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

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 Nicola´s Gelfo [[email protected]] and Francisco Goin [[email protected]. edu.ar], Divisio´n 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 di- 1997a) and indeterminate ceratodonts and verse and almost cosmopolitan (Schultze Ceratodus sp. from the Danian Santa Lucı´a 2004). However, most genera became extinct Formation of Bolivia (Schultze 1991). before the Cenozoic. Since the beginning of A fragmentary tooth plate found in the Cenozoic, lungfish have been almost latest Paleocene–earliest Eocene beds in exclusively represented by the Neoceratodon- Patagonia by two of us (JNG and FJG) tidae and Lepidosirenidae, and have become shows that non–lepidosirenid lungfish sur- Downloaded By: [Gelfo, Javier] At: 14:49 8 September 2010 restricted to southern continents (South vived until this time in southern South America, Africa and Australia; Nelson 2006). America. Terminology is according to The only previously known Cenozoic Kemp (1993, 1997a,b, 2001). lungfish other than Lepidosirenidae and Neoceratodontidae are the ceratodontid Ceratodus humei Priem, 1914 from the Paleocene and Eocene of Saharan Africa Geographic and stratigraphic (Longbottom 1984, Churcher & de Iuliis provenance 2001), C. diutinus Kemp, 1993 from the The main exposures of the continental Las Oligocene–Miocene of Australia, Metacer- Flores Formation (Raigemborn et al. 2009) atodus bonei Kemp, 1997[a] from the upper are at the eastern tip of Gran Barranca, Oligocene to middle Miocene of Australia, south of Lago Colhue Huapi (south-central M. palmeri Krefft, 1874 from the Pliocene Sarmiento department, Chubut province, and Pleistocene of Australia (Kemp 1993, Argentina; Fig. 1). Together with the underlying Las Violetas and Pen˜ as Color- ISSN 0311-5518 (print)/ISSN 1752-0754 (online) Ó 2010 Association of Australasian Palaeontologists adas formations, and the overlying Koluel DOI: 10.1080/03115518.2010.489418 Kaike Formation, it is currently included 2 ALBERTO L. CIONE et al. ALCHERINGA

within the Rio Chico Group, an essentially All evidence (sedimentary, mineralogical, continental sedimentary succession of late palaeobotanical) analyzed by Raigemborn Paleocene to middle Eocene age in the San et al. (2009) is consistent with the Las Flores Jorge Gulf Basin (Fig. 2). Stratigraphic Formation being deposited in ‘tropical’ or charts and profiles of these formations were ‘subtropical’ climates, with warm tempera- provided by Raigemborn et al. (2009). tures and abundant precipitation. Its mam- At Gran Barranca, the Las Flores For- mal content, including the impressive mation reaches 44 m thick. It consists marsupial fauna dominated by frugivorous mostly of greyish mudstones and minor forms, conforms to this interpretation. epiclastic and volcaniclastic sandstones de- posited in floodplain–shallow lacustrine en- vironments (Raigemborn et al. 2009). The Systematic palaeontology fossiliferous bed is a 52 m thick sandstone DIPNOI Mu¨ller, 1845 near the base of this formation (4584302600S, CERATODONTIDAE Gill, 1872 6883701400W). There is no evidence of re- worked material at this level and locality. Ceratodontidae indet. (Fig. 3A–E) Apart from the ceratodontid lungfish de- scribed here, around 1500 mammal remains Material. MLP 90-II-5-990, a fragmentary (mostly, isolated teeth) have been exhumed upper tooth plate preserving the greater part and are currently under study. This rich of the first ridge and the whole second ridge. mammalian fossil assemblage indicates an The biological wear was normal, and the Itaboraian age of the South American Chro- material does not show any evidence of nological Scale (Paleocene–earliest Eocene; significant post-mortem abrasion. Bond et al. 1995, Gelfo et al. 2009). Repository. Divisio´n Paleontologı´a Verte- brados, Museo de La Plata (W1900FWA) La Plata, Argentina.

