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Effaced preservation in the Ediacaran biota of Avalonia and its implications for the early macrofossil record
Abstract
Ediacaran structures known as ‘pizza discs’ or Ivesheadia have long been considered enigmatic. They are amongst the oldest known members of the Ediacara biota, apparently restricted to the Avalonian successions of Newfoundland and the UK, c. 579–560 Ma. Here, we suggest that these impressions are taphomorphs, resulting from the post-mortem decay of the frondose Ediacaran biota. Ediacaran fossils range from well-preserved, high-fidelity variants to almost completely effaced specimens. The effaced specimens are inferred to have undergone modification of their original morphology by post-mortem microbial decay on the sea floor, combined with sediment trapping and binding. In this style of preservation, morphological details within the organism became variously subdued as a function of the extent of organic decay prior to casting by overlying sediments. Decay and effacement were progressive in nature, producing a continuum of grades of preservation on Ediacaran bedding planes. Fossils preserved by such ‘effaced preservation’ are those that have suffered these processes to the extent that only their gross form can be determined. We suggest that the lack of detailed morphology in effaced specimens renders such fossils unsuitable for use as type material, as it is possible that several taxa may, upon degradation and burial, generate similar morphological taphomorphs. We here reinterpret the genus Ivesheadia as a taphomorph resulting from extensive post-mortem decay of frondose organisms. Blackbrookia, Pseudovendia and Shepshedia from beds of comparable age in England are likewise regarded as taphomorphs broadly related to Charnia or Charniodiscus spp. To reflect the suggestion that such impressions are likely to be taphomorphs, and not taxonomically discrete, we propose the term ivesheadiomorphs to incorporate all such effaced taphonomic expressions of Ediacaran macrofossil taxa in Avalonian assemblages. Our recognition of effaced preservation has significant implications for Ediacaran taxonomy, and consequently for measures of Ediacaran diversity and disparity. It is implied that Avalonian assemblages preserve both organisms that were alive and organisms that were already dead at the time of burial. As such, the fossil assemblages cannot be taken to represent census populations of living organisms, as in prior interpretations.
... Several Ediacaran fossiliferous localities have been discovered on the southeastern portion of the Avalon Peninsula in Newfoundland (see Liu et al. 2015). The oldest known fossils in the region occur close to Pigeon Cove in the MPER Liu et al. 2011Liu et al. , 2012 that have recently been re-dated at 576.17 ± 0.66 Ma, based on geochronological study of the tuffite immediately overlying the fossils updated from Pu et al. 2016). The best-known fossiliferous locality in the area is at Mistaken Point itself, where two of the most extensive bedding planes, the D and E surfaces, are exposed (Anderson & Misra, 1968;Misra, 1969). ...
... Fractofusus specimens range from high-fidelity preservationin which three orders of branches are typically preserved (Gehling & Narbonne, 2007;Brasier & Antcliffe, 2009)to effectively effaced smooth fusiform fossils that could be considered to be on the taphonomic pathway to becoming ivesheadiomorphs (Liu et al. 2011;Antcliffe et al. 2015). The importance of the inferred grades of preservation is that they show a continuum from well-preserved forms that represent the lower surface of Fractofusus smothered in life by the overlying tuffite to poorly preserved outlines that may represent ivesheadiomorphs constituting necromass on the pre-tuffite seafloor (Liu et al. 2011;Antcliffe et al. 2015). ...
... Fractofusus specimens range from high-fidelity preservationin which three orders of branches are typically preserved (Gehling & Narbonne, 2007;Brasier & Antcliffe, 2009)to effectively effaced smooth fusiform fossils that could be considered to be on the taphonomic pathway to becoming ivesheadiomorphs (Liu et al. 2011;Antcliffe et al. 2015). The importance of the inferred grades of preservation is that they show a continuum from well-preserved forms that represent the lower surface of Fractofusus smothered in life by the overlying tuffite to poorly preserved outlines that may represent ivesheadiomorphs constituting necromass on the pre-tuffite seafloor (Liu et al. 2011;Antcliffe et al. 2015). In most specimens, branching close to the longitudinal axis is well preserved and relatively high relief; however, at the distal tips of the frond and its lateral margins the first-order branches may show low-relief preservation (e.g. ...
The Ediacaran rangeomorph Fractofusus misrai is the most common and best-preserved of the E Surface fossil assemblage in the Mistaken Point Ecological Reserve of southeastern Newfoundland, Canada. Fractofusus has been interpreted as a fusiform epifaunal soft-sediment recliner, and like other rangeomorphs it has a self-similar, fractal-like branching morphology. The rangeomorph branching of Fractofusus has been considered to be identical on the upper and lower surfaces; however, study of specimens with complex biostratinomic histories suggests clear differences between the upper and lower surfaces. The first-order branches grew down�wards into the sediment from a high point near the midline but grew above the sediment–water interface at their lateral and distal margins. Our new three-dimensional appreciation of rangeo�morph branching in Fractofusus explains many of the taphomorphs of Fractofusus including straight, curved, kinked and tousled forms. The three-dimensional morphology, mode of life, taphonomy and palaeoenvironmental interactions of F. misrai are discussed along with a new three-dimensional reconstruction.
... The Ediacaran of Newfoundland has some of the most convincing candidates for early fossil poriferans, fossils with pyrite-replaced epidermis surrounding osculae of two sizes (Dufour & McIlroy 2017b;Fig. 5a) in a taxon previously assigned to the pseudofossil "Blackbrookia" (Hofmann et al., 2008;Liu et al., 2011), but which are closely comparable to the Cambrian genus Crumillospongia (cf. Walcott 1919; showing what the same rangeomorph unit would look like from above if incompletely furled; d) same frond as b, but completely furled creating a tubular rangemorph element (cf. ...
... The Ediacaran seafloors of Newfoundland preserve evidence for abundant surficial microbial mats and sulfidic porewaters without the ecosystem services provided by bioturbators and scavengers (McIlroy & Logan 1999;Herringshaw et al., 2017); indeed, persistent necromass is considered to have been a significant component of the seafloor in the form of the ivesheadiomorphs (Liu et al., 2011;Fig. 9). ...
... Sustaining a large-bodied (and gutless) organism through saprotrophy would likely require access to, and a regular supply of, large concentrations of organic matter, such as abundant phytodetritus or decaying carcasses. While there is currently no evidence for mycelium-like threads accessing the presumed OM-rich patches associated with dead Ediacaran macrobionts, the superposition of some fossilized recliners atop the decayed remnants of others (i.e. the ivesheadiomorphs (Fig. 9)) could provide evidence that they could absorb organic matter from necromass (Liu et al., 2011;Antcliffe et al., 2015) as well as the buried remains of the associated microbial matgrounds ( Fig. 8a and b). Nutrient uptake in such cases might occur without exoenzyme production and could therefore represent osmotrophy, but not saprotrophy. ...
The earliest record of animal life come s from the Ediacaran of Newfoundland , including dm scale fossil organisms , most of which are inferred to have be en epibenthic immotile eumetazoans. This work introduces the palaeobiology of the major fossil groups in the Newfoundland assemblages including strange fractal-like taxa and addresses some of biogeochemical challenges such as sulfide buildup that could most easily have been overcome by symbiogenesis. Specifically, the epibenthic reclining nature of some of the Ediacaran biota with their fractal-like high surface area lower surfaces-are considered to have been well designed for gaining nutriment from chemosynthetic, sulfur-oxidizing bacteria. This view constitutes a shift away from the view that most of the biota were anomalously large osmotrophs.
... Laflamme et al. 2004;Gehling and Narbonne 2007;Bamforth and Narbonne 2009). However, since the compression is anisotropic and there is no evidence that all 'holdfast' discs were originally circular (Liu et al. 2011), the degree of deformation is unlikely to be constant. In this manuscript, we present all fossils as they appear in the field to avoid introducing bias (following Liu et al. 2011). ...
... However, since the compression is anisotropic and there is no evidence that all 'holdfast' discs were originally circular (Liu et al. 2011), the degree of deformation is unlikely to be constant. In this manuscript, we present all fossils as they appear in the field to avoid introducing bias (following Liu et al. 2011). ...
... 5c). To have uniform upwards displacement of silt/clay grade material, the matground must first be degraded by smothering (McIlroy et al. 2009;Liu et al. 2011). It has also been suggested that microbial mats may have overgrown the upper surfaces of these seafloor organisms post-smothering (Gehling 1999), which in the case of Conception-type preservation may have enhanced the lithification of the lower surface of the overlying volcanic ash, enabling preservation of details of the upper surface of these organisms. ...
Newfoundland’s Mistaken Point is home to some of the world’s oldest known complex body fossils. Detailed observation of newly discovered specimens has led to a reconsideration of Hapsidophyllas flexibilis, which is diagnosed as being a complex
epifaunal multifoliate rangeomorph with a basal stolon. This study has revealed that published material of H. flexibilis includes a cryptic epifaunal recliner that grew on, and slightly into, the sealoor in a manner similar to the common Ediacaran epifaunal organisms Fractofusus and Beothukis. The new genus and species erected herein to accommodate these epifaunal organisms is Gigarimaneta samsoni, an organism that is broadly round in outline and composed of rows of allantoid units that are further sub-divided into smaller spherocylindrical units. There is no evidence of rangeomorph branching, instead the divisions seen in Gigarimaneta are considered to represent invaginations of the lower epithelium that increased the surface-area-to-volume ratio of these organisms without the creation of true branches. The resulting ‘pneu’-like divisions may have allowed this quasi-infaunal taxon to have gained nutriment from the substrate via the culturing of sulfur-oxidizing bacteria, either as endo- or epi-symbionts, perhaps coupled with the absorption of dissolved organic material from pore/seawater.
... The rangeomorphs of Avalonia are typically found as external molds and casts on bedding planes in a thick siliciclastic succession (e.g., Wood et al. 2003). Fossils are commonly found in high densities with variable preservation and some associated tectonic deformation (Narbonne 2005;Liu et al. 2011;Liu 2016). The fine-scale details of rangeomorph architecture and gross morphology are commonly used to delimit taxa at the level of genus (Laflamme and Narbonne 2008a;Brasier et al. 2012). ...
... While exceptional preservational quality is widespread in the Newfoundland sections, it does not extend to all specimens (Liu et al. 2011;Fig. 4). ...
... The specimens used were retrodeformed prior to study by applying a ''constant area method'' (Heywood 1933). The specimens are mathematically and photographically restored to their original shape, using the assumption that the associated fossil discs were originally circular (Wood et al. 2003;Hofmann et al. 2008;Liu et al. 2011;Laflamme et al. 2012). Each specimen has to be individually retrodeformed in this way, as some surfaces have undergone episodes of deformation in different directions (Hofmann et al. 2008;Liu et al. 2015). ...
The Avalon assemblage of Newfoundland, Canada contains abundant fossils of enigmatic soft-bodied Ediacaran organisms, many with remarkable preservation. One of the most numerically dominant groups of organisms in the assemblage is the Rangeomorpha, a frondose clade characterized by self-similar, repeating branching architecture known worldwide from rocks of Ediacaran age. Variations in branching characters and gross morphology have historically been used to divide this group, but there has been little consistency in taxonomic approach to the Rangeomorpha, concomitantly there are conflicting opinions that have resulted in some overlapping taxonomic diagnoses. Here we investigate one such taxonomic dispute, the Beothukis/Culmofrons problem. The two genera were recently synonymized into Beothukis based on the assertion that some characters were of different taxonomic rank than others. Subsequent debate has focused on which taxonomic characters displayed by the Rangeomorpha should be used for genus- and species-level subdivision. To test the validity of using continuous versus discrete characters in rangeomorph taxonomy we use a combination of morphometrics and statistical analysis to identify natural clusters within our specimen dataset which was collected from Beothukis sensu lato including material that was, until recently, attributed to Culmofrons. The results of the cluster assignment validates the differentiation between Beothukis mistakensis and Beothukis (Culmofrons) plumosa, but cannot—in isolation—be used to determine at what taxonomic rank that distinction should be made. We demonstrate a considerable degree of variation within Beothukis and Culmofrons, which has not yet been recorded for unifoliate rangeomorph taxa.
