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Home , Diplodon, Hyriidae, La Matilde Formation, Unionida

PalZ https://doi.org/10.1007/s12542-019-00498-3

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The (truly) frst freshwater molluscs from

Sergio Martínez1 · Roberto A. Scasso2 · Andrés Elgorriaga3 · Ignacio Capelli2 · Rodolfo del Valle4 · Pablo Puerta3 · Juan Manuel Lirio4 · Cecilia Rodríguez Amenábar4

Received: 19 December 2018 / Accepted: 24 October 2019 © Paläontologische Gesellschaft 2019

Abstract New collection work in Mount Flora, Hope Bay, Antarctic Peninsula, has confrmed the presence of bivalve moulds in the Mount Flora Formation. In contrast to a twenty-frst century article claiming to report the frst discovery of fossil freshwater molluscs in Antarctica, evidence of these molluscs was frst reported for Antarctica more than 110 ago by J. Gunnar Andersson. The bivalve was formally described and named some 50 years later, by Camacho, as Antediplodon esperanzaensis. The species was subsequently transferred to the for unknown reasons. Here, we illustrate specimens from the same locality for the frst time with photographs, considering them incertae saedis, in view of the absence of diagnostic characters. In fact, two morphotypes are present, one elongated, very similar to the nominal species A. esperanzaensis, and another one subelliptical in shape.

Keywords · Unionida · Jurassic · Mount Flora · Antarctica

Introduction Transantarctic Mountains. Thus far, this claim has remained unquestioned. The objective of this study was to resurrect a largely forgot- However, the fact is that Andersson (1906: 27) first ten fossil fnding, which led to an erroneous attribution of mentioned freshwater molluscs from Antarctica in a brief priority. account of the of Mount Flora, Hope Bay, Antarc- Ashworth and Preece (2003) reported the supposedly tic Peninsula. Halle (1913) cited this fnding, and Seward frst fnding of fossil freshwater molluscs from Antarctica. (1913), in a literature comment about the former publica- They corresponded to an indeterminate gastropod species tions, took note of it too. However, in the next few decades, belonging to the superfamily Lymnaeoidea and to a bivalve the reference to the bivalves was forgotten. assigned to the genus Pisidium (Sphaeridae), both found in Half a century later, Camacho (1957: 30) described and the late Neogene Meyer Desert Formation (Sirius Group), named for the frst time a species of an Antarctic freshwa- ter mollusc, Antediplodon esperanzaensis, on the basis of two moulds collected from the same area as that studied by Andersson (1906): the dark shales with fossil plants of the Handling Editor: Simon Schneider. Jurassic Mount Flora Formation (Fig. 1). The species was * Sergio Martínez later illustrated by a drawing in Herbst and Camacho (1970: [email protected] fg. 3, redrawn here in Fig. 2) as Diplodon esperanzaensis without any justifcation about the genus transfer. Subse- 1 Dpto. Paleontología, Facultad de Ciencias, Universidad de la República, Iguá 4225, 11400 Montevideo, Uruguay quently, this fnding was only mentioned by Martínez and Figueiras (1991), Martínez et al. (1993), Morton and Herbst 2 IGeBA, Departamento de Cs. Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos (2001), Watters (2001), and Parras and Grifn (2013). Aires, Int. Guiraldes 2160, Ciudad Universitaria, Pab. II, New collections from the type locality confrmed the C1428EHA Buenos Aires, presence of bivalves in Mount Flora and reminded us of 3 Museo Paleontológico Egidio Feruglio, Av. Fontana 140, the fact that the frst freshwater molluscs of Antarctica were 9100 Trelew, Chubut, Argentina reported almost 100 years before the most recent report. The 4 Instituto Antártico Argentino, Av. 25 de Mayo 1147, collected material is deposited in the Repositorio Antártico Villa Lynch, Provincia de Buenos Aires, Argentina

