Evolutionary Trends in Remarkable Fossil Preservation Across the Ediacaran–Cambrian Transition and the Impact of Metazoan Mixing

A solution to Darwin's dilemma of 1859: exceptional preservation in Salter's material from the late Ediacaran Longmyndian Supergroup, England

“…We find that Longmyndian microbes are preserved as carbonaceous films, as aluminosilicate permineralized filaments, and as moulds and impressions on bedding planes. These observations reinforce the hypothesis (Brasier & Callow 2007;Brasier et al 2009) that the Ediacaran fossil record appears to be biased towards the high-quality preservation of soft tissues. The relative scarcity of such exceptional preservation at later times, in a variety of taphonomic modes, suggests that these unusual taphonomic windows significantly narrowed following the Ediacaran-Cambrian transition.…”

“…In the Ediacaran Period, this type of preservation is more commonly known from large macrofossils such as Charnia (Narbonne 2005). In comparison with the Precambrian, the preservation of soft tissues within siliciclastic sediments is also notably rare from the Cambrian onwards (see Brasier et al 2009). Our investigations from the Longmyndian and other Ediacaran lagerstätten suggest that this style of preservation is reliant upon the rapid lithification of bedding plane interfaces.…”

“…The fine grain size means that is not possible to observe the structure of this microcrystalline mineral and the exact mineralogy remains speculative. Precambrian permineralized microbes are well known to occur in lagerstätten where silica, phosphate and even pyrite replace soft tissues (Grazhdankin & Gerdes 2007;Brasier et al 2009), but not hitherto preserved in aluminosilicates. Preservation of soft tissues in aluminosilicate clay minerals has been described from Phanerozoic lagerstätten including the Burgess Shale (Orr et al 1998;Butterfield et al 2007) and the Ordovician Soom Shale (Gabbott et al 2001), although the exact mechanisms of aluminosilicification are not yet fully resolved.…”

Microbial communities and their primary to early diagenetic mineral phases; the record from Neoproterozoic microbialites of Qarn Alam, Oman

“…In the Qarn Alam case, crinkly laminites exhibit both euhedral hexagonal crystals of phosphate and less well-formed stick-shaped crystals of phosphate (apatite) and trigonal crystals of calcite. In the rocks at Qarn Alam this is not an artefact, but it does suggest unusual geochemical conditions in these Neoproterozoic interstitial fluids, as suggested by Brasier et al (2010). However, the phosphorous may simply derive from degradation of organic matter in the sediment.…”

Is the fossil record of complex animal behaviour a stratigraphical analogue for the Anthropocene?

“…The global changes in marine burrowing organism communities record the diversification, and perhaps origination, of many modern coelomate metazoans early in the Cambrian Evolutionary Radiation, as well as a major change in the world ocean, which included the recycling of nutrients back into the water column by burrowing animals (Landing & Westrop 2004;Brasier et al 2011) It is important to remember that firstly, by recognising the base of a system through the first appearance of an ichnofauna at a specific locality, there is the possibility that globally, the onset of the T. pedum assemblage is diachronous. In some sections it may be that the first development of this trace fossil assemblage occurs later than at the GSSP.…”