... Here, we propose that the community preserved on NECP Bed-1 was relatively mature; and the character of the TOS and the presence of some apparently poorly preserved fossils suggest a form of time-averaging, with the assemblage consisting of both living and dead organisms at the time of burial. The concept of 'effaced preservation' of particular softbodied Ediacaran organisms was proposed by Liu et al. (2011) in reference to older Avalonian assemblages, where irregularly shaped forms with inconsistent textures among perfectly preserved fronds were observed, and Liu et al. (2011) argued that the former were effaced fronds partially decomposed by digestive microbial activity, prior to burial. suggested that the amount of preserved TOS corresponds to the time lapsed between sedimentation events. ...
... Here, we propose that the community preserved on NECP Bed-1 was relatively mature; and the character of the TOS and the presence of some apparently poorly preserved fossils suggest a form of time-averaging, with the assemblage consisting of both living and dead organisms at the time of burial. The concept of 'effaced preservation' of particular softbodied Ediacaran organisms was proposed by Liu et al. (2011) in reference to older Avalonian assemblages, where irregularly shaped forms with inconsistent textures among perfectly preserved fronds were observed, and Liu et al. (2011) argued that the former were effaced fronds partially decomposed by digestive microbial activity, prior to burial. suggested that the amount of preserved TOS corresponds to the time lapsed between sedimentation events. ...
... Half a billion years earlier, the sample Ediacaran community living on NECP Bed-1 might have demonstrated a similar pattern, where greater organismal diversity corresponded to the apparent complexity of the microbial mat. Furthermore, the same link between microbial mat complexity and organismal diversity has been observed at other Ediacaran fossil localities (Liu et al. 2011). ...
If we could capture a glimpse of the earliest macroscopic communities on Earth, what might they have looked like? The globally distributed fossils of the Ediacara biota represent the earliest-known examples of multicellular life, and are our best chance of understanding how early macroscopic life evolved on Earth. The Ediacaran fossils of the Flinders Ranges in South Australia (~ 555 million years old) record ancient marine-benthic communities as shallow impressions in large expanses of stratified, fossilized seafloors. The unique preservation style of Ediacaran fossils, where largely external impressions replicate the locations of individuals on the ancient seafloor as they were in life (pre-burial and subsequent fossilization), allows for the analysis of inter- and intra-taxon spatial distributions and interpretation of organism behaviour. Furthermore, crude yet detailed impressions of the individuals allows for the limited analysis of morphological characters, and occasionally tentative placement within specific phyla. Due to limitations in preservation, the phylogenetic affinities of Ediacaran fossils are still debated. Assignments have ranged from extinct relatives of extant marine animals, to terrestrial fungi and lichens, to an extinct kingdom of life altogether. However, many palaeontologists today recognize Ediacaran fossils as a diverse collective of enigmatic marine organisms, some of which might represent the earliest examples of molluscs, cnidarians, echinoderms, sponges and arthropods.
The Flinders Ranges of South Australia preserves some of the world’s most diverse Ediacaran communities, so Ediacaran seafloors from there have been the subject of many studies of Ediacaran palaeoecology. In my thesis I investigate the palaeoecology of select Ediacaran seafloors excavated from two main fossil sites from the western flanks of the Flinders Ranges: Ediacara Conservation Park and the National Heritage Listed fossil site in
Nilpena. Due to the high species diversity present on many Ediacaran seafloors, I explore the communities from a holistic perspective, comparing apparent ecological trends with living communities, as well as from a species-specific level.
The community ecology of a new fine-grained Ediacaran fossil bed recently discovered in Ediacara Conservation Park (NECP Bed-1) is explored. This fossil bed preserves a highly diverse community including dozens of specimens of the small enigmatic shield- shaped fossil Parvancorina, and two new undescribed genera. The diverse Ediacaran community, highly textured organic surface (TOS) and trace fossils are evident of successive events occurring on NECP Bed-1, and are indicative of a mature community at late-stage succession. Foremost, I focus on the small and relatively common shield-shaped fossil Parvancorina, which has been controversially interpreted as an early arthropod. Through nearest-neighbour cluster analyses of the Parvancorina population on NECP Bed-1 (n = 202), I demonstrate that two size-classes are present, distinguishing ‘juveniles’ from ‘adults’. Furthermore, orientation analysis of the population showed a strong bimodal orientation in alignment with benthic currents, suggesting that orientation played an important role in its autecology.
Globally, there are two described species of Parvancorina inferred from traditional bivariate analyses of specimen length and width, that demonstrate gross shape disparity: 1) P. minchami, specimens of which are laterally wider, whilst 2) P. saggita specimens are comparatively narrower. To more comprehensively assess the shape variability in the genus, I apply geometric morphometric shape analyses to 213 specimens from Ediacara Conservation Park, Nilpena and the White Sea of Russia collectively, revealing a continuous gradient in shape change from wide specimens through to narrow specimens. In light of the variability observed in its shape, I argue that the two currently described taxa are possibly
extreme morphotypes of a species that demonstrates a high degree of morphological plasticity.
In this thesis I also describe a new Ediacaran fossil with bilateral symmetry from Ediacara Conservation Park, an organism I have named Velocephalina greenwoodensis. This fossil shows a body structure previously undescribed among the Ediacaran genera, although it does share some similarities with the mollusc-grade Ediacaran fossil Kimberella. As such, I interpret Velocephalina to be a possible stem-group mollusc, and also suggest that bilaterian organisms were likely more prolific during the Ediacaran period than previously thought.
Finally, I examine the palaeoecology of major fossil beds excavated from Nilpena using species-diversity models applied to living communities, to see if the same ecological assembly rules pertained to th𝑧e earliest complex communities on Earth. The species-area richness (SAR) model, 𝑆 = 𝑐𝐴 , where species richness (S) increases as a power function (z) of habitat area (A), is a fundamental ecological law that applies to all living communities. I apply the fundamental ecological law of SAR to a sample of 18 Ediacaran seafloor surfaces from Nilpena to see if the same ecological assembly rules pertained to some of the earliest communities on Earth. Remarkably, despite a lack of predation –one of the main drivers of Phanerozoic evolution– in the sampled Ediacaran communities, and vast changes in species composition, this study demonstrates that this fundamental ecological assembly rule persisted for over half a billion years.
... Other groups are conspicuously scarce in Charnwood Forest and are poorly studied (Wilby et al., 2011), but may well prove to be amongst the most scientifically important in the succession. These include a short (typically <10 cm), gladius-shaped organism with simple transverse bars (Fig. 5A), which broadly resembles Hadryniscala from Newfoundland (Hofmann et al., 2008); a hemispherical organism with bifurcating radial ribs (Fig. 5C); and various rather nebulous forms (see Section 4.3) collectively referred to as 'ivesheadiomorphs' (see Liu et al., 2011). ...
... In Newfoundland, these structures were originally termed 'pizza discs', 'lobate discs' and 'bubble mats', based on their gross morphological appearances (Narbonne et al., 2001). Liu et al. (2011) interpreted them as the decayed ('effaced') remnants of organisms that had died prior to the event which killed the associated, definitively frondose, organisms on the surface. However, Laflamme et al. (2012b) considered them to simply be microbial colonies, while Wilby et al. (2011) suggested that at least some could be attributed to soft-sediment disruption associated with the collapse of buried organisms. ...
... 7B) are most convincingly interpreted as poorly preserved fronds (cf. Liu et al., 2011), though not necessarily as a result of decay. We note that sediment preserving the biota on the Lucloud surface is very obviously coarser than that capturing any of the higher biotas, and the resolution of preservation is correspondingly lower. ...
Charnwood Forest (UK) hosts some of the oldest and best-preserved macrofossils known from the Ediacaran. It is the counterpoint to the more widely studied fossil sites of south-eastern Newfoundland (Canada), which include the recently-designated UNESCO World Heritage Site of Mistaken Point. Discoveries made in Charnwood Forest since 2008 have the potential to revolutionise our understanding of the evolution of complex macroscopic life and the subsequent development of ‘modern’ (i.e. Phanerozoic) ecosystems. The sites in Charnwood include the holotypes for several iconic Ediacaran taxa, and potentially both the oldest and youngest representatives of the deep-water Avalon Assemblage. These communities provide a unique opportunity to test models of community ecology, biological endemism and environmental sensitivity and adaptability in the Ediacaran. Here, we review the geology of Charnwood Forest and the palaeobiology of its biotas, and we summarise recent scientific advances in the context of our developing understanding of early macroscopic life. We review the application of Reflectance Transformation Imaging to these ancient communities, and signpost exciting new directions for research in Charnwood Forest, almost 170 years after the fossils were first brought to light.
... Avalonian organisms share few features with living forms, making their biology, phylogenetic relationships, and ecological interactions difficult to assess Hoyal Cuthill and Conway Morris 2014;Liu et al. 2015;Dufour and McIlroy 2017). Even so, almost all of these Avalonian macroorganisms were sessile (Seilacher et al. 2005;Liu et al. 2011), so their typically in situ preservation provides a direct account of their biological and ecological processes. Significant insights into Avalonian community ecology have been gained from the statistical analysis of specimen positions using spatial point-process analyses (SPPA), with Clapham et al. (2003) demonstrating their nonrandom distribution on the seven principal surfaces at Mistaken Point, SE Newfoundland. ...
... Ivesheadiomorphs and Lobate Discs ( Supplementary Fig. S2J, F) are the two dominant putative taphomorphs found within Mistaken Point communities . Ivesheadiomorphs are characterized by a lack of consistent internal or external form, low preservation detail, and rarity of symmetrical features (Liu et al. 2011). Lobate Discs are also relatively irregular compared with other taxonomic groups such as the rangeomorphs, but they are characterized by a circular shape with high relief, and approximately radially symmetrical, irregular lobes. ...
... Interpreting the mechanisms behind the Lobate Discs-Charniid segregation is substantially hampered by the problematic nature of Lobate Discs, which lack a formal taxonomical definition or basic biological resolution; current interpretations range from a distinct macroscopic taxon to microbial colonies, taphomorphs, or even sedimentary intrusions (e.g., Laflamme et al. 2011;Liu et al. 2011). Nonetheless, the statistical evidence for segregation is unambiguous and demonstrates that the Lobate Discs were largely in place before Charniid establishment. ...