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Fig. 1 a Location map of the Hope Bay region in the Antarctic Penin- The orange arrows indicate the advance of the Flora Glacier and the sula. b Geological map of the region of Hope Bay (after Montes et al. area where fossil-rich blocks are abundant. c Main geological units in 2005). The uppermost, fossiliferous interval of the Mount Flora For- the Hope Bay region mation is marked, as well as its inferred trace below the Flora Glacier. de Colecciones Paleontólogicas y Geológicas of the Insti- 300-m-thick terrestrial clastic sedimentary unit of Jurassic tuto Antártico Argentino under the acronym and number age (see Rees 1993 for a discussion on the age of the unit), IAA-Pi 397. separated by an angular unconformity from the underly- ing Hope Bay Formation of Late Palaeozoic/ age. It is covered by the Kenney Glacier Formation (Antarctic Geological setting Peninsula Volcanic Group) of probable -Early age. The Mount Flora Formation (Caminos and Massabie 1980) The Mount Flora is a fning-upward succession depos- was discovered by Andersson (1906) and later studied in ited as an alluvial fan in a fault-controlled basin margin. detail by Bibby (1966), Elliot and Gracanin (1983), Farqu- Detailed facies analyses (Elliot and Gracanin 1983; Birken- harson (1984), Birkenmajer (1993), Montes et al. (2005) majer 1993) indicate a palaeoenvironment changing upwards and Birkenmajer and Ociepa (2008). It is an approximately from alluvial to fuvial, fnally capped by lacustrine beds. A

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(Holocene–Recent) and probably in former times. However, before the last glacier retreat the Flora Glacier and the rest of the NE-advancing glaciers in the area mostly delivered the blocks into the Antarctic Strait.

Systematic palaeontology

Classifcation follows Bieler et al. (2010).

Class Bivalvia Linnaeus, 1758 Subclass Newell, 1965 Fig. 2 Diplodon esperanzaensis. Redrawn from Herbst and Camacho Order Unionida Gray, 1854 (1970: fg. 3), with permission from the Asociación Paleontológica Argentina) incertae sedis, morphotype 1 Figure 3a–c large number of fossil plants, together with rare bivalves, 1957 Antediplodon esperanzaensis Camacho: p. 30. beetles and fsh remains (Halle 1913), were recovered from 1970 Diplodon esperanzaensis (Camacho)—Herbst and the lacustrine, uppermost part of the unit, which crops out in Camacho: fg. 3. the Mount Flora (Fig. 1) and from many large blocks spread by the glaciers all over a large area (Fig. 1). Description. Shell moderately infated. Umbo not prominent, The bivalves were exclusively found in loose, black-shale, situated in the anterior third. Dorsal margin short in its ante- moraine blocks in two close localities (63° 24′ 42.3″ S, 57° rior part; posteriorly it is straight, inclined downwards, and 00′ 18.7″ W and 63° 24′ 43.9″ S 57°00′ 21.0″ W; see Fig. 1). being truncated in its posterior portion. Anterior margin very The blocks lay on top of an outcrop of the Lower Member of convex. Posterior margin short, nearly straight. Ventral mar- the Mount Flora Formation. Their lithology is similar to that gin gently convex. From the umbo to the upper half of the of the lacustrine beds currently exposed in the north face of posterior margin there is an angulation of the shell. Imprints the Mount Flora, which also contains similar plant fossils. of growth lines present. The absence of bivalves in the outcrops can be attributed to minor, lateral paleoenvironmental changes. Shale beds not Dimensions. Length: x = 3.8 cm. Height: x = 2.1 cm l/h = 1.8. thicker than 0.5 m are interbedded with sandstones in the fossiliferous interval of the uppermost Mount Flora Forma- Original description. ‘Valva derecha representada por un tion, whereas thicker, well-laminated shale beds are repre- molde interno ovalado con el eje mayor orientado en la sented in the loose blocks of the glacial drift. This is prob- dirección ántero - posterior; extremidad anterior redondeada; ably related to lateral facies changes, expressed by thicker extremidad posterior subaguda; borde dorsal posterior rec- shale beds to the S, probably recording deeper lake deposits. tilíneo inclinado hacia atrás y formando un ángulo obtuso The blocks were eroded from the NE face of the Mount con el borde posterior que es corto; borde ventral suave- Flora Formation and delivered to their fnal location by the mente convexo, formando una concavidad casi imperceptible Flora Glacier, which spread most of the fossil-rich blocks en su unión con el borde posterior; borde anterior circular; along its NE pathway (Fig. 1). Holocene retreat of the gla- superfcie recorrida por líneas concéntricas de crecimiento, cier left exposed a thin cover of glacial detritus (lodgement con insinuación de algunas estrías radiales sobre el umbón. till) bounded by some prominent moraines, the latter being Longitud 4.4 cm; altura 2 cm.’ the result of retreat pulses of the Flora glacier during the Holocene. The fossiliferous blocks are part of the lodgement English translation. Right valve represented by an oval inter- till and moraine deposits. Their abundance decreases mark- nal mould, with the major axis oriented in the anteropos- edly out of the area marked with orange arrows in Fig. 1, terior direction; anterior margin rounded; posterior margin revealing their local provenance. They come from the ero- subacute; posterior dorsal margin straight, inclined back- sion of the beds in the uppermost part of the Mount Flora wards and forming an obtuse angle with the posterior mar- column which can be extrapolated into the Flora Glacier gin, which is short; ventral margin gently convex, forming an valley according to their strike. These beds were at the base almost imperceptible concavity when joining the posterior of the glacier during the last stages of the glacier evolution margin; anterior margin circular; surface with concentric

