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Annual Meeting 2015 - Cardiff - Abstracts & Programme
Rooted in Earth history: the Devonian transition to a forested planet
Christopher M. Berry1, William E. Stein2, Peter Giesen3, John E. A. Marshall4 and Honghe Xu5
1Cardiff University, UK
2Binghamton University, USA
3Wettinerstr. 55, Wuppertal, Germany
4University of Southampton, UK
5Nanjing Institute of Geology and Palaeontology, China
Modern forests lie at the centre of a web of interactions from which influence spreads far beyond the terrestrial realm into the wider Earth System, including atmospheric composition and marine geochemistry. The ‘transition to a forested planet’ during the Mid and early Late Devonian (393–372 Ma) must therefore have been a time of profound global change, the predicted effects of plant growth and plant-enhanced weathering being incorporated into, for example, models of atmospheric CO2 through time. Supporting knowledge of vegetation during this interval has, however, been very sketchy until recently. This talk will highlight the recent dramatic changes in concepts of the morphology, anatomy and growth of tree-sized plants which appeared and evolved during this time (aneurophytaleans, archaeopteridaleans, pseudosporochnaleans, lycopsids) with an emphasis on leaves, roots and wood. Definitive and spectacular evidence of plant community structure and ecology is available from the study of in situ tree bases, roots and rhizomes from New York and Svalbard, and allows interpretation of macrofossil assemblages further afield. Study of in situ and dispersed spore assemblages allows better sampling and stratigraphic resolution of the global migration of tree groups. Total evidence will allow better understanding and modelling of the environmental impact of early forests.
Something ate my fossil: from anecdote to testing hypotheses
Elizabeth M. Harper
University of Cambridge, UK
Predation, along with competition, is thought to play a major role in structuring modern marine communities. It has frequently been cited as a driving force in evolution, for example in explaining the rise of particular traits (e.g. life habits, morphologies or behaviours) perceived as defensive adaptations. But these familiar tales may be difficult to test in the fossil record. Palaeoecologists are familiar with recognizing particular trace fossils as evidence of predation in the fossil record. But how can we turn interesting fossils with an interesting story to tell into a source of plentiful robust data with which to test evolutionary hypotheses and to generate new ones? How can we dove-tail palaeontological data with those produced by neontological studies? How can we capture the wide variability in predation intensity seen in modern environments but routinely destroyed by taphonomy?
Fossil lichens
Rosmarie Honegger1, Dianne Edwards2 and Lindsey Axe2
1University of Zürich, Switzerland
2Cardiff University, UK
Before focusing on lichens and lichen-like organisms from Cenozoic amber to the Neoproterozoic Doushantuo fossils, a short overview on the phylogeny, morphology and anatomy, especially on mycobiont–photobiont interactions in extant lichens and on their fungal and bacterial cohabitants will be presented. Well-preserved Mesozoic lichens are rare. In the few Palaeozoic lichens known until now with well-preserved fungal partners, the cyanobacterial or green algal photobiont often did not fossilize. Dorsiventral thallus organization with internal stratification, i.e. optimal light exposure of the photobiont cell population, a characteristic of extant foliose and squamulose lichens, occurs in Cyanolichenomycites devonicus with cyanobacterial (Nostoc sp., mainly gelatinous sheaths being preserved) and Chlorolichenomycites salopensis with presumed green algal photobiont (preserved as pyrite framboids). These charcoalified fragments, resulting from wildfires, fossilized ex situ in marine sediments (siltstone) in the Lower Devonian (Lochkovian) of the Welsh Borderland. The microbiome of C. salopensis was ultrastructurally resolved: bacterial colonies on the cortical surface, endolichenic fungi between and actinobacterial filaments in close contact with medullary hyphae of the mycobiont, the same situation being found in extant lichens. Horizontal gene transfer (e.g. polyketide synthase genes) from bacteria to ancestors of extant lichens and non-lichenized ascomycetes with lichenized ancestors (Penicillium, etc.) occurred.
