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Keywords:

  • Limopsis;
  • Antarctica;
  • biogeography;
  • systematics;
  • evolutionary origins

Abstract

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. The fossil record of Limopsis in the southern high latitudes
  5. Systematic palaeontology
  6. Biogeographical history of Limopsis in the southern high latitudes
  7. Conclusions
  8. References

Abstract: Limopsis is one of the most speciose and widespread bivalve genera in the Southern Ocean at the present day. However, the fossil record of the genus is poorly known from the southern high latitudes. Here, we review the fossil record in this region to help understand the evolutionary origins of the genus. Limopsis infericola sp. nov. and additional specimens of a previously described species are added to the fossil record of Antarctica. The globally distributed limopsid clade had its earliest occurrences in the Early Cretaceous of Europe and New Zealand, then radiated during the Late Cretaceous (Maastrichtian, 70.6–65.5 Ma). Fossil evidence shows that the genus underwent a second, Cenozoic, radiation related to the isolation of Antarctica and the onset of cooling in the southern hemisphere. The genus has persisted in Antarctica for the last 50 myr, adapting to extreme changes in the environmental conditions, including surviving the last glacial maximum in marine refugia.

At the present day, the family Limopsidae Dall, 1895 (Arcoida) contains two genera: Empleconia (Dall, 1908) restricted to the North Pacific and Bering Sea with no known fossils, and LimopsisSassi, 1827 with a fossil record from the Mesozoic. At least forty extant and more than thirty extinct species of Limopsis are known (Tevesz 1977; Oliver 1981). Limopsis is described as having a cosmopolitan distribution, except for the high Arctic Ocean (Oliver 1981; Malchus and Warén 2005). However, L. minuta (Philippi, 1836) has been recorded as having a distribution that extends to above 70°N (Gofas et al. 2001). Bivalves of the genus Limopsis are epibenthic suspension feeders (Oliver and Allen 1980) and are lecithotropic nonbrooders (Malchus and Warén 2005). Species in the genus have a particular affinity to deep-sea habitats and the south polar regions (Nicol 1967; Vermeij 1978; Crame 1996). Members of the genus are characterized by having an orbicular, nearly equilateral shell shape, often with forward obliquity, by possessing strongly anisomyarian muscle scars (the anterior one being much larger than the posterior), a central resilifer and taxodont dentition (Newell 1969; Oliver and Allen 1980).

The global fossil record and evolutionary history of Limopsis is still poorly known (Oliver 1981). Tevesz (1977) suggested that the first recorded instance of Limopsis in the fossil record was in the Middle Jurassic (around 168 Ma) of Europe. However, the Jurassic species ‘Limopsis’ minima (Sowerby, 1825) and ‘Limopsis’ corallinensis (Buvignier, 1852) have been disregarded by Oliver (1981) and placed in the Grammatodontidae because of the ligament shape. Hallam (1976, 1977) described the radiation of Limopsis in the Jurassic, but his records were based on L. minima and thus are disregarded. Oliver (1981) believed that the first truly recognizable Limopsis sensu stricto specimens, assigned to L. albiensis (Woods, 1899), were from the Early Cretaceous (Albian, around 112 Ma) of England (Woods 1899). There is also evidence that Limopsis occurred uncommonly in late Early Cretaceous rocks of New Zealand, although species are unnamed (Speden 1975; Moore and Speden 1984). The genus underwent a Late Cretaceous (Maastrichtian) radiation into different life habits (Heinberg 1979; Oliver 1981), reaching a peak in the early Cenozoic (Oliver 1981).

Limopsis is a common element of the modern bivalve fauna in the Antarctic and sub Antarctic (Hain 1990; Linse 1999; Zelaya 2005; Aldea et al. 2008), occurring at all water depths of up to 4678 m (Griffiths et al. 2003). There are twelve known species from the Southern Ocean and adjacent South American Magellan region (Dell 1990; Linse 2002; http://www.antarctica.ac.uk/sombase, K. Linse unpublished data; Text-fig. 1). In the southern high latitudes, seventeen further Limopsis species were recorded from waters around Australia in water depths of up to 600 m (Lamprell and Healy 1998), four species were found around South Africa in water depths of up to 550 m (Ocean Biogeographic Information System (2010) http://www.iobis.org) and three species from New Zealand in depths from 422 to 1280 m (Beu 2006). The diversity of present-day Southern Ocean limopsids could be explained either by their migration into the region from elsewhere or by origination and diversification in situ. Beu (2009) suggests that Limopsis has little or no confirmed fossil record in Antarctica. In this study, we have been able to confirm further records in both Antarctica and the southern high latitudes, by studying specimens and published literature, and go on to use these to investigate the origins of the genus.

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Figure TEXT-FIG. 1..  The distribution of Recent Limopsis species in the Southern Ocean and adjacent Magellan Region, with locations of some fossil localities. 1 = Seymour Island, 2 = Snow Hill Island, 3 = McMurdo Sound, 4 = Victoria Land Basin, 5 = Deep Sea Drilling Project Site 270 and 6 = Vestfold Hills.

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Materials and methods

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. The fossil record of Limopsis in the southern high latitudes
  5. Systematic palaeontology
  6. Biogeographical history of Limopsis in the southern high latitudes
  7. Conclusions
  8. References

SOMBASE (Griffiths et al. 2003), SOMBASE-GSCM (the Cenozoic Marine Fauna Database, developed by H. Griffiths) and the Palaeobiology Database (http://paleodb.org) were used to access data on the distribution of fossil and Recent limopsids in Antarctica and the southern high latitudes. To confirm the affinity of new Antarctic fossil specimens of Limopsis, material was studied at the British Antarctic Survey and the Instituto de Geociências, Universidade de São Paulo, using an optical microscope, measured using vernier callipers, drawn with the aid of a camera lucida and photographed using a digital camera. Modern Antarctic specimens from the Scotia Arc region, the Antarctic Peninsula and the Weddell Sea are held in the British Antarctic Survey marine collections, and this material was also examined. Fossil specimens were also studied at the Natural History Museum in London. Published occurrences and systematic descriptions of Limopsis were consulted to ascertain the extent of the fossil record in the southern high latitudes, and fossil mollusc experts in the Southern Hemisphere were consulted for information on any unpublished material. Comparative drawings were made from specimens and from published photographs and line drawings.

