La Meseta Research Articles

A new Eocene crab (Crustacea, Decapoda) from Seymour Island, Antarctica

A new xanthid crab, Tumidocarcinus foersteri n. sp. is described from the La Meseta Formation on Seymour Island, Antarctica. The fossils were obtained from the Allomember Submeseta of Late Eocene age. As other representatives of the genus Tumidocarcinus were only known from New Zealand and Australia, this finding provides new insights on the palaeobiogeography of high latitude faunas during the Early Tertiary.

Iberian Triassic paleomagnetism revisited: Intraplate block rotations versus polar wandering

A paleomagnetic study of over 220 samples, obtained from 21 sites from Triassic redbeds in the Algarve (S Portugal) and La Meseta (SE Spain), yields two paleomagnetic poles at lat = 62°N,lon = 202°E, A95 = 9 and lat=54°N, lon=178°E, A95=7 respectively. The Algarve paleopole reflects a rotation associated with the Alpine evolution of the Iberian Atlantic margin. A comparison of the La Meseta pole with other data indicates a progressive clockwise rotation of the Eurasian Plate from the Late Paleozoic to Middle Triassic, followed by rapid drift until the Upper Triassic. This late Triassic drift event may be related to the opening and spreading of the Tethys towards the west.

Eocene land mammals from Seymour Island, Antarctica: palaeobiogeographical implications

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).

Antarctomithrax thomsoni,a new genus and species of crab (Brachyura; Majidae) from the La Meseta Formation (Eocene) of Seymour Island, Antarctica

The james ross basin, situated on the eastern margin of the Antarctic Peninsula, has yielded an extensive fauna of decapod crustaceans spanning Late Cretaceous through Eocene time. To date, 28 species in 22 genera and 18 families have been described (Feldmann, 1992; Feldmann, Tshudy, and Thomson, 1993), making this the most diverse fossil decapod fauna in the Southern Hemisphere. Within the basin, Seymour Island alone contains rocks of the Eocene age La Meseta Formation from which seven species of crabs, one galatheid, and one species of callianassid ghost shrimp have been described (Feldmann and Zinsmeister, 1984; Feldmann and Wilson, 1988; Feldmann, 1992). The fauna of the La Meseta is remarkable also because, although the organisms are preserved in rocks deposited in moderate- to high-energy, shallow-water habitats (Elliot and Trautman, 1982), many of the species represent early occurrences of taxa with living descendants that are characteristic of deeper water, lower latitude habitats (Zinsmeister and Feldmann, 1984).

Quaternary colonization or Paleogene persistence?: historical biogeography of skates (Chondrichthyes: Rajidae) in the Antarctic ichthyofauna

Seven endemic species of skates (Chondrichthyes: Rajidae) represent the only family of elasmobranchs currently known to live in Antarctic continental waters. Many previous authors believed skates colonized Antarctic waters from Patagonia during interglacial periods in the Quaternary. However, recent fossil material collected from the middle Eocene La Meseta Formation of Seymour Island, Antarctic Peninsula, indicates that they may have persisted in Antarctic waters since the Paleogene. Additionally, oceanographic barriers present in the Neogene and Quaternary would have prevented dispersal from southern continents to Antarctica. A revised dispersal scenario, based on skate fossils, biology, paleogeography, and present centers of skate diversity, suggests that skates evolved in the western Tethys and North Boreal seas of western Europe in the Late Cretaceous and early Paleogene and emigrated into Antarctica during the early to middle Eocene via a dispersal corridor along the continental margins of the western Atlantic Ocean. Skates probably populated the Pacific Basin by passing from this dispersal corridor through the Arctic Ocean. Vicariant events, such as opening of the Drake Passage, the development of the Circum-Antarctic Current, and formation of deep and wide basins around Antarctica in the late Paleogene, created barriers that isolated some species of skates in Antarctica and prevented movement of other species of skates into Antarctica from northern areas. Skates are the only group of fishes known to have survived the Oligocene cooling of Antarctica that killed or extirpated the Paleogene ichthyofauna; they persisted by a combination of cold-tolerance, generalized diet, and unspecialized bathymetric and habitat preferences.

Angular unconformity between the López de Bertodano and La Meseta formations (Campanian-Maastrichtian and Eocene), Cockburn Island, northern Antarctic Peninsula

