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Rev. bras. paleontol. 10(3):169-180, Setembro/Dezembro 2007
© 2007 by the Sociedade Brasileira de Paleontologia
PROVAS
169
TEMNOSPONDYL DIVERSITY OF THE PERMIAN-TRIASSIC COLONIA
OROZCO LOCAL FAUNA (BUENA VISTA FORMATION) OF URUGUAY
ABSTRACT – Temnospondyls are the most abundant constituent of the Colonia Orozco Local Fauna of the Uruguayan
Buena Vista Formation (Paraná Basin), contrasting with that observed at most latest Permian and earliest Triassic
assemblages elsewhere. The components of the Colonia Orozco fauna, appear to represent early stages of the turnover
evidenced in the communities of continental tetrapods at the Permo-Triassic boundary. They include plesiomorphic
representatives of groups present in Early Triassic assemblages as well as relicts of Late Permian taxa. In particular, the
presence of a close relative of the Russian dvinosauroid, Dvinosaurus, implies a dispersal event of this taxon to
Gondwana probably during the Late Permian. Comparisons of the Colonia Orozco fauna to other Permo-Triassic
communities indicate that it could be older than the Brazilian Lower Triassic Catuçaba Local Fauna of the Sanga do
Cabral Formation (Paraná Basin) and probably equivalent to the latest Permian Russian Vyazniki Community. Moreover,
the Colonia Orozco fauna could be close to the assemblages represented in the lowermost portion of the South African
Lower Triassic Lystrosaurus Assemblage Zone and probably to the Arcadia Formation of Australia.
Key words: Temnospondyli, Colonia Orozco Local Fauna, Buena Vista Formation, latest Permian, earliest Triassic.
RESUMO – Os Temnospondyli constituem o grupo mais abundante na Fauna Local de Colonia Orozco da Formação
Buena Vista no Uruguay (bacia do Paraná), contrastando com o observado na maior parte das associações conhecidas em
depósitos do final do Permiano e início do Triássico. A fauna de Colonia Orozco parece representar estágios primitivos
da substituição faunística que se constata nas comunidades de tetrápodos continentais no límite Permo-Triássico. Os
temnospondilos da Formação Buena Vista incluem representantes plesiomórficos de grupos presentes no início do
Triássico, como também relictos de componentes típicos do Permiano superior. Entre eles se destaca a presença de um
dvinosaurídeo proximamente relacionado com o gênero Dvinosaurus do Permiano superior da Rússia, o qual implicaría
na existência de um evento de dispersão deste táxon até o Gondwana, provavelmente no Permiano Tardío. A comparação
da Fauna de Colonia Orozco com outras asociaciones Permo-Triássicas, indica que a fauna uruguaya podería ser equivalente
a Comunidad de Vyazniki do Permiano mais superior da plataforma russa, y que podería ostentar um status bastante
próximo às associações presentes na porção mais basal da Zona de Lystrosaurus da África do Sul e na Formação Arcadia,
na Austrália. Por outro lado, a Fauna Local de Colonia Orozco sería mais antiga que a Fauna Local de Catuçaba registrada
na Formação Sanga do Cabral, bacia do Paraná (Brasil), considerada de idade Triássico inferior.
Palavras-chave: Temnospondyli, Fauna Local de Colonia Orozco, Formação Buena Vista, Permiano superior, Triássico
inferior.
GRACIELA PIÑEIRO
Departamento de Evolución de Cuencas, Universidad de la República, Iguá 422, CP.11400, Montevideo, Uruguay.
fossil@fcien.edu.uy
CLAUDIA MARSICANO
Departamento de Ciencias Geológicas, Universidad de Buenos Aires, Ciudad Universitaria, Pab. II. Buenos Aires,
Argentina. claumar@gl.fcen.uba.ar
CÉSAR GOSO & ELIZABETH MOROSI
Departamento de Evolución de Cuencas, Universidad de la República, Iguá 422, CP.11400, Montevideo, Uruguay.
INTRODUCTION
The Buena Vista Formation crops out in north-eastern
Uruguay (Figure 1) and was deposited under continental
fluvial conditions, thus revealing an important environmental
change from the brackish epicontinental sea that dominated
the underlying Permian succession. The Buena Vista
Formation consists of red brownish sandstones, intercalated
with thin layers of red brownish mudstones and
intraformational conglomerates (Bossi & Navarro, 1991; Goso
et al., 2001; Piñeiro & Ubilla, 2003), which provided most of
the known fossil specimens of the unit (Figure 2).