The fossil record of Limopsis in the southern high latitudes

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. The fossil record of Limopsis in the southern high latitudes
  5. Systematic palaeontology
  6. Biogeographical history of Limopsis in the southern high latitudes
  7. Conclusions
  8. References

Published literature has shown that Limopsis occurred in New Zealand from the Cretaceous to the Pleistocene (Text-fig. 2). Although the shallower water species became extinct during the Quaternary, Beu (2006) claimed that species previously assigned to the genus Pectunculina should be reassigned to Limopsis and therefore there are records of Recent Limopsis in New Zealand. A study of new material and published literature has shown that fossil specimens of at least five different species of Limopsis have been found in Antarctica, ranging in age from the Maastrichtian (Cretaceous) to the Pleistocene (Text-fig. 2). Published fossil evidence of the genus in southern South America appears to have been restricted to the presence of just two species, found from the Late Oligocene to the Late Miocene in several localities (Sowerby 1846; Ihering 1899; Doello Jurado, 1915; Zinsmeister 1981; Del Río and Martínez 1998; Frassinetti and Covacevich 1999; Del Río 2004; Griffin and Nielsen 2008; Casadío and Griffin 2009; Parras and Griffin 2009). Limopsis first appeared in the published fossil record of Australia from the Late Paleocene and continues to the present day (Chapman 1911).

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Figure TEXT-FIG. 2..  A, The fossil record of Limopsis in Antarctica and first occurrences in the fossil record of named Limopsis species (not subspecies) from the published literature in other southern high latitudes areas from the Maastrichtian (Late Cretaceous) to the Pleistocene. The water depths for the deposits in which the fossils were found are also given (see text for references). inline image = Bathyal; inline image = Outer Shelf; inline image = Shallow/Inner shelf; *the fauna may have been transported from shallower depths to the site of deposition. Cenozoic temperature curve from Zachos et al. (2001). B, C, Continental reconstructions with palaeocirculation for key time periods are shown (from Lawver and Gahagan 2003) and new occurrences of fossil limopsids are plotted on these. B, Maastrichtian–Eocene. C, Oligocene–Miocene. D, Pliocene–Pleistocene. Coloured dots represent the number of first occurrences of limopsid taxa. inline image = 1; inline image = 2; inline image = 3; inline image = 4; inline image = 5; inline image = over 5.

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Cretaceous–Eocene

The oldest named New Zealand species is the Early Paleocene (Danian) age (Text-fig. 2) L. (Limopsista) micropsFinlay and Marwick, 1937 from the Wangaloa Formation at Wangaloa and Boulder Hill, South Island, which was a shallow water deposit (Finlay and Marwick 1937; Beu and Maxwell 1990). The species is now referred to L. microps (Text-fig. 3A) as Beu (2006) did not consider the subgenus Limopsista to be valid. However, there are several records of unpublished and unnamed specimens of Limopsis recorded in New Zealand, from the Piripauan–Haumurian local stages (Santonian–Maastrichtian; FRED – The Fossil Record Electronic Database –http://www.fred.org.nz/index.jsp) and also some unnamed older occurrences in the Early Cretaceous (Speden 1975; Moore and Speden 1984), so it is clear that Limopsis had a much longer and more extensive fossil record in New Zealand than the published literature of described species shows. The Maastrichtian species L. antarcticaWilckens, 1910 (Text-figs 2, 4A) from the shallow-water López de Bertodano Formation of Seymour and Snow Hill islands (Text-fig. 1), is the oldest species of Limopsis to have been identified in Antarctica (Wilckens 1910; Zinsmeister and Macellari 1988). The oldest Australian species, of Late Paleocene age, is L. rupestrisDarragh, 1994 (Text-figs 2, 5A) from the Pebble Point Formation, Otway Basin, Victoria, which was interpreted as a high-energy, shallow water deposit (Darragh 1994).

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Figure TEXT-FIG. 3..  A–Q, Fossil Limopsis species found in New Zealand in order of first appearance in the fossil record, oldest to youngest. Unless otherwise stated, images were taken from the original descriptions. A, L. micropsFinlay and Marwick, 1937. B, L. campaAllan, 1926. C, L. waihaoensisAllan, 1926, picture from Beu and Maxwell (1990). D, L. parvicostata (Maxwell, 1992). E, L. parmaMarwick, 1929. F, L. catenataSuter, 1917; picture from Beu and Maxwell (1990). G, L. zealandicaHutton, 1873; picture from Beu and Maxwell (1990). H, L. propeinvalidaLaws, 1939. I, L. gisbornensis (Maxwell, 1978) originally described and illustrated as L. retifera by Marwick (1931). J, L. productaFinlay and McDowall, 1923. K, L. lawsiKing, 1933. L, L. aoteana (Vella, 1954). M, L. cookiMarwick, 1931. N, L. invalidaMarwick, 1928. O, L. marwickiPowell, 1938, picture from Beu (2006). P, L. peteriBeu, 1969; picture from Beu (2006). Q, L. turnbulliBeu, 2006. Scale bars represent 5 mm.

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Figure TEXT-FIG. 4..  A–D, Fossil Limopsis species found in Antarctica. A, L. antarcticaWilckens, 1910. B, L. antarcticominutaStilwell, 2000. C, L. psimolisAnelli et al., 2006. D, L. infericola sp. nov. DSDP and ODP specimens ?Limopsis sp., L. aff. marionenesis and Limopsis sp. are not illustrated in the original literature and thus could not be included in this figure. The Cape Melville specimens assigned to Limopsis sp. are not illustrated because of the poor preservation of the material. Scale bars represent 5 mm.

