Life just got complicated

The fossil record of ancient life is, in general, poor. Certainly, fossils are abundant in many rock successions and may reveal remarkable details about evolution and environmental change, but they typically consist of disarticulated or broken skeletal material, such as shells, bones and teeth. Even worse, the record of entirely (or largely) soft-bodied organisms, such as jellyfish and worms, is extremely scant, despite the fact that such animals dominate modern marine environments and presumably did so in the past. The reason is obvious — such organisms are highly susceptible to post-mortem decay and typically decompose more rapidly than the ‘normal’ processes of fossilisation operate. This significantly blurs our view of ancient life, with obvious consequences for those interested in understanding evolution and past ecosystems

The mechanisms and timing of mineralization of fossil phosphatized soft tissues

Fossil phosphatized soft tissues offer palaeontologists a unique opportunity to examine the biology and physiology of extinct organisms at the cellular and even macromolecular level. All phosphatized soft tissues are preserved by one or more of three preservational styles. These are: 1) phosphatized microbial infestations, 2) non-microbial (i. e. inorganic) phosphatic coatings, and 3) inorganic replacements. This suggests that three different (but related) processes are involved in the phosphatization of soft tissues. Each of these processes preserves the tissues at a predictable resolution; the most detailed preservation being afforded by inorganic replacements. In general, the soft tissues of closely related organisms have similar preservational styles. This reflects similarities in the biochemistry and taphonomy of closely related taxa. In the majority of cases of soft tissue phosphatization, the most important source of phosphorus appears to have been external to the organism undergoing mineralization. An accessible source of phosphorus is, however, not the only variable dictating mineralization; phosphatization is extremely taxon-, tissue-, and biomolecule-specific. Of particular importance is: a) the concentration of phosphorus in the organism's soft tissues; b) the tissue's proximity to the source of phosphorus; c) the rate of tissue decay relative to the onset of mineralization; and, d) the pH and chemical composition of the decay-induced microenvironment surrounding the carcass. Certain groups of organisms (e. g. crustaceans, squid, and fish) appear to be somewhat 'preconditioned' for phosphatization. All fossil phosphatized soft tissues exhibit evidence of decay. Taphonomic experiments suggest the period between death and phosphatization to have been as little as 55 hours. In the case of microbial infestation, decay would have permitted the microbes to gain access to the carcass, and to release organically-bound phosphorus from its tissues. In inorganic phosphatization, decay stimulates mineralization by: a) degrading membranes and thus accelerating the rate at which dissolved phosphorus and calcium may invade the tissues; b) creating new "reactive" organic substrates on which apatite may precipitate; c) destroying intracellular nucleation inhibitors; and, d) creating a favourable chemical microenvironment for the precipitation of apatite. Inorganic postmortem phosphatization may therefore be considered to be an "end-member" of pathological biomineralization

Role of low intensity environmental disturbance in structuring the earliest (Ediacaran) macrobenthic tiered communities

Rangeomorphs were important components of Ediacaran macrobenthic ecosystems, yet their biology and ecology remain poorly constrained. They formed high-density, tiered communities that were subjected to intermittent burial events, the largest of which killed entire communities. Abundant thin event beds in the Ediacaran succession of Charnwood Forest indicate the additional, frequent impact of minor obrution events. The type surface of Charnia masoni is immediately underlain by one such lamina (a tuff) and preserves a distinctly bimodal population. It is dominated by Charnia fronds that are of smaller or comparable length to the holotype (19.4. cm), but also includes notably larger specimens (>. 45. cm) that would traditionally have been assigned to Charnia grandis. Multiple morphological- and morphometric parameters (length, width, spacing of primary branches) demonstrate that these are indistinguishable from the holotype of C. masoni, affirming the synonymy of the two taxa. Nevertheless, these outsized individuals are distinguished by their proportionally fewer primary branches per unit length. Taphonomic evidence indicates that they were survivors of an incumbent population, the rest of which was culled by a minor ashfall. We suggest that this temporary reduction in competition from neighbours allowed the survivors to grow larger and thereby gain access to a greater proportion of the water column. As the community recovered, their large size would have continued to provide them with an advantage, divorcing them from the density-dependent competition seen in the new understory. The interlude between cohorts implies that new recruits were substrate-sensitive, presumably awaiting re-establishment of the biomat. Sub-lethal disturbance events thus played a significant role in structuring Ediacaran communities, and help explain the observed bed-by-bed variability. Taken as a whole, the growth trajectory of C. masoni resembles that of extant organisms with indeterminate growth programmes and no genetically-controlled upper size limit

