Evolutionary history of Antarctica

One of the most important breakthroughs in Antarctic geological research over the last three decades has been the elucidation of the continent’s fossil record. Although fossils have been known since the very earliest days of scientific exploration in the south polar regions, it is only comparatively recently that their study has been placed within a firm scientific framework. Detailed taxonomic studies of many key groups have been completed and it is now possible, for the first time, to take a broad perspective of the history of life on our southernmost continent. A surprising diversity of fossil plants and animals has now been found in Antarctica; the story they tell is every bit as important to the development of our understanding of the broad patterns of the history of life on Earth as that from other continents

Lower Cretaceous inoceramid bivalves from the Antarctic Peninsula region

The occurrence of rich faunas of Lower Cretaceous inoceramid bivalves in the Antarctic Peninsula region further emphasizes their widespread distribution, and enhances their potential for regional biostrati-graphic correlations. The Antarctic material is contained in approximately seven of twelve species groups that are recognized on a worldwide scale. Six of these are assigned to the genus Inoceramus and one to Birostrina. The comparatively rare genus, Anopaea, is left undivided.In the Fossil Bluff Formation of Alexander Island, Berriasian representatives of the I. ovatus group (I. cf. ovatus Stanton and I. sp. aff. ellioti Gabb) are succeeded by A. trapezoidalis (Thomson and Willey) which has undifferentiated Berriasian-Aptian affinities. This is in turn followed by an Aptian member of the I. neocomiensis group (I. deltoides sp. nov.) and in the Albian there are occurrences of Anopaea sp. nov. aff. mandibula (Mordvilko), B.? cf. concentrica (Parkinson) (B. concentrica gp.), I. cf. anglicus elongatus Pergament, I. sp. aff. bellvuensis Reeside, I. sp. aff. comancheanus Cragin (all I. anglicus gp.), and I.flemingi sp. nov. (I. liwerowskyae gp.). Aptian-Albian strata on James Ross Island have yielded both I. stoneleyi sp. nov. (I. liwerowskyae gp.) and Anopaea sp. nov. beta. These are followed by the Albian species I. cf. sutherlandi M'Coy and I. carsoni M'Coy (both I. carsoni gp.) and the highest Lower Cretaceous specimens within this sequence have been referred to B. concentrica (Parkinson).Although specimens of I. cf. heteropterus Pokhialainen (I. heteropterus gp.) and I. annenhovensis sp. nov. (unclassified) from Annenkov Island are of probable Hauterivian-Barremian age, it is noticeable that there is a marked lack of Valanginian-Barremian inoceramids in the Antarctic Peninsula region. This gap probably reflects a period of regional uplift and non-deposition.Representatives of the I. ovatus and I. heteropterus groups provide a means of correlation between the Berriasian-Barremian of the Antarctic Peninsula and the North Pacific region. I. deltoides sp. nov. can be closely matched with Northern Hemisphere Aptian members of the I. neocomiensis group and I. stoneleyi sp. nov. and I.flemingi sp. nov. have possible counterparts within the Aptian-Albian of Spitzbergen, south-east USSR and far eastern USSR. Of the various Albian species groups, that based on I. carsoni provides a direct link between Antarctica and Australia and those based on I. anglicus and B. concentrica facilitate a range of long-distance correlations. The latter category, in particular, may be one of the first truly cosmopolitan inoceramid groups

Late Mesozoic bivalve biostratigraphy of the Antarctic Peninsula region

Two groups of bivalves, the inoceramids and buchiids, are particularly useful zone fossils in the Mesozoic sedimentary formations of the Antarctic Peninsula region. In the Upper Jurassic, species of the genera Retroceramus, Malayomaorica, Buchia and Anopaea can be traced considerable distances around the margins of Gondwana, and as such are especially valuable for regional correlations. Some of them, such as the R. haasti-subhaasti group, can also be employed in detailed local correlations. In the Lower Cretaceous, the presence of cosmopolitan Inoceramus species, such as members of the neocomiensis, concentricus and anglicus groups, permits correlation with Northern Hemisphere faunas for the first time. Other stratigraphically important inoceramids are the I. ovatus group in the Lower Neocomian, the I. heteropterus group and Anopaea trapezoidalis in the Upper Neocomian and An. cf. mandibula in the Albian. The only buchiids present in the Lower Cretaceous of Antarctica belong to the extensive Aucellina andina-radiatostriata group. Two types of Antarctic Upper Cretaceous inoceramids that are particularly important for regional correlations are the Upper Cenomanian I. pictus group and the Turonian-Coniacian I. madagascariensis-ernsti group. Senonian inoceramids are still poorly known but would seem to offer considerable scope for further studie