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Figure TEXT-FIG. 5..  A–F, Fossil Limopsis species (not subspecies) found in Australia in order of first appearance in the fossil record, oldest to youngest. Unless otherwise stated, images were taken from the original descriptions. A, L. rupestrisDarragh, 1994. B, L. chapmaniSingleton, 1932. C, L. multiradiataTate, 1886. D, L. morningtonensisPritchard, 1901. E, L. beaumariensisChapman, 1911, external view from Ludbrook (1955). F, L. maccoyiChapman, 1911. G, L. affinitalisChapman and Crespin, 1928. H, L. werrikooensisSingleton, 1941. I, L. forteradiataCotton, 1930 picture from Lamprell and Healy (1998). J, L. tensioni (Tenison-Woods, 1878) picture from Lamprell and Healy (1998). Scale bars represent 5 mm.

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Three Limopsis species have been documented from the Eocene in New Zealand. The Bortonian (Lutetian–Bartonian: Middle Eocene) species L. campaAllan, 1926 (Text-figs 2, 3B) was found in the Waihao Greensand, Waihao Downs, South Island, a unit deposited in a deeper water, shelf environment (Beu and Maxwell 1990). The Kaiatan (Priabonian: Late Eocene) species L. waihaoensisAllan, 1926 (Text-figs 2, 3C; which ranged to the Runangan) and L. parvicostata (Maxwell, 1992; Text-fig. 2) were both found towards the top of the Waihao Greensand in the Tahu Member at McCulloch’s Bridge, South Island (Beu and Maxwell 1990), which was deposited in outer shelf to the uppermost bathyal waters (Maxwell 1992). The species L. parvicostata was originally assigned to the genus Pectunculina because of the presence of marginal crenulations (Text-fig. 3D). Maxwell (1992) considered that these crenulations made the species distinct from the smooth margined genus Limopsis. Pectunculina is a taxon which has a contentious taxonomic history. Although considered as a subgenus of Limopsis at the time, Vella (1954) also believed Pectunculina should be regarded as a separate genus because of its crenulated margin. However, Beu (2006) stated that the significance of a crenulate margin as a distinguishing character is unclear as the degree of crenulations can vary, meaning that there are intermediate species that cannot be placed in Pectunculina or Limopsis (Beu 2006; A. G. Beu, pers. comm. 2010). He also placed several New Zealand species previously assigned to Pectunculina into the genus Limopsis. Also, Lamprell and Healy (1998) placed Pectunculina as a subgenus of Limopsis, and Oliver (1981) referred all species previously named as Pectunculina to Limopsis (s.l.), but suggested that cladistics need to be employed to resolve this matter (Oliver, pers. comm. 2010).

The Eocene species L. antarcticominutaStilwell, 2000 (Text-figs 2, 4B) was restricted to erratics at McMurdo Sound in East Antarctica (Text-fig. 1), which were considered by Stilwell (2000) to be from shallow water facies. The age of the erratics was not accurately constrained, but the fauna present in the unit placed it around the late Early Eocene to Late Eocene (Stilwell 2000). The species L. chapmaniSingleton, 1932 (Text-figs 2, 5B) first occurred in an unnamed Middle–Late Eocene sandstone unit in the Carnarvon Basin of Western Australia (Darragh and Kendrick 2008). The unit was thought to have been deposited in a middle-shelf environment, although the fossils appeared broken, so transport may have occurred (Darragh and Kendrick 2008). The species also has other records from the Late Eocene, Oligocene and Early Miocene (Darragh and Kendrick 1980; Darragh 1985; Darragh and Kendrick 2008). The subspecies L. chapmani validaSingleton, 1932 was described from Birregurra, Victoria. Singleton (1932) stated that they differed slightly from L. chapmani in morphology, such as being more tumid; the specimens were tentatively dated as Miocene, but no geological information was given about the locality. The Aldingan (Bartonian–Priabonian: Late Eocene) species L. multiradiataTate, 1886 (Text-figs 2, 5C) was found in the shallow-water Blanche Point Formation of the St Vincent Basin at Kent Town and Aldinga Bay, South Australia (Ludbrook 1973).

Oligocene–Miocene

Early Oligocene specimens tentatively identified as ?Limopsis sp. (Text-fig. 2) were found in the CRP-3 drillhole in the Victoria Land Basin, Antarctica (Taviani and Beu 2001; Text-fig. 1). The stratigraphic units on either side of the unit in which the fossils were found were interpreted as having been deposited in inner- to middle-shelf environments (Taviani and Beu 2001). The identification was based on two fragments of a single valve of a specimen on which some shell sculpture and a small area of the hinge were preserved; the shell had a symmetrical, sub-circular shape, and the shell material was thick (Taviani and Beu 2001).

Four new species of Limopsis first appeared in the Early Miocene of Antarctica (Text-fig. 2). Several specimens identified as Limopsis aff. marionensis by Dell and Fleming (1975) were collected from mudstone and diamictite sediments from Deep Sea Drilling Project site 270 in the Ross Sea (Dell and Fleming 1975; Text-fig. 1). The identification was based on shell morphology, which was thought to resemble that of the Recent species L. marionensisSmith, 1885 (Dell and Fleming 1975). It was suggested that they had been transported to the deeper water depositional setting, without the separation of valves, by gravity slide or turbidity current (Dell and Fleming 1975). This assessment was based on the Recent distribution of L. marionensis; the possibility that the fossil specimens inhabited this depth was not considered. The oldest specimen from the drilling site, a broken juvenile, occurred just above the Oligocene/Miocene boundary (identified from microfossils in the core). Younger Miocene specimens included a left valve and fragments of an articulated pair of valves (Dell and Fleming 1975). Dell and Fleming (1975) suggested that the continuous occurrence of sea ice was unlikely, but the presence of diamictites in the samples indicated at least periodic glacial conditions.