Animal–animal and animal–microbial ecological interactions in ancient methane seep communities
Crispin T. S. Little
University of Leeds, UK
Modern methane seeps were only discovered in 1984, but are now known to be a very common feature of continental margins, both in shallow and deep water settings. Seep communities are ecologically complex and mirror coral reefs in that the bulk of the biomass in the ecosystem is formed of animals that have symbiotic relationships with bacteria, although these are chemosymbionts in the case of methane seeps (utilizing geochemical energy sources), rather than photosymbionts in coral reefs (utilizing sunlight). Chemosymbiosis at seeps includes relationships between microbial organisms (methanotrophic archaea and sulfide oxidizing bacteria), and vestimentiferan tubeworms and bivalve molluscs. Diversity in seep communities is relatively low, and a few taxa (all chemosymbiotic) dominate each site, these being vestimentiferans, bathymodiolin mussels and vesicomyid clams. The tubes and shells of these animals form the structural ‘framework’ of seep communities, projecting above the sediment–water interface, and in turn act as hard substrates for secondary communities of boring, grazing and filter-feeding animals. In this talk I will explore the fossil record of seep communities to show how a variety of traditional and more modern analytical techniques have been used recently to elucidate many similar animal–animal and animal–microbial palaeoecological interactions at ancient methane seeps.
Competition and symbiosis on marine hard substrates in the fossil record
Paul D. Taylor
Natural History Museum, London, UK
Many animals and plants that colonize hard surfaces in the sea are sessile and either bore into or cement permanently to the substrate surface. Because they retain their life positions after fossilization, these sclerobionts offer scope for studying biotic interactions in the fossil record. Encrusting sclerobionts compete actively for living space, with dominant competitors overgrowing the edges of subordinates. An alternative mode of spatial competition is fouling, whereby larvae recruit directly onto the living surfaces of sclerobionts. Spatial competition has been studied extensively in modern marine communities but there has been little research on competition between encrusters in ancient communities. This reflects poor knowledge of the taxonomy of the sclerobionts involved, as well as perceived difficulties in distinguishing between overgrowth in vivo and post-mortem. Whereas sclerobionts enter into a wide range of diffuse symbioses with other organisms cohabiting the same substrate, more specific fossil symbioses occur between pairs of sclerobiont species that become intergrown, sometimes with one of the symbionts being soft-bodied and preserved through bioclaustration within a skeletonized host. Here the in vivo nature of the association is unequivocal. The fossil record of sclerobionts is a largely untapped resource for studying the long-term dynamics of competition and symbiosis.
Leaving no stone unturned: the feedback between biotic diversity and early diagenesis
1Paul Wright1 and Lesley Cherns2
1Amgueddfa Cymru – National Museum of Wales, UK
2Cardiff University, UK
The Early Palaeozoic diversification of infauna led to increases in the depth of burrowing that affected the depth at which secondary carbonates precipitated in the sediment column. This resulted in changes in the mechanical behaviour of the shallow buried sediments, that in lower-mid Ordovician, low energy, subtidal settings led to the most extensive phase of submarine hardground formation during the Palaeozoic. These hard seafloor substrates promoted the diversification of a rich and diverse encrusting and boring biota. Thus diversification of the infauna fed back to changes in early diagenesis that triggered changes in the epifaunal community. Prior to this interval the zone of carbonate precipitation lay at a shallower depth in the sediment, subject to frequent current reworking. The thin sheets of the cemented layers became reworked to produce the well-documented Upper Cambrian–Lower Ordovician “flat pebble breccias”. By late Ordovician times, burrowing depth had increased further so that the depth of secondary carbonate precipitation was sufficiently great (>300mm) that scouring of the seafloor rarely exhumed the secondary carbonate horizons; hardgrounds became less common, but thick successions of diagenetic limestone-marl alternations formed in subtidal settings.