Bedding plane assemblages of Ediacaran fossils from Mistaken Point, Newfoundland, are among the oldest known records of complex multicellular life on Earth (~565 Ma). The in-situ preservation of these sessile, but otherwise deeply enigmatic organisms means that statistical analyses of specimen positions can be used to illuminate their underlying ecological dynamics, including the interactions between taxa. Fossil assemblages on Mistaken Point D and E surfaces were mapped to millimetre accuracy using differentiated GPS. Spatial correlations between ten well defined taxa (Bradgatia, Charniid, Charniodiscus, Fractofusus, Ivesheadiomorphs, Lobate Discs, Pectinifrons, Plumeropriscum, Hiemalora and Thectardis), were identified using Bayesian Network Inference (BNI), and then described and analysed using Spatial Point Process Analysis. BNI found that the E surface community had a complex web of interactions and associations between taxa, with all but one taxon (Thectardis) interacting with at least one other. The unique spatial distribution of Thectardis supports previous, morphology-based arguments for its fundamentally distinct nature. BNI revealed that the D surface community showed no inter-specific interactions or associations, a pattern consistent with a homogeneous environment. On the E surface, all six of the abundant taxonomic groups (Fractofusus, Bradgatia, Charniid, Charniodiscus, Thectardis and Plumeropriscum) were each found to have an unique set of interactions with other taxa, reflecting a broad range of underlying responses. Four instances of habitat associations were detected between taxa, of which two (Charniodiscus - Plumeropriscum, and Plumeropriscum - Fractofusus) led to weak competition for resources. One case of pre-emptive competition between Charniid and Lobate discs was detected. There were no instances of inter-specific facilitation. Ivesheadiomorphs interactions mirror those of Fractofusus and Charniodiscus, identifying them as a form-taxonomic grouping of degradationally homogenized taphomorphs. The absence of increased fossil abundance in proximity to these taphomorphs argues against scavenging/saprophytic behaviours dominating the E surface community.
... Avalonian organisms share few features with living forms, making their biology, phylogenetic relationships, and ecological interactions difficult to assess Hoyal Cuthill and Conway Morris 2014;Liu et al. 2015;Dufour and McIlroy 2017). Even so, almost all of these Avalonian macroorganisms were sessile (Seilacher et al. 2005;Liu et al. 2011), so their typically in situ preservation provides a direct account of their biological and ecological processes. Significant insights into Avalonian community ecology have been gained from the statistical analysis of specimen positions using spatial point-process analyses (SPPA), with Clapham et al. (2003) demonstrating their nonrandom distribution on the seven principal surfaces at Mistaken Point, SE Newfoundland. ...
... Ivesheadiomorphs and Lobate Discs ( Supplementary Fig. S2J, F) are the two dominant putative taphomorphs found within Mistaken Point communities . Ivesheadiomorphs are characterized by a lack of consistent internal or external form, low preservation detail, and rarity of symmetrical features (Liu et al. 2011). Lobate Discs are also relatively irregular compared with other taxonomic groups such as the rangeomorphs, but they are characterized by a circular shape with high relief, and approximately radially symmetrical, irregular lobes. ...
... Interpreting the mechanisms behind the Lobate Discs-Charniid segregation is substantially hampered by the problematic nature of Lobate Discs, which lack a formal taxonomical definition or basic biological resolution; current interpretations range from a distinct macroscopic taxon to microbial colonies, taphomorphs, or even sedimentary intrusions (e.g., Laflamme et al. 2011;Liu et al. 2011). Nonetheless, the statistical evidence for segregation is unambiguous and demonstrates that the Lobate Discs were largely in place before Charniid establishment. ...
Bedding-plane assemblages of Ediacaran fossils from Mistaken Point, Newfoundland, are among the oldest known records of complex multicellular life on Earth (dated to ~565 Ma). The in situ preservation of these sessile but otherwise deeply enigmatic organisms means that statistical analyses of specimen positions can be used to illuminate their underlying ecological dynamics, including the interactions between taxa.
Fossil assemblages on Mistaken Point D and E surfaces were mapped to millimeter accuracy using differentiated GPS. Spatial correlations between 10 well-defined taxa ( Bradgatia , Charniid, Charniodiscus , Fractofusus , Ivesheadiomorphs, Lobate Discs, Pectinifrons , Plumeropriscum , Hiemalora , and Thectardis ) were identified using Bayesian network inference (BNI), and then described and analyzed using spatial point-process analysis. BNI found that the E-surface community had a complex web of interactions and associations between taxa, with all but one taxon ( Thectardis ) interacting with at least one other. The unique spatial distribution of Thectardis supports previous, morphology-based arguments for its fundamentally distinct nature. BNI revealed that the D-surface community showed no interspecific interactions or associations, a pattern consistent with a homogeneous environment.
On the E surface, all six of the abundant taxonomic groups ( Fractofusus , Bradgatia , Charniid, Charniodiscus , Thectardis , and Plumeropriscum ) were found to have a unique set of interactions with other taxa, reflecting a broad range of underlying ecological responses. Four instances of habitat associations were detected between taxa, of which two ( Charniodiscus – Plumeropriscum and Plumeropriscum – Fractofusus ) led to weak competition for resources. One case of preemptive competition between Charniid and Lobate Discs was detected. There were no instances of interspecific facilitation. Ivesheadiomorph interactions mirror those of Fractofusus and Charniodiscus , identifying them as a form-taxonomic grouping of degradationally homogenized taphomorphs. The absence of increased fossil abundance in proximity to these taphomorphs argues against scavenging or saprophytic behaviors dominating the E-surface community.
... Additional factors that exert influences on Ediacaran fossil assemblages remain less well understood. Notwithstanding the complications arising from the time averaging of Ediacaran fossil communities, and from consideration of the presence of necromass (Liu et al. 2011(Liu et al. , 2015bWilby et al. 2015), potential biases on the composition of fossil assemblages can be exerted by processes that took place after fossilization and sediment lithification. The implications of these latter processes for the interpretation of Ediacaran fossil assemblages at Mistaken Point are the primary focus of this paper. ...
... This outcrop preserves the fossilized impressions of .4000 organisms, some recording morphological features ,0.5 mm in resolution, and its fossils have been the focus of studies into palaeoecology Darroch et al. 2013Darroch et al. , 2015Liu et al. 2015b;Mitchell et al. 2015), taxonomy (Laflamme et al. 2004;Flude & Narbonne 2008;Bamforth & Narbonne 2009;Brasier & Antcliffe 2009;Brasier et al. 2012) and taphonomy (Seilacher 1992;Liu et al. 2011;Liu 2016). The Yale outcrop of the 'E' Surface ( Fig. 1) is also the principal locality that tour groups, run by MPER staff, visit to observe the fossil horizons. ...
... Primocandelabrum is interestingly only found at the closely spaced Queens, Yale and Watern Cove West localities and comprises between 0 and 15.8% of the studied assemblages (Fig. 4). Ivesheadiomorphs, inferred to be the decayed, microbially colonized and modified remnants of dead Ediacaran organisms, are considered by us to be necromass rather than part of the standing crop (Liu et al. 2011(Liu et al. , 2015b. It is interesting to note that they form a significant component of the fossil assemblage at The Stumps, Watern Cove East and Cape Race, but are a relatively minor component of the biota on the Queens, Yale and Watern Cove West outcrops, constituting between 1.4 and 13.4% of the population. ...
Fossil assemblages from Newfoundland's Avalon Peninsula preserve diverse examples of the enigmatic Ediacaran macrobiota, offering some of the earliest evidence for large and complex multicellular life. These fossils are exposed on extensive coastal bedding planes in extraordinary abundances, permitting palaeoecological studies based on census data from spatially extensive palaeocommunities. Such studies have been used to constrain the reproductive strategy and phylogenetic placement of Ediacaran organisms. Geological mapping and stratigraphic correlation in the Mistaken Point Ecological Reserve reveal that some fossil-bearing surfaces can be tracked over distances of several kilometres. These laterally extensive surfaces reveal that the modern processes by which the sediment overlying a fossil surface is removed may impose important controls on the observed composition of fossil assemblages. Weathering and erosion – along with factors associated with tectonics, metamorphism and discovery – are here grouped as ‘post-fossilization processes’ and introduce biases that are often not explicitly accounted for in palaeoecological studies. Specifically, post-fossilization processes may differentially influence the preservational fidelity of individual specimens on a given surface and generate features that could be mistaken for original morphological characters. We therefore recommend that post-fossilization processes must be considered when undertaking palaeoecological studies in Ediacaran successions in Newfoundland and, potentially, elsewhere.
... Here, we propose that the community preserved on NECP Bed-1 was relatively mature; and the character of the TOS and the presence of some apparently poorly preserved fossils suggest a form of time-averaging, with the assemblage consisting of both living and dead organisms at the time of burial. The concept of 'effaced preservation' of particular softbodied Ediacaran organisms was proposed by Liu et al. (2011) in reference to older Avalonian assemblages, where irregularly shaped forms with inconsistent textures among perfectly preserved fronds were observed, and Liu et al. (2011) argued that the former were effaced fronds partially decomposed by digestive microbial activity, prior to burial. suggested that the amount of preserved TOS corresponds to the time lapsed between sedimentation events. ...
... Here, we propose that the community preserved on NECP Bed-1 was relatively mature; and the character of the TOS and the presence of some apparently poorly preserved fossils suggest a form of time-averaging, with the assemblage consisting of both living and dead organisms at the time of burial. The concept of 'effaced preservation' of particular softbodied Ediacaran organisms was proposed by Liu et al. (2011) in reference to older Avalonian assemblages, where irregularly shaped forms with inconsistent textures among perfectly preserved fronds were observed, and Liu et al. (2011) argued that the former were effaced fronds partially decomposed by digestive microbial activity, prior to burial. suggested that the amount of preserved TOS corresponds to the time lapsed between sedimentation events. ...
... Half a billion years earlier, the sample Ediacaran community living on NECP Bed-1 might have demonstrated a similar pattern, where greater organismal diversity corresponded to the apparent complexity of the microbial mat. Furthermore, the same link between microbial mat complexity and organismal diversity has been observed at other Ediacaran fossil localities (Liu et al. 2011). ...
Fossils of the Ediacara biota record the earliest evidence of animal communities and, as such, provide an invaluable glimpse into the abiotic and biotic processes that helped shape the evolution of complex life on Earth. A diverse community of Ediacaran macro-organisms is preserved with high resolution in a fossil bed recently excavated from north Ediacara Conservation Park (NECP) in the Flinders Ranges, South Australia. Many of the commonly described Ediacaran taxa from the Flinders Ranges are represented on the bed surface and include: Parvancorina, Rugoconites, Spriggina, Dickinsonia, Tribrachidium, Kimberella, Charniodiscus and Yorgia, including two new taxa. Numerous additional fossil-bed fragments from the same locality were analysed that preserve a similar suite of taxa and shared sedimentology. On all surfaces, preserved microbial mat appeared complex, both in topography and in texture, and the unique combination of fine grainsize, high diversity and trace fossils provide insights into the palaeoecology of the ancient organisms that lived during the Ediacaran Period some 550 Ma. Several trace fossils are overlapped by body fossils, indicative of successive events, and complex organismal behaviour. The complexity of this fossil surface suggests that the primordial community was relatively mature and possibly at late-stage succession. © 2016 Geological Society of Australia Inc., Australasian Palaeontologists.
... Sample DRK-10 was collected from the socalled "Pizza Disc Bed" at Pigeon Cove. This locality lies ∼25 m below the top of the Drook Formation and is notable for its preservation of large, lobate "pizza discs" also known as ivesheadiomorphs (Liu et al., 2011) as well as numerous small frondose fossils . The fossil-bearing horizon is directly overlain by ∼35 cm of green buff, highly cleaved volcaniclastic sediment ( Supplementary Information 1, Fig. S1A). ...