A thick, largely shallow marine succession of Cretaceous and Lower Tertiary strata, deposited in the James Ross Basin, is well exposed on an archipelago of islands at the northern end of the Antarctic Peninsula. This succession was thought to be relatively continuous, particularly on Seymour Island where a thick Upper Cretaceous succession passes up into Paleocene and Eocene strata. Several unconformities present in the succession were thought to be relatively minor and have been ascribed to sea level changes. Equivalent sedimentary deposits of the López de Bertodano and La Meseta formations, Campanian/Maastrichtian and Lower Eocene respectively, are exposed on Cockburn Island, less than 10 km from Seymour Island. The contact between the two units is an unconformity with an angular discordance varying from 20° to 55°. Rotation of the López de Bertodano Formation corresponds with syn-sedimentary disruption elsewhere in the basin throughout the Late Cretaceous and points to persistent instability. The ages of the strata on either side of the uncorformity have been dated on the palynological content of five samples and correlation with the Seymour Island succession suggests that at least 900 m of Cretaceous (650 m) and Lower Tertiary (250 m) strata are missing from, or were not deposited at, Cockburn Island. Reworked Maastrichtian palynomorphs in a breccia bed within the La Meseta Formation confirm that Upper Cretaceous strata were eroded although there is no evidence for reworking of Paleocene sediments. We conclude that Cockburn Island includes a continuation of the Eocene unconformity of Seymour Island, extending the trend for the base of the La Meseta Formation to onlap onto progressively older strata. This unconformity may mark a major phase of basin inversion, with tilting and uplift possibly affecting much of the James Ross Basin at this time.

Eocene crinoids from Seymour Island, Antarctic Peninsula: paleobiogeographic and paleoecologic implications

On the basis of recent collections from the Upper Eocene La Meseta Formation of Seymour Island, Antarctic Peninsula, the morphology, systematic position, taphonomy, and paleoecology of the isocrinid Metacrinus fossilis are investigated. A new species, Notocrinus rasmusseni, is described as the first comatulid crinoid known from the Antarctic fossil record. The systematic assignment of M. fossilis is maintained. Basal abrasion of calyxes and absence of long attached columns suggest that M. fossilis might have lost most of the column in adult stages and lived directly on the substratum, supported by some arms and a few cirri, similar to comatulids. About 10 percent of M. fossilis individuals show brachial regeneration, in contrast to regeneration frequencies of 70–90 percent among modern Japanese isocrinids. The anomalous occurrence of isocrinids in shallow-water facies of the La Meseta is attributed to a combination of reduced predation pressure, the presumed stalkless mode of life, and a favorable temperature regime in Antarctic surface waters prior to the onset of cooling at the close of the Eocene.

Stable carbon and oxygen isotope record in the Paleogene La Meseta Formation, Seymour Island, Antarctica

Stable carbon and oxygen isotopic relations have been analysed in brachiopod, gastropod, and bivalve fossils from the La Meseta Formation (Eocene-?early Oligocene), Seymour (Marambio) Island, West Antarctica. The results indicate a shift in δ13C by 6 permil beginning in the middle part of the Unit II of the formation. This shift may imply a change from a largely stratified to a vigorously mixed ocean. Such an interpretation is corroborated by changes in the elemental proportions in the shell material. Alternatively, the carbon isotopic shift may be regarded as reflecting a change in the local depositional enviornment. Such an interpretation agrees with isotopic data from the Weddell Sea, which do not confirm the pattern observed in the La Meseta Formation. In any event, the oxygen isotopic curve does not decline parallel to the carbon curve and may thus imply a considerable climatic cooling event. This effect is so profound that it might be interpreted as evidence for glaciation, especially when taking into account the fact that this phenomenon coincides with the well-known cooling trend throughout the Eocene. If this interpretation is correct, the hypothesized Glaciation may possibly be correlated with the Polonez Glaciation, the largest Cenozoic glaciation known in the Antarctic Peninsula sector. Alternatively, it may be regarded as a local phenomenon, predating development of the icesheet.

Eocene microplankton from La Meseta Formation, northern Seymour Island

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.

An Eocene wrasse (Perciformes; Labridae) from Seymour Island

A nearly complete lower pharyngeal tooth-plate from a large (over 60 cm long) fossil wrasse (Perciformes: Labridae) was recently recovered from the middle to late Eocene La Meseta Formation on Seymour Island, Antarctic Peninsula. This find increases the number of teleosts from the Eocene of Antarctica to five taxa, and further illustrates the diversity of the ichthyofauna in the Eocene Weddellian Sea prior to wide-scale climatic change in the Southern Ocean. The fossil wrasse represents the first occurrence of this family in Antarctica, and is one of the oldest fossils of this family from the Southern Hemisphere. Wrasses are not found in Antarctic waters today, and probably became extinct during the Oligocene due to a combination of climatic change, loss of shallow-water habitat, and changes in the trophic structure of the Wedell Sea.

Sharks from the La Meseta Formation (Eocene), Seymour Island, Antarctic Peninsula

ABSTRACT 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.

