Palaeontology, the biogeohistory of Victoria

The broad-scale distribution of fossils within Victoria is controlled by general global patterns in the biological evolution of life on Earth, the local development and environmental evolution of habitats, and the occurrence of geological processes conducive to the preservation of fossil floras and faunas. Early Palaeozoic fossils are mostly marine in origin because of the predominance of marine sedimentary rocks in Victoria and because life on land was not significant during most of this time interval. Middle Palaeozoic sequences have both terrestrial and marine fossil records. Within Victoria, marine rocks are only very minor components of strata deposited during the late Palaeozoic, so that few marine fossils are known from this time period. A similar situation existed during most of the Mesozoic except towards the end of this era when marine conditions began to prevail in the Bass Strait region. During long intervals in the Cainozoic, large areas of Victoria were flooded by shallow-marine seas, particularly in the southern basins of Bass Strait, as well as in the northwest of the State (Murray Basin). Cainozoic sediments contain an extraordinary range of animal and plant fossils. During the Quaternary, the landscape of Victoria became, and continues to be, dominated by continental environments including, at times, extensive freshwater lake systems. Fossil floras and faunas from sediments deposited in these lake systems and from other continental sediments, as well as from Quaternary sediments deposited in marginal marine environments, collectively record a history of rapid fluctuations in climate and sea level.<br /

Amplification of hypercharge electromagnetic fields by a cosmological pseudoscalar

If, in addition to the standard model fields, a new pseudoscalar field exists and couples to hypercharge topological number density, it can exponentially amplify hyperelectric and hypermagnetic fields in the symmetric phase of the electroweak plasma, while coherently rolling or oscillating. We present the equations describing the coupled system of a pseudoscalar field and hypercharge electromagnetic fields in the electroweak plasma at temperatures above the electroweak phase transition, discuss approximations to the equations, and their validity. We then solve the approximate equations using assorted analytical and numerical methods, and determine the parameters for which hypercharge electromagnetic fields can be exponentially amplified.Comment: 14 pages, 6 figure

Antarctica: Cretaceous cradle of austral temperate rainforests?

Although it is well known that certain Gondwanic elements of present-day austral temperate rainforests occurred on Antarctica during latest Cretaceous to early Tertiary times, there has been insufficient factual evidence for pinpointing the cradle of these forests. Fossil evidence from Antarctica and closely associated regions in the Creataceous southern Gondwanan assembly confirms that Antarctica was a Cretaceous origination and dispersal region of certain elements of today's southern hemispheric humid and perhumid forests. Antarctic origins are indicated for the fern Lophosoria, the podocarp gymnosperms Lagarostrobus and Dacrydium, Nothofagus, Ilex, and several lineages of the Proteaceae; migration to their present regions of distribution was probably step-wise. Antarctica also served as a Cretaceous dispersal corridor for other angiosperms represented today in mid to low latitude austral regions. These include Ascarina (or its stock), Myrtaceae, Gunneraceae, and Winteraceae, all of which had earlier histories in northern Gondwana or southern Laurasia. Origination and dispersal appears to be related to changing environmental circumstances associated with fragmentation of Gondwana and opening and enlargement of the southern oceans

Ultrastructure and biogeography of Balmeisporites Cookson and Dettmann, 1958

Ultrastructural and morphological analyses of Balmeisporites holodictyus reveal a two-layered wall conformable with that of spores of aquatic ferns. The spheroidal, trilete exospore comprises two zones with columnar structure sandwiched between homogeneous innermost and outermost zones. The outer wall layer, the epispore, has an inner reticulate-fibrillate zone and a homogeneous outer zone: the epispore forms the proximal tripartite acrolamella, prominent reticula in each equatorial radial region and surface sculpture. Ghoshispora shares with Balmeisporites wall ultrastructural and acrolamellate characters, but lacks protruding reticula in each equatorial radial region and possesses second order sculpturing of muri, striae or rugulae. The fossil record indicates that Balmeisporites originated in the Tethyan region during the Barremian-Aptian and for the remainder of the Cretaceous was concentrated in mid-high latitudes of both hemispheres. Ghoshispora had a shorter history with appearances in the Albian of Peru; during the Late Cretaceous its distribution range was centred in northern Laurasia, and, as reported herein, rare occurrences are in the Maastrichtian of Australia. Both genera are unknown in sediments younger than the Danian