... To date, a total of 22 distinct Ediacaran species have been formally reported within Mistaken Point Ecological Reserve , along with several taxa yet unnamed (e.g., "ostrich feathers," Clapham and Narbonne, 2002). Some previously described taxa (e.g., Aspidella and Hiemalora) have been re-interpreted as the holdfast discs of frondose taxa (Serezhnikova, 2007;Burzynski and Narbonne, 2015), and others such as ivesheadiomorphs are now regarded as taphomorphs (Liu et al., 2011). The combined stratigraphic ranges and temporal distributions of these fossils through the Mistaken Point Ecological Reserve section offer opportunities to identify and critically assess hypothesized evolutionary relationships between Ediacaran macro-organisms (e.g., Brasier and Antcliffe, 2009;Laflamme et al., 2013;Dececchi et al., 2017) and to recognize possible ecological or environmental factors that may have influenced such relationships through time (e.g., Darroch et al., 2013;Mitchell and Kenchington, 2018). ...
The Conception and St. John's Groups of southeastern Newfoundland contain some of the oldest known fossils of the Ediacaran macrobiota. The Mistaken Point Ecological Reserve UNESCO World Heritage Site is an internationally recognized locality for such fossils and hosts early evidence for both total group metazoan body fossils and metazoan-style locomotion. The Mistaken Point Ecological Reserve sedimentary succession includes ∼1500 m of fossil-bearing strata containing numerous dateable volcanogenic horizons, and therefore offers a crucial window into the rise and diversification of early animals. Here we present six stratigraphically coherent radioisotopic ages derived from zircons from volcanic tuffites of the Conception and St. John's Groups at Mistaken Point Ecological Reserve. The oldest architecturally complex macrofossils, from the upper Drook Formation, have an age of 574.17 ± 0.66 Ma (including tracer calibration and decay constant uncertainties). The youngest rangeo-morph fossils from Mistaken Point Ecological Reserve, in the Fermeuse Formation, have a maximum age of 564.13 ± 0.65 Ma. Fossils of the famous "E" Surface are confirmed to be 565.00 ± 0.64 Ma, while exceptionally preserved specimens on the "Brasier" Surface in the Briscal Formation are dated at 567.63 ± 0.66 Ma. We use our new ages to construct an age-depth model for the sedi-mentary succession, constrain sedimentary accumulation rates, and convert strati-graphic fossil ranges into the time domain to facilitate integration with time-calibrated data from other successions. Combining this age model with compiled stratigraphic ranges for all named macrofossils within the Mistaken Point Ecological Reserve succession , spanning 76 discrete fossil-bearing horizons, enables recognition and interrogation of potential evolutionary signals. Peak taxonomic diversity is recognized within the Mistaken Point and Trepassey Formations , and uniterminal rangeomorphs with undisplayed branching architecture appear several million years before multiterminal, displayed forms. Together, our combined stratigraphic, paleontological, and geochro-nological approach offers a holistic, time-calibrated record of evolution during the mid-late Ediacaran Period and a framework within which to consider other geochemical, environmental, and evolutionary data sets.
... Unlike hard parts, which can accumulate for thousands of years (Kidwell & Bosence 1991;Kowalewski & Bambach 2008), there was no potential for these soft-bodied Ediacaran organisms to accumulate over such a large temporal extent. Avalonian ecosystems pre-date macro-predation and vertical burrowing, and so also remained undisturbed post-mortem (Liu et al. 2011;Wilby et al. 2015;Mitchell & Butterfield 2018). Consequently, the size and position of each specimen can be considered an accurate record of the organism's life history, including its dispersal/reproduction (Seidler & Plotkin 2006), and the habitat ) and community interactions it was subject to (Getzin et al. 2006;Lingua et al. 2008;Getzin et al. 2008). ...
... These comprise thirteen taxonomically described groups and four forms that are widely recognised but remain to be formally described. Specimens that did not fit within these groups were assigned to one of two 'bin' groups (Shen et al. 2008), or to the taphomorph group (the decayed remains of already dead organisms, such as ivesheadiomorphs; Liu et al. 2011). Low abundance taxa (taken as < 30 specimens), organ taxa such as Hiemalora, and taphomorphs were excluded from analyses, leaving 12 abundant taxa: (1) Avalofractus, (2) Beothukis, (3) Bradgatia, (4) Charnia, (5) Charniodiscus, (6) Disc A (discs on the St. Shott's surface with multiple concentric circles); (7) 'Feather Dusters', which includes Plumeropriscum and some Primocandlebrum specimens in Newfoundland; (8) Fractofusus, including both F. andersoni and F. misrai; (9) Pectinifrons, (10) Primocandelabrum, (11) Thectardis and (12) Trepassia. ...
The relative influence of niche vs. neutral processes in ecosystem dynamics is an on‐going debate, but the extent to which they structured the earliest animal communities is unknown. Some of the oldest known metazoan‐dominated paleocommunities occur in Ediacaran age (~ 565 million years old) strata in Newfoundland, Canada and Charnwood Forest, UK. These comprise large and diverse populations of sessile organisms that are amenable to spatial point process analyses, enabling inference of the most likely underlying niche or neutral processes governing community structure. We mapped seven Ediacaran paleocommunities using LiDAR, photogrammetry and a laser line probe. We found that neutral processes dominate these paleocommunities, with niche processes exerting limited influence, in contrast with the niche‐dominated dynamics of modern marine ecosystems. The dominance of neutral processes suggests that early metazoan diversification may not have been driven by systematic adaptations to the local environment, but instead may have resulted from stochastic demographic differences.
... The work of Brasier and his colleagues initially focused on determining evolutionary relationships (Brasier and Antcliffe 2009) and taphonomic processes (e.g. Callow and Brasier 2009), and constraining the influence of time-averaging on fossil assemblage composition (Liu et al. 2011). It later expanded to incorporate taxonomy , ichnology (Liu et al. 2010), paleoecology , and most recently geochronology, stratigraphy, and sedimentology. ...
... Other paleoecological studies have suggested that rangeomorph ecosystems were structured in a similar way to those of modern benthic animals ; though see Liu et al. 2015). Efforts to determine the preservational history of specimens, and the impact of microbial activity on the macrobenthos, have also helped to distinguish true biological characters from taphonomic artefacts (Liu et al. 2011Laflamme et al. 2012a;Antcliffe et al. 2015;Liu 2016). ...
Mistaken Point Ecological Reserve (MPER) World Heritage Site, on the southeastern coast of Newfoundland, Canada, is one of the foremost global Ediacaran fossil localities. MPER contains some of the oldest known assemblages of the softbodied Ediacaran macrobiota, and its fossils have contributed significantly to Ediacaran paleobiological research since their initial discovery in 1967. Preservation of multiple in situ benthic paleocommunities, some comprising thousands of specimens, has enabled research into Ediacaran paleoecology,ontogeny, taphonomy, taxonomy and morphology, offering insights into the possible phylogenetic positions of Ediacaran taxa within the tree of life. Meanwhile, a thick and continuous geological record enables the fossils to be placed within a wellresolved temporal and paleoenvironmental context spanning an interval of at least 10 million years. This article reviews the history of paleontological research at MPER, and highlights key discoveries that have shaped global thinking on the Ediacaran macrobiota.
... Understanding these enigmatic organisms has been a challenge since their initial discovery (Gürich 1930;Ford 1958). The Ediacaran biota has been much explored in recent years, with research debating aspects of their phylogenetic affinity (Seilacher 1989(Seilacher , 1992Budd and Jensen 2017;Dunn and Donoghue 2018), ecology Darroch et al. 2018;Mitchell et al. 2020), mode of life (Glaessner 1985;Laflamme et al. 2009;Dufour and McIlroy 2017;McIlroy et al. 2021), and taphonomy (Gehling 1999;Narbonne 2005;Liu et al. 2011;Bobrovskiy et al. 2019). Inferences that most of the Ediacaran biota-particularly the fractal-branching frondose Rangeomorpha-lived erect within the water column during life (i.e., Glaessner 1985; Laflamme et al. 2007) have recently been contested Pérez-Pinedo et al. 2022). ...
Fossils from the deep-sea Ediacaran biotas of Newfoundland are among the oldest architecturally complex soft-bodied macroorganisms on Earth. Most organisms in the Mistaken Point–type biotas of Avalonia—particularly the fractal-branching frondose Rangeomorpha— have been traditionally interpreted as living erect within the water column during life. However, due to the scarcity of documented physical sedimentological proxies associated with fossiliferous beds, Ediacaran paleocurrents have been inferred in some instances from the preferential orientation of fronds. This calls into question the relationship between frond orientation and paleocurrents. In this study, we present an integrated approach from a newly described fossiliferous surface (the “Melrose Surface” in the Fermeuse Formation at Melrose, on the southern portion of the Catalina Dome in the Discovery UNESCO Global Geopark) combining: (1) physical sedimentological evidence for paleocurrent direction in the form of climbing ripple cross-lamination and (2) a series of statistical analyses based on modified polythetic and monothetic clustering techniques reflecting the circular nature of the recorded orientation of Fractofusus misrai specimens. This study demonstrates the reclining rheotropic mode of life of the Ediacaran rangeomorph taxon Fractofusus misrai and presents preliminary inferences suggesting a similar mode of life for Bradgatia sp. and Pectinifrons abyssalis based on qualitative evidence. These results advocate for the consideration of an alternative conceptual hypothesis for position of life of Ediacaran organisms in which they are interpreted as having lived reclined on the seafloor, in the position that they are preserved.
... If not adpressed onto the seafloor prior to the passage of sediment-laden currents then erect fronds could not lie on the E Surface, but would instead be present in the overlying tuffite, rendering them un-preservable except perhaps for their basal discs. The assemblage is thus best considered to be an obrution deposit that smothered the seafloor biomass and necromass (Liu et al., 2011) in its life position, probably due to ash-fall rather than felling and burial by an ash-rich turbidity current. ...
The assumption that the majority of the Ediacaran fossil taxa on the iconic Mistaken Point E lived erect in the water column underpins inferences concerning: 1) paleoecology of early macrofossil assemblages; 2) how they reproduced; 3) importance of tiering and 4) controls on community dynamics (Mitchell et al., 2015; Mitchell et al., 2019; Mitchell and Butterfield, 2018; Mitchell and Kenchington, 2018). Recent work has cast some doubt on the erect mode of life of some elements of the Mistaken Point biota (namely Beothukis mistakensis, Charnia masoni, Charniodiscus procerus and Gigarimaneta samsoni; McIlroy et al., 2020; McIlroy et al., 2021; Taylor et al., 2021). Careful consideration of morphology, taphonomy and sedimentology have led to the proposal that the fractal-like Rangeomorpha in particular could have harboured sulfur-reducing symbionts and lived as soft sediment recliners (Dufour and McIlroy, 2017; McIlroy et al., 2020, McIlroy et al., 2021). Critical to this type of palaeobiological assessment is determining life attitude. To this end, it has been proposed that—since it seems that rangeomorphs and relatives could feasibly live in the reclining position like Fractofusus—the null hypothesis for interpreting the mode of life of the organisms in this biota should be that they lived as they are found, flat upon the ancient seafloor (McIlroy et al., 2021). This challenge to the Ediacaran palaeobiological community included recommendations for evidence that might be sought to demonstrate an erect mode of life (McIlroy et al., 2021) such as the presence of associated scratch circles (Jensen et al., 2018). Those methodologies have been used to good effect in demonstrating that Charniodiscus concentricus and Arborea spinosus lived with the frond somewhat erect (sediment-parallel recumbent) in the water column, whereas C. procerus was probably a recliner (Pérez-Pindeo et al., 2022).
... In contrast, there are tens of specimens of T. avalonensis, all of which are cones of different sizes. Sperling et al. (2011) use a length-to-width ratio assuming a conical shape to suggest that Thectardis has poriferan affinity, but others suggest that Thectardis is instead a taphomorph of the late decay stage of other rangeomorphs such as Charniodiscus (Antcliffe et al. 2014), like the ivesheadiomorphs (Liu et al. 2011). ...
