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New records of the sharks Isurus and Hexanchus from the Eocene of Seymour Island, Antarctica
Abstract
Most of the information about the Tertiary ichthyofauna in the peri-Antarctic Ocean comes from Seymour Island, close to the tip of the Antarctic Peninsula. We present here new records which improve our knowledge of the ancient high latitude biotas and allow a better understanding of the origin of the Recent local marine fauna. In this paper, sharks' teeth of Isurus praecursor and an indeterminate species of Hexanchus are reported from the Eocene of Seymour Island. They come from an assemblage with a predominance of Carcharias macrota, Squatina sp., Pristiophorus sp., and Myliobatis sp.
... Remarks. Despite of being poorly preserved, the material here described can be confidently referred to Macrorhizodus praecursor on the basis of the following unique combination of characters: large teeth having absent or greatly reduced lateral denticles, smooth enamel and cutting edges, anterior teeth relatively elongated, lateral teeth broadly triangular, and reduced crown height and relatively stout crowns (Glikman, 1964;Cione and Reguero, 1994). Regrettably, no autapomorphy is known from this species, all dental features being plesiomorphic for lamniforms (see Cione and Reguero, 1994). ...
... Despite of being poorly preserved, the material here described can be confidently referred to Macrorhizodus praecursor on the basis of the following unique combination of characters: large teeth having absent or greatly reduced lateral denticles, smooth enamel and cutting edges, anterior teeth relatively elongated, lateral teeth broadly triangular, and reduced crown height and relatively stout crowns (Glikman, 1964;Cione and Reguero, 1994). Regrettably, no autapomorphy is known from this species, all dental features being plesiomorphic for lamniforms (see Cione and Reguero, 1994). M. praecursor is widely known from Eocene deposits around the world (Cappetta, 1980), including Seymour Island, in Antarctica (Cione and Reguero, 1994) and the Eocene of southern Austral Basin in Chile (Loreto and Man Aike Formations; see Otero et al., 2012;2013a,b). ...
... Regrettably, no autapomorphy is known from this species, all dental features being plesiomorphic for lamniforms (see Cione and Reguero, 1994). M. praecursor is widely known from Eocene deposits around the world (Cappetta, 1980), including Seymour Island, in Antarctica (Cione and Reguero, 1994) and the Eocene of southern Austral Basin in Chile (Loreto and Man Aike Formations; see Otero et al., 2012;2013a,b). ...
The fossil record of chondrichthyans in Argentina is still poorly known. The aim of the present contribution is to describe teeth representing a chondrichthyan assemblage from Man Aike Formation (late Eocene) exposed in the Lago Argentino area, at Santa Cruz province, Argentina. This report includes Striatolamia macrota, Macrorhizodus praecursor, Carcharias sp., a possible member of the family Pristiophoridae, for the Argentine territory. Previous Eocene reports of Striatolamia macrota from Argentina are based on incorrect determination of specimens. The shark association, especially the abundance of lamniforms, may be indicative of litoral and shallow (less than 30 m depth) temperate to cold waters, as suggested by micropaleontological content.
... Telm3 (locality IAA 1/94), Telm4 (locality DPV 2/84), and especially in Telm5 at localities DPV 1/84, IAA 1/90, IAA 1/80 (= DPV 9/84), DPV 6/84 (=RV 8200) known as " Mammal Site " , and IAA 4/80 (= IAA 2/90), see (Fig. 2 and Marenssi et al. 1994, Bargo and Reguero 1998, Reguero et al. 1998 ...
... ). These localities, beside diversified marine in− vertebrates (see Stilwell and Zinsmeister 1992), contain remains of diverse fossil terrestrial vertebrates with small and medium – size mammals (Marenssi et al. 1994; Woodburne and Case 1996; Vizcaino et al. 1998; Reguero, Marenssi and Santillana in press). Marine vertebrates also are present. ...
... Marine vertebrates also are present. Among them penguin re− mains as well as ichthyofauna represented by numerous isolated shark teeth were recovered (Long 1992a, b; Cione and Reguero 1994) The depositional setting of these beds is a shallow marine environment; mammal−bearing strata are in re− worked, moderate to high energy subtidal facies (Marenssi et al. 1994). 8 Andrzej Myrcha et al. ...
... Telm3 (locality IAA 1/94), Telm4 (locality DPV 2/84), and especially in Telm5 at localities DPV 1/84, IAA 1/90, IAA 1/80 (= DPV 9/84), DPV 6/84 (=RV 8200) known as " Mammal Site " , and IAA 4/80 (= IAA 2/90), see (Fig. 2 and Marenssi et al. 1994, Bargo and Reguero 1998, Reguero et al. 1998 ...
... ). These localities, beside diversified marine in− vertebrates (see Stilwell and Zinsmeister 1992), contain remains of diverse fossil terrestrial vertebrates with small and medium – size mammals (Marenssi et al. 1994; Woodburne and Case 1996; Vizcaino et al. 1998; Reguero, Marenssi and Santillana in press). Marine vertebrates also are present. ...
... Marine vertebrates also are present. Among them penguin re− mains as well as ichthyofauna represented by numerous isolated shark teeth were recovered (Long 1992a, b; Cione and Reguero 1994) The depositional setting of these beds is a shallow marine environment; mammal−bearing strata are in re− worked, moderate to high energy subtidal facies (Marenssi et al. 1994). 8 Andrzej Myrcha et al. ...
Eocene penguin remains from Seymour Island (Antarctica) are so far the old− est−known record of extinct Sphenisciformes. Rich Argentine and Polish collections of pen− guin bones from the La Meseta Formation are taxonomically revised on tarsometatarsal morphology. Two genera and four species are erected: Mesetaornis polaris gen. et sp. n., Marambiornis exilis gen. et sp. n., Delphinornis arctowskii sp. n. and D. gracilis sp. n. Moreover, the diagnoses of already described species: Anthropornis nordenskjoeldi, A. grandis, Palaeeudyptes klekowskii, P. gunnari, Archaeospheniscus wimani and Delphi− nornis larseni are revised as well. Gradual cooling of climate, changes of environment and trophic relationships, that lasted several millions years, were most probably responsible for the intense speciation and taxonomic diversification of the Middle–Late Eocene La Meseta penguins.
... These changes caused extirpations in high latitudes. The modification in composition of the Antarctic faunas during the Cenozoic constitutes a remarkable example (Cione & Reguero, 1994). However, there are other pseudoextinctions that cannot be related to these global processes. ...
... The extirpation of high-latitude biota was directly related to global and local cooling (Cione, 1988;Cione & Reguero, 1994, 1998. However, the extirpations of some sharks and teleosts (and some marine mammals) from the Atlantic Ocean are not explained by temperature changes because these fishes persisted in similar environments with similar temperatures in the Pacific and Indian Oceans. ...
... The Recent species Hemipristis elongatus occurs in Australia, southern Asia, Red Sea, east Africa, Madagascar and the western coast of Africa (Compagno et al., 2005) Eocene of Egypt, USA, Guinea Bissau and Peru; Miocene of eastern USA, Argentina, Germany, France, Belgium, Italy, Cabinda and Zaïre, Java, India, Japan and Australia; Pliocene of Angola, Zanzibar; Pleistocene of Celebes (Cappetta, 1987;Cione, 1988) Oplegnathus (Oplegnathidae) Oplegnathid fishes inhabit the fringe of the tropics and seem to be mostly limited by the summer isotherm of surficial waters of about 20°C (Cione & Azpelicueta, 2002) Recent species are patchily distributed in western Australia, Tasmania, Japan, Hawaii, northern Chile, Galápagos and Easter Islands, and the east coast of South Africa (Cione & Reguero, 1994;Cione & Azpelicueta, 2002) Eocene of Antarctica, Oligocene of Europe and Miocene of Chubut, Australia and western North America (Cione & Reguero, 1994;Cione & Azpelicueta, 2002). The family was extirpated from Antarctica after the middle Eocene and from the Atlantic Ocean after the early Miocene ...
Two biogeographical units are generally recognized in the present shelf area of Argentina: the Magellanian and Argentinian Provinces. The two provinces differ in their fossil record. The evolution of these provinces has been characterized by migrations, extinctions, pseudoextinctions and, perhaps, even speciation events. Marine vertebrate assemblages with some similarities to the Argentinian fauna were already present in the Miocene, whereas no associations similar to those of the Magellanian fauna have been found in South America before the Pleistocene. Two successive major marine transgressions flooded northern Patagonia during the Miocene: the 'Patagoniense' (Early Miocene) and the 'Entrerriense' (Middle to Late Miocene). We analyse three rich fossil assemblages that were formed during these transgressions. The absence of Magellanian Miocene vertebrate assemblages is consistent with the hypothesis of a more southern distribution of the cold-temperate fauna at that time. In Patagonia, as in other regions, an increased number of living groups appeared from the Lower to Upper Miocene. The Late Miocene aquatic mammals had a modern aspect, and some of the fish species are still living in the South Atlantic Ocean. In this contribution, we stress that warm-temperate fishes and a high diversity of penguins are found together at the base of the Gaiman Formation. We hypothesize that penguins were adapted to live in warmer waters than those of the latest Cenozoic and the Recent. Finally, we recall that many taxa became extirpated because of the global temperature drops of the late Cenozoic. However, some fishes and pinnipeds which were extirpated only in the Atlantic Ocean are discussed here.
... Neverthe− less, slight differences in antero−lateral tooth morphology have been regarded as key diagnostic characters allowing distinction between the two living species in many hand− books (Whitehead et al. 1984; Compagno 1984). Cione and Reguero (1994) subsequently suggested that most of the den− tal features were too variable to be employed for separation of the two living species, whereas Herman et al. (1994) con− sidered that there were three living species within the genus Hexanchus based on odontological characters. Other Palaeo− gene fossils of Hexanchus have been found since the work of Ward (1979) and it is sometimes difficult to assign them to a particular species. ...