Of time and taphonomy: preservation in the Ediacaran

The late Neoproterozoic witnessed a revolution in the history of life: the transition from a microbial world to the one we know today. The enigmatic organisms of the Ediacaran hold the key to understanding the early evolution of metazoans and their ecology, and thus the basis of Phanerozoic life. Crucial to interpreting the information they divulge is a thorough understanding of their taphonomy: of what is preserved andhow it is preserved, and also of what is not preserved. Fortunately, this Period is also recognized for its abundance of soft-tissue preservation, which is viewed through a wide variety of taphonomic windows. Some of these, such as pyritization and carbonaceous compression, are also present throughout the Phanerozoic, but the abundance and variety of moldic preservation of body fossils in siliclastic settings is unique to the Ediacaran. In rare cases, one organism is preserved in several preservational styles which, in conjunction with our increased understanding of the taphonomic processes involved in each style, allow us to more confidently interpret aspects of the biology and ecology of the organisms preserved. Several groundbreaking advances in this field have been made since the 1990s, and have paved the way for increasingly thorough analyses and elegant interpretations

Wettest December in the Lake District for over 200 years

Wettest December in the Lake District for over 200 year

Revealing rangeomorph species characters using spatial analyses

Rangeomorphs dominate the Ediacaran Avalonian macrofossil assemblages of Charnwood Forest, UK (~562Ma). However, their unfamiliar fractal architecture makes distinguishing phylogenetically reliable characters from intraspecific features difficult. Fortunately, spatial analysis of large in-situ populations offers an independent means of assessing their taxonomy. Populations of a single biological species are likely to exhibit similar spatial distributions due to their shared responses to the biological and ecological processes acting upon them. As such, spatial analyses can be used to interrogate which are the most taxonomically deductive characters in similar species. We used Random Labelling Analyses to investigate the presence/absence of characters of Primocandelabrum boyntoni, P. aethelfalaedia and P. aelfwynnia on the North Quarry ’B’ surface. The resultant spatial distributions were compared to observed characters using goodness-of-fit tests to determine which characters were associated with unique populations, and which were found across multiple populations. We found that P. boyntoni and P. aelfwynnia had statistically indistinguishable character distributions, suggesting that they represent a single biological species, and that they exhibited significantly different distributions to P. aethelfalaedia, suggesting that there are two (rather than three) Primocandelabrum species present on the B surface. Furthermore, we found that the distribution of Concealed versus Unconcealed 1st order branches across all specimens exhibited significantly different, density-dependant behaviour, with Unconcealed branching occurring in areas of higher density populations, and Concealed branching occurring in the lower Primocandelabrum density areas. We speculate that unconcealed branches may have been a response to the reduced availability of resources in higher density areas, implying rangeomorphs were capable of ecophenotypic responses.EGM has been supported by the Natural Environment Research Council [grant number NE/P002412/1], Gibbs Travelling Fellowship from Newnham College, Cambridge and a Henslow Research Fellowship from Cambridge Philosophical Society. Phil Vixseboxse is thanked for his help in producing the RTIs. CGK and PRW were funded by National Environment Research Council grant NE/1005927/1. CGK also acknowledges a Research Studentship funded by the Cambridge Philosophical Society

Anatomy of the Ediacaran rangeomorph Charnia masoni.

The Ediacaran macrofossil Charnia masoni Ford is perhaps the most iconic member of the Rangeomorpha: a group of seemingly sessile, frondose organisms that dominates late Ediacaran benthic, deep-marine fossil assemblages. Despite C. masoni exhibiting broad palaeogeographical and stratigraphical ranges, there have been few morphological studies that consider the variation observed among populations of specimens derived from multiple global localities. We present an analysis of C. masoni that evaluates specimens from the UK, Canada and Russia, representing the largest morphological study of this taxon to date. We describe substantial morphological variation within C. masoni and present a new morphological model for this species that has significant implications both for interpretation of rangeomorph architecture, and potentially for existing taxonomic schemes. Previous reconstructions of Charnia include assumptions regarding the presence of structures seen in other rangeomorphs (e.g. an internal stalk) and of homogeneity in higher order branch morphology; observations that are not borne out by our investigations. We describe variation in the morphology of third and fourth order branches, as well as variation in gross structure near the base of the frond. The diagnosis of Charnia masoni is emended to take account of these new features. These findings highlight the need for large-scale analyses of rangeomorph morphology in order to better understand the biology of this long-enigmatic group.NER

The developmental biology of <i>Charnia</i> and the eumetazoan affinity of the Ediacaran rangeomorphs.