The timing of early animal evolution remains one of the biggest conundrums in biology. Molecular data suggest Porifera diverged from the metazoan lineage some 800 Ma to 650 Ma, which contrasts with the earliest widely accepted fossils of sponges at 535 Ma. However, the lack of criteria by which to recognize the earliest animals in the fossil record presents a challenge. The sponge body plan is unchanged since the early Cambrian, which makes a sponge-type animal a good candidate for the earliest fossils. Here we propose a method for identifying an organism as sponge grade by translating the sponge pump character into a quantifiable morphological trait. We show that the ratio between the two major components of the aquiferous system, the cross-sectional area of the osculum (OSA) and the surface area of the whole sponge (SA), is an effective metric of the pump character of extant sponges and that the slope of this ratio is distinct for three classes of Porifera: Demospongiae, Calcarea, and Hexactinellida. Furthermore, this metric is effective at distinguishing as sponges both extant taxa and fossils from two extremes of the Phanerozoic, the Cambrian and Paleogene. We tested this metric on the putative Ediacaran sponge Thectardis avalonensis from Mistaken Point, Newfoundland, and found Thectardis fits both with Cambrian sponges and with modern demosponges. These analyses show that the OSA/SA ratio is a reliable character by which to identify fossils as sponge grade, opening up exciting possibilities for classifying new fossils as sponges.
... During periods of low sedimentation rates or hiatus, Ediacaran seafloors were commonly colonized by microbial matgrounds-likely mainly photosynthetic in shallow marine settings and chemosynthetic or chemoheterotrophic in deep marine settings. Matgrounds in waters of all depths in the Ediacaran were exceptionally well developed and well preserved, owing to the rarity of motile macrobionts (e.g., Liu et al., 2010), macrobioturbation (McIlroy andLogan, 1999), and ecosystem services like scavenging and grazing (Herringshaw et al., 2017); this would also have led to the persistence of abundant seafloor necromass (Liu et al., 2011;McIlroy et al., 2021). The importance of matgrounds for soft bodied preservation of Ediacaran organisms has been extensively explored based around the death mask model of mouldic preservation proposed by Gehling (1999) and extended to encompass aspects of early diagenetic mineralization (Mapstone and McIlroy, 2006;Liu, 2016) and preservation as original carbonaceous compressions (e.g., Steiner and Reitner, 2001;Xiao et al., 2002). ...
Charniodiscus is one of the most iconic and first described of the Ediacaran frondose taxa. Since the diagnosis of the holotype of C. concentricus in 1958, the scarcity and poor preservation of unequivocal specimens has resulted in genus-level taxonomic uncertainty. Since the recent reinterpretation of C. concentricus as a multifoliate frond, other Charniodiscus species—all of which are bifoliate—have been left in taxonomic limbo, with most authors comparing them to the clade Arboreomorpha and also the
Rangeomorpha. Reconsideration of the taphonomy of the holotype of C. concentricus
has revealed that the frond is bifoliate as first described, and also that the frondose portion was broadly conical rather than planar as previously inferred. The conical frond of
Charniodiscus is thus morphologically quite different from all other frondose taxa within
the Arboreomorpha. Our emendation of the generic diagnosis of Charniodiscus to
encompass bifoliate arboreomorphs with conical fronds without a backing sheet
distinguishes Charniodiscus concentricus and C. procerus from more planar leaf-like
arboreomorphs such as Arborea, A. longa and A. spinosa, all of which has a distinctive
backing sheets. Additionally, we find no evidence of rangeomorph-type fractal branching in Charniodiscus.
... Data from new publications were not added to the database after March 2021. 2 Simple discoidal fossils (such as Aspidella, Beltanella, Eoporpita, Hiemalora and Inaria) were excluded, since they have either been confirmed as, or are suspected to be, the holdfast structures of frondose taxa or microbial colonies, rather than being discrete organisms Grazhdankin and Gerdes, 2007;Serezhnikova, 2013;Burzynski et al., 2017). Impressions widely interpreted as trace fossils (such as Epibaion; Ivantsov, 2013) or taphomorphs (such as Ivesheadia and other Ivesheadiomorphs; Liu et al., 2011), were also excluded (though see Trace Fossils below). ...
Macrofossils of the late Ediacaran Period ( c. 579–539 Ma) document diverse, complex multicellular eukaryotes, including early animals, prior to the Cambrian radiation of metazoan phyla. To investigate the relationships between environmental perturbations, biotic responses and early metazoan evolutionary trajectories, it is vital to distinguish between evolutionary and ecological controls on the global distribution of Ediacaran macrofossils. The contributions of temporal, palaeoenvironmental and lithological factors in shaping the observed variations in assemblage taxonomic composition between Ediacaran macrofossil sites are widely discussed, but the role of palaeogeography remains ambiguous. Here we investigate the influence of palaeolatitude on the spatial distribution of Ediacaran macrobiota through the late Ediacaran Period using two leading palaeogeographical reconstructions. We find that overall generic diversity was distributed across all palaeolatitudes. Among specific groups, the distributions of candidate ‘Bilateral’ and Frondomorph taxa exhibit weakly statistically significant and statistically significant differences between low and high palaeolatitudes within our favoured palaeogeographical reconstruction, respectively, whereas Algal, Tubular, Soft-bodied and Biomineralizing taxa show no significant difference. The recognition of statistically significant palaeolatitudinal differences in the distribution of certain morphogroups highlights the importance of considering palaeolatitudinal influences when interrogating trends in Ediacaran taxon distributions.
Supplementary material: Supplementary information, data and code are available at https://doi.org/10.6084/m9.figshare.c.5488945
Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/cc/advances-cambrian-explosion
... In addition, because a majority of discoidal Ediacaran fossils (including Aspidella) have been interpreted as representing holdfast structures (and moreover, holdfasts than cannot convincingly be tied to any one frondose taxon-see Burzynski et al., 2017), Aspidella was excluded. Similarly, Liu et al. (2011Liu et al. ( , 2012; although see Laflamme et al., 2011) have suggested that the Ivesheadiomorphs preserved around Mistaken Point represent taphomorphs of other taxa whose morphology has Journal of Paleontology 95(2):236-251 been decayed and obscured by the growth of microbial mats over carcasses, and so these too were excluded. Lastly, Helminthoidichnites recorded from the Nilpena communities is a convincing bilaterian trace fossil (Buatois et al., 2014), and as such, counts of this ichnotaxon cannot be used to infer the relative abundance of the associated tracemaker. ...
The late Ediacaran (Nama) Fossil Assemblage from the Kushk Series in the Kushk and Chahmir areas of Central Iran highlights a diverse community of globally distributed, soft-bodied (non-skeletonized) Ediacara biota coexisting with skeletonized tubular forms of likely metazoan affinities. Several biostratigraphically and biogeographically important taxa are reported (i.e., erniettomorphs, rangeomorphs, cloudinomorphs, kimberellomorphs, Chuaria , Corumbella ), including Convolutubus dargazinensis new genus new species, a new organic-walled tubular organism, allowing for paleoecological studies to be performed. This study highlights the need for continued investigations into the late Ediacaran of Iran, and suggests a biosphere in transition, with a shift in diversity and abundance from large Ediacara biota to organic-walled and skeletonized tubular organisms at the dawn of the Cambrian Explosion.
UUID: http://zoobank.org/350bb98c-5322-488d-a9a5-22c911ab7e53
... Few feeding appendages or internal digestive structures have been recognized in Ediacaran organisms (e.g. Fedonkin et al., 2007;Schiffbauer et al., 2020), although this may be in part due to taphonomic biases (see Wade, 1968;Norris, 1989;Liu et al., 2011;Gibson, Schiffbauer, & Darroch, 2018). Consequently, the mechanisms by which many Ediacaran groups fed remain unclear. ...
Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft-bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in-depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.
... The preservation of time-averaged communities has the potential to bias our analyses (see [21,25]). In Avalonian royalsocietypublishing.org/journal/rsfs Interface Focus 10: 20190109 communities, taphomorphs interpreted to record the decaying remains of organisms are identified by their poor preservational fidelity, irregular morphologies, and often high topographic relief [102]. This interpretation is consistent with data suggesting that the spatial interactions of some taphomorph populations mirror those of other taxa they are considered to be derived from [21]. ...
The broad-scale environment plays a substantial role in shaping modern marine ecosystems, but the degree to which palaeocommunities were influenced by their environment is unclear. To investigate how broad-scale environment influenced the community ecology of early animal ecosystems, we employed spatial point process analyses (SPPA) to examine the community structure of seven late Ediacaran (558–550 Ma) bedding-plane assemblages drawn from a range of environmental settings and global localities. The studied palaeocommunities exhibit marked differences in the response of their component taxa to sub-metre-scale habitat heterogeneities on the seafloor. Shallow-marine (nearshore) palaeocommunities were heavily influenced by local habitat heterogeneities, in contrast to their deeper-water counterparts. The local patchiness within shallow-water communities may have been further accentuated by the presence of grazers and detritivores, whose behaviours potentially initiated a propagation of increasing habitat heterogeneity of benthic communities from shallow to deep-marine depositional environments. Higher species richness in shallow-water Ediacaran assemblages compared to deep-water counterparts across the studied time-interval could have been driven by this environmental patchiness, because habitat heterogeneities increase species richness in modern marine environments. Our results provide quantitative support for the ‘Savannah’ hypothesis for early animal diversification—whereby Ediacaran diversification was driven by patchiness in the local benthic environment.
... External mould fossils are far more common but are problem- Brasier, 2011). Tentacles decay quickly when exposed outside the polyp hood and would not be visible in an external mould if the tentacles had been retracted. ...
An experimental decay methodology is developed for a cnidarian model organism to serve as a comparison to the many previous such studies on bilaterians. This allows an examination of inherent bias against the fossilisation of cnidarian tissue and their diagnostic characters, under what conditions these occur, and in what way. The decay sequence of Actinia equina was examined under a series of controlled conditions. These experiments show that cnidarian decay begins with an initial rupturing of the epidermis, followed by rapid loss of recognisable internal morphological characters. This suggests that bacteria work quicker on the epidermis than autolysis does on the internal anatomy. The data also show that diploblastic tissue is not universally decayed more slowly under anoxic or reducing conditions than under oxic conditions. Indeed, some cnidarian characters decay more rapidly under anoxic conditions than they do under oxic conditions. This suggests the decay pathways acting may be different to those affecting soft bilaterian tissue such as soft epidermis and internal organs. What is most important in the decay of soft polyp anatomy is the microbial community, which can be dominated by oxic or anoxic bacteria. Different Lagerstätte, even of the same type, will inevitably have subtle difference in their bacterial communities, which among other factors, could be a control on soft polyp preservation leading to either an absence of compelling soft anthozoans (Burgess Shale) or an astonishing abundance (Qingjiang biota).