Although there is a general consensus among authors
about the fluvial environmental characterization of the
Buena Vista Formation, its age has remained contentious.
For a long time, only one fossil specimen has been found
in this formation (Marsicano et al., 2000), thus precluding
good correlations with other fossiliferous Permo-Triassic
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successions like those of Brazil, South Africa, Australia
and Russia. Therefore, the Triassic age previously
assigned to the Buena Vista Formation was only based on
lithostratigraphic similarities with the Sanga do Cabral
Formation of southern Brazil (Bossi & Navarro, 1991).
Nevertheless, a significant tetrapod assemblage has
recently been recovered from several localities of the
Buena Vista Formation at Cerro Largo County. This
assemblage appears to be different from that recovered in
the Sanga do Cabral Formation, mainly in the presence of
pelycosaurian-grade synapsids in the Uruguayan beds
(Piñeiro et al., 2003, Piñeiro, 2004). In addition, the Buena
Vista Formation has yielded procolophonoid and
prolacertiform reptiles (Piñeiro et al., 2004; Piñeiro, 2004),
and temnospondyl amphibians (Piñeiro, 2004; Piñeiro et
al., 2007a,b), taxa which are also components of the
Brazilian Catuçaba Local Fauna of the Sanga do Cabral
Formation (Lavina, 1983; Barberena et al., 1985a; Cisneros
& Schultz, 2002; Abdala et al., 2002; Dias-da-Silva et al.,
2005; 2006), although the Uruguayan fauna apparently
represents an older assemblage (Piñeiro & Ubilla, 2003;
Piñeiro, 2004; Piñeiro et al., 2007a,b).
The aim of this paper is to provide an overview of the
taxonomic composition of the temnospondyl fauna produced
by the intraformational conglomerates of the Buena Vista
Formation and to compare it to those described for other
Pangaean regions, particularly South Africa, Brazil, Australia
and Russia. In addition, the biostratigraphic and
paleobiogeographic implications of the Uruguayan
temnospondyls are discussed.
Figure 1. Detailed area at the Cerro Largo County, northeastern Uruguay, showing the location of the fossiliferous outcrop (asterisk) of
the Buena Vista Formation.
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PIÑEIRO ET AL. – TEMNOSPONDYL DIVERSITY OF THE PERMIAN-TRIASSIC OF URUGUAY
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Figure 2. Combined profile of the Buena Vista Formation, including the stratigraphic sections present near the Colonia Orozco town, those
along the Ruta Nº 7, and those around the Tres Boliches area, along the Ruta Nº 8.
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MATERIALS AND METHODS
The materials on which we based this contribution are
deposited in the Colección de Vertebrados Fósiles de la
Facultad de Ciencias of Montevideo (FC-DPV),
Montevideo (Uruguay). The comparative materials
examined are from the Bernard Price Institute for
Palaeontological Research of South Africa, examined by
Claudia Marsicano, and from the Museu de Paleontologia,
Fundação Zoobotânica do Rio Grande do Sul and the
Instituto de Geociencias, Universidade Federal do Rio
Grande do Sul (UFRGS) of Brazil, studied by Graciela
Piñeiro and Claudia Marsicano.
SYSTEMATIC PALAEONTOLOGY
TEMNOSPONDYLI
LAIDLERIIDAE
Uruyiella liminea Piñeiro, Marsicano & Lorenzo
Material. FC-DPV 1598 (Figure 3), a partial skull from the
lowermost intraformational conglomerates of the Buena
Vista Formation at Colonia Orozco Town, Cerro Largo
County, Uruguay.
Remarks. According to both anatomical and phylogenetic
studies, Uruyiella appears to lie close to the Lower or
Middle Triassic species Laidleria gracilis of South Africa,
due to the triangular shape of the skull, the ornamentation
of the dermal bones and the lateral position of the orbits
in both taxa (Piñeiro et al., 2007b). However, Uruyiella
displays several autapomorphic characters which are not
observed in any Triassic taxa. For instance, all the
postorbital bones in Uruyiella are remarkably large and
anteroposteriorly elongated, being almost twice as long
as they are wide. This arrangement is observed in
Trucheosaurus major from Australia (Marsicano & Warren,
1998), the only known Permian rhytidosteid. Moreover,
the palatine ramus of the pterygoid in Uruyiella extends
well anteriorly, thus excluding the ectopterygoid and at
least the posterior part of the palatine from the
interpterygoid vacuity, a condition which is only
comparable to that present in Palaeozoic temnospondyls
(e.g. Watson, 1962; Gubin, 1991; Schoch & Milner, 2000).