... According to calculations of body size (Appendix 1), species of Hexanchus species did not exceed 1 metre in total length during the Palaeocene and 1.9 metres during the Early to Middle Eocene, the maximum size also observed for the living H. nakamurai. The first large form comes from the Late Eocene of Antarctica (Cione and Reguero 1994) with a size exceeding 2 metres (see Appendix 1). This size contrast, never observed in living H. nakamurai, is perhaps the first step in a trend towards larger forms of Hexanchus belonging to the grisiform group which are better known in later faunas. ...
... 1979) pointed out taxonomic difficulties caused by the ontogenetic devel− opment of the lower teeth in Recent Hexanchus. Neverthe− less, slight differences in antero−lateral tooth morphology have been regarded as key diagnostic characters allowing distinction between the two living species in many hand− books (Whitehead et al. 1984; Compagno 1984). Cione and Reguero (1994) subsequently suggested that most of the den− tal features were too variable to be employed for separation of the two living species, whereas Herman et al. (1994) con− sidered that there were three living species within the genus Hexanchus based on odontological characters. Other Palaeo− gene fossils of Hexanchus have been found since th ...
A biometric analysis of the lower teeth of Recent cow sharks (Hexanchidae) investigates the ontogenetic and phylogenetic aspects of the dental characters employed by many ichthyologists and palaeontologists. The dental characters currently used to separate two extant species of sixgill sharks (Hexanchus griseus and H. nakamurai) are analysed and the fossil record of their relatives reviewed. The main results suggest that the cusp number ratio (number of cusps per mm) is preferable to width of the lower tooth for inference of total body size, at least in species of Hexanchus. The presence of a
serrated edge or an enlarged acrocone appears to depend on ontogeny and care must be taken when using these as taxomomic characters. Three Eocene species of Hexanchus, H. collinsonae, H. hookeri, and H. agassizi, and a new assemblage of fossil teeth from the late Ypresian/early Lutetian (Early/Middle Eocene) of south−western France, are also analysed. The first two of these species may be ontogenetic states of H. agassizi. Hexanchus agassizi, belonging to the vituliform lineage and closely related to the living H. nakamurai, is considered here to be the only species of Hexanchus
in the Lower to Middle Eocene. A brief overview of Palaeogene Hexanchus, suggests no evidence of the grisiform group (closely related to living H. griseus) before the Late Eocene.
... Ward (1979) (Cappetta, 1987). Eocene Hexanchus has been described from Seymour Island, Antarctica (Cione and Reguero, 1994 Fig. 5O-P Description: The tooth is 45 mm long, 15 mm wide and 7 mm thick at the base of the crown. The proximal half of the tooth is thickest, and the tooth tapers distally to a much thinner 3 mm. ...
... Geographic distribution: Macrorhizodus praecursor is widely known from all middle and late Eocene Tethyan deposits of Europe, North America and some late Eocene marine vertebrate localities in Egypt (Adnet et al., 2011), Middle to Late Eocene of the Seymour Island in Antarctica (Cione and Reguero, 1994), Priabonian of the southernmost Chile (Otero et al., 2012b). Eocene deposits in Belgium, Syria, Nigeria, Togo, Guinea Bissau and England (Cappetta, 1987). ...
Well preserved vertebrate remains of Shark and ray fauna from the Middle and Late Eocene succession of Fayoum depression, at Gebal Qasr El-Sagha area have been documented and studied in details. Four stratigraphic sections are measured, described and sampled in the field at Hussein Wally Village, Birket Qarun, Qasr el-Sagha and Wadi el-Afreet. Lithostratigraphically, the studied succession is divided into three formations arranged from ba se to top into Gehannam, Birket Qarun and Qasr el-Sagha formations. This Eocene sequence provides by far the most complete view of the endemic African vertebrate fauna. Identification of the basic pattern of fish remains and taxonomic evaluation revealed that the recorded shark and rays taxa belong to 3 classes, 7 orders, 12 families, 18 genera, and 21 species. The identified taxa are macro-scale, collected on the surface, and known either from teeth or rostral remains. A taxonomic account and detailed morphologic description of the fossils shark, rays and bony fish teeth have been achieved. The depositional environments in the studied Middle-Late Eocene age sequence are interpreted. The abundance of recognized vertebrate fauna indicates environments varying from open marine shelf with low energy conditions to restricted marine shallow water conditions. However, the frequent distribution of macrofauna with intense bioturbation in sandstones of Birket Qarun Formation is a good indicator of restricted shallow water conditions.
... Comments and age: The species Macrorhizodus praecursor (=Isurus praecursor) was previously reported from Eocene deposits in Belgium, Syria, Egypt, Nigeria, Togo, Guinea Bissau and England (Cappetta, 1987). It was also reported from the Middle-Late Eocene of Chesapeake Bay, U.S. (Kent, 1994), and the Middle-Late Eocene of Seymour Island, Antarctica (Cione and Reguero, 1994). ...
... Comments and age: The genus is known since the Early Jurassic to Recent (Cappetta, 1987), with a cosmopolitan distribution. Regionally, Eocene Hexanchus has been described from Seymour Island, Antarctica (Cione and Reguero, 1994 Description: Small tooth with relatively high and sharp crown. This is slightly recurved backwards and has a ventral extension over the root. ...
We present new data on the paleoichthyology, paleobotany and radiometric results of the Loreto Formation in the Brunswick Peninsula of southernmost Chile, that allow us to propose a Late Eocene age. The rich diversity of fossil cartilaginous fishes (Chondrichthyes, Elasmobranchii) recognized in upper levels of this unit includes the taxa Carcharías aff. 'hopef (Agassiz), Odontaspis sp., Carcharoides catticus (Philippi), Striatolamia macrota (Agassiz), Anomotodon sp., Macrorhizoduspraecursor (Leriche), Galeorhinus sp., Abdounia sp., Hexanchus sp., Squatina sp., Hexanchidae indet.,Myliobatis sp., Myliobatoidea indet., and Ischyodus dolloi Leriche. This assemblage has clear ecological affinities with Eocene Tethyan fauna previously described in the Northern Hemisphere, and also has common elements with Eocene cartilaginous fishes from Antarctica. Additionally, a paleobotanic study of this unit identified leaf imprints ofAsplenium sp., Pteris sp., Podocarpus sp., and abundant angiosperms including Nothofagus lanceolata Dusén, N. simplicidens Dusén, N. variabilis Dusén, N. cf. alessandri Espinosa, N. subferruginea (Dusén), Hydrangea sp. and Phyllites spp. Wood remains of Nothofagoxylon scalariforme Gothan and Araucariaceae cf. Araucarioxylon Kraus were also identified. Additionally, pollen grains indicate gymnosperms and angiosperms: Podocarpidites otagoensis Couper, Retitricolpites sp., Tricolpites sp., Liliacidites sp., Polyporina sp., Nothofagidites cincta Cookson, and Nothofagidites cranwellae Couper, having affinities with Eocene florae, and being consistent with the age of the fossil fishes. Finally, a SHRIMP U-Th-Pb analysis of two samples collected from the studied beds provided thirty-eight and sixty zircon grains, indicating a clear main peak at 36.48±0.47 Ma (MSWD=1.5) and 36,73±0.50 Ma (MSWD=0.65). The integrated results indicate that the upper part of the Loreto Formation has a minimum Priabonian age, supporting previous reassignations of this part of the formation into the Late Eocene, and differing from the Oligocene age proposed in its original definition.
... Comments and age: The species Macrorhizodus praecursor (=Isurus praecursor) was previously reported from Eocene deposits in Belgium, Syria, Egypt, Nigeria, Togo, Guinea Bissau and England (Cappetta, 1987). It was also reported from the Middle-Late Eocene of Chesapeake Bay, U.S. (Kent, 1994), and the Middle-Late Eocene of Seymour Island, Antarctica (Cione and Reguero, 1994). ...
... Comments and age: The genus is known since the Early Jurassic to Recent (Cappetta, 1987), with a cosmopolitan distribution. Regionally, Eocene Hexanchus has been described from Seymour Island, Antarctica (Cione and Reguero, 1994 Description: Small tooth with relatively high and sharp crown. This is slightly recurved backwards and has a ventral extension over the root. ...
We present new data on the paleoichthyology, paleobotany and radiometric results of the Loreto Formation in the Brunswick Peninsula of southernmost Chile, that allow us to propose a Late Eocene age. The rich diversity of fossil cartilaginous fishes (Chondrichthyes, Elasmobranchii) recognized in upper levels of this unit includes the taxa Carcharias aff. 'hopei' (Agassiz), Odontaspis sp., Carcharoides catticus (Philippi), Striatolamia macrota (Agassiz), Anomotodon sp., Macrorhizodus praecursor (Leriche), Galeorhinus sp., Abdounia sp., Hexanchus sp., Squatina sp., Hexanchidae indet., Myliobatis sp., Myliobatoidea indet., and Ischyodus dolloi Leriche. This assemblage has clear ecological affinities with Eocene Tethyan fauna previously described in the Northern Hemisphere, and also has common elements with Eocene cartilaginous fishes from Antarctica. Additionally, a paleobotanic study of this unit identified leaf imprints of Asplenium sp., Pteris sp., Podocarpus sp., and abundant angiosperms including Nothofagus lanceolata Dusén, N. simplicidens Dusén, N. variabilis Dusén, N. cf. alessandri Espinosa, N. subferruginea (Dusén), Hydrangea sp. and Phyllites spp. Wood remains of Nothofagoxylon scalariforme Gothan and Araucariaceae cf. Araucarioxylon Kraus were also identified. Additionally, pollen grains indicate gymnosperms and angiosperms: Podocarpidites otagoensis Couper, Retitricolpites sp., Tricolpites sp., Liliacidites sp., Polyporina sp., Nothofagidites cincta Cookson, and Nothofagidites cranwellae Couper, having affinities with Eocene florae, and being consistent with the age of the fossil fishes. Finally, a SHRIMP U-Th-Pb analysis of two samples collected from the studied beds provided thirty-eight and sixty zircon grains, indicating a clear main peak at 36.48±0.47 Ma (MSWD=1.5) and 36,73±0.50 Ma (MSWD=0.65). The integrated results indicate that the upper part of the Loreto Formation has a minimum Priabonian age, supporting previous reassignations of this part of the formation into the Late Eocene, and differing from the Oligocene age proposed in its original definition.