... As other evidence was considered, it was shown that a number of such discoid forms were holdfast impressions of frondose organisms (with preserved pieces of fronds) (Droser et al., 2006) and that their morphology was, in many cases, related to taphonomic biases (Tarhan et al., 2010(Tarhan et al., , 2015. Thus, taphonomy will always be imperative to understanding the taxonomic composition of such important biotas (e.g., Gehling et al., 2000;Grey and Willman, 2009;Liu et al., 2011) and improving our comprehension of paleobiological (Laflamme et al., 2007;Flude and Narbonne, 2008;Elliott et al., 2011;Meyer et al 2012;Narbonne et al 2014), geobiological (Mapstone and McIlroy, 2006), and sedimentological processes (Warren et al., 2013). This is the case for the shelly fossil Cloudina, whose taxonomy is still controversial despite being one of the most geographically widespread and abundant fossils in the latest Ediacaran carbonate rocks (Germs, 1972;Grant, 1990;Conway-Morris et al., 1990;Hofmann and Mountjoy, 2001;Hua et al., 2003Hua et al., , 2005Cortijo et al., 2010;Becker-Kerber et al., 2013. ...
The arrival of animals with hard parts at the end of the Ediacaran Period was an important evolutionary innovation. Biomineralized structures serve a number of biological functions and pose environmental challenges. Those same hard parts that once played a role in living organisms also affect their postmortem histories. Taphonomic scenarios may create biases that can impact perceptions on the systematic, morphological, biostratigraphic, and paleogeographic patterns in the fossil record. This is well exemplified by the taxonomic controversies regarding Cloudina, the most geographically widespread and abundant shelly fossil of the uppermost Ediacaran. In this study, we discuss new taphonomic data on Cloudina-bearing strata deposits from the Tamengo Formation (Corumbá Group, Brazil) and how influential this taphonomy is on a robust taxonomy of this fossil. Our observations suggest that allochthonous Cloudina deposits from the Tamengo Formation present evidence of taphonomic influences on the transporting/reworking of fragmentation and disarticulation of Cloudina tubes. Differences in size distributions between some of the localities have demonstrated that this trait is not reliable for defining or synonymizing species of Cloudina, and these differences probably reflect a myriad of taphonomic and paleobiological phenomena. Moreover, in some outcrops of the Tamengo Formation, shell walls are usually poorly preserved due to plastic deformations and diagenetic dissolution/recrystallization processes, which conceal morphological diagnostic features used in Cloudina taxonomy. Similar taphonomic biases may be of equal importance to the taxonomy of Cloudina preserved in other upper Ediacaran carbonates. Hence, earlier claims in favor of the synonymization of Cloudina species from the Tamengo Formation cannot currently be justified.
... The 'E' Surface preserves the fossilised impressions of > 4000 organisms, some recording morphological features < 0.5 mm in resolution (Fig. 2). The 'E' Surface has the best preserved and most diverse assemblage in the Reserve and has been the focus of studies in palaeoecology (Clapham et al. 2003;Darroch et al. 2013Darroch et al. , 2015Liu et al. 2015;Mitchell et al. 2015;Dufour and McIlroy 2017), taxonomy (Laflamme et al. 2004;Gehling and Narbonne 2007;Flude and Narbonne 2008;Bamforth and Narbonne 2009;Brasier and Antcliffe 2009;Brasier et al. 2012), and fossil preservation (Seilacher 1992;Liu et al. 2011Liu et al. , 2016. The volcanic ash-rich bed directly overlying the 'E' Surface has been dated to 566.25 Ma (Pu et al. 2016) The Mistaken Point outcrops of the 'D' and 'E' Surfaces are also the principal locality that tour groups, run by MPER staff, visit to observe the fossil horizons. ...
The fossils at the Mistaken Point UNESCO World Heritage Site represent evidence of the oldest known, large, architecturally complex, life on Earth and are protected by the Government of Newfoundland and Labrador as part of an Ecological Reserve. Following concerns that foot traffic across the fossil surfaces was having a deleterious effect on the geoheritage, visitors were made to wear quilted ‘Bama Sokkets’ starting in 2009—though the efficacy of this management technique has never been tested. Previous studies in the materials sciences have revealed that footwear erosion of rock surfaces is primarily caused by the action of sediment between the foot and the surface; however, these findings have not before been applied to geoconservation research. In this study, we examine the adhesion of sediment to several footwear types. Our experiments reveal that under wet conditions, the ‘Bama Sokkets’ perform poorly in repelling sediment, and as such their use as a geoconservation management tool is discouraged. This study recommends the use of hydrophobic footwear for walking on geoheritage rock surfaces and has led to policy change at the Mistaken Point UNESCO World Heritage Site.
... Ediacaran macrofossils preserved in Nama style have been hypothesized to capture only details of soft organic 'skeletons' 12,43 , instead of the morphology of the organism itself. However, when it comes to fossils preserved in negative hyporelief, all cementation models 19,20,24,47 imply that the sandstone imprinted the upper surface of the organism; otherwise, the 'death mask' would have captured the organism at different stages of decomposition depending on the timing of cementation, as is possibly observed in some Conception-style fossils 48 . In contrast, according to the rheological model, the preserved impression could have been left by a degradation-resistant and relatively more rigid organic structure, such as dorsal or ventral external cuticle or a soft internal 'skeleton' . ...
The soft-bodied Ediacara biota (571–541 million years ago) represents the oldest complex large organisms in the fossil record, providing a bridge between largely microbial ecosystems of the Precambrian and the animal-dominated world of the Phanerozoic, potentially holding clues about the early evolution of Metazoa. However, the nature of most Ediacaran organisms remains unresolved, partly due to their enigmatic non-actualistic preservation. Here, we show that Flinders-style fossilization of Ediacaran organisms was promoted by unusually prolonged conservation of organic matter, coupled with differences in rheological behaviour of the over- and underlying sediments. In contrast with accepted models, cementation of overlying sand was not critical for fossil preservation, which is supported by the absence of cement in unweathered White Sea specimens and observations of soft sediment deformation in South Australian specimens. The rheological model, confirmed by laboratory simulations, implies that Ediacaran fossils do not necessarily reflect the external shape of the organism, but rather the morphology of a soft external or internal organic ‘skeleton’. The rheological mechanism provides new constraints on biological interpretations of the Ediacara biota. Taphonomic experiments show that sedimentary flows constrained Ediacara biota preservation and that Ediacaran fossils do not necessarily reflect the external shape of the organism.
... Gravity cast fossils (MacGabhann, 2007a), also termed 'lower surface preservation' (Liu et al., 2011), exhibit a mold (the part specimen) preserved in negative epirelief on the top surface of a bed, with a corresponding positive hyporelief cast (the counterpart) on the sole of the overlying bed. In this gravity cast taphonomic style, the underlying sediment was able to maintain a mold, despite decay or removal of the organism positioned directly above, until cast by overlying sediment moving downwards under the force of gravity. ...
Much of our knowledge of early metazoan evolution is derived from unmineralized death mask or endorelief mold and cast fossils in Ediacaran clastic sedimentary rocks. This record is often regarded as a unique ‘Ediacaran taphonomic window’; however, the prevalence of soft-bodied molds and casts in Paleozoic clastic rocks has been increasing, begging an extension, or modification, to our understanding of this preservational motif. Chief amongst such fossils are eldonids, a non-biomineralized group of stem deuterostomes. Because eldonids are also preserved as compressed or flattened fossils from deposits like the Burgess Shale, Chengjiang and Kaili, they offer a comparative case study for evaluating the taphonomic fidelity of mold/cast-style preservation during this interval. EDS and Raman microspectroscopic analysis of Ordovician and Devonian eldonid molds and casts, and comparison with Burgess Shale eldonids, suggests the mold/cast taphonomic style produces significantly lower fidelity of fossil preservation. We propose that eldonid mold/cast fossils are preserved by the adsorption of reduced iron ions onto tissues composed primarily of high molecular weight (HMW) biopolymers which require enzymatic degradation prior to decay. Nucleation and growth of aluminosilicates and/or sulfides around these adsorbed ions forms a fossilizable surface veneer, preserving a death mask mold. More labile tissues could not be fossilized in this mold and cast style. Ediacaran mold and cast fossils from South Australia, the White Sea region of Russia, Namibia, and Newfoundland exhibit preservational characteristics consistent with this new proposed model. Analysis of their preservational mode suggests that the first metazoans, which would have lacked HMW biopolymeric tissues, could not have been fossilized in this particular style. Thus, understanding the origin and earliest evolution of the Metazoa requires a focus on alternative modes of fossilization.
... The limited taphonomic windows offered by most Ediacaran localities preserve impressions of two-dimensional casts and molds in medium to coarse sandstones (Narbonne, 2005;Kenchington and Wilby, 2014), limiting morphological information to external structures. Taphonomic studies distinguishing between genuine structures and morphological "mistakes" resulting from bending, folding, or overlapping relationships have been essential in forwarding taxonomic and phylogenetic research (Laflamme et al., 2007;Liu et al., 2011;Brasier et al., 2013;Matthews et al., 2017). Rare glimpses into three-dimensional morphology are offered by exceptional sites in Namibia (Vickers-Rich et al., 2013;Ivantsov et al., 2016), Newfoundland (Narbonne, 2004;Narbonne et al., 2009), and the White Sea (Grazhdankin, 2014;Ivantsov, 2016). ...
Exquisitely preserved three-dimensional examples of the classic Ediacaran (late Neoproterozoic; 570–541 Ma) frond Charniodiscus arboreus Jenkins and Gehling, 1978 (herein referred to as Arborea arborea Glaessner in Glaessner and Daily, 1959) are reported from the Ediacara Member, Rawnsley Quartzite of South Australia, and allow for a detailed reinterpretation of its functional morphology and taxonomy. New specimens cast in three dimensions within sandy event beds showcase detailed branching morphology that highlights possible internal features that are strikingly different from rangeomorph and erniettomorph fronds. Combined with dozens of well-preserved two-dimensional impressions from the Flinders Ranges of South Australia, morphological variations within the traditional Arborea morphotype are interpreted as representing various stages of external molding. In rare cases, taphomorphs (morphological variants attributable to preservation) represent composite molding of internal features consisting of structural supports or anchoring sites for branching structures. Each primary branch consists of a central primary branching stalk from which emerge several oval secondary branches, which likely correspond to similar structures found in rare two-dimensional specimens. Considering this new evidence, previous synonymies within the Arboreomorpha are no longer justified, and we suggest that the taxonomy of the group be revised.
... The material collected for this study does not have the high relief and marked quilting of the types (Fig. 6) and shows varying degree of effacement, decay and fragmentation. These are common taphonomic variations of fossil leaves (Ferguson 1985;Spicer 1991) and of vendobionts (Retallack 2007;Liu et al. 2011). Segmentation persisted longer at the margin than the middle, but the midline crease persisted even when quilting was obscure. ...
Protonympha is an enigmatic fossil represented by two species from the Middle Devonian (Protonympha transversa) and Late Devonian (Protonympha salicifolia) of New York. Although interpreted in the past as a polychaete worm or starfish arm, Protonympha is not found with marine fossils, but with fossil plants. This fossil plant community was a swamp woodland of Lepidosigillaria whitei, with ground cover of Haskinsia colophylla, fringing brackish to freshwater coastal lagoons of the Catskill Delta. Protonympha shares with Ediacaran Vendobionta a quilted body of unskeletonized biopolymer that is unusually resistant to burial compaction. In overall form, Protonympha is most like the Ediacaran genus Spriggina. Protonympha has branching and tapering tubular structures radiating from the bottom. These rhizine-like structures, thallus stratification and internal chambers revealed by petrographic thin sections suggest affinities with lichenized fungi. As for Cambrian Swartpuntia and Ordovician–Silurian Rutgersella, Protonympha may have been a post-Ediacaran vendobiont.