Cretaceous palynomorphs from the James Ross Island area, Antarctica - a pilot study

Faunas of ammonites and bivalves, aquatic floras of dinocysts and prasinophycean/chlorophycean algae, and land-plant florules of spores, pollen, and fungal palynomorphs are reported from Cretaceous sedimentary rocks of James Ross Island, Dundee Island, and Cape Longing, Antarctic Peninsula. Ages adduced from the megafaunas are mostly verified by the dinocyst floras. Mid- to Late Cretaceous dinocyst assemblages of the Antarctic Peninsula confirm wide distribution, in southern high latitude oceanic regions, of the successive Muderongia, Heterosphaeridium, and Isabelidinium floras. Contemporaneous land-plant floras comprised a succession of rainforest communities having affiliations with vegetation fringing the southern Atlantic Ocean and in Australasia. Mid-Cretaceous-araucarean/podocarp rainforests were modified during the Campanian by the introduction of Nothofagus. Evidence is advanced for step-wise migration of certain cryptogam and angiosperm elements within southern Gondwana. The palynofloras comprise 62 cryptogam-spore, 54 pollen, 80 dinocyst, and nine prasinophycean/chlorophycean taxa. A trilete spore species, Kraeuselisporites laceratus Norris 1968 (senior synonym of K. jubatus Dettmann and Playford 1968) is newly combined with the genus Perotrilites Erdtmann ex Couper 1953. - from Author

Pollen of proteaceous-type from latest Cretaceous sediments, southeastern Australia

Abundant and diverse proteaceous-like triaperturate pollen from Campanian-Maastrichtian sediments in the Otway Basin, southeastern Australia are systematically documented and compared with pollen of extant Proteaceae. Segregation of fossil and extant pollen types has been effected on apertural characters of which six states have been identified. Apertures are colpoid, poroid or porate. Pores of Propylipollis Martin & Harris, 1974 conform with those of subfamilies Grevillioideae and Carnarvonioideae. Colpoids of Beaupreaidites Cookson emend. Martin, 1973, poroids of Lewalanipollis gen. nov., and pores of Cranwellipollis Martin & Harris, 1974 are represented in subfamilies Proteoideae and Persoonioideae. Pores of Proteacidites Cookson ex Couper, 1953 occur in subfamilies Proteoideae and Sphalmioideae. In the Otway Basin fossil record, triporate apertures appear earlier than tricolpoids, triporoids and biporates; and diversity levels of proteaceous pollen are higher than reported from elsewhere implying the region may have been a diversification centre during Campanian and Maastrichtian times. Represented among the fossil pollen are types that conform with pollen of extant Proteaceae: Adenanthos, Beauprea, Beaupreopsis, and Stirlingia (subfamily Proteoideae); Persoonia (subfamily Persoonioideae); Carnarvonia (subfamily Carnarvonioideae); and Bleasdalia, Grevillea, Knightia, Macadamia and Telopea (subfamily Grevillioideae). The Late Cretaceous pollen record thereby implies the presence of sclerophyll and rainforest taxa in a vegetation which was composed of diverse podocarps (Dacrydium, Dacrycarpus, Lagarostrobos, Podocarpus, Microcachrys), araucarians, and a range of angiosperms (Nothofagus, Gunnera, Ilex, Ascarina, Callitriche, Trimeniaceae, Winteraceae, Ranunculaceae and possibly Epacridaceae). Thirty-one pollen species are described and referred to five genera, of which Lewalanipollis is new. New species include Lewalanipollis senectus, L. trycheros, Propylipollis areolatus, P. crotonoides, Proteacidites cooksoniae and Proteacidites variverrucatus

Where now for taxonomy?

