil (MCN-PV 1779); F: moveable osteoderm
/osteodermo móvil (MCT 2081-M); G: caudal osteodermlosteodermo caudal (MCN-PV 1777); H: moveable osteodermlosteodermo
móvil (MLP 75-XIl-26-l).
A.P.A. Publicación Especial 5. 1998
PALEOCENE ARMADILLO FROM BRAZIL
the oldest armadillos in the Stegotheriidae and
Astegotheriidae, separated from the extant Dasypodidae
(including Praopidae). Other authors arrangement group
the early armadillo s in the Stegotheriinae as a subfamily
ofDasypodidae (Simpson, 1945; Hoffstetter, 1958; Paula
Couto, 1979). A third scheme placed the armadillo s in
different tribes within the Dasypodinae (Patterson and
Pascual, 1972; Scillato- Yané, 1980, 1986; Vizcaíno,
1994). As currently conceived, Dasypodidae comprises a
numerous taxa placed in the subfamilies Dasypodinae,
Euphractinae and Peltephilinae, with a record s from the
middle Paleocene to Recent (Simpson, 1945; Scillato-
Yané, 1986; Vizcaíno, 1994), i.e. a temporal range of
about 60 Ma. However, the inclusion of astegotheriines
in the family Dasypodidae is not clearly justified by
characters in most works cited above. Vizcaíno (1994)
considered the presence of epidermal scales covering two
or three adjoining osteoderms to be a synapomorphy
uniting Astegotheriini and Dasypodini within
Dasypodinae. However, this synapomorphy should be
viewed with caution. Carapaces of extant (e. g., Dasypus)
or extinct (e. g., Propraopus Ameghino) dasypodids have
weIl-articulated osteoderms (not necessarily a rigid
articulation), with well-developed spicular sutures along
the lateral borders. These sutures provide strong support
for the delicate and complex epidermal scutes covering
the osteoderms. Conversely, this kind of support is absent
in astegotheriines, because the osteoderms have almost
smooth articular surfaces. In Stegotherium and
Astegotherium dichotomus, for example, the osteoderms
were thought to have been joined by "cartilaginous"
tissue in life (Ameghino, 1897, 1902). Even if the
presence of anterolateral fields in the osteoderms of
astcgotheriines indicates a complex arrangement of
epidermal scales, this feature does not provide definitive
support for Vizcaíno's (1994) interpretation, because the
presence of anterolateral fields in the osteoderms of the
glyptodontid Glyptatelus Ameghino suggests that this
character is widespread within the cingulates (see
Ameghino, 1897).
COMMENTS ON THE OLDEST SOUTH
AMERICAN TERTIARY XENARTHRANS
Riostegotherium yanei is the oldest xenarthran
known, as the Paleocene putative Xenarthra Sudamerica
ameghinoi, (Scillato-Yané and Pascual, 1985), is now
considered to be a derived multituberculate (Krause and
Bonaparte, 1990). We concur with Rose and Emry (1993)
that the presence of osteoderms is a derived xenarthran
trait (not dasypodoid as suggested) as it is also a feature
of some tardigrades. Osteoderms are not present in any
other mammal or mammal like-reptiles.
Although very important in documenting the
Paleocene diversification of dasypodoids, the remains
described herein offer little ro the understanding of the
origin and relationships of the xenarthrans. However,
39
despite the absence of important fossils, so me
hypotheses ha ve been proposed concerning the origin
of this enigmatic group. The concept of Paratheria
involves an ancient Gondwanan group of mammals,
with African (Pholidota) and South American
(Edentata) derivatives of the original stock, and with
West Gondwana as a possible are a of origin (Scillato-
Yané, 1986; Pascual et al., 1985). This proposition is in
part supported by the record of a "true"
Myrmecophagidae, Eurotamandua joresi Storch, from
the middle Eocene of Europe (Storch, 1981; but see
Rose and Emry, 1993) and other possible Eurasian
"edentates" (Chow, 1963; Ding, 1987). The
synapomorphies that support a close relationships
between Xenarthra, Pholidota, and fossil "edentates"
were interpreted by Rose and Emry (1993) as related to
fossorial behavior and myrmecophagy. It is suggestive,
however, that no South American or African
Cretaceous or Tertiary fossils that support a close
relationship of these groups have been recovered.
The absence of xenarthrans in the uppermost
Cretaceous or lower Paleocene of Patagonia and Bolivia
have been considered as suggestive (Pascual and Ortiz-
Jaureguizar, 1991), but not conclusive (Carlini
el
al.,
1994) evidence, against the origin or early diversification
of the group in South America. However, we agree with
the latter suggestion taking into account the presence of
some xenarthran postcranial bones in the Itaboraí Basin
(Bergqvist and Oliveira, 1995a, 1995b) and the
comments of Scillato- Yané (1976, 1986) on the
dasypodoids of the Paleocene of South America.
According to Scillato- Yané (1976), the distinctive basic
dasypodoid traits were already developed in the
Itaboraian and Riochican armadillos and, therefore, their
ancestors should be recorded in older horizons. The
finding of new astragali in Itaboraí shows that two or
three distinct dasypodoids (possibly two farnilies) were
already present in Itaboraian times; one Euphractinae-
like morph and two other Peltephilidae-like morphs
(Ciffeli, 1983; Bergqvist and Oliveira, 1995b). This,
coupled with the presence of unpublished material of
Peltephilidae and Astegotheriini from the Riochican of
Patagonia (Scillato- Yané, 1986), argues in favor of an
older history (early Paleocene at least) of the xenarthrans
in South America. On this basis, the absence of
xenarthrans in the early Paleocene of South America may
be an artifact of the fossil record, despite the fact that
already Patagonia was apparently a distinct
biogeographical unit, closely related to East Gondwana
(Pascual, in press). Furthermore, known latest
Cretaceous and early Paleocene mammal-bearing beds in
South America are almost entirely restricted to Argentina
and Bolivia. The intertropical region of South America
and Africa, obviously representing a large part of a still
not well known West Gondwana, has not been
sufficiently prospected yet, and it may contain clues on
early xenarthra evolution.
A.P.A. Publicación Especial 5, 1998
40
ACKNOWLEDGMENTS
E.Y. OLIVEIRA and L.P. BERGQVIST
We are particularly grateful to J. G. Scillato- Yané and
S. F. Vizcaíno, from the Museo de La Plata, for helpful
advice and comments; J. F. Bonaparte and A. Kramartz
for their assistance in the Museo Argentino de Ciencias
Naturales "Bernardino Rivadavia" and R. Cifelli, M.
Woodburne and A. M. Báez for general comments. This
work was partly supported by Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq),
Museu de Ciencias Naturais da Fundacáo Zoobotánica do
Rio Grande do Sul and Universidade Federal do Rio
Grande do Sul (UFRGS).
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Recibido: 10 de junio de 1996.
Aceptado: 15 de enero de 1998.
