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Abstract: A new ornithopod dinosaur from Antarctica, Trinisaura santamartaensis n. gen. et n. sp. is diagnosed by a unique combination of characters that includes a scapula with a spike-like acromial process with a strong and sharp lateral crest and longer than other ornithopods, a humerus with a rudimentary deltopectoral crest represented as a thickening on the anterolateral margin of the humerus, and shaft strongly bowed laterally, and an ischium gently curved along its entire length. The holotype specimen comprises vertebral and appendicular elements. The presence of axially elongate distal caudal vertebrae, pubis with long prepubic and postpubic processes, as well as a femur with a distinct anterior trochanter, pendant 4th trochanter and shallow anterior intercondylar groove constitute a combination of characters present in the Late Cretaceous Patagonian Gasparinisaura, Anabisetia and Talenkahuen. The materials were found on the surface enclosed in a hard sandstone concretion collected near the Santa Marta Cove, James Ross Island, from the lower levels of the Snow Hill Island Formation (Campanian). This is the first ornithopod taxon identified from this unit, and the second ornithischian dinosaur, after the ankylosaur Antarctopelta oliveroi. However, other ornithopod reports from nearby localities of James Ross and Vega islands in outcrops of the overlying Lopez de Bertodano Formation suggest that this clade was widely represented in the Campanian and Maastrichtian of the James Ross Basin, Antarctic continent. [Copyright &y& Elsevier]

We report and describe two new small diamictite outcrops on Isla Marambio (Seymour Island), Antarctic Peninsula. These rocks rest on an erosional unconformity on top of the Eocene La Meseta Formation and are unconformably covered by glaciomarine rocks of the ?Pliocene-Pleistocene Weddell Sea Formation. The lithology, fossil content and isotopic ages obtained strongly suggest that the rocks belong to the Hobbs Glacier Formation and support a Late Miocene age for this unit. Additionally, the dated basalt clast provides the oldest age (12.4 Ma) for the James Ross Island Volcanic Group recorded up to now. The here described diamictite cannot be confidently correlated with a glaciomarine unit previously assigned to the Late Eocene-Lower Oligocene taken as proof that initial expansion of ice on Antarctica encompassed the entire continent synchronously in the earliest Oligocene. However, it is now evident that there are likely to be more, short but important, stratigraphic sequences of key regional and Antarctic wide interest preserved on the plateau of Isla Marambio. [ABSTRACT FROM AUTHOR]

The community of encrusting and boring organisms developed on shells of the gastropod Antarctodarwinella ellioti from the lower section of the La Meseta Formation (Eocene) exposed on Seymour (Marambio) Island, Antarctic Peninsula, allows inference that the shells were inhabited by hermit crabs. A Chi-square Independence Test revealed that the community - dominated by polychaetes and bryozoans - shows preference for the aperture interior area of the shell. A subsequent Cochran Q Test indicated that the differences in frequency of encrusting and boring organisms as counted on the different interior sectors of the aperture were statistically significant. Thus, polychaetes, boring bryozoans, and encrosting bryozoans, do not show the same frequency in each interior sector of the aperture; they are more frequent on the columella (P < 0.0001, P < 0.01 and P < 0.001 respectively). Encrusting bryozoans also appear to show a preference - albeit not as high as on the columella - for the outer lip. This community of boring and encrusting organisms and their distribution on the shell confirms that the shells were inhabited by hermit crabs. The community is similar to that described in Recent hermitted shells from mid-latitude temperate water environments, suggesting that such communities were already established in the Eocene. [ABSTRACT FROM AUTHOR]

Worm tubes, which exhibit the replaced tube-lining membrane, have been collected from the lowermost Lower Eocene Acantilados Allomember of the La Meseta Formation, Seymour Island, Antarctica. The discovery represents the oldest examples of preservation of the tube-lining membrane of tube-dwelling Polychaeta in the fossil record. A new genus and species,Caprascolex antarcticus, are described. The specimens are preserved as thin coatings of amorphous iron oxide on the inner surface of the moulds interpreted to be the replaced tube-lining membrane. Examination of the rarely described tube-lining mucosoid membrane in extant polychaetes shows that the fossils are nearly identical in morphology and scale to extant forms. These fossils record in remarkable detail the morphology of the tube-lining membrane, which appears to be composed of growth bands formed as the worm constructed the tube. The tube-lining is believed to have been originally preserved as pyrite, with subsequent oxidation to iron oxide. The tube-lining membrane of worm tubes possibly is known from only one other fossil occurrence. [ABSTRACT FROM AUTHOR]

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 Rı´o 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. [Copyright &y& Elsevier]

The biogeographic hypothesis more accepted today is that Antarctica (West Antarctica) and southern South America (Magellan region, Patagonia) were connected by a long and narrow causeway (Weddellian Isthmus) between the Antarctic Peninsula and South America since the Late Cretaceous (Campanian) until the Early Paleogene allowing terrestrial vertebrates to colonize new frontiers using this land bridge. Stratigraphically calibrated phylogenies including large, terrestrial native ungulates Litopterna and Astrapotheria taxa reveal long ghost lineages that extended into the Late Paleocene and provide evidence for the minimum times at which these “native ungulates” were present both on Antarctica and South America. Based on these results we estimate that the Weddellian Isthmus was functional as a land bridge until the Late Paleocene. Our data place the disconnection between Antarctica and South America in the Late Paleocene, indicating that the terrestrial faunistic isolation (Simpson's “splendid isolation”) in South America begun at the end of the Paleocene (~ 56 to 57 m.y.). This faunistic isolation is documented to have occurred at least 25 Ma before the existence of deep-water circulation conditions in Drake Passage (~ 30 m.y.) based on the onset of seafloor spreading in the west Scotia Sea region. We hypothesize that in the early stages of extension (Late Paleocene, ~ 55 m.y.) a wide and relatively shallow epicontinental sea developed between the Antarctic Peninsula and South America drowning the Weddellian Isthmus and preventing the faunal interchange for obligate cursorial terrestrial forms. [ABSTRACT FROM AUTHOR]