Description. The tooth plate is small. The very deep second cleft would indicate that Downloaded By: [Gelfo, Javier] At: 14:49 8 September 2010 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 junc- tion 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 sec- ond), 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 Fig. 1. Location map. Star indicates the fossil locality. Kemp 2001 absent) and cover the occlusal ALCHERINGA SOUTH AMERICAN TERTIARY LUNGFISH 3

Downloaded By: [Gelfo, Javier] At: 14:49 8 September 2010 Fig. 2. Stratigraphic chart of the Paleogene of Argentina. SALMAs, South American Land Mammal Ages.

surface. Some punctations appear to be pulp cavity, lack of petrodentine, obtuse crest arranged in radiating series. Most are angle and relatively well marked inner angle irregular. No occlusal pits are evident. and the occlusal profile (as preserved) sepa- Tooth plates appear to have not been in rates the tooth plate from those of Mesozoic close contact. The small size of the tooth and Cenozoic Lepidosirenidae, Asiatocera- plate and the large size of the punctations todontidae, Arganodontidae, Ptychocerato- suggest a juvenile. A pterygopalatine process dontidae, Ferganoceratodus Kaznyshkin & is present, just behind the first and second Nessov, 1985, Atlantoceratodus Cione et al., ridge (Fig. 3B–C). 2007 and some genera of Neoceratodontidae and Ceratodontidae. Comparisons. The combination of sharp, The tooth plate, although fragmentary, slender, high, straight, acute crests that clearly differs from the South American originate anteriorly, deep and rounded clefts, Lepidosirenidae and neoceratodontid gen- irregular punctations arranged in lines, ab- era Mioceratodus Kemp, 1998 and Archae- sence of occlusal pits, absence of cusps, large oceratodus Kemp, 1997[b] in the occlusal 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 MLP 90-II-5-990 is similar to some also does not resemble Neoceratodus tooth plates of the Cretaceous to Pleistocene Castelnau, 1876. ceratodontid genus Metaceratodus. Crest The material is similar to tooth plates of shape and a concave lingual edge resemble some Ceratodontidae such as Ceratodus those of the Australian Cretaceous species Agassiz, 1838 and Metaceratodus in occlusal M. ellioti Kemp, 1997[a]. However, we have Downloaded By: [Gelfo, Javier] At: 14:49 8 September 2010 profile. However, it differs from the type not observed the typical occlusal pits of that species of Ceratodus, C. latissimus Agassiz, genus. 1838, from C. humei from the Paleocene and Eocene of Africa and from other Ceratodus by its deep clefts; sharp, slender, high, Discussion straight crests; and apparent absence of Dipnoans were cosmopolitan during the occlusal pits (see Kemp 1993, Churcher early Mesozoic, but gradually became re- et al.2006).ItdiffersfromC. diutinus from stricted to their current distribution in the the Miocene of Australia in occlusal profile, Southern Hemisphere during the Cretaceous from the putative new genus of Ceratodonti- (Fig. 4). There is no explanation for their dae from the Danian of Bolivia (Schultze demise in the Northern Hemisphere. 1991) in the occlusal surface pattern and from The youngest record of non–lepidosirenid ‘Ceratodus sp.’ from the Upper Cretaceous of lungfish in Africa is from the Eocene and in Pajcha Pata of Bolivia (Gayet et al.2001)in South America from the late Paleocene– the occlusal profile, the different inner angle earliest Eocene (Longbottom 1984; this and orientation of crests, and the mesiolin- paper). Presently, lepidosirenids inhabit gual concave profile. Africa and South America (Nelson 2006). 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. Downloaded By: [Gelfo, Javier] At: 14:49 8 September 2010 In Australia, lungfish remained diverse be related to environmental changes. Their during the Cenozoic, with two families extinction closely matched a peak in global (Ceratodontidae and Neoceratodontidae) temperatures, the early Eocene Climatic incorporating several genera and species. Optimun (EECO) (Fig. 2), and with the Ceratodontidae, a cosmopolitan family dur- diversification of many teleost orders. ing much of the Mesozoic, became extinct in Australia (Ceratodus in the Miocene and Metaceratodus in the Pleistocene; Kemp Acknowledgements 1993, 1997a, 2001). Neoceratodontidae, For partial financial support: ANPCYT known with certainty only in Australia, (PICT 913), CONICET (PIP 5608), Uni- included three genera: Archaeoceratodus, versidad Nacional de La Plata. For valu- Mioceratodus and Neoceratodus (Kemp able information: Anne Kemp, Alison 1997b). Presently, N. forsteri Krefft, 1870 Longbottom. For permision to examine is the only dipnoan living in Australia dipnoan material: Museo Padre Molina, (Nelson 2006). Rı´o Gallegos, Argentina (Adan Tauber), The extinction of non-lepidosirenid Museo de La Plata, La Plata, Argentina lungfish in Africa and South America may (Marcelo Reguero), Museo Argentino de 6 ALBERTO L. CIONE et al. ALCHERINGA

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