On the other hand, the presence of a trough on the ventral
surface of the quadratojugal which forms an ‘overhang’ in
occipital view in Uruyiella and Laidleria, is a characteristic
that they share with the plagiosaurids. It is important to
note that the phylogenetic affinities of both Laidleria and
the plagiosaurids have been the subject of controversy
among authors. Laidleria was alternatively considered as
a trematosaurid by Kitching (1957), a laidleriid within the
superfamily Rhytidosteoidea (Cosgriff, 1965, 1974), or as
a member of a different family (Laidleriidae) within
Temnospondyli (Cosgriff & Zawiskie, 1979). The
plagiosaurids in turn have been recognized as stem
Lissamphibia close to Peltobatrachus (Milner, 1990). A
recent comprehensive study of temnospondyl
relationships showed that Laidleria and the plagiosaurids
are closely related taxa within the Stereospondyli (Yates
& Warren, 2000); however, a new analysis including
Uruyiella indicated that all these taxa form a clade related
to the Dvinosauria, and that they fall outside the
Stereospondyli (Piñeiro et al., 2007b).
Figure 3. FC-DPV 1598, holotype of the laidleriid Uruyiella liminea from the lowermost intraformational conglomerates of the Buena Vista
Formation (northeastern Uruguay), in dorsal (A) and ventral (B) views. Scale bar = 10 mm.
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PIÑEIRO ET AL. – TEMNOSPONDYL DIVERSITY OF THE PERMIAN-TRIASSIC OF URUGUAY
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TEMNOSPONDYLI
MASTODONSAURIDAE
Materials. FC-DPV 1280, 1305, 1600 (Figure 4); partial
mandibles preserving the post-glenoid area (PGA), from
middle and upper conglomerate levels of the Buena Vista
Formation at Colonia Orozco town, Cerro Largo County,
Uruguay.
Remarks. The fragmentary nature of the materials and the
absence of associated skulls preclude a more precise
taxonomic assignation. The placement of these specimens
within Mastodonsauridae is supported by the distinctive
morphology of the PGA, the nature of its dorsal muscular
crests, and by the presence of a well developed hamate
process. Although their general morphology is consistent
with that described for most basal members of
Mastodonsauridae (sensu Damiani, 2001), the Uruguayan
mandibles may represent new taxa that display some
Figure 4. Mastodonsaurid mandibles from the intraformational conglomerates of the Buena Vista Formation (northeastern Uruguay): A-C,
FC-DPV 1280, partial left mandible in labial (A), lingual (B) and dorsal (C) views; D-F, FC-DPV 1600, post glenoid area (PGA) of a rigth
mandible in labial (D), lingual (E) and dorsal (F) views; G-I, FC-DPV 1305, PGA of a left mandible in labial (G), lingual (H) and dorsal (I) views.
Scale bars = 10 mm.
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Figure 5. FC-DPV 285, dvinosaurid skull fragment including the left orbit, from the uppermost intraformationalconglomerates of the Buena
Vista Formation, in dorsal (A) and lateral (B) views. Scale bar = 10 mm.
characters not previously described in Mesozoic
temnospondyls. Among them, the presence of a continuous
tooth row on at least the posterior and middle coronoids
appears to be convergent with the Late Permian rhinesuchids
of southern Brazil (personal observation, Piñeiro et al.,
2007a).
TEMNOSPONDYLI
DVINOSAURIA (sensu Yates & Warren, 2000)
Material. FC-DPV 285 (Figures 5, 6). A partial skull, preserving
part of the skull table at the level of the left orbital region. It
comes from intraformational conglomerates of the Buena Vista
Formation exposed at the wedge of Ruta Nº 7, Cerro Largo
County, Uruguay.