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Fig. 3 Selected specimens (Unionida inc. sed.) from lot IAA-Pi 397. a–c Morphotype 1 (elongated). d–f Morphotype 2 (subelliptical)

growth lines, with an insinuation of some radial grooves in Dimensions. Length: x = 3.1 cm. Height: x = 2.2 cm. the umbo. Length 4.4 cm; height 2 cm. L/H = 1.4.

Type locality. Mount Flora, Hope Bay, Antarctic Peninsula. Studied material. IAA-Pi 397, specimens 11-15 (Andrés Elgorriaga, Pablo Puerta, Ignacio Capelli, Roberto A. Scasso Type material. After a careful search in the Argentinean and Juan Manuel Lirio, collectors). repositories, we did not fnd the two moulds that constitute the syntype of the species, which can be considered lost. Remarks. The morphotype 2 difers from morphotype 1 in being more rounded, and without a posterior angulation. Its Studied material. IAA-Pi 397, specimens 1–10 (Andrés characteristics do not coincide with those of Antediplodon Elgorriaga, Pablo Puerta, Ignacio Capelli, Roberto A. Scasso esperanzaensis and it represents another species. But as and Juan Manuel Lirio, collectors). in the case of the morphotype 1, we consider it as - nida incertae sedis considering the absence of diagnostic Remarks. Although our specimens lack the insinuation of characteristics. radial grooves in the umbo described by Camacho (1957), the identity with his material can be established. Neverthe- less, we choose to consider them Unionida incertae sedis, Discussion since the moulds do not have any important distinct char- acteristics to justify a more refned taxonomic assignment. Camacho (1957) described his material as belonging to Antediplodon Marshall, 1923, but later Herbst and Cama- incertae sedis, morphotype 2 cho (1970) transferred it to Diplodon without any justifca- Figure 3d–f tion. Antediplodon was defned for Triassic North-Ameri- can freshwater species with traces of an umbonal sculpture Description. Shell subelliptical. Umbo not prominent, situ- [(‘Characterized by elongate form, abrupt anterior end, and ated anteriorly, near the middle of the valve. Dorsal margin especially by the sculpture of the beak, which consists of gently inclined downwards anteriorly and posteriorly. Ante- several fne, clear-cut, direct, radiating riblets’ (Marshall rior and posterior margins rounded. Ventral margin convex. 1923: 4)], which made it very similar to the neotropical Imprints of growth lines present. Diplodon.