Early Miocene limopsids also occurred in the Cape Melville Formation, King George Island (South Shetland Islands; Text-fig. 6). This outer shelf to upper slope glacial unit was dated using Sr isotopes from bivalve specimens at 22.6 ± 0.4 Ma (Early Miocene; Dingle and Lavelle 1998). Five specimens of Limopsis psimolis Anelli, Rocha-Campos, Dos Santos, Perinotto and Quaglio, 2006 were identified; this species was characterized by large, thick shells and strongly anisomyarian muscle scars (Text-figs 4C, 7A). Two additional specimens from the BAS collections (P. 2702.696 right and left valve preserved and P. 2702.25, internal mould of both valves, hinge region missing) have been assigned to L. psimolis based on shell shape, shell thickness and shape of the muscle scars (Text-figs 4D, 7B). Three specimens from the BAS collections have been identified as Limopsis sp. (P. 2702.226, P. 2702.170 and P. 2702.735); species designation is not possible because of abrasion and preservation as internal moulds. Finally, four specimens have been assigned to a new species of Limopsis (L. infericola sp. nov. see systematic palaeontology below; Text-figs 4E, 7C).

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Figure TEXT-FIG. 6..  A, Location of the South Shetland Islands in relation to the Antarctic Peninsula. B, King George Island, showing the location of Cape Melville. A, B, from: Birkenmajer (1987). C, Cape Melville geology and site localities (P. 2702 and P. 2707) for Limopsis infericola n. sp. specimens. (From Feldmann and Crame 1998).

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Figure TEXT-FIG. 7..  A–D. Limopsis specimens from the Cape Melville Formation, King George Island, South Shetland Islands, Antarctica. A, L. psimolisAnelli et al., 2006. B, L. psimolis P. 2702.696 from British Antarctic Survey collection. C, L. infericola sp. nov, holotype P. 2702.736. D, Specimen GP/1T 2177, previously identified as a paratype of L. psimolis by Anelli et al. (2006), is re-assigned to L. infericola sp. nov. Scale bars represent 10 mm.

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Limopsis insolita (Sowerby, 1846; Text-figs 2, 8) was a long-ranging species known from Patagonia. It was common throughout the tertiary shallow marine molluscan assemblages of Argentina, which ranged from the Oligocene to Middle Miocene (Del Río 2004). The species was found at several localities, in three geological units – the San Julian, Monte León and Chenque Formations (Zinsmeister 1981; Griffin and Nielsen 2008; Casadío and Griffin 2009; Parras and Griffin 2009). L. insolita was also identified from the Late Oligocene to Early Miocene Guadal Formation, Pampa Castillo, Región de Aisén in Chile (Frassinetti and Covacevich 1999). Two specimens of an undescribed Miocene species of Limopsis were found in the Navidad Formation of Chile (see GSA Data Repository item 2010262 of Kiel and Nielsen 2010); however, they have not yet been described or figured. The species L. modestaDoello Jurado, 1915 (Text-figs 2, 8B) was found in rocks deposited in shallow water from the Late Miocene Arroyo Pescado borehole in the Buenos Aires Province (Del Río and Martínez 1998).

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Figure TEXT-FIG. 8..  A, B, Fossil Limopsis from South America. A, L. insolita (Sowerby, 1846) from South America (From Griffin and Nielsen 2008). B, L. modestaDoello Jurado, 1915 (From Del Río and Martínez 1998). Scale bars represent 5 mm.

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There are several early references to L. insolita occurring in New Zealand in the Oligocene–Miocene (Zittel 1864; Hutton 1873). However, these records have not been substantiated. Shells originally assigned to L. insolita by Zittel (1864) and Hutton (1873) were then referred to L. zitteli, Ihering, 1907 (inIhering 1905–1907). This name was considered to be a nomen dubium by Beu and Maxwell (1990), who assigned the specimens to L. catenataSuter, 1917. Also, material recorded by Hutton (1873) as L. insolita could not be traced (Beu and Maxwell 1990). There were poorly illustrated Australian specimens assigned to L. insolita by Chapman (1911), who stated that Dennant and Kitson (1903) synonymized the specimens with L. morningtonensisPritchard, 1901. Tate (1886) also referred several specimens to L. insolita. These occurrences of L. insolita in Australia were disputed by Singleton (1932), who placed them all in the species L. chapmani.

Several Early Miocene Limopsis species have been recorded from Australia (Text-fig. 2). L. morningtonensisPritchard, 1901 (Text-fig. 5D) first occurred in the Fishing Point Marl, Horden Vale, Victoria, which was a shallow water deposit (Darragh 1985). L. beaumariensisChapman, 1911 (Text-fig. 5E) (Ludbrook 1955) is associated with the Gellibrand Marl Formation at Lake Bullenmerri in the Otway Basin, Victoria (Chapman 1911; Bock and Cook 2001); this was thought to be a cool, deep water deposit (Nicolaides 1995). Chapman (1911) also stated that the variant L. beaumariensis var. depressaChapman, 1911 could be distinguished from L. beaumariensis by its thin, depressed form, apiculate umbo and stronger concentric striae. Finally, L. maccoyiChapman, 1911 (Text-fig. 5F) also occurred in the Gellibrand Marl Formation from Brown’s Creek, Victoria (Nicolaides 1995).