... The chondrichthyan fossil record from Antarctica is scant and patchy. It is restricted to some Devonian primitive sharks (Young 1982), a palaeospinacid tooth from Early Cretaceous beds (Kriwet 2003), some sharks, rays, and holocephalan from late Cretaceous beds of Ross, Vega, and Seymour Islands, and especially the diverse record of the Eocene La Meseta Formation of Seymour Island (Cione et al. 1977, Welton & Zinsmeister 1980, Cione & Medina 1987, Grande & Chatterjee 1987, Richter & Ward 1990, Long 1992, Cione & Reguero 1994, 1998, Klug et al. 2005). Hexanchiformes present a single dorsal fin without preceding spine, more than five branchial slits, and peculiar teeth. ...
... The following combination of characters allows us to distinguish the present material from teeth of other recent and fossil Hexanchiformes such as Notidanodon, Pachyhyexanchus, Heptranchias, Notorynchus, Clamydoselachus, Weltonia, Welcommia, ''Eonotidanus'' serratus (Kriwet & Klug 2004), Paranotidanus, Notidanoides pockrandti, and typical Hexanchus (see Cappetta 1987, Ward & Thies 1987, Cione & Reguero 1994, Cione 1996, Underwood & Ward 2004): reduced mesiodistal length; crown labiolingually compressed; absence of mesial cusplets or serrations; moderately developed main cusp; three or four distal cusps, gradually decreasing in size and with convex mesial and distal cutting edges; deep, tabular, and compressed root; lingual longitudinal protuberance straight and well developed, close to the root-crown junction. It also differs from the Jurassic–Cretaceous Pseudonotidanus, which combines characters of Hexanchiformes and Synechodontiformes (Underwood & Ward 2004, Kriwet & Klug 2004). ...
The oldest record of the hexanchiform sharks from the Southern Hemisphere and the second chondrichthyan report known from Carboniferous to Early Cretaceous beds in Antarctica is given. The material was collected in late Aptian rocks of the Kotick Point Formation outcropping in the western part of James Ross Island, near Antarctic Peninsula. It consists of an isolated tooth assignable to a hexanchiform different from the other described genera. The tooth shows putative plesiomorphic cusp (few cusps, no serrations) and apomorphic root characters (relatively deep, quadrangular). It could be related to a species close to the origin of Hexanchus (unknown in beds older than Cenomanian).
... The black oval indicates the location of the SSWA across time. Modified from Figueroa et al. (2013). in the development of the Antarctic Circumpolar Current, which had a global effect on climate and was responsible for the climatic isolation of Antarctica (Clarke & Johnston, 1996;Eastman, 1991aEastman, , 2000Kock, 1992), also contributing to drastic changes in the biota of South America (Cione & Reguero, 1994; Figure 1d). During the Pleistocene (about 2.5 Mya), several glaciation events occurred, among which the greatest at about 18,000 years ago (Mercer, 1976). ...
Here we highlight the geological processes that resulted in the current conformation of the southern Southwest Atlantic Ocean, and explore the heterogeneous composition of the marine ichthyofauna found between 33º and 56º from a paleobiological perspective. During the early Cretaceous (140 Mya), the South Atlantic was still not formed, and Gondwana was probably a set of united plates with shallow continental waters. In the middle Cretaceous (112 Mya), the major Gondwanan plates started diverging from each other, allowing shallow marine intrusions and the diversification of an endemic fish fauna. By the end of the Mesozoic (66 Mya), the proto-South Atlantic connected with the North Atlantic, which was still part of the Tethys Sea, allowing its ichthyofauna to colonize the south and reach the Antarctic region. The opening of the Drake Passage in the Oligocene (33 Mya) enabled the cold waters of the Pacific Ocean to reach the South Atlantic, causing drastic effects on the thermophilic fauna and favoring the dispersion of cold-water species. Successive glaciations during the Quaternary (2 Myr to 10,000 yr ago) resulted in the prevalence of Antarctic climatic conditions in the southern Southwest Atlantic. The long history of changing scenarios in the constitution of the southern Southwest Atlantic is reflected in the heterogeneous composition of the marine ichthyofauna between 33º and 56ºS, which is characterized by a mixture of cosmopolitan, Tethyan, Pacific, Gondwanan, Antarctic, and endemic origins.
... Long (1992) reported three new Hexanchidae teeth from the base of the Early or Middle Eocene Cucullaea I Allomember (Montes et al. 2019, or TELMs 4 and 5 of Sadler 1988) of the La Meseta Formation, next to the locality 'Punta Sergios' (64°14 ′ 10.08 ′′ S, 56°4 0 ′ 15.84 ′′ W), at northern Seymour Island, recognising one of these specimens as an upper lateral tooth of the species Heptranchias howelli (Reed 1946). From a little further northern locality (64°14 ′ 15 ′′ S, 56°36 ′ 21 ′′ W, 'Punta Campamento/Arroyo de la Traición') and upper stratigraphical position (the top of the Cucullaea I Allomember, TELM 5 of Sadler, 1988), Cione and Reguero (1994) reported a moderately large (27 mm of estimated length) left lower anterolateral tooth and attributed it to Hexanchus sp., representing an animal with around 2.2 m in total length (Adnet 2006). Later, Engelbrecht et al. (2017) reported a single upper and a lower fragmentary tooth from the same provenance (region and stratum) of the Hexanchidae reported by Long (1992), also identifying this new material as Hexanchus sp. ...
Sharks are virtually absent from coastal Antarctica since the Late Eocene glaciations, but this group exhibited a notable austral diversity during the Cretaceous and Paleogene. Several species have already been described from the Aptian-Eocene successions of the Larsen Basin exposed in the James Ross Island area (northern Antarctic Peninsula) and the predominantly deep-water Hexanchiformes have a record that, although still rare, has been continually increased. Four species of this group are currently known from that basin: Notidanodon pectinatus, Xampylodon dentatus, Rolfodon thompsoni, and Rolfodon tatere. Such records are especially concentrated in the Gamma Member of the Snow Hill Island Formation (or Herbert Sound Member of Santa Marta Formation), on James Ross Island. Here we described four teeth assigned to X. dentatus and one identified as R. tatere from upper Campanian sections of James Ross Island, highlighting the nomenclatural changes that led to the definition of Xampylodon and Rolfodon. Some specimens of X. dentatus presented here are considerably more complete or represent teeth of different positions than most previous records. The material assigned to R. tatere represents the oldest record of this species in the world, extending its time range by more than 10 million years.
... These localities, besides diversified marine invertebrates (see , contain remains of diverse fossil terrestrial mammals with small-and medium-size mammals (Figures 10e, 13, 14) (Goin et al., 1991;Marenssi et al., 1994;Reguero et al., 2013). Marine vertebrates are also present, among them penguin remains as well as ichthyofauna represented by numerous isolated shark teeth (Long, 1992a(Long, , 1992bCione and Reguero, 1994;Appendix ...
Antarctica has significant environmental, scientific, historic, and intrinsic values, all of which are worth protecting into the future. This continent has a discrete number of places of scientific interest that exhibit great potential as natural heritage sites; its geodiversity is of fundamental importance to scientific values of the continent, and the pursuit of geological and paleontological knowledge has had a strong influence on its historical values. Seymour Island was once called the 'Rosetta Stone' of Southern Hemisphere paleobiology, because this small island provides the most complete and richly fossiliferous Late Cretaceous-Paleogene sequence in Antarctica. In particular, fossil vertebrates form part of the evidence used in reconstructing the history of life on Antarctica. Paleontological heritage is considered a subset of geo-heritage that embodies both natural and historical components which has received only indirect recognition. Seymour Island is an outstanding paleontological area with high heritage value of its Late Cretaceous/Paleogene vertebrates and should be considered for geo-conservation and protection. This paper reviews vertebrate fossil occurrences and outcrops on Seymour Island and discusses some threats to these fossil sites.
... Eocene neoselachian faunas are widespread globally [20] and particularly rich in Pakistan [49], Egypt [23,50], Jordan [56], West Africa [28], India [57], Morocco [58,59], Europe [60], Antarctica [61][62][63], and North America [26, 55-57, 64, 65]. In contrast, published accounts of Paleogene and Neogene marine and terrestrial vertebrates from Madagascar are few [14]. ...
We report here the first neoselachian fossil fauna from Eocene nearshore marine deposits of the Mahajanga Basin, northwestern Madagascar. The fauna includes seven species of shark: Nebrius blankenhorni, Brachycarcharias koerti, Galeocerdo eaglesomei, two species of Carcharhinus (one of which is described as a new species), Physogaleus, Rhizoprionodon and Sphyrna. Three species of rays were also recovered: Pristis, Myliobatis and an undetermined dasyatid ray. This fauna represents the first Cenozoic neoselachian fossil record from the Eocene of Madagascar and broadens our understanding of their evolutionary and biogeographic history in the southern hemisphere during this time. Although the diversity of the genera and species of the fauna is very low, the age and similarity of genera to those in Congo, west Africa, Arabia, Asia, Europe, and North, Central, and South America suggests that these genera were broadly distributed and diverse within the shallow marine settings of the Tethyan and southern provinces during middle and late Eocene.
... So far, seven fossil species have been described: H. gracilis Davis (1887) Cappetta, 1990;Davis, 1887;Ward, 2014, 2015;Adolfssen et al., 2017;Reinecke et al., 2014;Adnet, 2000Adnet, , 2006Zhelezko and Kozlov, 1999;Takakuwa, 2006). Cione and Reguero (1994) presented the first record of Hexanchus from the Eocene of Antarctica, which is the southern-most occurrence. The single specimen comes from TELM 5 of Seymour Island and represents a nearly complete lower anterolateral tooth. ...