Molecular timescales estimate that early animal lineages diverged tens of millions of years before their earliest unequivocal fossil evidence. The Ediacaran macrobiota (~574 to 538 million years ago) are largely eschewed from this debate, primarily due to their extreme phylogenetic uncertainty, but remain germane. We characterize the development of Charnia masoni and establish the affinity of rangeomorphs, among the oldest and most enigmatic components of the Ediacaran macrobiota. We provide the first direct evidence for the internal interconnected nature of rangeomorphs and show that Charnia was constructed of repeated branches that derived successively from pre-existing branches. We find homology and rationalize morphogenesis between disparate rangeomorph taxa, before producing a phylogenetic analysis, resolving Charnia as a stem-eumetazoan and expanding the anatomical disparity of that group to include a long-extinct bodyplan. These data bring competing records of early animal evolution into closer agreement, reformulating our understanding of the evolutionary emergence of animal bodyplans

Anatomy of the Ediacaran rangeomorph Charnia masoni

The Ediacaran macrofossil Charnia masoni Ford is perhaps the most iconic member of the Rangeomorpha: a group of seemingly sessile, frondose organisms that dominates late Ediacaran benthic, deep‐marine fossil assemblages. Despite C. masoni exhibiting broad palaeogeographical and stratigraphical ranges, there have been few morphological studies that consider the variation observed among populations of specimens derived from multiple global localities. We present an analysis of C. masoni that evaluates specimens from the UK, Canada and Russia, representing the largest morphological study of this taxon to date. We describe substantial morphological variation within C. masoni and present a new morphological model for this species that has significant implications both for interpretation of rangeomorph architecture, and potentially for existing taxonomic schemes. Previous reconstructions of Charnia include assumptions regarding the presence of structures seen in other rangeomorphs (e.g. an internal stalk) and of homogeneity in higher order branch morphology; observations that are not borne out by our investigations. We describe variation in the morphology of third and fourth order branches, as well as variation in gross structure near the base of the frond. The diagnosis of Charnia masoni is emended to take account of these new features. These findings highlight the need for large‐scale analyses of rangeomorph morphology in order to better understand the biology of this long‐enigmatic group

U-Pb geochronology and global context of the Charnian Supergroup, UK: constraints on the age of key Ediacaran fossil assemblages

U-Pb (zircon) ages for key stratigraphic volcanic horizons within the ∼3200-m-thick Ediacaran-age Charnian Supergroup provide an improved age model for the included Avalonian assemblage macrofossils and, hence, temporal constraints essential for intercomparisons of the Charnian fossils with other Ediacaran fossil assemblages globally. The Ives Head Formation (Blackbrook Group), the oldest exposed part of the volcaniclastic Charnian Supergroup of the late Neoproterozoic Avalonian volcanic arc system of southern Britain, contains a bedding plane with an impoverished assemblage of ivesheadiomorphs that is constrained to between ca. 611 Ma and 569.1 ± 0.9 Ma (total uncertainty). Higher-diversity biotas, including the holotypes of Charnia, Charniodiscus, and Bradgatia, occupy the upper part of the volcaniclastic succession (Maplewell Group) and are dated at 561.9 ± 0.9 Ma (total uncertainty) and younger by zircons interpreted as coeval with eruption and deposition of the Park Breccia, Bradgate Formation. An ashy volcanic-pebble conglomerate in the Hanging Rocks Formation at the very top of the supergroup yielded two U-Pb zircon populations: an older detrital one at ca. 604 Ma, and a younger population at ca. 557 Ma, which is interpreted as the approximate depositional age. The temporal association of the fossiliferous Charnian Supergroup with comparable fossiliferous deep-water successions in Newfoundland, and the probable temporal overlap of the youngest Charnwood macrofossils with those from different paleoenvironmental settings, such as the Ediacaran White Sea macrofossils, indicate a primary role for ecological sensitivity in determining the composition of these late Neoproterozoic communities