The youngest non-lepidosirenid lungfish of South

The youngest non-lepidosirenid lungfish of South
America (Dipnoi, latest Paleocene–earliest Eocene,
Argentina)
ALBERTO L. CIONE, SOLEDAD GOUIRIC-CAVALLI*, JAVIER N. GELFO AND
FRANCISCO J. GOIN
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CIONE, A.L., GOUIRIC-CAVALLI, S., GELFO, J.N. & GOIN, F.J., iFirst article. The youngest non-lepidosirenid lungfish
of South America (Dipnoi, latest Paleocene–earliest Eocene, Argentina). Alcheringa, 1–6. ISSN 0311-5518.
The first lungfish tooth plate from the Las Flores Formation, Chubut, southern Argentina, is described. This is the
youngest ceratodontid known from the continent. In Africa, ceratodonts disappeared in the Eocene. Afterwards, they
are only known from Australia until their extinction during the Pleistocene. The Las Flores tooth plate also
represents the southernmost lungfish known since the Coniacian (early Late Cretaceous).
Alberto Luis Cione [[email protected]]; Soledad Gouiric-Cavalli* [[email protected].
edu.ar]; Javier Nicolás Gelfo [[email protected]] and Francisco Goin [[email protected].
edu.ar], División Paleontologı´a Vertebrados, Museo de La Plata, Paseo del Bosque s/n, W1900FWA La Plata,
Argentina. *Corresponding author. Received 8.3.2010, revised 29.3.2010, accepted 13.4.2010.
Key words: Ceratodontidae, South America, extinction, diversity.
DURING the Mesozoic, lungfish were diverse and almost cosmopolitan (Schultze
2004). However, most genera became extinct
before the Cenozoic. Since the beginning of
the Cenozoic, lungfish have been almost
exclusively represented by the Neoceratodontidae and Lepidosirenidae, and have become
restricted to southern continents (South
America, Africa and Australia; Nelson 2006).
The only previously known Cenozoic
lungfish other than Lepidosirenidae and
Neoceratodontidae are the ceratodontid
Ceratodus humei Priem, 1914 from the
Paleocene and Eocene of Saharan Africa
(Longbottom 1984, Churcher & de Iuliis
2001), C. diutinus Kemp, 1993 from the
Oligocene–Miocene of Australia, Metaceratodus bonei Kemp, 1997[a] from the upper
Oligocene to middle Miocene of Australia,
M. palmeri Krefft, 1874 from the Pliocene
and Pleistocene of Australia (Kemp 1993,
ISSN 0311-5518 (print)/ISSN 1752-0754 (online)
Ó 2010 Association of Australasian Palaeontologists
DOI: 10.1080/03115518.2010.489418
1997a) and indeterminate ceratodonts and
Ceratodus sp. from the Danian Santa Lucı́a
Formation of Bolivia (Schultze 1991).
A fragmentary tooth plate found in
latest Paleocene–earliest Eocene beds in
Patagonia by two of us (JNG and FJG)
shows that non–lepidosirenid lungfish survived until this time in southern South
America. Terminology is according to
Kemp (1993, 1997a,b, 2001).
Geographic and stratigraphic
provenance
The main exposures of the continental Las
Flores Formation (Raigemborn et al. 2009)
are at the eastern tip of Gran Barranca,
south of Lago Colhue Huapi (south-central
Sarmiento department, Chubut province,
Argentina; Fig. 1). Together with the
underlying Las Violetas and Peñas Coloradas formations, and the overlying Koluel
Kaike Formation, it is currently included
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ALBERTO L. CIONE et al.
within the Rio Chico Group, an essentially
continental sedimentary succession of late
Paleocene to middle Eocene age in the San
Jorge Gulf Basin (Fig. 2). Stratigraphic
charts and profiles of these formations were
provided by Raigemborn et al. (2009).
At Gran Barranca, the Las Flores Formation reaches 44 m thick. It consists
mostly of greyish mudstones and minor
epiclastic and volcaniclastic sandstones deposited in floodplain–shallow lacustrine environments (Raigemborn et al. 2009). The
fossiliferous bed is a 52 m thick sandstone
near the base of this formation (458430 2600 S,
688370 1400 W). There is no evidence of reworked material at this level and locality.