Limopsis species were common throughout the Oligocene and Miocene (Text-fig. 2) in New Zealand in a variety of different environments. The Duntroonian (Chattian: Late Oligocene) species L. parmaMarwick, 1929 from the Chatton Formation, Shell Gully, Chatton, South Island was preserved in a shallow water assemblage (Beu and Maxwell 1990; Text-fig. 3E). During the Duntroonian (Chattian: Late Oligocene), the first specimens of L. catenataSuter, 1917 (Text-fig. 3F) were found from the upper part of the Wharekuri Greensand, Lake Waitaki, South Island in a mid-shelf depth assemblage. The species also occurred in shallow water assemblages until the Waiauan (Serravallian: Middle Miocene; Beu and Maxwell 1990). Waitakian (Aquitanian: Early Miocene) aged examples of L. zealandicaHutton, 1873 (Text-fig. 3G) were identified from two localities on South Island: first, from the Mount Harris Formation in the Tengawai River near Trap Creek and second, in the Otekaike Limestone Formation at Trig Z, Otiake. At both of these localities, deeper water assemblages were preserved (Beu and Maxwell 1990). L. zealandica was a long-ranging species, with records until the Altonian (Burdigalian–Langhian: Early–Middle Miocene) and possibly younger (Burdigalian–Serravallian; A. G. Beu, pers. comm. 2010). The Otaian (Aquitanian: Early Miocene) L. propeinvalidaLaws, 1939 (Text-fig. 3H), from the Pakaurangi Formation, Pakaurangi Point, Kaipara Harbour, North Island was preserved within an outer shelf assemblage (Laws 1939; Beu and Maxwell 1990). This species ranged until the Altonian (Burdigalian–Langhian: Early–Middle Miocene; Beu and Maxwell 1990). The Lillburnian (Serravallian: Middle Miocene) species L. gisbornensisMaxwell, 1978 (Text-fig. 3I) occurred in the Tutamoe Conglomerate, Pangopango Stream, Gisborne District, North Island (Maxwell 1978). The Tutamoe Conglomerate was a deeper water unit that also contained shallow water molluscs, suggesting a degree of transport for some aspects of the fauna (Beu and Maxwell 1990). L. gisbornensis was previously designated as L. retiferaMarwick, 1931; however, the name L. retifera had already been assigned to another specimen (Maxwell 1978; Beu and Maxwell 1990). The Waiauan (Serravallian: Middle Miocene) L. productaFinlay and McDowall, 1923 (Text-fig. 3J) was found in the Dowling Bay Limestone, Dowling Bay, Dunedin, South Island (Beu and Maxwell 1990); the unit was thought to represent an outer shelf depositional setting (Finlay and McDowall 1923). However, this specimen came from a highly tectonised locality and was possibly a distorted specimen of other common species at the locality such as L. zealandica or L. gisbornensis (Beu, pers. comm. 2010). The early Tongaporutuan (Tortonian: Late Miocene) L. lawsiKing, 1933 (Text-fig. 3K), from the Hurupi Series, Hurupi Creek, Palliser Bay, Southern Wairarapa, North Island and Blind River, Malborough, north South Island, was described as a shelf dwelling species (Beu 2006). The Middle Tongaporutuan (Tortonian: Late Miocene) species L. aoteana (Vella, 1954) (Text-fig. 3L) from bathyal mudstones at Bell’s Creek, Southern Wairarapa, North Island (Vella 1954; Beu and Maxwell 1990) was originally assigned to the genus Pectunculina. Late Miocene specimens of L. cookiMarwick, 1931 (Text-fig. 3M) were described from the Ormond Formation, Gisborne District, North Island, which has been interpreted as a shallow water deposit (Marwick 1931). Beu (pers. comm. 2010) suggested that there are probably many unidentified specimens of Limopsis in New Zealand fossil collections, including several unnamed new species in the richly diverse, shelf depth successions at Clifden, Southland from the Altonian–Waiauan (Burdigalian–early Tortonian: Early–Late Miocene).

Pliocene–Pleistocene

Several species first appeared in the Late Pliocene to Early Pleistocene fossil record of New Zealand (Text-fig. 2). The Waipipian–Mangapanian (Piacenzian–Gelasian: Late Pliocene) species L. invalidaMarwick, 1928 (Text-fig. 3N) from the Whenuataru Tuff, Pitt Island, Chatham Islands probably inhabited deep, cold waters (Marwick 1928; Beu and Maxwell 1990). The Nukumaruan (Gelasian: Late Pliocene) L. marwickiPowell, 1938 (Text-fig. 3O) occurred in the Castlepoint Formation, Castlepoint, East Wairarapa, North Island, which was originally considered to be a mixed shelf and upper bathyal fauna, but Beu (2006) considered it to be entirely bathyal. Another Nukumaruan (Gelasian: Late Pliocene) species was L. peteriBeu, 1969 (Text-fig. 3P), from a mudstone stratigraphically lower than the Pukenui Limestone, from Palliser Bay as well as from the Ruakokopatuna and Mangaopari valleys in South Wairarapa, North Island; this was deposited in deep, cold waters (Beu 2006). Finally, the Castlecliffian (Pleistocene) species L. turnbulliBeu, 2006 (Text-fig. 3Q) occurred in a Pleistocene mudstone, Wilson River, SW Fiordland, South Island, which was also interpreted as a deep, cold water deposit (Beu 2006; Turnbull et al. 2007). The shallower water Limopsis species were absent in New Zealand from the Late Pleistocene (Beu 2006); Beu stated that bathyal species (assigned to Pectunculina, which he placed in Limopsis) are present in waters around New Zealand at the present day and suggested that the genus retreated to deep water around New Zealand as temperatures fell during the late Neogene (Beu 2006).

A Pliocene occurrence of L. marionensis (Text-fig. 2) was recorded from an unnamed sandstone horizon at Marine Plain in the Vestfold Hills, East Antarctica (Pickard et al. 1988; Text-fig. 1). The depositional setting was thought to have been shallow water, less than 50 m deep, in an interglacial period, warmer than at present (Pickard et al. 1988). Unfortunately, there was no description or illustrations of the specimens. In Australia, the Pliocene species L. affinitalisChapman and Crespin, 1928 (Text-figs 2, 5G) was recorded from a borehole on the Mornington Peninsula, Victoria, in sandy sediments thought to have been deposited in shallow waters (Chapman 1928). The Late Pliocene species L. werrikooensisSingleton, 1941 (Text-figs 2, 5H) occurred in the Werrikoo Limestone, Glenelg River, Victoria, Australia, a unit that was deposited in very shallow water (Singleton 1941; Darragh 1985). In Australia, two of the species that arose during the Miocene, L. beaumariensis and L. maccoyi, had a continuing record into the Pliocene (Chapman 1911; Ludbrook 1955). Chapman (1911) also stated that in the Pliocene, L. maccoyi was ‘moderately rare; passing into L. tenisoni (living)’ suggesting that there was a continuous record of some species of Limopsis in Australia. This is also shown by L. forteradiataCotton, 1930 (Text-figs 2, 5I) and L. tensioni (Tenison-Woods, 1878; Text-figs 2, 5J), which were both recorded in the Early Pleistocene in the east of Western Australia, in the shallow water Roe Calcarenite (Ludbrook 1978). These two species both range until the present (Lamprell and Healy 1998).