Rare remains of predominantly deep-water sharks of the families Hexanchidae, Squalidae, Dalatidae, Centrophoridae, and Squatinidae are described from the Eocene La Meseta Formation, Seymour Island, Antarctic Peninsula, which has yielded the most abundant chondrichthyan assemblage from the Southern Hemisphere to date. Previously described representatives of Hexanchus sp., Squalus weltoni, Squalus woodburnei, Centrophorus sp., and Squatina sp. are confirmed and dental variations are documented. Although the teeth of Squatina differ from other Palaeogene squatinid species we refrain from introducing a new species. A new daliatid taxon, Eodalatias austrinalis gen. et sp. nov. is described. This new material not only increases the diversity of Eocene Antarctic elasmobranchs but also allows assuming that favourable deep-water habitats were available in the Eocene Antarctic Ocean off Antarctica in the Eocene. The occurrences of deep-water inhabitants in shallow, near-coastal waters of the Antarctic Peninsula agrees well with extant distribution patterns.
... Odontaspidids were more widely distributed during the Cenozoic than today. They inhabited Antarctica until at least the Eocene and southern South America until at least the Early Miocene (Leriche, 1936;Cione et al., 1977;Long, 1992;Cione and Reguero, 1994;Arratia y Cione, 1996). The present authors studied morphological variations in different areas (Lucifora et al., 2003) and the distribution of Cenozoic specimens from different localities of Argentina (Cione et al., 2000). ...
Fossil record has shown that the genus Carcharias and probably species C. taurus Rafinesque, 1810 occupied the western coast of South America during the Miocene and part of the Pliocene. The genus is absent in the area today. It is suggested that its local extinction was the consequence of a drop of global temperatures during the middle Pliocene and Pleistocene and the coeval lowering of sea level that shrinked the area of distribution to the northern areas and provoked the disappearance of suitable environments when the shelf area became extremely reduced. After approximately 3 Ma it would have not been possible for the species to migrate from the north to the region due to the establishment of the Panamanian isthmus.
... Ciertamente, la extirpación de la biota de altas latitudes es directamente explicada por el enfriamiento global (Cione, 1978;Cione y Reguero, 1994. Sin embargo, las extirpaciones del Océano Atlántico austral mencionadas arriba no pueden ser explicadas por cambios de temperatura porque estos peces y mamíferos persistieron en ambientes similares con similares temperaturas en los ...
... Ciertamente, la extirpación de la biota de altas latitudes es directamente explicada por el enfriamiento global (Cione, 1978;Cione y Reguero, 1994. Sin embargo, las extirpaciones del Océano Atlántico austral mencionadas arriba no pueden ser explicadas por cambios de temperatura porque estos peces y mamíferos persistieron en ambientes similares con similares temperaturas en los ...
... For this reason we prefer to keep the Pristiophorus specimen from the Coquimbo Formation in open nomenclature. The fossil record of Pristiophorus in Chile includes Bahía Inglesa (Walsh, 2001;Suárez et al., 2002), Navidad (Suárez & Encinas, 2002;Suárez et al., 2006), Horcón (Carrillo-Briceño et al., 2013) and La Cueva formations (Suárez & Marquardt, 2003 (Cione & Reguero, 1994). In Chile, Hexanchus griseus and Hexanchus sp. have been referred to the Bahía Inglesa and Horcón formations (Long, 1993;Walsh, 2001;Suárez & Marquardt, 2003;Carrillo-Briceño et al., 2013). ...
Neogene marine sediments from Chilean geological formations contain a diverse marine fossil fauna. In Chile, the "Norte Chico" (27 degrees S to 32 degrees S) is composed of two important sedimentary marine deposits, the Bahia Inglesa and Coquimbo formations. Diverse vertebrate taxa including fish, birds, mammals and abundant chondrichthyans have been described from Bahia Inglesa Formation. However, the vertebrate fauna from Coquimbo Formation has been poorly documented. Based upon field trips and the analysis of collections from the Coquimbo Formation, the elasmobranch fossil fauna is composed of at least nine taxa, two of which are extinct (Carcharocles megalodon and Carcharodon plicatilis). The rest of the taxa are related with living elasmobranch species that are inhabitants of the Eastern Pacific Ocean and Tropical America coast.
... The remains of selachians (mainly isolated teeth, spines and vertebrae) are common fossils in the deposits of different age in all continents, including Antarctica (Glikman, 1967(Glikman, , 1980Cappetta, 1987;Cione & Reguero, 1994; and many others). In the Eastern Asia, rich complexes of fossil selachians are known from the Mesozoic and Cenozoic beds of the Japanese archipelago (Yabumoto & Uyeno, 1994). ...
An isolated upper anterior shark tooth from the Early Miocene Holmsk Formation, Sakhalin
Island, Russia, is identified as an Alopias close to extant Alopias superciliosus Lowe, 1841. This
is the first reliable record of a fossil shark from the S akhalin Neogene, and the most northern
finding of a fossil thresher shark in Eastern Asia.
... The La Meseta Formation would then be deposited within the warm epoch of high Lutetian±Bartonian sea stand termed the Arctowski interglacial, and continued till the Oligocene Polonez Glaciation (Birkenmajer and Zastawniak, 1989 ). This is consistent with the paleontological dating as late early to late Eocene (Case, 1992; Long, 1992; Cione and Reguero, 1994). The faunal evidence indicates the deposition of the La Meseta Formation in warmtemperate conditions, although not so warm as when underlying Cretaceous Lo Âpez de Bertodano Formation was deposited (Ditch®eld et al., 1994). ...
A short-term return of environmental conditions similar to those of the end-Cretaceous is marked by the reappearance of nautiloid cephalopods in the lower-middle Eocene La Meseta Formation of Seymour Island, Antarctic Peninsula. Previous findings have been supplemented by a collections of 33 specimens. The nautiloids come from several horizons, the oldest sample apparently being located close to the base of the formation (Telm1), the most numerous coming from the Cucullaea bed of Telm2 and 3. A few specimens were collected from Telm4–6. The La Meseta Formation nautiloid assemblages developed apparently in response to one of the Eocene warmings and resulting transgression of a warm sea. The incursion of nautiloids into southern high latitudes was roughly coeval with their expansion to the northern European seas and the succession of faunas was parallel in both regions.Based on the analogy with the lower Eocene London Clay nautiloid assemblages an estimate of bathymetric evolution of the environment can be made by. The presence of a relatively shallow-water form similar to Cimomia imperialis close to the base of the lower-middle Eocene La Meseta Formation (Telm1) marks the beginning of the marine transgression. The dominant La Meseta species, Euciphoceras argentinae, was apparently an analogue of the English E. regale, the occurrence of which in the London Clay corresponds to the highest sea level stand. The presence of Aturia in the higher part (Telm4 and 5) of the La Meseta Formation suggests that cold oceanic waters possibly entered the area, accompanied by a sea-level drop. The last nautiloid (Telm6) is an Euciphoceras sp., interpreted to be indicative of shallower habitat depth limits. Both incursion of the nautiloids to, and their disappearance from the Eocene high latitudes were connected with a fundamental rearrangement of the geographic distribution of particular lineages.
... It is also similar to the Oligocene species 'I.' flandricus but it differs in being less gracile. It clearly differs from the Eocene species 'Isurus' praecursor in proportions ( Fig. 3; see discussion in Cione and Reguero, 1994), the Miocene species 'I.' planus in the absence of crown curvature, the Miocene-Pliocene species 'I.' plicatilis in the narrower crown, the recent I. oxyrinchus Rafinesque, 1810 in the completeness of the distal cutting edge, and the recent I. paucus Guitart, 1966 in the absence of strong lingual curvature (see Cione, 1988). ...
Middle Cenozolc marine fossil-bearing beds crop out in the Cerro Plataforma (western Chubut Province. Argentina) at about 1,400 m a.s.l. They are located 500 km far from the modern Atlantic coast and only 50 km from the Pacific Ocean. Well preserved penguin bones and a shark tooth were found therein. Invertebrates include corals, bryozoans, abundant mollusks, echinoids, and crabs. Morphogeometric analysis and comparative description confirmed that the penguin humerus is referable to Palaeospheniscus bergi Moreno and Mercerat, 1891. Most of the fossils indicate a Miocene age. However, there is a debate about if the bearing beds are of Pacific or Atlantic origin. Fossil invertebrates identifiable at species level reveal Pacific affinity, the shark species is cosmopolitan, and Palaeospheniscus bergi is known from early Miocene Atlantic units of southern South America. Yet, Palaeospheniscus Moreno and Mercerat, 1891 is also known from Miocene Pacific beds but it has not been identified at specific level yet. This is the highest site in topographic terms in which penguin fossils occur. This indicates a remarkable uplift for the area, probably from the middle Miocene.
... Ciertamente, la extirpación de la biota de altas latitudes es directamente explicada por el enfriamiento global (Cione, 1978;Cione y Reguero, 1994 et al., 2001). Las áreas de plataforma se redujeron grandemente durante los períodos fríos del Pleistoceno. ...
... Ciertamente, la extirpación de la biota de altas latitudes es directamente explicada por el enfriamiento global (Cione, 1978;Cione y Reguero, 1994. Sin embargo, las extirpaciones del Océano Atlántico austral mencionadas arriba no pueden ser explicadas por cambios de temperatura porque estos peces y mamíferos persistieron en ambientes similares con similares temperaturas en los ...
Peces del Mioceno marino y continental en Entre Ríos, Oriente central de Argentina
... It is also similar to the Oligocene species 'I.' flandricus but it differs in being less gracile. It clearly differs from the Eocene species 'Isurus' praecursor in proportions ( Fig. 3; see discussion in Cione and Reguero, 1994), the Miocene species 'I.' planus in the absence of crown curvature, the Miocene-Pliocene species 'I.' plicatilis in the narrower crown, the recent I. oxyrinchus Rafinesque, 1810 in the completeness of the distal cutting edge, and the recent I. paucus Guitart, 1966 in the absence of strong lingual curvature (see Cione, 1988). ...