Remarks. This skull fragment was the first specimen
discovered in the Buena Vista Formation and for a long time
it was the only known fossil from this unit (Marsicano et
al., 2000). The fragmentary nature of the specimen precludes
a precise taxonomic assignation, but regarding its short and
broad skull and the presence of a bone which forms the
anterolateral margin of the orbit in the position of the
lacrimal or the lateral exposure of the palatine (LEP) (Figure
6), the material was related to the Dvinosaurus-
Tupilakosauridae clade (Marsicano et al., 2000). The poor
preservation of the skull hamper a secure identification of
that bone as the lacrimal. On the one hand, it displays the
same ornamentation of the other preserved skull table
elements as occurs in those taxa where the lacrimal is
present. Tupilakosaurids display the unusual condition
among temnospondyls of a large postorbital that contacts
both the frontal (Milner & Sequeira 2004) and the parietal
(Warren, 1999) because of the unusually small size of the
postfrontal. This condition is not observed in FC-DPV 285,
which in turns shows a large postfrontal in contact with the
prefrontal, thus precluding the frontal from contacting the
postorbital and also excluding it from the orbital margin
(Figures 5A, 6). The absence of a postorbital-parietal contact
can be also inferred because the postorbital is laterally
displaced by the large postfrontal, and thus does not
contact the parietal. Among brachyopids, which also have
a short and parabolic skull, the lacrimal and the LEP are
absent in most cases, and only the Russian
Batrachosuchoides lacer and the Australian Xenobrachyops
allos have a LEP (Shishkin, 1967; Damiani & Warren, 1996).
As the only known specimen of Batrachosuchoides consists
of an antorbital area of a skull, the configuration of the
postorbital bones cannot be compared to that present in
FC-DPV 285. Along with the presence of a LEP,
Batrachosuchoides shares some other characters with
dvinosaurians (see Warren, 1999; Warren and Marsicano,
2000; Marsicano et al., 2000), thus its affinities will remain
unclear until more complete specimens can be discovered.
Therefore, we consider the skull bone configuration present
in FC-DPV 285 as more consistent with that described for
the Permian Dvinosaurus (Bystrow, 1938) than for
tupilakosaurids and brachyopids.
DISCUSSION
Geological overview of the Buena Vista Formation
Currently, the succession that includes the end of the
Permian and probably the beginning of the Triassic in
Uruguay is represented by two units, the Yaguarí and the
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PIÑEIRO ET AL. – TEMNOSPONDYL DIVERSITY OF THE PERMIAN-TRIASSIC OF URUGUAY
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Buena Vista formations. For a long time both the
characterization and the age of these units have been the
subject of controversy among authors (see Falconer, 1937;
Delaney & Goñi, 1963). The difficulty in establishing the
boundary between the Yaguarí Formation and the
overlying Buena Vista Formation lead some geologists to
consider them as a single unit, assigned to the Upper
Permian (e.g. Falconer, 1937; Bossi, 1966; Elizalde et al.,
1970). Other authors, in turn, differentiated the red, mostly
arenaceous upper portion of the succession as an
independent and well defined unit, the Buena Vista
Formation, which was considered to represent the Lower
Triassic in Uruguay (Caorsi & Goñi, 1958; Ferrando &
Andreis, 1986; Bossi & Navarro, 1991), although no fossils
were yet discover from it.
At present, local and regional stratigraphic studies
support the recognition of the Buena Vista Formation as a
separate unit from the Yaguarí Formation (Goso et al., 2001;
de Santa Ana, 2005), but the tetrapod assemblage recently
found in the Buena Vista Formation, designated the Colonia
Orozco Local Fauna by Piñeiro & Ubilla (2003) and Piñeiro
(2004), points to an older age than that previously
recognized, closer to the Permian-Triassic boundary (Piñeiro
et al., 2003; Piñeiro & Ubilla, 2003; Piñeiro, 2004; Piñeiro et
al., 2004; Piñeiro et al., 2007b).
Biostratigraphic relations of the Colonia Orozco Local
Fauna with other Pangaean communities
The Catuçaba Local Fauna of the Brazilian Sanga do Cabral
Formation. The lithological similarities observed between the
Uruguayan Buena Vista and the Brazilian Sanga do Cabral
formations, in addition to the fact that both are part of the
infilling of the Paraná Basin, strongly suggested that they
could be stratigraphic equivalents. Nevertheless, the
Uruguayan Colonia Orozco Local Fauna does not seem to be
contemporaneous with the Catuçaba Local Fauna of the
Brazilian Sanga do Cabral Formation. In particular, their
temnospondyls and procolophonoid reptiles show important
differences (Piñeiro & Ubilla, 2003; Piñeiro et al., 2004). Thus,
Pintosaurus magnidentis, at present the only described
procolophonoid from the Buena Vista Formation, is more
closely allied to the basal representatives known from the
Lower Triassic of South Africa and Russia (Piñeiro, 2004;
Piñeiro et al., 2004) than to Procolophon, the most common
taxon in the Catuçaba Local Fauna (Lavina, 1983; Barberena
et al., 1985a; Cisneros & Shultz, 2002; Dias-da-Silva et al.,
2006; Cisneros, in press).