A Middle Pleistocene record of Limopsis (Text-fig. 2) was found in an unnamed carbonate-rich unit in the CRP-1 drillhole, Cape Roberts, Victoria Land Basin, Antarctica (Taviani et al. 1998; Text-fig. 1). However, the age of this unit was not precise, and there was no description or image of the Limopsis specimen. Taviani et al. (1998) estimated water depth at the time of deposition to have been approximately within the range of 100–200 m. There are currently no published records of Limopsis from southern South America in the Pliocene–Pleistocene.

Recent

Oliver (1981) divided Recent Limopsis species into three major groups (limopsiform, glycymeriform and abyssate) and thirteen morphological classes based on shell characters and anatomical features. In Antarctica, there is a diversity of Limopsis species at the present day in comparison with other genera (Text-fig. 9), with current circum-Antarctic and Magellan Region species belonging to three of the morphological classes (I, V and XIII) described by Oliver (1981). Classes I and V belong in Oliver’s limopsiform group and class XIII belongs to the abyssate group. There are no members of glycymeriform group in Antarctica, this class being present in the Indo-Pacific and Australia (Oliver 1981). Oliver (1981) stated that class I limopsids are cosmopolitan, except for the Arctic Ocean, and are typically ploughing forms living semi-infaunally in soft sediments. They are represented by L. marionensis (Text-fig. 9A) and L. tenella dalliLamy, 1912 (Text-fig. 9B), which are found in Antarctic waters and the Magellan Region, and L. tenella tenellaJeffreys, 1879 (Text-fig. 9C) from Antarctic waters (Text-fig. 1). Class V limopsids are cosmopolitan, except for the Arctic Ocean; they are more sedentary and have an infaunal habit. Representatives from Antarctic waters are L. longipilosaPelseneer, 1903 (Text-fig. 9D) and L. scabraThiele, 1912 (Text-fig. 9E); L. mabillianaDall, 1908 (Text-fig. 9F) is found both in Antarctic waters and in the Magellan Region (Text-fig. 1). Class XIII limopsids are only found in the Antarctic Ocean and are thought to have a shallow burrowing mode of life (Oliver 1981). The Antarctic species L. enderbyensisPowell, 1958 (Text-fig. 9G), L. lillieiSmith, 1915 (Text-fig. 9H), and L. scotianaDell, 1964 (Text-fig. 9I) belong to this group, and Oliver (1981) also included L. hirtella Mabille and Rochebrune, 1911 (inRochebrune and Mabille 1889; Text-fig. 9J), which is found in Antarctic waters and the Magellan Region (Text-fig. 1). Finally, Recent Southern Ocean species that have not been assigned to a morphological group include Limopsis sp. 1 (Text-fig. 9K) and Limopsis sp. 2 (Text-fig. 9L), which have been identified by K. Linse from Antarctic waters (unpublished data) and L. knudseniDell, 1990 (Text-fig. 9M), known from the Antarctic and Magellan Region (Text-fig. 1).

image

Figure TEXT-FIG. 9..  A–M, Recent Limopsis species from waters around Antarctica and the Magellan region. Images were used from the original descriptions, unless otherwise stated. A, L. marionensisSmith, 1885 (specimen MR 597 from the BAS marine collection). B, L. tenella dalliLamy, 1912 (image from Dell 1990). C, L. tenella tenellaJeffreys, 1879 (image from Dell 1990). D, L. longipilosaPelseneer, 1903. E, L. scabraThiele, 1912 (image from Dell 1990). F, L. mabillianaDall, 1908 (image from Dell 1990). G, L. enderbyensisPowell, 1958. H, L. lillieiSmith, 1915. I, L. scotianaDell, 1964. J, L. hirtella Mabille and Rochebrune, 1889 inRochebrune and Mabille (1889) (image from Lamy 1911). K, Limopsis undescribed sp. 1 BAS marine collection. L, Limopsis undescribed sp. 2 BAS marine collection. M, L. knudseniDell, 1990. Scale bars represent 5 mm.

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Modern Limopsis species are also found in South African and Australian waters in depths of up to 600 m (Oliver 1981; Lamprell and Healy 1998). Several species have been described from bathyal depths around New Zealand; however, they were originally assigned to Pectunculina as they possess crenulate inner ventral margins. Beu (2006) included L. lata (Smith, 1885; placed in morphological class VII, limopsiform group by Oliver, 1981), L. proceritas (Crozier, 1966) and L. tasmani (Dell, 1956; placed in morphological class V, limopsiform group by Oliver (1981)) in Limopsis. Therefore, several deep-water Limopsis species are present in New Zealand waters.

Systematic palaeontology

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. The fossil record of Limopsis in the southern high latitudes
  5. Systematic palaeontology
  6. Biogeographical history of Limopsis in the southern high latitudes
  7. Conclusions
  8. References

Order ARCOIDA Stoliczka, 1871 Superfamily LIMOPSOIDEA Dall, 1895 Family LIMOPSIDAE Dall, 1895 Genus LIMOPSIS Sassi, 1827

Type species. Arca auritaBrocchi, 1814 by original designation.

Remarks.  Specimens have been assigned to Limopsis based on their shell shape, strongly anisomyarian muscle scars (the anterior one being much larger than the posterior), central resilifer and taxodont dentition (Newell 1969; Oliver and Allen 1980). Extensive study of literature and material has confirmed these morphological characters, and new specimens agree with this description.

Limopsis infericola sp. nov. Text-figures 4E, 7C–D

Derivation of name.  Latin inferus– southern; cola– dweller.

Holotype.  P. 2702.736 (Text-fig. 7c) is designated as the holotype. The specimen consists of the left valve only.