... Remarks d Teeth referred to this species were reported in the WBP, particularly the Middle to Late Eocene of the La Meseta Formation on Seymour Island in Antarctica (Cione and Reguero, 1994) and in the Priabonian of the Loreto Formation, in southernmost Chile (Otero et al., 2012b). Tethyan records include Eocene deposits in Belgium, Syria, Egypt, Nigeria, Togo, Guinea Bissau and England (Cappetta, 1987). ...
This paper discusses a well-represented fossil record of cartilaginous fishes (Chondrichthyes) from southern South America. The recovered samples allow the recognition of three assemblages with chronostratigraphic and paleogeographic value: i) typical Maastrichtian sharks and rays with affinities to eastern Pacific fauna, including the taxa Ischyrhiza chilensis, Serratolamna serrata, Centrophoroides sp. associated to Carcharias sp., and Dasyatidae indet.; ii) a scarce reworked assemblage of Paleocene–Early Eocene age including the taxa Otodus obliquus and Megascyliorhinus cooperi; iii) a rich assemblage with reworked taxa of Early to Middle Eocene age, together with autochthonous deposited Middle to Late Eocene taxa with close affinities to paleoichthyofaunas recovered from the North Atlantic, represented by Carcharias ‘hopei’, Odontaspis winkleri, Carcharoides catticus, Macrorhizodus praecursor, Carcharocles auriculatus, Striatolamia sp., Striatolamia macrota, Hexanchus agassizi, Notorhynchus sp., Myliobatis sp., Abdounia sp., Pristiophorus sp., Squatina sp., cf. Rhizoprionodon sp., Ischyodus sp., and one new species, Jaekelotodus bagualensis sp. nov. The studied samples include for the first time taxa with well established chronostratigraphic resolutions as well as taphonomic information that help clarifying the age of the fossil-bearing units. In addition, they provide relevant information about the evolution of the Magallanes (=Austral) Basin from the Upper Cretaceous to the Paleogene, suggesting a probable connection with the Quiriquina Basin of south-central Chile during the latest Cretaceous. Finally, the studied assemblages indicate a latitudinal pattern of distribution that provides valuable data on the environmental evolution and temperature of southern South America during the Paleogene.
... The shark fauna from the Ypresian Cucullaea shell bed (Telm 4, basal horizon of the Cucullaea I Allomember) of La Meseta Formation is one of the most diverse and abundant Early Eocene temperate neoselachian assemblages known from the Southern Hemisphere. So far, 22 selachian taxa within 14 families (including two batoids) have been reported from different localities on Seymour Island and from different levels of the Cucullaea I Allomember within the La Meseta Formation (Cione & Reguero, 1994Long, 1992a, b, c;Welton & Zinsmeister, 1980). All these taxa have the oldest record in the Cucullaea I shell bed (Telm 4). ...
The La Meseta Formation crops out in Seymour/Marambio Island, Weddell Sea, northeast of the Antarctic Peninsula and contains one of the world's most diverse assemblages of Weddellian marine/coastal vertebrates of Early Eocene (Ypresian) age. The La Meseta Formation is composed of poorly consolidated, marine sandstones and siltstones which were deposited in a coastal, deltaic and/or estuarine environment. It includes marine invertebrates and vertebrates as well as terrestrial vertebrates and plants. The highly fossiliferous basal horizon (Cucullaea shell bed, Telm 4 of Sadler 1988) of the Cucullaea I Allomember is a laterally extensive shell bed with sandy matrix. The fish remains, including 35 species from 26 families, of the Ypresian Cucullaea bed represent one of the most abundant and diverse fossil vertebrate faunas yet recorded in southern latitudes. Stratigraphic distribution and phylogenetic relationships of the Weddellian sphenisciforms are consistent with a first radiation of this group in the Early Eocene. The first inquestionable archaeocete from Antarctica is recorded in this unit and is referred to a new taxon.
... The shark fauna from the Ypresian Cucullaea shell bed (Telm 4, basal horizon of the Cucullaea I Allomember) of La Meseta Formation is one of the most diverse and abundant Early Eocene temperate neoselachian assemblages known from the Southern Hemisphere. So far, 22 selachian taxa within 14 families (including two batoids) have been reported from different localities on Seymour Island and from different levels of the Cucullaea I Allomember within the La Meseta Formation (Cione & Reguero, 1994 Long, 1992a, b, c; Welton & Zinsmeister, 1980). All these taxa have the oldest record in the Cucullaea I shell bed (Telm 4). ...
The La Meseta Formation crops out in Seymour/Marambio Island, Weddell Sea, northeast of the Antarctic Peninsula and contains one of the world's most diverse assemblages of Weddellian marine/coastal verte-brates of Early Eocene (Ypresian) age. The La Meseta Formation is composed of poorly consolidated, marine sandstones and siltstones which were deposited in a coastal, deltaic and/or estuarine environment. It includes marine invertebrates and vertebrates as well as terrestrial vertebrates and plants. The highly fossiliferous basal horizon (Cucullaea shell bed, Telm 4 of Sadler 1988) of the Cucullaea I Allomember is a laterally extensive shell bed with sandy matrix. The fish remains, including 35 species from 26 families, of the Ypresian Cucullaea bed represent one of the most abundant and diverse fossil vertebrate faunas yet recorded in southern latitudes. Stratigraphic distribution and phylogenetic relationships of the Weddellian sphenisciforms are consistent with a first radiation of this group in the Early Eocene. The first inquestionable archaeocete from Antarctica is recorded in this unit and is referred to a new taxon.
... The terrestrial vertebrates recovered from the Cucullaea I Allomember , though numerically small, strongly suggest a middle Eocene age (Bartonian, V37 to V41 Ma, Woodburne and Case, 1996) or middle Eocene (Goin et al., 1999). This temporal assignment is consistent with the middle Eocene age assigned to the ichthyofauna found in the same depositional horizon (Cione and Reguero, 1994, 1998). Age data from dino£agellates from the underlying levels (Acantilados Allomember) are consistent with a late-early Eocene age (Coccozza and Clarke, 1992). ...
Middle Eocene land mammals from La Meseta Formation, Seymour (Marambio) Island are reviewed. A taxonomically diverse fossil land-vertebrate assemblage with small and medium-size mammals has been recovered from four localities. The depositional setting is shallow marine and most of the mammal-bearing beds are in reworked, moderate to high energy subtidal facies. The characteristics of these mammals not only confirm but also strengthen the biogeographical relationships between southern South America (Patagonian Province) and the Antarctic Peninsula during the Paleogene and rule out the possibility of a major barrier between these areas. The Antarctic ungulates (Astrapotheria and ?Litopterna) are plesiomorphics in retaining low crowned cheek teeth and are more similar to those from the Pancasamayoran local faunas of southern South America (Patagonia).
... The terrestrial vertebrates recovered from the Cucullaea I Allomember , though numerically small, strongly suggest a middle Eocene age (Bartonian, V37 to V41 Ma, Woodburne and Case, 1996) or middle Eocene (Goin et al., 1999). This temporal assignment is consistent with the middle Eocene age assigned to the ichthyofauna found in the same depositional horizon (Cione and Reguero, 1994, 1998). Age data from dino£agellates from the underlying levels (Acantilados Allomember) are consistent with a late-early Eocene age (Coccozza and Clarke, 1992). ...
The Eocene of Seymour Island contains the only association of Cenozoic plants and land vertebrates known from anywhere in Antarctica and lies at about latitude 63° south. The late Early to latest Eocene La Meseta Formation fills an incised valley and comprises sediments representing deltaic, estuarine and very shallow marine environments. The Paleogene sequence in southern South America (Patagonia) and the Antarctic Peninsula reveals floristically distinct periods (late Paleocene, early and middle Eocene and latest Eocene), based largely on leaf assemblages. The late Paleocene Cross Valley flora (Seymour Island) contains ferns and other elements suggesting a much warmer climate than at this latitude today. The Middle Eocene Fossil Hill (South Shetland Islands) and the Rı́o Turbio (Santa Cruz Province, southern Patagonia) floras have a mixture of both Neotropical and Antarctic elements. The La Meseta paleoflora is distinctive in having a predominance of Antarctic taxa especially Nothofagus, podocarps, and araucarian conifers in the Eocene deciduous and evergreen forests. This suggests a cooling trend during the Eocene of Antarctica with mid- to late Eocene seasonal, cool-temperate, rainy climates and latitudinal and altitudinal gradients. The Seymour Island La Meseta Fauna (Cucullaea Allomember, middle Eocene) contains at least 10 mammal taxa, predominantly tiny marsupials (mostly endemic and new taxa). The endemism of these marsupials suggests the existence of some form of isolating barrier (climatic and/or geographic) during the Eocene. Faunal similarity between the La Meseta Fauna and the fauna assigned to the Riochican (late Paleocene) South American Land Mammal Age of Patagonia strongly suggests that the former derived from the latter. The occurrence on Seymour Island of sudamericids, that had become extinct in South America in the Paleocene, also indicates that isolation may have allowed extended survival of this Gondwanan group in the Eocene of Antarctica and the factors that caused their extinction did not affect this continent. Global warming and intercontinental dispersal have been major influences on the timing and magnitude of terrestrial biotic change in the late Paleocene and early Eocene epochs. The faunistic evidence indicates that the La Meseta mammalian fauna derived from late Paleocene/early Eocene Riochican/Vacan faunas. The dispersal and vicariance events may have occurred during the onset of the climatic optimum of the Cenozoic (late Paleocene–early Eocene) when major regressive events are recorded either in the northern Antarctic Peninsula and southernmost Patagonia (between 58.5 and 56.5 Ma). The absence of notoungulates in the La Meseta fauna is noteworthy. We speculate that the notoungulates could have passed into Antarctica during the latest part of the Paleocene when the environmental conditions were warmer, and then became extinct at the onset of the climatic deterioration during the early Eocene.