Apart from the ceratodontid lungfish described here, around 1500 mammal remains
(mostly, isolated teeth) have been exhumed
and are currently under study. This rich
mammalian fossil assemblage indicates an
Itaboraian age of the South American Chronological Scale (Paleocene–earliest Eocene;
Bond et al. 1995, Gelfo et al. 2009).
ALCHERINGA
All evidence (sedimentary, mineralogical,
palaeobotanical) analyzed by Raigemborn
et al. (2009) is consistent with the Las Flores
Formation being deposited in ‘tropical’ or
‘subtropical’ climates, with warm temperatures and abundant precipitation. Its mammal content, including the impressive
marsupial fauna dominated by frugivorous
forms, conforms to this interpretation.
Systematic palaeontology
DIPNOI Müller, 1845
CERATODONTIDAE Gill, 1872
Ceratodontidae indet. (Fig. 3A–E)
Material. MLP 90-II-5-990, a fragmentary
upper tooth plate preserving the greater part
of the first ridge and the whole second ridge.
The biological wear was normal, and the
material does not show any evidence of
significant post-mortem abrasion.
Repository. División Paleontologı́a Vertebrados, Museo de La Plata (W1900FWA)
La Plata, Argentina.
Fig. 1. Location map. Star indicates the fossil locality.
Description. The tooth plate is small. The
very deep second cleft would indicate that
there were few ridges, perhaps five (Fig. 3E).
The medial edge of the plate is convex, and
the mesiolingual edge appears to have been
relatively concave. The mediolingual junction is angled (ca 1188). The loss of enamel
and dentine on the mediolingual face is
slight. The two preserved ridges are sharp,
slender, high, straight and acute (the second), and originate anteriorly. The first ridge
tip is broken. The labial profile of the second
ridge is steep and there are no cusps.
The angle between the preserved ridges is
288. The first cleft is relatively shallow and
rounded. The pulp cavity is large. The
enamel strongly ascends in the cleft labially.
Punctations are simple (petrodentine sensu
Kemp 2001 absent) and cover the occlusal
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ALCHERINGA
SOUTH AMERICAN TERTIARY LUNGFISH
3
Fig. 2. Stratigraphic chart of the Paleogene of Argentina. SALMAs, South American Land Mammal Ages.
surface. Some punctations appear to be
arranged in radiating series. Most are
irregular. No occlusal pits are evident.
Tooth plates appear to have not been in
close contact. The small size of the tooth
plate and the large size of the punctations
suggest a juvenile. A pterygopalatine process
is present, just behind the first and second
ridge (Fig. 3B–C).
Comparisons. The combination of sharp,
slender, high, straight, acute crests that
originate anteriorly, deep and rounded clefts,
irregular punctations arranged in lines, absence of occlusal pits, absence of cusps, large
pulp cavity, lack of petrodentine, obtuse crest
angle and relatively well marked inner angle
and the occlusal profile (as preserved) separates the tooth plate from those of Mesozoic
and Cenozoic Lepidosirenidae, Asiatoceratodontidae, Arganodontidae, Ptychoceratodontidae, Ferganoceratodus Kaznyshkin &
Nessov, 1985, Atlantoceratodus Cione et al.,
2007 and some genera of Neoceratodontidae
and Ceratodontidae.
The tooth plate, although fragmentary,
clearly differs from the South American
Lepidosirenidae and neoceratodontid genera Mioceratodus Kemp, 1998 and Archaeoceratodus Kemp, 1997[b] in the occlusal
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4
ALBERTO L. CIONE et al.
ALCHERINGA
Fig. 3. Ceratodontidae indet. tooth plate. A, occlusal view; B, dorsal view; C, labial profile; D, detail of bone and
enamel on the base of the tooth plate; E, reconstruction of the tooth plate. Scale bar ¼ 2 mm. Arrows indicate
pterygoid process.
profile and the absence of petrodentine. It
also does not resemble Neoceratodus
Castelnau, 1876.