The temnospondyl composition at the Brazilian Sanga do
Cabral Formation includes probable lydekkerinids and
rhytidosteids (Lavina & Barberena, 1985; Dias-da-Silva et
al., 2005; 2006) which are absent in the Buena Vista fauna.
Both groups are widely represented in Early Triassic
successions in Gondwana (e.g.Yates & Warren, 2000;
Damiani, 2001; Damiani & Yates, 2003) and there is an isolated
record of Rhytidosteidae from Upper Permian deposits of
Australia (Marsicano & Warren, 1998). This evidence, in
addition to the presence of Procolophon in the Sanga do
Cabral beds, strongly suggest an Early Triassic age for this
unit. This is in concordance with the ‘impoverished zone’ or
Procolophon subzone sensu Neveling et al. (1999) recognized
in the South African Permo-Triassic succession (Cisneros &
Schultz, 2002; Dias-da-Silva et al., 2006).
In contrast, the Uruguayan Colonia Orozco fauna includes
some temnospondyl taxa that although related to essentially
Triassic groups (e.g. Laidleriidae and Mastodonsauridae),
they possess several features that locate them in basal
positions within those groups (Piñeiro et al., 2007a,b). In
addition, the presence in the Colonia Orozco fauna of a
temnospondyl probably related to the Russian taxon
Dvinosaurus, an exclusively Late Permian taxon, indicates
that the age of that assemblage is older than the Brazilian
fauna and might be placed in the Late Permian or close to the
Permian-Triassic boundary.
The chronological hypothesis discussed above is also
corroborated by recent radiometric studies on bentonite ashes
from the Yaguarí Formation (de Santa Ana et al., 2006), which
place this unit in the Middle Permian (269.8 ± 4.7 Ma).
Considering its conformable contact with the Buena Vista
Formation, an Early Triassic age for the latter unit becomes
improbable.
It is important to remark that recent radiometric data from
the Upper Paleozoic Brazilian succession revealed older
Figure 6. Interpretive drawing of FC-DPV 285 in dorsal view,
showing the presence of a probable lacrimal and also the
morphology of the preserved prefrontal, postfrontal and postorbital
(see text). Abbreviations: f, frontal; j, jugal; l, lacrimal; mx, maxilla;
pf, postfrontal; prf, prefrontal; po, postorbital; sos, supraorbital
sulcus.
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ages for the constituent units than those previously
assigned to them. For instance, zircons from the Iratí
Formation indicate an Early Permian (Cisuralian) age for this
unit (Ventura-Santos et al., 2006) which is significantly older
than the Late Permian (old Guadalupian) age traditionally
assigned to it (e.g. Daemon & Quadros, 1970). This has
resulted in a new stratigraphic scheme where the Rio do
Rasto Formation (the unit that stratigraphically underlies
the Sanga do Cabral Formation) is placed mostly within the
Guadalupian (268.0±0.7 Ma, Middle Permian) (Ventura-
Santos et al., 2006), thus contrasting with most previous
studies which placed the Rio do Rasto Formation entirely
within the Late Permian (e.g. Barberena et al., 1985a;
Barberena et al., 1985b; Langer, 2000). The contact between
the Rio do Rasto and Sanga do Cabral formations was
described as conformable by some authors (Gamermann,
1973; Faccini, 1989), but in more recent studies it has been
regarded as not conformable (Scherer et al., 2000; Zerfass
et al., 2003). However, this disagreement may be because of
‘missing’ stratigraphy in some places where the contact is
described (Faccini, 1989).
Most of the fossils recovered from both the Sanga do
Cabral Formation in Brazil and from the Buena Vista
Formation in Uruguay come from intra-formational
conglomerate levels present in both units. Two bodies of
conglomerates separated by a thin mudstone layer have
been described for the Sanga do Cabral Formation by Zerfass
et al. (2003), correlating the upper body with the
fossiliferous Procolophon Range Zone from South Africa.
