The phylum Ascomycota is by far the largest group in the fungal kingdom. Ecologically important mutualistic associations such as mycorrhizae and lichens have evolved in this group, which are regarded as key innovations that supported the evolution of land plants. Only a few attempts have been made to date the origin of Ascomycota lineages by using molecular clock methods, which is primarily due to the lack of satisfactory fossil calibration data. For this reason we have evaluated all of the oldest available ascomycete fossils from amber (Albian to Miocene) and chert (Devonian and Maastrichtian). The fossils represent five major ascomycete classes (Coniocybomycetes, Dothideomycetes, Eurotiomycetes, Laboulbeniomycetes, and Lecanoromycetes). We have assembled a multi-gene data set (18SrDNA, 28SrDNA, RPB1 and RPB2) from a total of 145 taxa representing most groups of the Ascomycota and utilized fossil calibration points solely from within the ascomycetes to estimate divergence times of Ascomycota lineages with a Bayesian approach. Our results suggest an initial diversification of the Pezizomycotina in the Ordovician, followed by repeated splits of lineages throughout the Phanerozoic, and indicate that this continuous diversification was unaffected by mass extinctions. We suggest that the ecological diversity within each lineage ensured that at least some taxa of each group were able to survive global crises and rapidly recovered.
The Carnian Pluvial Episode (Late Triassic) was a time of global environmental changes and possibly substantial coeval volcanism. The extent of the biological turnover in marine and terrestrial ecosystems is not well understood. Here, we present a meta-analysis of fossil data that suggests a substantial reduction in generic and species richness and the disappearance of 33% of marine genera. This crisis triggered major radiations. In the sea, the rise of the first scleractinian reefs and rock-forming calcareous nannofossils points to substantial changes in ocean chemistry. On land, there were major diversifications and originations of conifers, insects, dinosaurs, crocodiles, lizards, turtles, and mammals. Although there is uncertainty on the precise age of some of the recorded biological changes, these observations indicate that the Carnian Pluvial Episode was linked to a major extinction event and might have been the trigger of the spectacular radiation of many key groups that dominate modern ecosystems.
Amber is fossilised plant resin. It can be used to provide insights into the terrestrial conditions at the time the original resin was exuded. Amber research thus can inform many aspects of palaeontology, from the recovery and description of enclosed fossil organisms (biological inclusions) to attempts at reconstruction of past climates and environments. Here we focus on the resin itself, the conditions under which it may have been exuded, and its potential path to fossilisation, rather than on enclosed fossils. It is noteworthy that not all plants produce resin, and that not all resins can (nor do) become amber. Given the recent upsurge in the number of amber deposits described, it is time to re-examine ambers from a botanical perspective. Here we summarise the state of knowledge about resin production in modern ecosystems, and review the biological and ecological aspects of resin production in plants. We also present new observations on conifer-derived resin exudation, with a particular focus on araucarian conifer trees. We suggest that besides disease, insect attacks and traumatic wounding from fires and storms, other factors such as tree architecture and local soil conditions are significant in creating and preserving resin outpourings. We also examine the transformation of resin into amber (maturation), focusing on geological aspects of amber deposit formation and preservation. We present new evidence that expands previous understanding of amber deposit formation. Specific geological conditions such as anoxic burial are essential in the creation of amber from resin deposits. We show that in the past, the production of large amounts of resin could have been linked to global climate changes and environmental disruption. We then highlight where the gaps in our knowledge still remain and potential future research directions.
Terrestrial ecosystems of the long-isolated former Gondwanan landmass of NewZealand are hotspots of modern global biodiversity, based on the level of endemism and distinctiveness of the biota. However, little is known of the evolutionary history of the rarely-preserved but diverse, distinctive, fragile, mainly soft-bodied organisms such as arthropods and fungi that comprise 95% of biodiversity in forest ecosystems. Our discovery of fossils preserved in Oligocene/Miocene amber of araucarian origin reveals a diverse invertebrate and fungal biota and complex ecological networks. These fossils comprise 10 orders and approximately 20 families of terrestrial arthropods and include representatives of Pseudoscorpiones, Acari, Araneae, Collembola, Hemiptera, Psocoptera, Hymenoptera, Coleoptera, Lepidoptera and Diptera, together with nematodes, mold fungi and araucarian wood. Ecologically the fossils encompass predators such as spiders with web remains, soil and bark mites, detritivores, parasites, fungivores and decomposers, fungi that grew on solidified resin flows, as well as predatory fungi. This is the first major amber deposit with an abundance of biological inclusions from the Southern Hemisphere and the only Cenozoic one of verified araucarian origin. These fossils expand the global record and evolutionary history of many arthropod and fungal groups, providing insights into mid-Cenozoic araucarian forest ecosystems and resolving controversial issues around the antecedents of the modern New Zealand terrestrial biota.
Some higher plants, both angiosperms and gymnosperms, can produce resins and some of these resins can polymerize and fossilize to form ambers. Various physical and chemical techniques have been used to identify and profile different plant resins and have then been applied to fossilized resins (ambers), to try to detect their parent plant affinities and understand the process of polymerization, with varying levels of success. Here we focus on resins produced from today’s most resinous conifer family, the Araucariaceae, which are thought to be the parent plants of some of the Southern Hemisphere’s fossil resin deposits. Fourier transform infrared (FTIR) spectra of the resins of closely related Araucariaceae species were examined to test whether they could be distinguished at genus and species level and whether the results could then be used to infer the parent plant of a New Zealand amber. The resin FTIR spectra are distinguishable from each other, and the three Araucaria species sampled produced similar FTIR spectra, to which Wollemia resin is most similar. Interspecific variability of the FTIR spectra is greatest in the three Agathis species tested. The New Zealand amber sample is similar in key shared features with the resin samples, but it does differ from the extant resin samples in key distinguishing features, nonetheless it is most similar to the resin of Agathis australis in this dataset. However on comparison with previously published FTIR spectra of similar aged amber and older (Eocene) resinites both found in coals from New Zealand and fresh Agathis australis resin, our amber has some features that imply a relatively immature resin, which was not expected from an amber of the Miocene age.
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