The material is similar to tooth plates of
some Ceratodontidae such as Ceratodus
Agassiz, 1838 and Metaceratodus in occlusal
profile. However, it differs from the type
species of Ceratodus, C. latissimus Agassiz,
1838, from C. humei from the Paleocene and
Eocene of Africa and from other Ceratodus
by its deep clefts; sharp, slender, high,
straight crests; and apparent absence of
occlusal pits (see Kemp 1993, Churcher
et al. 2006). It differs from C. diutinus from
the Miocene of Australia in occlusal profile,
from the putative new genus of Ceratodontidae from the Danian of Bolivia (Schultze
1991) in the occlusal surface pattern and from
‘Ceratodus sp.’ from the Upper Cretaceous of
Pajcha Pata of Bolivia (Gayet et al. 2001) in
the occlusal profile, the different inner angle
and orientation of crests, and the mesiolingual concave profile.
MLP 90-II-5-990 is similar to some
tooth plates of the Cretaceous to Pleistocene
ceratodontid genus Metaceratodus. Crest
shape and a concave lingual edge resemble
those of the Australian Cretaceous species
M. ellioti Kemp, 1997[a]. However, we have
not observed the typical occlusal pits of that
genus.
Discussion
Dipnoans were cosmopolitan during the
early Mesozoic, but gradually became restricted to their current distribution in the
Southern Hemisphere during the Cretaceous
(Fig. 4). There is no explanation for their
demise in the Northern Hemisphere.
The youngest record of non–lepidosirenid
lungfish in Africa is from the Eocene and in
South America from the late Paleocene–
earliest Eocene (Longbottom 1984; this
paper). Presently, lepidosirenids inhabit
Africa and South America (Nelson 2006).
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ALCHERINGA
SOUTH AMERICAN TERTIARY LUNGFISH
5
Fig. 4. Eocene palaeogeographic map (modified from Blakey 2009) showing the distribution of Cenozoic dipnoans in
different continents. Stars, distribution of Metaceratodus; circles, neoceratodontids; squares, Ceratodus; asterisks,
lepidosirenids; arrow, fossil locality.
In Australia, lungfish remained diverse
during the Cenozoic, with two families
(Ceratodontidae and Neoceratodontidae)
incorporating several genera and species.
Ceratodontidae, a cosmopolitan family during much of the Mesozoic, became extinct in
Australia (Ceratodus in the Miocene and
Metaceratodus in the Pleistocene; Kemp
1993, 1997a, 2001). Neoceratodontidae,
known with certainty only in Australia,
included three genera: Archaeoceratodus,
Mioceratodus and Neoceratodus (Kemp
1997b). Presently, N. forsteri Krefft, 1870
is the only dipnoan living in Australia
(Nelson 2006).
The extinction of non-lepidosirenid
lungfish in Africa and South America may
be related to environmental changes. Their
extinction closely matched a peak in global
temperatures, the early Eocene Climatic
Optimun (EECO) (Fig. 2), and with the
diversification of many teleost orders.
Acknowledgements
For partial financial support: ANPCYT
(PICT 913), CONICET (PIP 5608), Universidad Nacional de La Plata. For valuable information: Anne Kemp, Alison
Longbottom. For permision to examine
dipnoan material: Museo Padre Molina,
Rı́o Gallegos, Argentina (Adan Tauber),
Museo de La Plata, La Plata, Argentina
(Marcelo Reguero), Museo Argentino de
6
ALBERTO L. CIONE et al.
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Ciencias Naturales ‘Bernardino Rivadavia’,
Buenos Aires, Argentina (Alejandro
Kramarz), Museo ‘Carmen Funes’, Plaza
Huincul, Argentina (Rodolfo Coria), Museo Patagónico de Ciencias Naturales,
General Roca, Rı́o Negro, Argentina (Pablo
Chafrat), Museo Prof. Dr. Juan Olsacher
(Alberto Garrido), Museo ‘Carlos Ameghino’ (Carlos Muñoz), Natural History Museum, London, England.
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