Taking into account the differences in faunal composition
between the Uruguayan and the Brazilian units, it seems
possible that the fossiliferous conglomerates present in the
Buena Vista Formation correspond to the lower body,
therefore explaining the older age suggested by its tetrapods.
As the mapped area of the Sanga do Cabral Formation
suggests topographic highs to the west (Zerfass et al.,
2003), it is possible that the upper body of conglomerates is
not present in Uruguay (César Schultz, pers. comm. 2007).
In fact, the isopachic map that includes the Buena Vista
Formation shows that it increases its thickness to the
northwest portion of the basin, where it attains more than
600 meters thickness (de Santa Ana et al., 2006), contrasting
with the sharply erosive processes that can be seen near
the Colonia Orozco town, at the eastern part of the basin.
That erosion is related to the late Hercinian tectonic activities
produced in the inner cratonic Gondwana (Cobbold et al.,
1992).
Lystrosaurus Assemblage Zone of South Africa. Permian
and Triassic terrestrial strata are represented in the South
African Karoo Basin and their fossil vertebrates were the
subject of several recent papers (Ward et al., 2000, 2005;
Smith & Ward, 2001; Steiner et al., 2003; Smith & Botha,
2005; Botha & Smith, 2006). According to these studies, the
uppermost Permian strata (Dicynodon Assemblage Zone;
Lower Palingkloof Member of the Balfour Formation) have
yielded non mammalian therapsids (e.g. Dicynodon,
Lystrosaurus maccaigi and Moschorhinus), but
temnospondyl remains have not been found in that deposits
at present. The Early Triassic is represented in several
localities by the tetrapods of the Lystrosaurus Assemblage
Zone (upper Palingkloof Member of the Balfour Formation
and the overlying Katberg Formation) where the therapsid
Lystrosaurus is the most common taxon (Botha & Smith,
2006). However, a lowermost Triassic locality at Barendskraal
shows a different faunal composition (Damiani et al., 2003),
dominated by basal procolophonoids (Modesto et al., 2001,
2003, Modesto & Damiani, 2007; Reisz & Scott, 2002) and
other amniote taxa, but temnospondyls appear still to be
absent. With the exception of the dissorophid Micropholis,
which first record is in the upper Palingkloof Member and
the lydekkerinid Lydekerina, which is for the first time
recorded in the basal Katberg Formation (Smith & Botha,
2005; Botha & Smith, 2006), the stratigraphic position of
the remaining temnospondyl taxa in the Karoo
(Rhinesuchidae, Tupilakosauridae, Rhytidosteidae,
Mastodonsauridae and Trematosauridae) is poorly
constrained (Damiani, 2004). Rhinesuchidae are
characteristic in Permian strata, while lydekkerinids
(particularly represented by Lydekkerina huxleyi) are a
conspicuous component of the Lower Triassic beds
(Rubidge et al., 1995). None of these taxa have been found
in the Colonia Orozco Fauna at present, neither other
characteristic Triassic temnospondyls of the Karoo as
rhytidosteids, tupilakosaurids and trematosaurids. Despite
the Uruguayan mastodonsaurids display a similar
morphology to that found in basal Triassic representatives
of this group, they appear to be more plesiomorphic (Piñeiro
et al., 2007). Nevertheless, this hypothesis needs to be
confirmed by the discovery of more complete specimens in
the Uruguayan beds.
The Early Triassic Arcadia Formation of Australia. The
Permo-Triassic succession in Australia is represented by
the Rewan Group, which includes the Upper Permian-
lowermost Triassic Sagittarius Sandstone conformably
overlied by the Lower Triassic Arcadia Formation (Warren
et al., 2006). The age of the Sagittarius Sandstone is
supported by palinological and radiometric data (Foster,
1982; Archbald & Dickens, 1996 in Warren et al., 2006) thus
suggesting an earlier Triassic age than that previously
proposed for the Arcadia Formation, closer to the P-T
boundary (Warren et al., 2006). Nevertheless and according
to Warren et al., (2006), the P-T boundary in Australia
remains controversial. The recent discovery of the
temnospondyl Lydekkerina huxleyi in the Arcadia
Formation might help to constrain the age of this unit. In
South Africa Lydekkerina has been recovered from the lower
part of the Lystrosaurus Assemblage Zone, thus suggesting
a probable correlation between the Arcadia Formation and
the lower part of the Katberg Formation of South Africa
(Warren et al., 2006). This hypothesis is supported by the
presence of taxa as the Lapillopsidae, which display a basal
position in most recent temnospondyl phylogenies (Yates,
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1999; Yates & Warren, 2000) and also by some plesiomorphic
representatives of known Triassic groups (Warren et al.,
2006).