An additional record of a placental mammal (Order Astrapotheria) from the Eocene of West Antarctica

Recently, fossil land mammals have been recorded in the James Ross Island area, east of the Antarctic Peninsula, from the marine middle-late Eocene strata of Seymour Island. These include two endemic species of polydolopid marsupial: Antarctodolops dailyi Woodburne & Zinsmeister 1984, and Eurydolops seymourensis Case, Woodburne & Chaney 1988, and three partly determinate placentals identified as a tardigrade edentate, a sparnotheriodontid litoptern and a trigonostylopid astrapothere (Bond et al. 1989). The marsupials are represented by fragmentary jaw and complete dental material, the litoptern and astrapothere only by tooth fragments. All are recorded from Unit TELM 5 of the La Meseta Formation (Sadler 1988), the two ungulates at a lower level than the rest. The subject of the present note is a second tooth fragment from Seymour Island identified as an astrapothere. It is worth recording because such mammal remains are rare and it is from TELM 4, the unit below that yielding the other land mammals.

First articulated teleost fish from the Paleogene of West Antarctica

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.

Chimaeroid fish remains from Seymour Island, Antarctic Peninsula

Ischyodus dolloi Leriche 1902, the youngest record of the species, and Chimaera seymourensis sp. nov. are described from the La Meseta Formation, Late Eocene of Seymour Island, Antarctic Peninsula.

Late Eocene gadiform (Teleostei) skull from Seymour Island, Antarctic Peninsula

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).

Stratigraphy and paleontology of Campanian and Eocene sediments, Cockburn Island, Antarctic Peninsula

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, northeastern 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 López 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.

Late Eocene Decapod Crustacea from North Westland, South Island, New Zealand

Eight species of brachyuran decapod crustaceans are recorded from coastal outcrops of Island Sandstone between Perpendicular Point and Punakaiki, Westland, New Zealand. The fauna consists of three raninids—Laeviranina pororariensis (Glaessner), L. keyesi n. sp., Lyreidus bennetti n. sp.; two portunids—Rhachiosoma granuliferum (Glaessner), Pororaria eocenica Glaessner; a goneplacid—Carcinoplax temikoensis n. sp.; and two majids—Leptomithrax griffini n. sp., Notomithrax allani n. sp. Together, they form the most diverse brachyuran assemblage yet described from New Zealand. The decapods are preserved in unusual elliptical masses, with their long axes typically parallel to bedding, containing superbly preserved cuticle often surrounded by well-formed fecal pellets, probably of decapod origin. The accumulations are interpreted to be mechanical concentrations within depressions produced by decapods or associated spatangoid echinoids. Although seven of the species have been recorded only from the Island Sandstone, Rhachiosoma granuliferum (Glaessner) is now known to occur in the correlative deep-water facies of the Kaiata Formation in North Westland, as well as in the Tapui Sandstone, North Otago (middle Eocene), and from coeval rocks at Snowdrift Quarry, southeast Otago. The raninids suggest comparison with congeneric forms from Snowdrift Quarry and the Tapui Sandstone, as well as with the La Meseta Formation, Seymour Island, Antarctica. Based upon associated foraminiferans, a Kaiatan–Runangan (late Eocene) age is assigned to this fauna. The occurrences of Carcinoplax, Leptomithrax, and Notomithrax represent paleobiogeographic and stratigraphic records for the genera.

A new species of fossil penguin from Seymour Island, West Antarctica

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.

A New Cetacean from the Late Eocene La Meseta Formation Seymour Island, Antarctic Peninsula

The new genus and species Llanocetus denticrenatus is described based on a cranial endocast and portion of a dentary fragment bearing two teeth from the Eocene La Meseta Formation, Seymour Island, Antarctic Penninsula. Llanocetus new genus is designated the type genus for the new family Llanocetidae. The Llanocetidae is placed within the new infraorder Crenaticeti, co-ordinate with the new Mysticete infraorder Chaeomysticeti. Llanocetus denticrenatus new species shows relationship with both Archaeoceti and Mysticeti. Revision of archaeocete and mysticete classification includes proposal of the new taxa Kekenodontinae, Mammalodontidae, and the new ranks Protocetoidea, Remingtonocetoidea, Basilosauroidea, and Eschrichtioidea. The endocast shows evidence of intracranial retial hypertrophy, taken as evidence of enhanced diving abilities. The large deeply notched teeth are widely spaced on the lower jaw. I hypothesize that filter feeding in whales arose first in species in which teeth with deep notches, forming widey spaced tubercles, comprised part of a straining apparatus analogous to the serrated teeth of the phocid seal Lobodon carcinophagus.

Note on the Antarctic Tertiary brachiopods and museum registry of specimens described by E. F. Owen, 1980

During the course of fieldwork by a joint Argentine-American expedition to Seymour Island (Elliot et al., 1975) during the austral summer of 1974-1975, a number of brachiopods were collected from the Late Eocene La Meseta Formation. A representative collection of these brachiopods was sent to E. F. Owen, Department of Palaeontology, British Museum (Natural History) for study. Owen (1980) published a revision of the brachiopods from Seymour and nearby Cockburn Islands. The study was based on material collected by W. N. Croft of the Faulkland Islands Dependencies Survey (now British Antarctic Survey) and the material which I sent.