With the increasing financial squeeze faced by taxonomists, the time may now have come to dispense with massive herbarium collections. Indeed, the clear-out might lead to a better quality of taxonomic research

Community associations and structure in the Late Cretaceous vegetation of southeast Australasia and Antarctica

The structure and species richness of the Late Cretaceous (Santonian-Maastrichtian) vegetation in the Otway Basin, southeast Australia is reconstructed based on knowledge of palaeolatitudes, palaeotemperatures, plant taxa identified from fossil spores and pollen, and ecophysiological relationships established for present-day ecosystems. The vegetation, which grew at palaeolatitudes of 60-65°S and at mean annual palaeotemperatures of 16.5-19°C, comprised tall open-forests (Foliage Projective Cover 60-70%, height about 30 m) containing austral conifer and proteaceous taxa having coriaceous, notophyll-sized leaves. Today the taxa (Podocarpus, Dacrydium, Dacrycarpus, Knightia, Gevuina, Macadamia) from a minor component of upland closed-forests (usually termed rainforests) of tropical northeast Australia and New Caledonia. A conical-shaped crown to the trees of the tall open-forests situated in high latitudes during the Cretaceous would enable some light to penetrate the canopy to a shrubby understorey (of Proteaceae, Winteraceae, Trimeniaceae, Nothofagus, and Ilex) and a ground stratum of diverse cryptogams. On nutrient-poor, waterlogged sites fringing the forest, sclerophyllous leaved taxa (Adenanthos, Stirlingia, Epacridaceae, and possibly Beauprea) developed, with wetland swamps of Callitriche, ferns and some epacrids. In cooler localities in New Zealand and Antarctica, the productivity of the forests would have been greater, and the canopy taxa mainly with coriaceous, microphyll-sized leaves. Austral podocarps and Proteaceae occurred in the canopy of New Zealand forests, whereas the canopy of Antarctic forests contained podocarps and Nothofagus

The age of the base of the Gustav Group in the James Ross Basin, Antarctica

The Lagrelius Point Formation from its type area in north-west James Ross Island, Antarctica has yielded dinoflagellate cysts indicative of an earliest Aptian age. Reworked palynomorphs presumed to be from the Nordenskjöld Formation (Kimmeridgian-Berriasian) were also encountered. The Lagrelius Point Formation also contains Early Cretaceous spore-pollen floras of Austral aspect. The indigenous stratigraphically significant dinoflagellate cysts includeHerendeenia postprojecta,Muserongiaspp.,Odontochitinaspp. andOvoidinium cinctum. This assemblage indicates that the Lagrelius Point Formation, the oldest formation of the Gustav Group, is Aptian rather than Barremian in age. This in turn means that the base of the extensive Cretaceous marine succession in the James Ross Basin can be dated accurately for the first time. The Lagrelius Point Formation is correlated with the AustralianOdontochitina operculatadinoflagellate cyst Oppel Zone and theCyclosporites hughesiispore-pollen Interval Zone. The extensive record of Aptian marine sedimentation within the James Ross Basin can be correlated directly with that of other key localities in the Antarctic Peninsula and Scotia arc regions. There is still the possibility of a major stratigraphical hiatus in the preceding Hauterivian-Barremian stages

Not so ancient: the extant crown group of Nothofagus represents a post-Gondwanan radiation

This study uses a molecular-dating approach to test hypotheses about the biogeography of Nothofagus. The molecular modelling suggests that the present-day subgenera and species date from a radiation that most likely commenced between 55 and 40 Myr ago. This rules out the possibility of a reconciled all-vicariance hypothesis for the biogeography of extant Nothofagus. However, the molecular dates for divergences between Australasian and South American taxa are consistent with the rifting of Australia and South America from Antarctica. The molecular dates further suggest a dispersal of subgenera Lophozonia and Fuscospora between Australia and New Zealand after the onset of the Antarctic Circumpolar Current and west wind drift. It appears likely that the New Caledonian lineage of subgenus Brassospora diverged from the New Guinean lineage elsewhere, prior to colonizing New Caledonia. The molecular approach strongly supports fossil-based estimates that Nothofagus diverged from the rest of Fagales more than 84 Myr ago. However, the mid-Cenozoic estimate for the diversification of the four extant subgenera conflicts with the palynological interpretation because pollen fossils, attributed to all four extant subgenera, were widespread across the Weddellian province of Gondwana about 71 Myr ago. The discrepancy between the pollen and molecular dates exists even when confidence intervals from several sources of error are taken into account. In contrast, the molecular age estimates are consistent with macrofossil dates. The incongruence between pollen fossils and molecular dates could be resolved if the early pollen types represent extinct lineages, with similar types later evolving independently in the extant lineages