Marcelo Reguero

Antarctic Peninsula and South America (Patagonia) Paleogene terrestrial faunas and environments: biogeographic relationships

Abstract 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 Rio 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.

The first duck-billed dinosaur (Family Hadrosauridae) from Antarctica

Department of Earth Sciences, University of California, Riverside, California 92521Duck-billed dinosaurs or hadrosaurs are a very common family ofdinosaurs in the Late Cretaceous of North America and Eurasia withrare occurrences in South America. Here, we report the first hadrosaurrecovered in Antarctica from sandstones of late Maastrichtian age, VegaIsland, Antarctic Peninsula (Fig. 1) during a joint U.S.-Argentinian geo-logical and paleontological field expedition to the island. This discoverysupports the hypothesis of a dispersal route between southern SouthAmerica and Antarctica in the Maastrichtian.Dinosaurs are extremely rare in the dominantly marine deposits ofLate Cretaceous age in Antarctica, so the discovery of a single hadro-saur tooth (Fig. 2) by the third author (DSC) was unexpected. Hadro-saurs are not the first dinosaurs from Late Cretaceous deposits in theJames Ross Basin. Theropod, ornithopod, and ankylosaur specimenshad been previously recorded (Gasparini et al., 1987; Hooker et al.,1991; Molnar et al., 1996). However, these dinosaur groups representeither cosmopolitan taxa or native Gondwanan taxa, thus the duck-billeddinosaur represents a new immigrant family of dinosaurs into this south-ernmost continent.The fossil-bearing deposit occurs at 61 51 S and 53 33 W, at Sand-wich Bluff on Cape Lamb, Vega Island, Antarctic Peninsula. The ‘‘Rep-tile Horizon,’’ named for the numerous mosasaur and plesiosaur spec-imens recovered from this stratigraphic level, is in the upper third ofthe Sandwich Bluff Member (Crame et al., 1991; Pirrie et al., 1991) orUnit C (Olivero, 1992) of the Lopez de Bertodano Formation. Thismember is a nearshore marine deposit of composed of fine-grained,ferruginous, loosely consolidated sandstones that are latest Maastrich-tian age (approximately 66–68 million years ago), based on correlationsof ammonite and palynological taxa (Crame et al., 1991; Pirrie et al.,1991).In addition to the hadrosaur, at least four different bird species (whichcan be referred to modern avian orders, including charadriiform andgaviid birds, based on the morphology of their respective tarsometatar-sals), have been recovered from this same stratigraphic level. Addition-ally, numerous specimens of plesiosaurs and mosasaurs were collectedfrom this same horizon, as well as the 5-meter horizon immediatelybelow (Martin et al., 1999a, b). At least five taxa of marine reptiles arerepresented on Vega Island, and numerous specimens of juvenile indi-viduals were collected, concentrations of which are relatively rare inthe North American marine reptile record.SYSTEMATIC PALEONTOLOGYREPTILIAA

Late Eocene penguins from West Antarctica: systematics and biostratigraphy

Abstract Penguins are by far the most dominant group of marine vertebrates in the Eocene La Meseta Formation (Seymour Island, Antarctica). We analysed the penguin fauna recovered there from both a systematic and a biostratigraphic point of view. We have added two new species (Tonniornis mesetaensis and T. minimum) and have defined a biostratigraphic unit, the Anthropornis nordenskjoeldi Biozone. This interval of strata, easily distinguishable by the numerous occurrence of penguin bones and the phosphatic brachiopod Lingula, is located nearly 30–35 m below the top of the 145 m-thick Submeseta Allomember. The highest morphological and taxonomic penguin diversity living sympatrically (organisms that live simultaneously in the same place), including giant and tiny species, is documented in this interval. Fossil penguins bones studied in this paper, recovered from rocks interpreted as shallow-marine deposits, accumulated between 34.2 and 36.13 Ma (late Late Eocene).

New Discoveries of “Opposum-Like” Marsupials from Antarctica (Seymour Island, Medial Eocene)

Five new species of marsupials are described from the middle Eocene La Meseta Formation of Seymour Island, Antarctic Peninsula. Three are derorhynchid didelphimorphians; one species is a prepidolopid polydolopimorphian, and the last is a microbiotheriid australidelphian. Additionally, fragmentary specimens representing an indetermined derorhynchid and a possible marsupial are also described. The prepidolopid and one of the derorhynchids are sufficiently derived as to preclude any close relationship to other members of that family, but the remaining taxa show the closest affinity with species otherwise known only from Itaboraian and older faunas in Patagonia. This differs from the affinity to early Eocene (Casamayoran) taxa shown by the polydolopid marsupials and placental mammals previously known from the La Meseta Formation. The newly described marsupials indicate that the relict La Meseta Fauna is composed of forms that must have dispersed to Antarctica no later than about early late Paleocene, whereas the previously known taxa apparently arrived in the early Eocene. Ecologically, the La Meseta Fauna is composed mostly of small-sized marsupials of likely insectivorous to frugivorous habits and larger-sized placental herbivores. Whereas the ratite bird of the La Meseta Fauna was probably also herbivorous, the phorusrhachoid and falconid birds comprised a large and smaller carnivorous to possibly scavenging component, respectively. Compared to contemporary faunas of Patagonia, the medium- to large-sized marsupial carnivores are lacking in the Antarctic Peninsula. Nevertheless, the La Meseta Fauna is Patagonian in origin and affinity. In conjunction with new faunas of Itaboraian age (early late Paleocene) in Patagonia, the evidence available indicates that from at least Itaboraian time onward the land mammal fauna of Patagonia and northern South America, as well, is a self-contained unit, developing the diversity characteristic of the Paleogene in that continent, including the australidelphian (but South American) microbiotheres. This, in combination with the apparent separation of Australia from Antarctica at ca. 64 Ma, reinforces interpretations that the precursors of the Australian marsupial fauna most likely dispersed from South America to Australia in the late Cretaceous–early Paleocene.