... In particular, the assemblages from the Maplewell and Blackbrook groups are almost unique in consisting of deeper-water communities otherwise known only from Mistaken Point in Newfoundland. The significance of these assemblages is reflected in recent literature addressing the taphonomy of the assemblage (Liu et al., 2011), palaeoecology , systematics (Antcliffe and Brasier, 2008) and the application of novel techniques such as using silicon rubber moulds for recording and conservation Edwards and Williams, 2011) (Fig. 3). The silicon rubber moulds are durable and when cast can provide a precise replica of outcrops. ...
Geoconservation in England, as in Great Britain more widely, is very well established. Sites of national or international scientific importance, as determined by a systematic site assessment and selection exercise, can be protected by designation as Sites of Special Scientific Interest. Sites of local importance e.g. Local Geological Sites may also be taken into account when planning decisions are made that could have an impact on them. As a whole, the network of conserved geosites represents the key elements of our current understanding of the geology and geomorphology of England. Site selection and safeguard and management of this network are dependent on geoscience information, and in return continued geoscience fieldwork is dependent on having conserved sites available for study. Here, we review the relationship between geoconservation and geoscience, and how it has developed since the first geoconservation legislation nearly 70 years ago. We discuss the achievements, challenges and where and how this relationship needs to strengthen further to meet future needs of both geoscience and nature conservation. In a changing world, there will continue to be a need for innovative geoscience supported by effective geoconservation. Those interested in conserving England’s geological heritage will need to engage the wider geoscience community more than ever to deliver a shared vision for the natural environment.
... Although matground textures, in the form of simple microbially induced sedimentary structures (MISS), are present in many of the older, Avalon-type Ediacara Biota fossil assemblages, such as the fossiliferous successions of Charnwood Forest and the Avalon Peninsula, these are commonly characterized by low abundance and diversity and sparse spatial coverage. MISS associated with Avalon-type assemblages are limited largely to features such as elephant-skin textures (Gehling et al. 2000) and simple wrinkle marks, so-called "bubble trains," and the circular ivesheadiomorph structures [these last two have alternatively been mooted as, respectively, load casts (Brasier et al. 2013a) and the decayed remnants of Ediacara macroorganisms (Liu et al. 2011)] (Callow & Brasier 2009, Laflamme et al. 2012). ...
The evolutionary trajectory of early complex life on Earth is interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota, which appeared and evolved during a time of dynamic biogeochemical and environmental fluctuation in the global ocean. The Ediacara Biota is historically divided into three successive Assemblages—the Avalon, the White Sea, and the Nama—whichare marked by the appearance of novel biological traits and ecological strategies. In particular, the younger White Sea and Nama Assemblages record a “second wave” of ecological innovations, which included the development of not only uniquely Ediacaran body plans and ecologies, such as matground adaptations, but also the dual emergence of bilaterian-grade animals and Phanerozoic-style ecological innovations, including spatial heterogeneity, complex reproductive strategies, ecospace utilization, motility, and substrate competition. The late Ediacaran was an evolutionarily dynamic time characterized by strong environmental control over the distribution of taxa in time and space. Expected final online publication date for the Annual Review of Earth and Planetary Sciences Volume 45 is May 30, 2017. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... The overall texture of the surface, however, appears mainly smooth, in contrast to other excavated Ediacara Member fossil surfaces such as NECP Bed-1 ( Coutts et al., 2016), which records a range of high relief, deeply textured forms over relatively large regions of the surface. There is also a noted absence of large decayed or effaced organisms on the Crisp Wall surface, in comparison with surfaces such as that explored by Liu et al. (2013), which records a number of decayed organisms overprinted by a younger, juvenile community (see also Liu et al., 2011;Liu et al., 2012). A partial Dickinsonia footprint (Gehling et al., 2005; Fig. 3K) is present on the largest Crisp Wall slab, preserving an incomplete impression of lower surface units of at least 30 mm in length. ...
Ediacara fossil surfaces from the Flinders Ranges (South Australia) commonly record excellent preservation quality and can provide a palaeoecological window into some of the oldest communities on Earth (ca. 555 Ma). An excavated semi-contiguous sandstone bed of 6.5 m² from a fossil locality at Crisp Gorge in the central Flinders Ranges records an abundance of taxa and structures characteristic of White Sea assemblage communities. Stratigraphic analysis places the fossil surface within the Oscillation Rippled Sandstone Facies of the Ediacara Member at Crisp Gorge. The community appears to be predominantly juvenile forms, with Dickinsonia costata, Parvancorina minchami and Tribrachidium heraldicum present only within interpreted juvenile size ranges. The textured organic surface contains structures including low relief ridges and round bosses, but overall records a smooth bed surface and is interpreted as representing a surface with only an immature microbial mat developed before burial. No effaced or decayed organisms were identified. Community analysis describes an intermediate Shannon diversity (1.27) and an uneven community dominated by the population of D. costata, which comprises more than 50% of the individuals. The examined parameters, when combined with the presence of small, juvenile taxa and an immature organic mat, suggests that the community inhabiting this surface prior to its catastrophic burial may have been comparable to a modern early-stage, primary successional community. The Crisp Gorge bed emphasizes that Ediacara fossil surfaces from South Australia span a range of developmental stages and offer a window into Ediacaran sea-floor communities at various stages of maturity.
... Explanations for the profligacy of high-quality preservation of late Ediacaran macrofossils focus on evidence for widespread benthic microbial mats, and a perceived absence of scavengers, predators, and pervasive bioturbating organisms (Fedonkin 1985;Allison and Briggs 1993;Callow and Brasier 2009;Liu et al. 2011). The favored explanation for late Ediacaran moldic preservation in siliciclastic sediments involves the smothering of paleocommunities on microbe-covered seafloors by event beds (e.g., volcanic ash, or storm sands; Narbonne 2005), followed by microbially induced precipitation of pyrite around the organisms ; though see Serezhnikova 2011 for an alternative view). ...
... Through the careful drawing of new material (Fig. 4), including juvenile forms , various taphomorphs (Liu et al. 2010a) and several new rangeomorph/frondose taxa -including Beothukis and Vinlandia (Brasier & Antcliffe 2009;) -several repeating morphological elements were determined that could form the basis for a formal taxonomy Liu et al. 2016b), with the allowance that there may be some element of ecophenotypism , although the latter is questioned by multivariate statistical analyses using the Brasier descriptive scheme as its basis (Kenchington & Wilby 2017). Through all this careful descriptive work, the group remained open-minded to the possibility that the Ediacarans might not have been animals (Antcliffe et al. 2016). ...
Understanding early life has been one of the hottest topics in palaeobiology for many years, attracting some of the finest palaeontological minds. Three of the most fundamental innovations in the history of life being: the appearance of the first cells, evolution of multi-cellularity, and the evolution of animals. The MOFAOTYOF principle (my oldest fossils are older than your oldest fossils) commonly clouds the discussions around the oldest fossil evidence, requiring a rigorous and critical approach to determining which fossils are reliable and should form the basis of our understanding of early life. Additionally, evidence for early fossils must be considered within their spatial context, we need to understand the conditions under which they were preserved and how they were preserved.
This volume summarizes recent progress in the fields of: 1) cellular preservation of early microbial life; and 2) early evolution of macroscopic animal life, including the Ediacara biota. Deciphering the evidence for early life requires some degree of exceptional preservation, employment of state-of-the-art techniques, and also understanding gleaned from Phanerozoic lagerstätte and modern analogues. This integrated approach to understanding fossils, combined with adoption of the null-hypothesis that all putative traces of life are abiotic until proven otherwise, characterized the work of Martin Brasier as is well demonstrated by the papers in this volume.
... Martin also contributed to the recognition that some impressions on Ediacaran fossil-bearing surfaces previously described as valid taxa (e.g. Ivesheadia, Shepshedia and Blackbrookia; Boynton & Ford 1995) may instead reflect decayed carcasses of other Ediacaran organisms (Liu et al. 2011; although see also Laflamme et al. 2011;Wilby et al. 2011). The recognition that time averaging occurs on Ediacaran bedding planes was a revolutionary idea at the time; it has been built upon by several other studies recognizing the presence of multiple successive communities preserved on individual Ediacaran bedding planes (e.g. ...
Martin Brasier's work spanned almost the entire geological column, but the origin of animals and the nature of the Cambrian explosion were areas of particular interest to him. Martin adopted a holistic approach to the study of these topics that considered the interplay between multiple geological and biological phenomena and he sought to interpret the fossil record within the broad context of geological, biogeochemical and ecological changes in the Earth system. Here we summarize Martin's main contributions to this area of research and assess the impact of his findings on the development of this field.
The Ediacaran period records the appearance of the first multicellular and complex organisms in Earth's history. Within the West African Craton, just a few simple discoidal structures have been previously reported within the supposed Ediacaran successions. Here, we describe for the first time a slightly diversified Ediacaran assemblage of micro- and macro-fossils from Ediacaran volcano-sedimentary rocks of Northwest Africa. Fossils occur in shallow water carbonate-bearing siliciclastic sediments of the Izelf Formation (567–550 Ma), in the Moroccan Anti-Atlas. Macrofossils are represented by Aspidella, ivesheadiomorphs and other problematic structures with putative biotic origin. The macrofossil assemblage is dominated by taphomorphs that indicate different degrees of preservation due to progressive decaying processes, possibly extending the effacement preservation mode outside of Avalonia assemblages. Microbially induced sedimentary structures (MISS), stromatolites and spheroidal microfossils are also reported. In particular, spheroidal microfossils may occur as isolated individuals or as concatenated spheres with potentially cell-division processes and were preserved through carbonate and silica permineralization. Morphologically, spheroidal microfossils are compared to sphaeromorph acritarchs and sulfur-oxidizing bacteria such as genus Thiomargarita. The depositional environment and age interval provide new information concerning paleogeographic and paleoenvironmental conditions of Ediacaran biota living on the West African Craton; hence, fills a gap in the Ediacaran biota in the West African Craton.
Ferruginous biofilms are a form of preservation of fossil leaves making detailed imprints of venation even in coarse sandstone. In modern examples, the biofilm is robust enough to persist after separation, or rotting of the leaf. The biofilms are created by filamentous, iron-oxidizing bacteria such as Leptothrix and Sphaerotilus, and have distinctive felted microscopic textures. Ediacaran vendobionts with fine detail preserved in coarse sandstone show these diagnostic felted textures under the scanning electron microscope. These biofilms were thus pre-depositional ferruginous death masks, and lack distinctive framboidal textures or pyritohedral textures of pyrite. Pyritic external-only “death masks” are undocumented from any geological age or locality. Ediacaran fossils are also preserved by silica permineralization, silica-cemented molds and casts, and pyrite permineralization and replacement after burial. This examination of unskeletonized Ediacaran fossils from Australia, Russia, Namibia, California, and Newfoundland in thin section and scanning electon microscope shows no evidence for a uniquely Ediacaran style of fossil preservation.
The Ediacaran fossils of the Mistaken Point E surface have provided crucial insight into early animal communities, including how they reproduced, the importance of Ediacaran height and what the most important factors were to their community dynamics. Here, we use this iconic community to investigate how morphological variation between eight taxa affected their ability to withstand different flow conditions. For each of Beothukis, Bradgatia, Charniodiscus procerus, Charniodiscus spinosus, Plumeropriscum, Primocandelabrum, Thectardis and Fractofusus we measured the orientation and length of their stems (if present) and their fronds. We statistically tested each taxon's stem and frond orientation distributions to see whether they displayed a uniform or multimodal distribution. Where multimodal distributions were identified, the stem/frond length of each cohort was tested to identify if there were differences in size between different orientation groups. We find that Bradgatia and Thectardis show a bimodal felling direction, and infer that they were felled by the turbulent head of the felling flow. In contrast, the frondose rangeomorphs including Beothukis, Plumeropriscum, Primocandelabrum, and the arboreomorphs were felled in a single direction, indicating that they were upright in the water column, and were likely felled by the laminar tail of the felling flow. These differences in directionality suggests that an elongate habit, and particularly possession of a stem, lent greater resilience to frondose taxa against turbulent flows, suggesting that such taxa would have had improved survivability in conditions with higher background turbulence than taxa like Bradgatia and Thectardis, that lacked a stem and had a higher centre of mass, which may have fared better in quieter water conditions.