Several paleontological field expeditions of Danish-US team took place in the Jameson Land Basin, in East Greenland. Their objective was to recover vertebrate fossils for understanding the evolution of the vertebrate fauna of the region and its dynamics with the surrounding through geological times. In the Triassic, the basin was located at 41° N in the northern rim of Pangea and bordered in the North by the Boreal Sea. During Late Triassic, the region was an ephemeral to perennial lake systems in dry steppe-like climate, crossed by rivers. This work focus on the microvertebrate remains recovered by expeditions from 1991 to 2016. The specimens have been photographed and listed in a catalogue. 867 specimens out of 993 could be identified. The main groups of Vertebrate are all present (Chondrichthyes, Actinopterygii, Amphibia, Reptilia, Mammalia) with new taxa never described nor reported in Greenland, such as Lissodus, Parvodus, Rhomphaiodon, Gyrolepis, Nothosauridae and the first batrachian ilium found in the region. The revision of two sphenodontians jaws fragment as Clevosauridae, with in association of the previously mentioned taxa that are highly documented in Europe and Asia, confirms a relationship between faunas of Greenland and Eurasia during the Late Triassic.
Since two centuries, the fossil record of selachians (Sharks, Skates and Rays) is mainly constituted by fossil shallower fishes of epi-continental seas. The discovery of new selachian faunas from the bathyal marls of the Paleogene of Landes (South-western of France) allows to take into account the real diversity of fossil deepwater communities in comparison with the Recent ones. The systematic study of that inedit material fills the considerable gap in our nowledge of the diversity of fossil deepwater selachians. In addition to numerous unnamed taxa, 31 species and 9 genera have
been described for the first time, thus testifying to the great diversity of the order Squaliformes (17 species). A cladistic analysis on dental characters of most squaloid genera has been performed, and
has led to propose an evolutionary history of Squaliformes. The latter seems to have been strongly related to major events that occurred in cretaceous seas. In a second part, the observation of the global distribution of Recent selachians showed complex but real
relationships between the faunal structure and geographic or bathymetric parameters. In this context, several paleoecological
approaches have been investigated and tested on selachian faunas, as paleobathymetric and paleogeographic indicators. The interests of such studies are obvious for paleoenvironmental reconstitutions and are discussed.
Keywords : Selachians, Paleogene, Landes, Squaloid, cladistic analysis, macroecology,
paleoecology
Eocene deposits of the famous La Meseta Formation of Seymour Island, Antarctic Peninsula, yielded the most diverse Paleogene fossil elasmobranch association of the Southern Hemisphere. In this assemblage, sharks clearly dominate the fauna, whereas batoids are very rare components. Herein, we describe two new taxa of cold water tolerant skates, Marambioraja leiostemma gen. et sp. nov., and Mesetaraja maleficapelli gen. et sp. nov., two new species of the genus Raja, Raja amphitrita sp. nov. and Raja manitaria sp. nov., as well as remains of warm water adapted myliobatiforms. It is, however, not possible to unambiguously assign these remains either to Myliobatidae or Rhinopteridae, or to any specific genus. Previously reported remains of Raja/Bathyraja sp. are assigned to the new described species Raja manitaria sp. nov. The biogeographic distribution of extant and extinct rays and skates clearly shows that both groups are more widely distributed today than in the past, and additionally seem to have been more diverse in the Northern than the Southern Hemisphere. The occurrence, albeit rare of isolated teeth of skates (Rajidae) and rays (Myliobatidae) in the La Meseta Formation representes a minimum age constraint for their first appearance in the Southern Ocean.
http://www.zoobank.org/urn:lsid:zoobank.org:pub:E507D86C-FFEC-4047-A337-AE77606BB1A6
Seymour Island, Antarctic Peninsula, is known for its wealth of fossil remains. This island provides one of the
richest fossiliferous Paleogene sequences in the world. Chondrichthyans seemingly dominate this Eocene marine
fauna and offer a rare insight into high-latitude faunas during the Palaeogene. So far, only a few isolated teeth of carcharhinid sharks have been reported from Seymour Island. Bulk sampling in the well-exposed La Meseta and Submeseta formations yielded new and abundant chondrichthyan material, including numerous teeth of carcharhinid and triakid sharks. Here, we present a reevaluation of the previously described carcharhinid remains and a description of new taxa: Meridiogaleus cristatus, gen. et sp. nov., Kallodentis rythistemma, gen. et sp. nov.,
Abdounia richteri, sp. nov., and Abdounia mesetae, sp. nov. The carcharhiniforms Mustelus sp. and Galeorhinus sp. are reported based on rare material, whereas teeth previously assigned to Scoliodon represent a nomen dubium.
One of the most intriguing paleobiogeographical phenomena related to the final stage of Gondwanan breakup is the close similarities and, in most cases, inferred sister-group relationships, of a number of terrestrial and marine/coastal vertebrate taxa recovered from Paleogene deposits of West Antarctica with those from other continents (South America, Australia). These continents are today separated by large and deep ocean floors, which was not the case in the geological past. However, the inferred timing of continental separation does not always match with the inferred time of vertebrate dispersals.
Fossil record has shown that the genus Carcharias and probably species C. taurus Rafinesque, 1810 occupied the western coast of South America during the Miocene and part of the Pliocene. The genus is absent in the area today. It is suggested that its local extinction was the consequence of a drop of global temperatures during the middle Pliocene and Pleistocene and the coeval lowering of sea level that shrinked the area of distribution to the northern areas and provoked the disappearance of suitable environments when the shelf area became extremely reduced. After approximately 3 Ma it would have not been possible for the species to migrate from the north to the region due to the establishment of the Panamanian isthmus.
Late Cretaceous/Paleogene strata of the James Ross Basin, West Antarctica (63°S), yield the only association of marine and terrestrial vertebrates and plants known from anywhere in the continent. Fossil marine vertebrates from the extensive Cretaceous (Coniacian, Campanian and Maastrichtian) marine deposits of the James Ross Basin include marine reptiles (plesiosaurs and mosasaurs), turtles, and neoselachian and teleostean fishes. The ichthyofauna recovered from levels of the early-middle Eocene (Ypresian/Lutetian) Cucullaea I Allomember include 35 species referable to 26 families, thus making it one of the most abundant and diverse fossil marine vertebrate faunas yet recorded in southern latitudes. The diversity of the Seymour Island penguin fauna of the late Eocene (Priabonian) Submeseta Allomember indicates that this group was significantly more abundant and diverse in the Paleogene than it is today. The first significant radiation of the Weddellian penguins took place by early Eocene (Ypresian) times (basal Cucullaea I Allomember), with eight sympatric species.
Fragmentary skull bones and vertebra from the Upper Eocene La Meseta Formation on Seymour (Marambio) Island, Antarctic Peninsula have been described as gadiform fishes, informally named "Mesetaichthys". Here we describe jaws as Mesetaichthys jerzmanskae n. gen. and n. sp., and refer this taxon to the perciform suborder Notothenioidei. This group is almost unknown as fossils. Similarities to the living, "primitive" nototheniid Dissostichus eleginoides are indicated in the dentition. Gadiform evolution in the Paleocene-Eocene is discussed, and the possibility of a correlation between the origin and evolution of notothenioids in connection with the deterioration of the climate in Antarctica during the Late Eocene-Oligocene is concluded.
Fossil record has shown that the genus Carcharias and probably species C. taurus Rafinesque, 1810 occupied the western coast of South America during the Miocene and part of the Pliocene. The genus is absent in the area today. It is suggested that its local extinction was the consequence of a drop of global temperatures during the middle Pliocene and Pleistocene and the coeval lowering of sea level that shrinked the area of distribution to the northern areas and provoked the disappearance of suitable environments when the shelf area became extremely reduced. After approximately 3 Ma it would have not been possible for the species to migrate from the north to the region due to the establishment of the Panamanian isthmus.
Since Dr. Otto Nordenskjold, leadership of the Swedish South Polar Expedition, first
stepped on shore at Penguin Point, Seymour Island, 100 years have passed. The discoveries of the last three decades have shown how visionary his statement about the importance of Seymour Island and the surrounding islands has been in the evolution of the biota in the Gondwana.The Antarctic Peninsula region contains an unparalleled record of Antarctic marine and terrestrial
vertebrates from the last 100 million years. A unique collection of latest Cretaceous marine and terrestrial
vertebrates has been recovered from Seymour (López de Bertodano Fm.), Vega (López de
Bertodano Fm.), and James Ross (Santa Marta, Hidden Lake and Rabbot formations) islands. Five
genera of mosasaurs, Leiodon, Mosasaurus, Hainosaurus, Plioplatecarpus, and Lakumasaurus, and at least two genera of plesiosaurs, Aristonectes and Mauisaurus, documents one of the greatest diversity of marine reptiles in the south of Gondwana. Ankylosaur, theropod (James Ross Island), hypsilophodontid (Vega Island), and hadrosaur (Seymour and Vega islands) dinosaurs have also been recorded in coastal facies of the same units. Frequently associated to remains of marine reptiles and
dinosaurs shark teeth (mostly hexanchids) were exhumated. The Cretaceous avifauna consists entirely of representatives of modern birds orders (charadriiforms, gaviids, and presbyornithids), which is absolutely unique compared to avian faunas from elsewhere in Gondwana. A numerous and very rich collection of Tertiary marine and terrestrial vertebrates has been recovered from Seymour Island. From the marine realm skeletons of archaeocete whales (Basilosaurus
and Zygorhiza), turtles, sharks (17 species), chimeroids, rays, oplegnathids, billfihes, merluccids, and penguins have been recovered partially. Noteworthy, the Eocene La Meseta Fm. contains the only association of Cenozoic plants and land vertebrates known from the whole Antarctic Continent at about latitude 63° south. The La Meseta Fauna (Cucullaea Allomember, Middle Eocene, Seymour Island) contains at least ten mammal taxa, predominantly tiny marsupials (mostly endemic and new taxa), ungulates, sudamericids, and edentates. The endemism of these marsupials suggests the existence of some form of isolating barrier (climatic and topographic) during the Eocene. Faunistic evidence, mainly from the ungulates (Trigonstylopidae and Sparnotheriodontidae), strongly suggests that this Antarctic fauna derived from Paleocene Patagonian ones. The occurrence of sudamericids on Seymour Island, that had
become extinct elsewhere in the Paleocene of South America, also indicates that isolation may have allowed extended survival of this Gondwanic group in the Eocene of Antarctica, and the factors that caused their extinction elsewhere did not affect Antarctica. The Eocene avifauna, besides penguins, consists of representatives of modern flying birds orders (pelagornithids, falconids, and presbyornithids) and cursorial phorhoracoids and ratites. Finally, Antarctica as the central component of Gondwana was connected to all the other landmasses (Africa, South America, Australia, India, New Zealand) and played an importante role in creating the strongly disjunct distribution patterns of the biota through the last 100 million years as we can see in the Southern Hemisphere today.
