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The recognition of fossilized charcoal has revealed a long history of wildfire, although the earliest (pre-Late Devonian) records remain conjectural. A variety of approaches (experimental and natural charring, comparative anatomy of a range of plant tissues following combustion, and preliminary reflectance studies) demonstrates that smoldering surface fires already occurred ∼405 million years ago (Lochkovian; Early Devonian) in a vegetation of short stature composed mainly of small plants with smooth stems and terminal sporangia. In addition, the textures recorded in pyrite permineralizations are anomalous when compared with those of Lower Devonian and later examples, and indicative of the involvement of different taphonomic processes. From comparison with experimentally pyritized charcoal, they further suggest that the plants were burned before fossilization. The small millimeter-sized fossils (mesofossils) with remarkable, uncompressed cellular preservation indicate the importance of charcoalification in the determination of affinities and functioning of early land plants, and hence the reconstruction of ancient ecosystems.
Australia has numerous fossil floras suitable for paleoclimatic analysis, with potential to improve understanding of Southern Hemisphere climatic evolution. Leaf-margin analysis (LMA) is a widely used method that applies present-day correlations between the proportion of woody dicot species with untoothed leaves and mean annual temperature to estimate paleotemperatures from fossil megafloras. Australia's unique history and vegetation imply that its leaf-margin correlation might differ from other regions; these possible differences are investigated here to improve paleoclimatic interpretations.
Australian rainforest vegetation shows nearly the same regression slope as recorded in East Asia and the Americas, indicating a globally convergent evolutionary response of leaf form to temperature. However, Australian sites tend to have fewer toothed species at localities with the same temperature as Asian and American sites. The following factors, singly or in combination, may account for this difference: (1) Australia's Cenozoic movement into lower latitudes, insulation from global cooling, and isolation from high-latitude cold-tolerant vegetation sources; (2) lack of high mountains as sources and refuges for cold-adapted taxa; (3) Pleistocene extinctions of cold-adapted taxa; and (4) the near absence of a cold-climate forest ecospace in Australia today.
Application of Australian LMA to Australian Cenozoic floras resulted in cooler temperature estimates than other LMA regressions. However, Australian paleotemperature estimates should account for the relative importance of cold-deciduous taxa. The timing and magnitudes of the extinctions of cold-adapted lineages are not known, and the most conservative approach is to use Australian LMA as a minimum and non-Australian LMA as a maximum temperature estimate.
Many early Tertiary nummulitic limestones contain broken Nummulites tests (commonly referred to as nummulithoclastic debris) that display breakage ranging from damage to the terminal chamber, to disintegration into sand- and silt-sized (and probably finer) fragments. Little consideration previously has been given to the processes responsible for this damage, or whether test abrasion can be used as an indicator of the degree of transportation or wave reworking. Studies of modern larger benthic foraminifera suggest that transport-induced abrasion is a likely candidate for the test damage seen in many fossil Nummulites. However, experimental reconstruction of the transportation of Nummulites within a traction carpet of skeletal material, using the structurally similar and related extant form Palaeonummulites venosus, failed to reproduce the degree of test damage seen in fossil forms, despite simulating transport up to approximately 71 km. Evidence from experimental and field observations suggests that the additional damage noted in Eocene Nummulites possibly is the result of transportation within turbidity currents and/or predation by relatively large bioeroders, such as fish and echinoids. Processes such as dissolution and microboring are considered to have played only a minor, if any, role in the comminution of Nummulites.
These observations have been used to define a scale of taphonomic features observed in fossil Nummulites, to aid identification of autochthonous and allochthonous Nummulites populations in thin-section studies of nummulitic limestones, and to facilitate comparison between different facies and carbonate-platform environments.
The Toolebuc Formation (Late Albian) is a thin (<40m), very widely distributed unit marking the maximum deepening of the Cretaceous epicontinental sea recorded by the infill of the Great Artesian Basin, eastern Australia. It consists of organic-rich shale, with TOC ranging to 35%, and limestone as laminae and thin beds comprised of Inoceramus sutherlandi McCoy and, less commonly, Aucellina hughendenensis Etheridge. Finely interlayered organic-rich shale and coquina are typical of the formation, resulting in a distinctively black-and-white, thinly bedded to laminated rock. Inoceramus valves are commonly disturbed by breakage, reorientation, and imbrication, and, in many cases, have disintegrated into prism horizons. Sedimentary laminae show that the sea floor was subject to some current activity, but benthic scavengers are considered to have been active agents of shell disturbance. Although shelly substrate suitable for encrusting epibenthos or colonization by endoliths was available in abundance, other benthic elements, inclusive of trace fossils, are very poorly represented. The formation contains diverse planktonic, pelagic, and nektonic fossil remains attesting to deposition beneath a water column of normal salinity, supporting a complex food chain. It displays a negative δ13Corg excursion, considered to relate to sea floor bacterial reworking of detrital organic material derived from plankton. In the context of the Toolebuc Formation, Inoceramus sutherlandi and Aucellina hughendenensis represent ecological specialists, with shell-growth strategies designed to cope with soft substrates and physiologies that were tolerant of oxygen-poor bottom conditions. Their intimate association with organic-rich shale suggests a trophic link with sea-floor bacterial productivity, supported from the organic-rich substrate. The lateral extent of Toolebuc coquinas suggests that Inoceramus sutherlandi and Aucellina hughendenensis were filter feeders rather than dependent on chemotrophic symbionts. Fine-scale interlayering of coquina and organic-rich shale attests to frequent alternation of sea-floor conditions conducive to colonization by bivalve communities and those that were not. Alternation is attributed in part to an autocyclic mechanism, with sea-floor accumulation of shelly debris having progressively isolated bivalve communities from trophic support, causing their episodic demise.
Avian and non-avian dinosaur eggshell contains clues that are helpful in the reconstruction of ancient habitats and behaviors. Fossilized eggshell often shows signs of corrosion attributed to acid dissolution of the calcium carbonate, but this process has never been quantified in controlled experiments. In work reported here, extant avian dinosaur eggshell fragments were placed in buffered solutions of varying pH and temperature for varying periods of time. Changes in the appearance, mass, surface area, and thickness were described and compared with naturally weathered eggshell. Treatment resulted in corrosion and pitting of the outer surface and corrosion of the mammillary structure of the inner surface. Fragment mass, surface area, and thickness generally decreased in response to decreased pH and to increased temperature and exposure time. A classification scheme for eggshell corrosion is proposed.
Small shelly fossils (SSFs) are a group of mostly problematic, small skeletal elements preserved primarily through secondary phosphatization. They dominate lower Cambrian diversity, but appear to suffer a sharp decline in the Botomian Stage or equivalent levels outside Siberia. This observed decline coincides with a significant reduction in phosphogenesis, suggesting that it may be attributable to the closure of a phosphatization taphonomic window. The influence of taphonomic bias on observed patterns of SSF extinction at the end of the Botomian was tested using a dataset consisting of 558 Cambrian skeletal genus occurrences compiled from 109 references. Analyses indicate that SSF preservation is significantly enhanced by, and for most taxa, restricted to, a phosphatization window. Independent proxies indicate that prevalence of secondary phosphatization declined from 74% and 64% of all preservational modes during Nemakit-Dal'dynian Tommotian and Atdabanian Botomian times, respectively, to 40% of all modes during Toyonian middle Cambrian times, coincident with a severe reduction in observed SSF diversity. Subsampling methods that control for variations in the phosphatization window were used to test whether observed SSF diversity trajectories are biased. The corrected curve suggests that although the decline of SSFs was real, it may have been significantly exaggerated by the closure of a phosphatization window.