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Here, we report the presence of two morphotypes of Acknowledgements We would like to express our sincere gratitude to Unionida in the same locality; one of them can be identifed the Asociación Paleontológica Argentina for permission to reproduce Antediplodon esperanzaensis Fig. 3 of Herbst and Camacho (1970), published in Ameghiniana; to with , and the other represents the Instituto Antártico Argentino for the logistic support and Martín a new morphotype. In the two cases, in the absence of diag- Sakamoto and the crew of the Esperanza Argentine Antarctic station nostic characters, we do not give a more precise taxonomic for their help in the feld work; and to Mike Reich and Simon Schneider assignment than Unionida incertae sedis. (PalZ editors), Arthur E. Bogan and an anonymous reviewer, whose comments and suggestions greatly contributed to improve an early ver- The chronologically and geographically closer freshwa- sion of the paper. ter fossil bivalves are Diplodon simplex Morton, 2001 and D. matildensis Morton, 2001 (both reported in Morton and Herbst 2001) from the La Matilde Formation (Middle Juras- sic) of Santa Cruz Province, Argentina, and cf. Diplodon References sp. (Martínez et al. 2007) from the Cañadón Asfalto Forma- tion (Middle Late Jurassic) of Chubut Province, Argentina. Andersson, J.G. 1906. On the geology of Graham Land. Geological Farther away, there are Diplodon batoviensis Martínez and Institution of Upsala, Bulletin 7: 19–74. Figueiras, 1991 and D. dasilvai Martínez and Figueiras, Ashworth, A.C., and R.C. Preece. 2003. The frst freshwater molluscs from Antarctica. Journal of Molluscan Studies 69: 89–92. 1991 from the Tacuarembó Formation (Late Jurassic) of Bibby, J.S. 1966. The stratigraphy of part of north-east Graham Land Uruguay. and the James Ross Island group. British Antarctic Survey Scien- The southern records of present unionids in South Amer- tifc Report 53: 1–37. ica are in the province of Chubut (Argentina) (Pereira et al. Bieler R., J.G. Carter, and E.V. Coan. 2010. Classifcation of Bivalve families. In Nomenclator of Bivalve Families, eds. P. Bouchet, and 2014; Torres et al. 2018). J.P. Rocroi. Malacologia 52(2): 113–133. Concerning biogeographical hypotheses, they have been Birkenmajer, K. 1993. Jurassic terrestrial clastics (Mount Flora Forma- centred mostly in . Parodiz (1969) hypothesised tion) at Hope Bay, Trinity Peninsula (West Antarctica). Bulletin of the Polish Academy of Sciences: Earth Sciences that the hyriids originated in North America and Herbst 41: 23–38. Birkenmajer, K., and A.M. Ociepa. 2008. Plant-bearing Jurassic strata and Camacho (1970) in Antarctica. Later, Graf et al. (2015) at Hope Bay, Antarctic Peninsula (West Antarctica): geology and claimed that the most common ancestor of Hyriidae should fossil-plant description. Studia Geologica Polonica 128: 5–96. be Gondwanic and post-Triassic, its descendants being the Camacho, H.H. 1957. Observaciones geológicas y paleontológicas ancestor of modern clades before the isolation of South en Bahía Esperanza, Puerto Paraíso e Islas Shetland del Sur y Melchior. 2. (Geologic and paleontologic observations in Hope America, Antarctica and by means of terrestrial Bay, Paradise Port and Southern Shetland and Melchior islands). barriers. The presence of unionids in the Jurassic of Antarc- Publicaciones del Instituto Antártico Argentino 4: 25–30. tica, although not noted by these authors, is in concordance Caminos, R., and A. Massabie. 1980. Antártida Argentina e Islas del with their hypothesis, being candidates to fll the distribu- Atlántico Sur. In Segundo Simposio de Geología Regional Argen- tina, ed. J.C.M. Turner. Academia Nacional de Ciencias de Cór- tional gap between Australia and . doba 2: 1529–1575. Unionoids are benthic and are considered very important Cummins, R.H. 1994. Taphonomic processes in modern freshwater members of freshwater systems (Cummins, 1994). Accord- molluscan death assemblages: Implications for the freshwater fos- Palaeogeography, Palaeoclimatology, Palaeoecology ing to Good (2004), an optimal Unionid habitat is a peren- sil record. 108: 55–73. nial aquatic one, with clean and shallow water, pH slightly Elliot, O.H., and T.H. Gracanin. 1983. Conglomeratic strata of Meso- alkaline, and a stable substrate. Anyhow, they are able to live zoic Age at Hope Bay, northern Antarctic Peninsula. In Antarctic in a rather wide spectrum of freshwater environments (Mar- Earth Science, eds. R.L. Oliver et al., 303–307. Canberra: Austral- tinez and Rojas 2004). Hence, the presence of these fossils ian Academy of Science. Farquharson, G.W. 1984. Late non-marine conglomeratic is coherent with the results of the facies analyses mentioned sequences of northern Antarctic Peninsula (the Botany Bay in the “Geological settings” section. Group). British Antarctic Survey Bulletin 65: 1–32. Good, S.C. 2004. Paleoenvironmental and paleoclimatic signifcance of freshwater bivalves in the Upper Jurassic Morrison Formation, Western Interior, USA. Sedimentary Geology 167: 163–176. Conclusions Graf, D.L., H. Jones, A.J. Geneva, J.M. Pfeifer III, and M.W. Klun- zinger. 2015. Molecular phylogenetic analysis supports a Gond- wanan origin of the Hyriidae (: Bivalvia: Unionida) and Although here considered as Unionida incertae sedis, the the paraphyly of Australasian taxa. Molecular Phylogenetics and nominal species Antediplodon esperanzaensis Camacho, Evolution 85: 1–9. Gray, J.E. 1854. A revision of the arrangement of the families of 1957 is the frst one found, mentioned, described and the bivalve shells (Conchifera). The Annals and Magazine of Natural oldest freshwater mollusc of Antarctica. Together with History (series 2) 13(77):408–418. another morphotype here described from the same locality, Halle, T.G. 1913. The Mesozoic fora of Graham Land. In Wissen- they show the presence of Jurassic Unionida in Antarctica, schaftliche Ergebnisse der Schwedischen Südpolar-Expedition (1901–1903), 3(14), 1–123. Stockholm: Lithographisches Institut very early into the history of the group. des Generalstabs.

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