Late Cretaceous/Paleogene West Antarctica Terrestrial Biota and its Intercontinental Affinities

Introduction.- West Antarctica (WANT): tectonics and paleogeography.- -East Antarctica (EANT)/West Antarctica (WANT), gondwanic paleobiogeography.- Late Cretaceous/Paleogene stratigraphy of the James Ross Basin.- -Late Cretaceous.- -Paleogene.- South America/West Antarctica: Pacific affinities of the Paleogene Weddellian marine/coastal vertebrates.- -Late Cretaceous/Paleogene marine fossil vertebrates of the James Ross Basin.- -Weddellian Sphenisciformes: systematics, stratigraphy, biogeography and phylogeny.- The terrestrial biotic dimension of WANT.- -West Antarctica paleoflora.- -Late Cretaceous terrestrial vertebrates of the James Ross Basin.- -Paleogene terrestrial vertebrates of the James Ross Basin.- -Paleogene reconstruction of the Cucullaea I (Ypresian) and Submeseta (Priabonian) biotas.- -Correlation of the Cucullaea I terrestrial fauna with Early Paleogene Patagonian faunas.- -WANT terrestrial biota and its intercontinental relationships.

A middle Eocene basking shark (Lamniformes, Cetorhinidae) from Antarctica.

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, Cetorhinus maximus. 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.

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).

A POORLY KNOWN RODENTLIKE MAMMAL (PACHYRUKHINAE, HEGETOTHERIIDAE, NOTOUNGULATA) FROM THE DESEADAN (LATE OLIGOCENE) OF ARGENTINA. PALEOECOLOGY, BIOGEOGRAPHY, AND RADIATION OF THE RODENTLIKE UNGULATES IN SOUTH AMERICA

Abstract The cranial anatomy of the Deseadan species Medistylus dorsatus (Ameghino, 1903) is described based on new and complete material from Cabeza Blanca (Chubut, Argentina). Medistylus is the largest of the Pachyrukhinae and the specimen described here is probably the best-preserved pachyrukhine skull known in the Paleogene of South America. Previously, the validity of the species and its phylogenetic affinities with Interatheriidae (Notoungulata, Typotheria) were ambiguous and not conclusive. The syntypes, now reported lost, were isolated teeth poorly described by Ameghino in 1903. This almost complete skull with teeth provides more diagnostic features in order to complete the knowledge of genus. Details about cranial and dental morphology allow the reassessment of Medistylus dorsatus and its inclusion within the subfamily Pachyrukhinae (Hegetotheriidae, Notoungulata). Its cranial and dental specializations and the apparent sympatry with its close relatives Prosotherium garzoni Ameghino, 1897 and Propachyrucos smithwoodwardi Ameghino, 1897 all imply a narrow niche partitioning among the Pachyrukhinae during the Deseadan (late Oligocene). The occurrence of three euhypsodont genera of Pachyrukhinae in the Deseadan of Patagonia reflects the major radiation of the rodentlike ungulates in the Cenozoic of South America and suggests a great paleoenvironmental difference between the late Oligocene faunas of Patagonia and those from Bolivia and Uruguay, where they did not live.

The first record of a sauropod dinosaur from Antarctica

Sauropoda is one of the most diverse and geographically widespread clades of herbivorous dinosaurs, and until now, their remains have now been recovered from all continental landmasses except Antarctica. We report the first record of a sauropod dinosaur from Antarctica, represented by an incomplete caudal vertebra from the Late Cretaceous of James Ross Island. The size and morphology of the specimen allows its identification as a lithostrotian titanosaur. Our finding indicates that advanced titanosaurs achieved a global distribution at least by the Late Cretaceous.

A new species of Eopachyrucos (Mammalia, Notoungulata, Interatheriidae) from the Late Oligocene of Uruguay

Abstract A new species of the notoungulate Eopachyrucos is described on the basis of mandibles and lower cheek teeth from the upper Oligocene Fray Bentos Formation of Uruguay. Eopachyrucos ranchoverdensis, sp. nov., is most similar to the pre-Deseadan/post-Mustersan (late Eocene) Eopachyrucos pliciferus from Patagonia, but is much larger and less hypsodont. The new species has a well-developed postmetacristid on p3 similar to that of Notopithecinae but with higher crowned teeth. The Oligocene record of Eopachyrucos greatly extends its chronologic range. A cladistic analysis of Eopachyrucos and other interatheriids supports the hypothesis that Eopachyrucos is the most primitive interatheriine, retaining a number of primitive features also found in advanced Notopithecinae. The Fray Bentos Fauna shares a few typical elements with Deseadan faunas from Patagonia, but an important distinction between the two faunas is the persistence of some archaic taxa in the Fray Bentos Fauna. The overall composition of the Fray Bentos Fauna is more similar to late Oligocene Deseadan faunas of Bolivia, and this may be attributed to temporal (younger than the Deseadan of Patagonia) or ecological factors.