A proximal fragment of a gill raker identified as belonging to a shark of the genus Cetorhinus was collected from middle Eocene deposits of the La Meseta Formation in the northern part of Seymour Island, Antarctica. This is the first record of a fossil basking shark from Antarctica and one of the earliest records of the genus. The minimum age of Cetorhinidae is middle Eocene. The only living species of the family Cetorhinidae is a very large plankton feeder, Cetorhinusmaximus. Basking sharks are unknown in subantarctic or Antarctic waters but occur on both South American coasts today. The evolution of filter-feeding vertebrates is discussed.
The first record of the knifejaw family Oplegnathidae in the Atlantic Ocean and in South America is reported. It comes from the lowermost beds of the Early Miocene Gaiman Formation at the lower Río Chubut valley, central-eastern Patagonia. The family Oplegnathidae does not occur in the Atlantic today, but it was widespread in comparison to other knifejaw fishes, such as scarids and odacids. Several aquatic vertebrates were extirpated from the southern Atlantic Ocean in the Late Neogene. This record establishes a minimal age (Early Miocene) for the extirpation of the family Oplegnathidae in the Atlantic Ocean.
The Seymour Island beds include a remarkable representation of the continental flora and fauna and marine fauna of Eocene in southern
high latitudes. We suggest that, at least during the deposition of the best sampled unit, the Cucullaea I Allomember of the La Meseta
Alloformation in the Seymour Island area, a cold temperate terrestrial environment co-existed with relatively warmer temperatures in the
adjacent shallow shelf sea. This is suggested by the fish and invertebrate fauna and could have been due to the presence of warmer waters
of a current reaching the region from the north. The temperature drop proposed for the time of deposition of the uppermost part of
the La Meseta Formation (Submeseta Allomember) appears to correspond to the global drop of the end of the Eocene and beginning of Oligocene and not to the establishment of the Antarctic Circumpolar Current.
A vertebra from the La Meseta Formation in Seymour Island is tentatively assigned to the rare genus Xiphiorhynchus (Teleostei, Perciformes, Xiphiorhynchidae. It belongs to one of the largest fossil osteichthyes ever described.
Body size variation of a predator is a simple way to follow the main changes in its food source during its life history or along its evolution in ecology and paleoecology, respectively. Here, we present possible first evidence of such predator-prey co-evolution through the study of the body size evolution among sixgill sharks (genus Hexanchus) inferred from their fossil record and by comparison to the life history of its two recent species. As for the observed ontogenic diet change of the living bluntnose sixgill shark (H. griseus), its ancestors appear to have developed a similar penchant for dining on marine mammals at the end of the Paleogene with a remarkably well-correlated timing.
Skeletal remains of penguins from the Eocene La Meseta Formation (Seymour Is− land, Antarctica) constitute the only extensive fossil record of Antarctic Sphenisciformes. No articulated skeletons are known, and almost all fossils occur as single isolated elements. Most of the named species are based on tarsometatarsi (for which the taxonomy was revised in 2002). Here, 694 bones (from the Polish collection) other than tarsometatarsi are reviewed, and allocated to species. They confirm previous conclusions and suggest that ten species grouped in six genera are a minimal reliable estimate of the Eocene Antarctic penguin diver− sity. The species are: Anthropornis grandis, A. nordenskjoeldi, Archaeospheniscus wimani, Delphinornis arctowskii, D. gracilis, D. larseni, Marambiornis exilis, Mesetaornis polaris, Palaeeudyptes gunnari and P. klekowskii. Moreover, diagnoses of four genera (Anthropornis, Archaeospheniscus, Delphinornis and Palaeeudyptes) and two species (P. gunnari and P. klekowskii) are supplemented with additional, non−tarsometatarsal features. Four species of the smallest penguins from the La Meseta Formation (D. arctowskii, D. gracilis, M. exilis and M. polaris) seem to be the youngest taxa within the studied assemblage – their remains come exclusively from the uppermost unit of the formation. All ten recognized species may have co−existed in the Antarctic Peninsula region during the Late Eocene epoch. Key wo r d s: Antarctica, La Meseta Formation (Eocene), paleontology (penguins), taxon− omy.
On the basis of a skull from the late Eocene La Meseta Formation on Seymour Island, Antarctic Peninsula, a gadiform fish is reported from the Antarctic region for the first time. This specimen, the most completely preserved fossil teleost cranium yet described from Antarctica, provides convincing evidence for the presence of Gadiformes in a far southerly location under temperate climatic conditions 40 m.y. ago. The exoccipital condyles, supraoccipital and lambdoidal crests, and post-temporal and supratemporal fossae are well preserved, as are the roofing bones on the posterior half of the skull. Comparative osteological study indicates that these features are very similar in apppearance to those of merlucciids (hakes) and gadids (cods). -Authors
Argentine-Polish geological investigations on Seymour (Marambio) Island, Antarctica, 1988 ABSTRACT: This report describes aims and preliminary results of geological fieldwork carried out by a joint Argentine-Polish party on Seymour (Marambio) and Cockburn islands. Antarctic Peninsula, during austral summer of 1987 88. Seymour Island exposes chiefly shallow-marine, fossiliferous siliciclastic sediments that form an upper, 2000 m thick part in the Mesozoic-Tertiary backarc basin-infill of the Antarctic Peninsula. The fieldwork centered on paleontology and sedimentology of the La Meseta Formation (upper Eocene-?lower Oligocene), although some observations of older deposits were carried out also. Clupeoid fishes were discovered in the La Meseta Formation. This is the first record of such fish fossils on the Antarctic continent.
TONNI, E. & A.L. CIONE. 1978. Una nueva colección de vertebrados del Terciario inferior de la isla Vicecomodoro Marambio (Seymour Island), Antártida. Obra del Centenario del Museo de La Plata 5: 73-79. Argentina.
The marine waters of present-day Antarctica contain an exceedingly depauperate elasmobranch fauna. Recent investigations into the Eocene marine sediments of the La Meseta Formation of Seymour Island, Antarctic Peninsula yielded 13 fossil sharks new to the Antarctic region. Two, Stegostoma cf. S. fasciatum and Pseudoginglymostoma cf. P. brevicaudatum, were unknown as fossils. Squalus woodburnei, S. weltoni, and Anomotodon multidenticulata are new species. Heptranchias howelli, Centrophorus sp., Deania sp., Dalatias licha, Odontaspis rutoti, O. winkleri, Lamna cf. L. nasus, and Scoliodon sp. are reported in Antarctica for the first time. In addition, the new fossil shark material increases the representation of the four previously known fossil sharks from Seymour Island: Squatina sp., Pristiophorus lanceolatus, Carcharias macrota, and Carcharocles auriculatus.
A new species of Early Tertiary fossil penguin from Seymour Island is described on the basis of tarsometartarsi from the collection acquired during the Argentinian-Polish field party of 1985. Palaeeudyptes klekowskii sp. nov. is bigger than earlier described species of this genus from the same locality. Information is given on the new collection of fossil penguin bones, a large part of which was found in one horizon of Unit III of the La Meseta Formation. The collection also includes much of the accompanying invertebrate and vertebrate fauna.
On the basis of a skull from the late Eocene La Meseta Formation on Seymour Island, Antarctic Peninsula, a gadiform fish is reported from the Antarctic region for the first time. This specimen, the most completely preserved fossil teleost cranium yet described from Antarctica, provides convincing evidence for the presence of Gadiformes in a far southerly location under temperate climatic conditions 40 m.y. ago. The exoccipital condyles, supraoccipital and lambdoidal crests, and post-temporal and supratemporal fossae are well preserved, as are the roofing bones on the posterior half of the skull. Comparative osteological study indicates that these features are very similar in appearance to those of merlucciids (hakes) and gadids (cods).
Isolated fish remains including a tooth of the oldest described frilled shark, Chlamydoselachus
thomsoni sp. nov. are described and figured from the Santa Marta Formation (Santonian–Campanian, Late Cretaceous) of James Ross Island, Antarctic Peninsula. Their geological and palaeoecological context is considered in the light of recent geological studies.
Approximately 150 meters of fine-grained Campanian sediments and over 100 meters of fine-to medium-grained Eocene sands underlie Pliocene basalts and conglomerates on Cockburn Island, north-eastern Antarctic Peninsula. The Campanian beds are part of the "Unnamed strata" of the Marambio Group and contain invertebrate and palynomorph fossils that predate the adjacent Seymour Island Lopez de Bertodano succession. Rich palynomorph floras suggest a middle Campanian age. Deposition was in low energy, shallow shelf environments. Invertebrate and palynomorph fossils, and lithology, all indicate correlation of the Eocene beds with the basal La Meseta Formation, members Telm 1 and lower Telm 2 of Seymour Island. The age of these beds is probably late early Eocene. The basal La Meseta sands are marginal marine to shallow shelf sediments that fill a broad valley probably incised during latest Paleocene-earliest Eocene as a result of tectonism and sea-level lowstands.