Paratype.  P. 2702.225 internal mould; preserves both the right and left valves.

Material.  P. 2702.35: a partial internal mould of the right valve, P. 2707.20: both the right and left valves are preserved, the posterior of the shell is missing and specimen GP/1T 2177 (Fig. 7D) described as L. psimolis by Anelli et al. (2006), but unfigured in their original description.

Diagnosis.  Fossil Limopsis species with a long straight hinge margin, oblique shell shape and large lenticular resilifer.

Description.  Thin-shelled species, orbicular, obliquely elongate towards the posterior. Height 27.4 mm (P. 2702.736), length 26.9 mm (P. 2702.736) and inflation 14 mm (P. 2702.225). The dorsal margin is straight and the ventral margin is well rounded. The postero-dorsal margin is long, over twice the length of the anterior dorsal margin. The antero-ventral margin is almost twice the length of the postero-ventral margin. The postero-ventral and antero-ventral margins are curved and the antero- and postero-dorsal margins are slightly curved. The umbones are abraded but appear to be small on P. 2702.736; they cannot be seen on additional specimens as they are missing on GP/1T 2177 and the other material consists of internal moulds.

The species possesses strongly anisomyarian muscle scars; the posterior muscle scar is over twice the width of the anterior muscle scar. There is a very prominent anterior ridge and within this is located the ovate anterior muscle scar, which is positioned more dorsally than the posterior muscle scar. There are commarginal growth ridges on the external surface of the shell and fine radial linear striations indenting the shell at a density of 2–3/mm. Internally, the ventral margin of the shell shows very clear striations immediately dorsal to the pallial line, at a density of about 3–4/mm. The species exhibits taxodont dentition, with 12 anterior teeth and 11 posterior teeth (P. 2702.736). The anterior teeth are more closely spaced than the posterior teeth on P. 2702.736. P. 2702.225 has 12 posterior teeth and 12 anterior teeth. P. 2702.35 is incomplete and abraded, so not all of the teeth were visible, but 7 teeth can be seen posteriorly and 10 can be seen anteriorly. The resilifer is large and lenticular.

Remarks. Limopsis infericola sp. nov. differs from the holotype of the other Cape Melville Formation species, L. psimolis, as it is smaller, more elongate, has a thinner shell, and in the shape and position of the posterior muscle scars (Text-fig. 7). Unfortunately, the hinge line is incomplete in all specimens of L. psimolis, so a direct comparison of this feature cannot be made. The new species is very similar to GP/1T 2177, which was designated as a paratype of L. psimolis by Anelli et al. (2006). This paratype differs significantly from the holotype of L. psimolis. GP/1T 2177 and L. infericola are both thin shelled, with fine ornament and posterior elongation. Therefore, specimen GP/1T 2177 should be re-assigned from L. psimolis to L. infericola sp. nov.

Limopsis infericola sp. nov. resembles several Limopsis species from the Cenozoic of New Zealand in general size and shape, including L. campaAllan, 1926 and L. zealandicaHutton, 1873. However, L. infericola differs from these species in having a longer hinge margin, a slightly different shell outline and in the muscle scar shape. The dentition of L. infericola is similar to that of L. parmaMarwick, 1929, but the new species differs as it has a straighter dorsal margin, the umbones are less pronounced, the anterior and posterior margins are different and the resilifer is much larger. L. catenataSuter, 1917 has a large resilifer similar in shape to L. infericola, but has a shell that is less oblique and a wider hinge line. L. infericola also has a much longer and straighter dorsal margin. L. infericola differs from L. turnbulliBeu, 2006 in having a longer dorsal margin and less pronounced umbones.

The holotype has a very similar hinge line to Recent specimens (MR 597; Text-fig. 9A), identified as L. marionensisSmith, 1885. L. infericola differs only in the shape of the ventral part of the shell, which is more rounded and less oblique towards the posterior in comparison with MR 597, and in the length of the dorsal margin, which is shorter than in MR 597. It is possible that these two species are related and L. infericola may be an ancestral form of this modern Antarctic taxon.

Occurrence.  Cape Melville, King George Island, South Shetland Islands, Antarctica in the Early Miocene (Aquitanian) Cape Melville Formation, Moby Dick Group, 62°02′S, 57°38′W (Text-fig. 6).

Biogeographical history of Limopsis in the southern high latitudes

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. The fossil record of Limopsis in the southern high latitudes
  5. Systematic palaeontology
  6. Biogeographical history of Limopsis in the southern high latitudes
  7. Conclusions
  8. References

The first published occurrence of a named species of the genus Limopsis in the southern high latitudes (Wilckens 1910; Zinsmeister and Macellari 1988) is coincident with the initial Late Cretaceous (Maastrichtian) radiation of the genus documented by Heinberg (1979) and Oliver (1981), although other older unpublished and unnamed occurrences of Limopsis are known from New Zealand (Speden 1975; Moore and Speden 1984 FRED – The Fossil Record Electronic Database –http://www.fred.org.nz/index.jsp). Subsequently, throughout the Paleocene and Eocene, there were sporadic occurrences of Limopsis species in the southern high latitudes (Text-fig. 2). In the Oligocene to Miocene, the genus underwent a second radiation; species numbers increased in Antarctica as well as in temperate New Zealand and Australia (Text-fig. 2). Three new Limopsis taxa appeared in the Early Miocene of Antarctica, three in the early to Middle Miocene of Australia, and nine of the seventeen species described from New Zealand appeared from the Late Oligocene and throughout the Miocene (Text-fig. 2). Specimens of L. insolita and L. modesta first occurred in Chile and Argentina during the Late Oligocene to Late Miocene, and L. insolita was common and abundant throughout this time period. The first radiation of the genus in the Late Cretaceous was probably related to habitat differentiation (Oliver 1981), with new species developing both endobyssate and epibyssate modes of life. The second radiation in the southern high latitudes appears to have been related to environmental changes occurring throughout the southern region at the time, linked to the isolation of the continental shelves following the final breakup of the southern high-latitude continents. This distribution history is not unique to the limopsid clade, as a similar pattern of Mesozoic ancestry in the northern hemisphere followed by a Cenozoic radiation in the Southern Ocean is shown by marine isopods (Brandt et al. 1999).