This situation could be comparable with that seen in the
Colonia Orozco fauna, but it remains rather different if we
consider that unambiguous Triassic fossil index are absent
from the Uruguayan community.
The Vyazniki community from Russia. In Russia, the
uppermost Permian is represented in the Vyazniki Community
(Vyatkian Horizon) (Sennikov, 1996; Sennikov & Golubev,
2006), which seems to be different to other Late Permian
continental faunas from Pangaea (Sennikov, 1996; Sennikov
& Golubev, 2006). Tetrapods and other groups from Vyazniki
include taxa that are characteristic in Late Permian
communities, together with taxa known to be present in the
Early Triassic, a feature that was used to infer a transitional
status for this Russian assemblage (Sennikov, 1996; Sennikov
& Golubev, 2006).
A similar condition is observed for the Colonia Orozco
fauna, where a mixture of continental tetrapods including
some putative Permian groups (e.g. varanopids and
Dvinosaurus-type temnospondyls) and earlier components
of well established Early Triassic taxa (e.g. Laidleriidae and
Mastodonsauridae) are found. Although pareiasaurids have
not yet been recovered from the Buena Vista levels, this might
not be a relevant difference between both assemblages as
this group is consider relictual in the Vyazniki Community,
only represented by few elginiid taxa (see Sennikov &
Golubev, 2006).
While Dvinosaurus is a typical taxon in the Russian
Vyazniki Assemblage (Goluveb, 2000; Sennikov & Golubev,
2006), it is not registered in the overlying Lower Vetluga
Community, which represents the beginning of the Triassic
in that area. Thus, the presence of a Dvinosaurus-like
temnospondyl in the Buena Vista Formation of Uruguay
could represent, as for the Russian Vyazniki community, the
latest known record of this taxon close to the P-T boundary.
It also suggests a dispersal event for dvinosaurians between
Russian and South American areas at the end of the Permian,
where they could have survived in refuges until the very
end of the Permian or even until the beginning of the
Triassic.
This biogeographic hypothesis was already
established by several authors and largely documented
by taxonomical similarities found between Russian and
South African therapsids (Ochev & Shishkin, 1989; Milner,
1990; Warren, 1999, Yates & Warren, 2000; Battail, 2000;
Sidor et al., 2005; Surkov et al., 2005; Smith et al., 2006;
Shishkin et al., 2006).
CONCLUSIONS
Temnospondyls were a conspicuous and abundant
component of the Uruguayan Colonia Orozco Fauna, thus
contrasting with that observed in the lowermost Triassic of
South Africa, where this group of tetrapods was not yet found.
Analyses of the Colonia Orozco temnospondyls show
that they include Permian and Triassic lineages, thus
suggesting a transitional status for this fauna, as also occurs
in the latest Permian Russian Vyazniki Community. Therefore,
the previously suggested Permo-Triassic age for the
fossiliferous conglomerates of the Buena Vista Formation is
also supported by its temnospondyl fauna.
Dvinosaurus-type temnospondyls seem to have been
present in the Colonia Orozco Fauna representing the first
record of this taxon in Gondwanan areas of Pangaea, and
probably its latest known record. Considering both the
presence of Dvinosaurus in Eastern Europe and Dvinosaurus-
like temnospondyls in Gondwana, a probable faunal
connection between these two geographically distant areas
during the Permian is proposed, as it was also inferred by
similar therapsid taxa present in both South African and
Russian Permo-Triassic deposits.
ACKNOWLEDGMENTS
The authors are grateful to Y. Pardiñas for his
hospitality and help during fieldwork at Cerro Largo
County; to M. Verde, A. Rojas, M. Ubilla, D. Picchi and F.
Kuczera for collaboration in the fieldwork. They also thank
to A. Warren for comments for determination of the
affinities of FC-DPV 285 and providing us with valuable
literature, and to F. Abdala for the reading and improvement
of the manuscript. To R. Damiani and an anonymous
reviewer for their important suggestions, which highly
improved this paper. This study was supported by the
Dirección Nacional de Ciencia y Tecnología, Programa de
Desarrollo Tecnológico operating grant 29/104 (GP and
CG); and PIP-CONICET 5120 (CM).
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