The upper Eocene La Meseta Formation on Seymour Island contains one of the most important Tertiary marine faunas from the Southern Hemisphere. The fauna contains elements from both southern South America and Australasia and provides the key to the understanding of the biogeographic history of the southern circum-Pacific during the final break-up of Gondwana during the Early Tertiary and to the origin of many modern-day groups of Pacific molluscs. The bivalves described in this paper were collected during the 1974-1975 joint Argentine-American expedition to Seymour Island. This paper describes 22 new species and 3 new genera of bivalves: Nucula (Leionucula) palmeri n.sp., Australoportlandia antarctica n.sp., Australoneilo rossi n.gen., n.sp., Solemya peteri n.sp., Cucullaea raea n.sp., Auclacomya anderssoni n.sp., Modiolus turneri n.sp., Modiolus thomsoni n.sp., Pinna sobrali n.sp., Ostrea antarctica n.sp., Ostrea seymourensis n.sp., Lahillia wilckensi n.sp., Gomphina iheringi n.sp., Gaimardia flemingi n.sp., Oxyperas (Beudoxyperas) ortmanni n.sp., Eurhomalia florentinoi n.sp., Eurhomalia inflata n.sp., Eurhomalia carlosi n.sp., 'Cyclorismina' marwicki n.sp., Cockburnia n.gen., Periploma topei n.sp., Mya (Arenomya) sowerbyi n.sp., and Panopea philippii n.sp. Ten previously described species are redescribed, figured and their taxonomy modernized. -Author
Several problems which have arisen in the stratigraphic nomenclature of the Upper Cretaceous sedimentary sequence from the James Ross Island Group are analyzed. This discussion is based on a lithostratigraphic viewpoint. -from Author
Diverse and abundant organic walled microplankton have been recovered from the only known outcrops of lower Tertiary marine sediments in the Antarctic area. The 70 samples collected from the Paleogene Seymour Island deltaic complex yielded 43 genera and 74 species of dinoflagellate cysts; 2 genera and 9 species are new, and a number of new combinations and taxonomic emendations are proposed. Specimens attributable to the Acritarcha, Pterospermatales, and Chlorococcales also were noted. Sediments of the Cross Valley Formation in the Cape Wiman area are early late Paleocene in age. The exact source of samples reputedly collected from the Cross Valley Formation at the type locality in Cross Valley is uncertain. This is because faults and surface slumps in the area were only partially mapped at the time of sampling. The lower 100 m of Section 12-13 are Eocene in age, whereas the overlying 20 m are no younger than early late Paleocene. The deposits of the stratigraphicaliy higher La Meseta Formation can be subdivided into beds of late early and middle to late Eocene age. Deposition occurred within the subenvironments of the Seymour Island Paleocene- Eocene deltaic complex. Specific paleoenvironments identified include distributary channels, interdistributary bays, lagoons, and perhaps, prodelta areas. The Paleocene dinoflagellate cyst floras are composed of cosmopolitan taxa. Eocene floras include cosmopolitan and provincial taxa. The cosmopolitan taxa have been reported from regions as widely separated as Europe, North America, and Australia. The provincial taxa belong to the hypothesized transantarctic flora that was well developed in and around Antarctica during the Eocene. The distribution of the transantarctic flora suggests that a marine seaway across West Antarctic connected the southwest Atlantic and southwest Pacific oceans during Eocene time. Rare, extra-Antarctic occurrences of some species included in the transantarctic flora suggest that such species should not be considered part of this flora, that the distribution of these taxa was bipolar, or that the complete distribution of the transantarctic flora is yet to be documented.
Lower Tertiary strata on Seymour Island comprise two formations that are in fault contact. The older (Paleocene) Cross Valley Formation is a 105-m-thick sequence of sandstone and pebbly sandstone, representing distributary channel fills. The younger (late Eocene) La Meseta Formation has a composite thickness of about 450m and is divisible into three units, representing a delta- slope, a tide dominated environment and a lagoon. The major megastructure in this formation is large-scale 'slump-and-fill' formed by mass movement of sediment and subsequent infilling of the submarine valley that resulted. Deltaic environments are suggested for the two formations. These rocks are the youngest exposed strata of the late Mesozoic-early Cenozoic depositional basin on the SE flank of the northern Antarctic Peninsula. -from Authorsfault Paleocene channel fills Eocene delta slope lagoon mass movementInst of Polar Studies and Dept of Geology & Mineralogy, The Ohio State Univ, Columbus, Ohio 43210, USA.
The Cretaceous-Paleogene sequence on Seymour Island has been mapped in terms of four previously named units: the Lopez de Bertodano Formation (Cretaceous- Paleocene), the Sobral Formation (Paleocene), the Cross Valley Formation (late Paleocene), and the La Meseta Formation (Eocene). The basal surfaces of the Sobral and Cross Valley Formations include portions with clear evidence of erosional unconformity. The base of the La Meseta Formation laps onto a steep buttress unconformity at both of its exposed margins. The scale of lenticularity of the units increases upward throughout the sequence. The Lopez de Bertodano Formation and most of the Sobral Formation are built of essentially tabular units, and have been effectively characterized by isolated measured sections. The Cross Valley Formation is a channel-filling lens. The La Meseta Formation has a complex, asymmetric, trough-like form. It is built of large-scale lenses characterized by different shelly facies that do not all extend across the full width of the trough. Consequently, mapping between measured sections is essential to establish the lateral relationships. Even then, the geometric relationships do not identify time lines; establishing the real age relationships will require very carefully located faunas. The observed relationships between the length and height of lenticular units can be used to estimate the expected vertical error when faunas are projected into a composite section. The whole sequence is essentially a gently dipping homocline. The youngest units have slightly gentler dips, indicating progressive or repeated tilting. But a larger component of the variance in bedding attitude is contributed by steeper dips in the sedimentary filling of channels and slump scars. The regional tilt, the development of growth faults, facies changes, and the orientation of erosional surfaces have a symmetrical arrangement from which a common cause is inferred. The best estimates of the timing of the major unconformities and erosional episodes are only partially compatible with current models of global sea-level change.
A new species of Megascyliorhinus (M. trelewensis) comes from the Monte León Formation (“Patagoniano” partim; upper Oligocene–lower Miocene) of eastern Patagonia. It is compared with other species of Megascyliorhinus, in particular M. miocenicus, although there is no implication of relationship to the latter. An Eocene–Pleistocene size increase in the species of Megascyliorhinus appears to be demonstrated. The supposed relationships with Megachasma pelagios are discussed.
Examination of a larger number of sixgill sharks (family Hexanchidae) from the coasts of North America than have hitherto been available shows that two well-differentiated species occur in the western North Atlantic. The larger of the two Atlantic species, Hexanchus griseus, has been taken rarely in the western North Atlantic where it is known only from specimens 2.90 meters or more in length. The smaller Atlantic species, Hexanchus vitulus, is described and illustrated from types collected off Bimini, Bahamas. The small species becomes sexually mature at about 1.40 to 1.75 meters and apparently does not reach a much greater length.
Marambionella
andreae gen. et sp. nov. from the La Meseta Formation (Upper Eocene–?Lower Oligocene) on Seymour Island is the first fossil clupeid found in Antarctica and the first articulated teleost from the Antarctic Paleogene. It shows a mosaic of similarities and differences compared with various clupeid genera. This and the uncertainty about the polarity of characters within clupeids do not allow precise assessment of the phylogenetic relationships of Marambionella.
Twenty two samples collected from the Tertiary La Meseta Formation of Cape Wiman, Seymour Island, Antarctic Peninsula yielded abundant and moderately diverse assemblages of marine palynoflora, dominated by dinoflagellate cysts, together with acritarchs and chlorophyta. The assemblages can be divided into three association: Association 1, characterized by low diversity dinoflagellate assemblage of late Early Eocene age which are dominated by Enigmadinium
cylindrifloriferum; Association 2 characterized by more diverse dinoflagellate cyst assemblages, which show a marked decrease in the dominance of E.
cylindrifloriferum, and an increase in relative abundance of Areosphaeridium cf. diktyoplokus; and Association 3 which is characterized by a decrease in dinoflagellate cyst diversity up section. Changes in dinoflagellate cyst dominance and diversity throughout the section suggests a gradation from a stressed, shallow marine palaeoenvironment to a more open near-shore, shallow marine system becoming progressively more nearshore up section. The assemblages are no older than late Early Eocene in age, and possibly as young as Mid–Late Eocene.
The Ypresian locality of Burnham-on-Crouch(Essex) has yielded numerous Selachian species, some of which are new: Hexanchus agassizi sp. nov., Scyliorhinus burnhamensis sp. nov., S. casieri sp. nov., S. pattersoni sp. nov., S. woodwardi sp. nov., Pararhincodon ypresiensis sp. nov., Triakis wardi sp. nov., Mustelus whitei sp. nov. The Hexanchid teeth classicaly refered to Notidanus serratissimusAg. include in fact two separate species belonging to different genera: Notorhynchus serratissimus (Ag.) and Hexanchus agassizi sp. nov. Lamna affinis (Casier) is arranged in the genus Isurolamna nov. in consideration of his dental peculiarities. The genus Burnhamia nov. is created for Rhinoptera daviesiWoodward that can be regarded as a Mobulid. Oxyrhina sheppeyensisCasier must be classified in the genus Anomotodon. The genus Triakis, Mustelus, Anomotodon and Pararhincodon are pointed out for the first time in the Ypresian.
A fossil land mammal, apparently the first found in Antarctica, belongs to the extinct marsupial family Polydolopidae. The fossils were recovered from rocks about 40 million years old on Seymour Island, in the northern Antarctic Peninsula. The newly discovered marsupials support theories that predicted their former presence in Antarctica and strengthen proposals that Australian marsupials perhaps originated from South American species that dispersed across Antarctica when Australia still was attached to it, prior to 56 million years ago.
Les vertébrés sossiles de gisements de Phosphates (Maroc-Algérie-Tunisie)
- Arambourg
Ungulados de la Formación La Meseta (Eoceno medio-superior) de la Isla Marambio
- M Bond
- M A Reguero
Stratigraphy and paleontology of Campanian and Eocene sediments, Cockburn Island, Antarctic Peninsula
- Askin
Megascyliorhinus trelewensis nov sp. (Galeomorphi incertae sedis) from the upper Oligocene-lower Miocene of Eastern Patagonia, Argentina
- Cione
Los peces de las formaciones marinas del Cenozoico de Patagonia.
- Cione
Eocene micro-plankton from La Meseta Formation, northern Seymour Island
- Cocozza