The onset of deep water associated with the formation of the Antarctic Circumpolar Current (ACC) resulted in cooling temperatures in Antarctica, but the exact dates for these events have not been firmly established (Pfuhl and McCave 2005; Scher and Martin 2006; Livermore et al. 2007; Lyle et al. 2007). Most studies place the onset of the ACC around Eocene/Oligocene boundary to Early Oligocene (Barker et al. 2007). The timing for the onset of a deepwater connection around Antarctica has been a matter of debate, with the oldest date to be given as 31 ± 2 Ma (Early Oligocene; Lawver and Gahagan 2003). However, Pfuhl and McCave (2005) stated that there is little sedimentary evidence for this date and suggest the younger age range of 29.7–21.8 Ma (Late Oligocene–Early Miocene), as given in Eagles and Livermore (2002) and Livermore et al. (2004). More recently, Pfuhl and McCave (2007) stated that sedimentary evidence from the Southern Ocean suggested that the onset of the ACC immediately preceded the Oligocene/Miocene boundary. Ocean Drilling Program and Deep Sea Drilling Project results suggested that the full development of the ACC resulted in faunal turnover, with cool water cosmopolitan and true Antarctic endemic forms increasing in prominence (Lazarus and Caulet 1993; Brown et al. 2006).This fits with molecular evidence from Linse (unpublished data), which suggested a deep-sea origin for Recent Antarctic limopsids in the mid-Cenozoic. This was also consistent with the discovery of Limopsis marionensis-like specimens from the Early Miocene onwards (Dell and Fleming 1975, and L. infericola sp. nov.). Recent Antarctic Limopsis species are cool-adapted; therefore, cooling temperatures might have been a key factor in the increase in the number of Antarctic limopsids in the Early Miocene. These Early Miocene Antarctic limopsids are found in glacial sediments from King George Island, dated at 22.6 ± 0.4 Ma (Dingle and Lavelle 1998; Troedson and Riding 2002).

Australian and New Zealand limopsids also appear to have undergone a radiation in the Late Oligocene to Early Miocene (Text-fig. 2). The separation of Antarctica, the onset of the ACC and the establishment of the Polar Front meant that Australia and New Zealand became physically isolated from Antarctica. In Australia, some fossil species of Limopsis had extensive ranges indicating that the genus was less affected by Cenozoic palaeoenvironmental changes (Chapman 1911). In New Zealand, tectonic movements throughout the Neogene led to the formation of localized basins, providing a variety of habitats for molluscs (Beu and Maxwell 1990). The appearance of species in basins of different water depths suggests that Limopsis adapted to new niches that were opening up because of these tectonic movements. There are four species identified from New Zealand in the Late Pliocene to Early Pleistocene. After this, the species with smooth (as opposed to crenulated) inner ventral margins characteristic of the genus in New Zealand became extinct (Beu and Maxwell 1990).

Few fossils are found from the Quaternary in Antarctica as a result of erosion of sediments after the last glacial maximum. Another factor in the lack of Quaternary fossils was the extension of ice sheets onto continental shelves, which displaced the marine fauna; many groups are thought to have migrated northwards away from Antarctic waters at this time (Clarke and Crame 1992). That the genus does have a Quaternary record shows that it managed to adapt and survive the extreme cooling in Antarctica, probably by living in refugia. The Limopsis population appears to have been an incumbent element of the Antarctic fauna, as fossils are found from the Late Maastrichtian and throughout the Cenozoic in the region. The genus appears to have adapted to the changing conditions of the Southern Ocean during this period, radiating into new niches that formed, and this has led to Limopsis being one of the most speciose bivalve genera in Antarctic waters at the present day.

Conclusions

  1. Top of page
  2. Abstract
  3. Materials and methods
  4. The fossil record of Limopsis in the southern high latitudes
  5. Systematic palaeontology
  6. Biogeographical history of Limopsis in the southern high latitudes
  7. Conclusions
  8. References

The oldest identified species of the genus Limopsis was from the Early Cretaceous of Europe, and records of Limopsis sp. also occurred at this time in New Zealand; the genus subsequently radiated into different life habits in the northern hemisphere in the Maastrichtian. This initial radiation coincided with the first occurrence of a named species in the southern high latitudes. Southern high latitude records in the Paleocene were sparse, but the Late Oligocene to Early Miocene marked a period of diversification in Antarctica, New Zealand and Australia. This Cenozoic radiation of the genus in the southern high latitudes may have been related to adaptation to cooling temperatures as well as environmental changes, which created new niches for the genus. It is clear from this study that at least some of the diversity within Limopsis at the present day in Antarctica can be attributed to origination and diversification of species within the southern high latitudes.

Acknowledgements.  This study is a part of the British Antarctic Survey Polar Science for Planet Earth Programme. It was funded by The Natural Environment Research Council. We thank J. A. Crame for advice about the manuscript and for collecting the Cape Melville Formation Limopsis samples in the 1994–1995 field season. We appreciate the help of H. Blagbrough, M. Tabecki and L. Wilson with access to BAS collections, databases and technical support. We acknowledge the use of information contained in the New Zealand Fossil Record File. We are grateful to F. Quaglio, L. E. Anelli and the Instituto de Geociências, Universidade de São Paulo for their hospitality and the chance to view their Limopsis material. We acknowledge J. Todd and J. D. Taylor from the Natural History Museum, London for discussion and access to comparative material. We thank Alan Beu and an anonymous referee for information and suggestions for improvement to the manuscript. We thank S. Neilsen, C. Del Río, J. Crampton, T. Darragh and G. Oliver for information and discussion.

Editor. Svend Stouge

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  4. The fossil record of Limopsis in the southern high latitudes
  5. Systematic palaeontology
  6. Biogeographical history of Limopsis in the southern high latitudes
  7. Conclusions
  8. References
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