The tempo and mode of early animal evolution remains one of the biggest conundrums in biology. Stratigraphy shows that there is a gap, not attributable to poor preservation, of at least ~100 Myr between the oldest animal fossils and the divergence times implied by molecular phylogenies. Sponges, due to their position in the metazoan tree, are a good candidate for the earliest fossil evidence for the diversification of animals. Nevertheless, the search for the earliest animals represents a major challenge due to the lack of criteria by which to recognize such organisms in the fossil record. Here I describe a way to quantify the sponge filtration or ‘sponge pump character’ by analyzing the ratio between the two major components of the aquiferous system: external surface area–SA and osculum cross-sectional area–OSA, which allows comparison between extant sponges and many fossil forms. Second, I addressed the question of whether sponges make use of induced flow, an often-made assumption when interpreting fossils as sponges.
The analysis includes the three major classes of Porifera: Demospongiae, Hexactinellida and Calcarea, both are represented by extant and fossil taxa from two extremes of the Phanerozoic, the Cambrian and Eocene. The data show that this ratio is narrow, 0.01 – 0.001 in modern sponges, and the slope of the ratio can be used to distinguish classes of sponges. I then examined the ratio of OSA/SA for the putative Ediacaran sponge Thectardis avalonensis, and found it to be similar to some Cambrian sponge genera. Moreover, the slope of the ratio across different sizes of T. avalonensis is similar to that of demosponges. However, the original argument for the Poriferan affinity of T. avalonensis was based on the idea that the main mechanisms that sponges use to filter water is through current induced flow, meaning that shape alone drives the flow in and out of a sponge at no extra metabolic cost. I tested this hypothesis in the second chapter of this thesis by analyzing data from tank experiments in the demosponge Geodia barretti. The analysis of the filtration to respiration ratio showed increased filtration at ambient currents below 10 cm s-1 but a reduction at higher ambient current speeds, which contrast the traditional view of shape induced flow. Instead, these results support the evidence that sponges have a high degree of control over their filtration, with the consequence that induce flow should not be taken as a criterion for ascribing to the sponges any structure based on this assumption.
Overall, my work shows that a more solid understanding of the biology of modern sponges provides a wealth of information with which to examine the Precambrian record of sponges in particular, and the greater picture of early animal evolution in general. This is because having a correct interpretation of the fossil record is essential to properly calibrating molecular phylogenies.
Rock outcrops of the sedimentary-stratigraphic record often reveal bedding planes that can be considered to be true substrates: preserved surfaces that demonstrably existed at the sediment–water or sediment–air interface at the time of deposition. These surfaces have high value as repositories of palaeoenvironmental information, revealing fossilized snapshots of microscale topography from deep time. Some true substrates are notable for their sedimentary, palaeontological and ichnological signatures that provide windows into key intervals of Earth history, but countless others occur routinely throughout the sedimentary–stratigraphic record. They frequently reveal patterns that are strikingly familiar from modern sedimentary environments, such as ripple marks, animal trackways, raindrop impressions or mudcracks: all phenomena that are apparently ephemeral in modern settings, and which form on recognizably human timescales. This paper sets out to explain why these short-term, transient, small-scale features are counter-intuitively abundant within a 3.8 billion year-long sedimentary-stratigraphic record that is known to be inherently time-incomplete. True substrates are fundamentally related to a state of stasis in ancient sedimentation systems, and distinguishable from other types of bedding surfaces that formed from a dominance of states of deposition or erosion. Stasis is shown to play a key role in both their formation and preservation, rendering them faithful and valuable archives of palaeoenvironmental and temporal information. Further, the intersection between the time–length scale of their formative processes and outcrop expressions can be used to explain why they are so frequently encountered in outcrop investigations. Explaining true substrates as inevitable and unexceptional by-products of the accrual of the sedimentary–stratigraphic record should shift perspectives on what can be understood about Earth history from field studies of the sedimentary–stratigraphic record. They should be recognized as providing high-definition information about the mundane day to day operation of ancient environments, and critically assuage the argument that the incomplete sedimentary–stratigraphic record is unrepresentative of the geological past.
The Precambrian Ediacara Biota-Earth's earliest fossil record of communities of macroscopic, multicellular organisms-provides critical insights into the emergence of complex life on our planet. Excavation and reconstruction of nearly 300 m2 of fossiliferous bedding planes in the Ediacara Member of the Rawnsley Quartzite, at the National Heritage Ediacara fossil site Nilpena in South Australia, have permitted detailed study of the sedimentology, taphonomy and palaeoecology of Ediacara fossil assemblages. Characterization of Ediacara macrofossils and textured organic surfaces at the scale of facies, bedding planes and individual specimens has yielded unprecedented insight into the manner in which the palaeoenvironmental settings inhabited by Ediacara communities-particularly hydrodynamic conditions-influenced the aut- and synecology of Ediacara organisms, as well as the morphology and assemblage composition of Ediacara fossils. Here, we describe the manner in which environmental processes mediated the development of taphofacies hosting Ediacara fossil assemblages. Using two of the most common Ediacara Member fossils, Arborea and Dickinsonia, as examples, we delineate criteria that can be used to distinguish between ecological, environmental and biostratinomic signals and reconstruct how interactions between these processes have distinctively shaped the Ediacara fossil record.
Problematic fossils are described from Late Ediacaran to Early Cambrian red sandstones of the Arumbera Sandstone, Grant Bluff, and Central Mount Stuart Formations in central Australia, within a new systematic classification of Vendobionta. Arumberia banksi has been one of the most problematic of Ediacaran fossils, at first considered a fossil and then a sedimentary or organo-sedimentary structure. Our re-examination of the type material and collection of new material reveals misconceptions about its topology: it was a recessive fossil on the bed top, protruding down from the counterpart overlying slab. The concave-up body was 3 mm thick and chambered above a diffuse lower surface, so not a sedimentary structure. Also re-evaluated is the discoid fossil Hallidaya brueri, here including “Skinnera brooksi’ as its upper surface. A new species (Noffkarkys storaaslii gen. et sp. nov.) is a multilobed frond with regular, fine, trapezoidal quilts. Three new records of Trepassia wardae, Dickinsonia costata, and Ernietta plateauensis are reported from the Arumbera and Grant Bluff Formations. Reevaluation of palaeomagnetic and biostratigraphic data suggest an hiatus of 26 million years at the Ediacaran–Cambrian boundary within the Arumbera Formation, but some of this missing time is filled by the Grant Bluff and Central Mount Stuart Formations.
The broad-scale environment plays a substantial role in shaping modern marine ecosystems, but the degree to which palaeocommunities were influenced by their environment is unclear. To investigate how broad-scale environment influenced the community ecology of early animal ecosystems we employed spatial point process analyses to examine the community structure of seven bedding-plane assemblages of late Ediacaran age (558–550 Ma), drawn from a range of environmental settings and global localities. The studied palaeocommunities exhibit marked differences in the response of their component taxa to sub-metre-scale habitat heterogeneities on the seafloor. Shallow-marine palaeocommunities were heavily influenced by local habitat heterogeneities, in contrast to their deep-water counterparts. Lower species richness in deep-water Ediacaran assemblages compared to shallow-water counterparts across the studied time-interval could have been driven by this environmental patchiness, because habitat heterogeneities correspond to higher diversity in modern marine environments. The presence of grazers and detritivores within shallow-water communities may have promoted local patchiness, potentially initiating a chain of increasing heterogeneity of benthic communities from shallow to deep-marine depositional environments. Our results provide quantitative support for the “Savannah” hypothesis for early animal diversification – whereby Ediacaran diversification was driven by patchiness in the local benthic environment.
Author Contributions
E. Mitchell conceived this paper and wrote the first draft. N. Bobkov, A. Kolesnikov, N. Sozonov and D. Grazhdankin collected the data for DS surface. N. Bobkov and N. Sozonov performed the analyses on DS surface. N. Bykova, S. Xiao, and D. Grazhdankin collected the data for WS, KH1 and KH2 surfaces and E. Mitchell performed the analyses. A. Dhungana and A. Liu collected the data for FUN4 and FUN5 surfaces and A. Dhungana performed the analyses. T. Mustill and D. Grazhdankin collected the data for KS and T. Mustill and E. Mitchell performed the analyses. I. Hogarth developed the software for preliminary KS surface analyses. E. Mitchell, N. Bobkov, N. Bykova, A. Dhungana, A. Kolesnikov, A. Liu, S. Xiao and D. Grazhdankin discussed the results and prepared the manuscript.
Rocks of Ediacaran age (~635–541 Ma) contain the oldest fossils of large, complex organisms and their behaviors. These fossils document developmental and ecological innovations, and suggest that extinctions helped to shape the trajectory of early animal evolution. Conventional methods divide Ediacaran macrofossil localities into taxonomically distinct clusters, which may represent evolutionary, environmental, or preservational variation. Here, we investigate these possibilities with network analysis of body and trace fossil occurrences. By partitioning multipartite networks of taxa, paleoenvironments, and geologic formations into community units, we distinguish between biostratigraphic zones and paleoenvironmentally restricted biotopes, and provide empirically robust and statistically significant evidence for a global, cosmopolitan assemblage unique to terminal Ediacaran strata. The assemblage is taxonomically depauperate but includes fossils of recognizable eumetazoans, which lived between two episodes of biotic turnover. These turnover events were the first major extinctions of complex life and paved the way for the Cambrian radiation of animals.
Attenborites janeae gen. et sp. nov., is a new enigmatic fossil from the Ediacara Member of the Rawnsley Quartzite, South Australia. Attenborites is a well-defined irregular oval to circular fossil preserved in negative hyporelief ranging in length from 4.5–24 mm. Preserved internal grooves and ridges, variable in number and running parallel to the long axis, typically converge towards one end of the specimen. This taxon is unlike any previously described both in terms of overall morphology and in terms of the irregular nature of the outer and inner morphology. While there are no direct morphological characters that suggest that this organism was pelagic, the nature of preservation suggests that a pelagic lifestyle should at least be considered. However, it is not possible to say whether this animal was likely a ctenophore, cnidarian or a pelagic organism of unknown affinity.
A long-running debate over the affinities of the Neoproterozoic 'Ediacara biota' has led to contrasting interpretations of Ediacaran ecosystem complexity. A 'simple' model assumes that most, if not all, Ediacaran organisms shared similar basic ecologies. A contrasting 'complex' model suggests that the Ediacara biota more likely represent organisms from a variety of different positions on the eukaryotic tree and thus occupied a wide range of different ecologies. We perform a quantitative test of Ediacaran ecosystem complexity using rank abundance distributions (RADs). We show that the Ediacara biota formed complex-type communities throughout much of their stratigraphic range and thus likely comprised species that competed for different resources and/or created niche for others ('ecosystem engineers'). One possible explanation for this pattern rests in the recent inference of multiple metazoan-style feeding modes among the Ediacara biota; in this scenario, different Ediacaran groups/clades were engaged in different methods of nutrient collection and thus competed for different resources. This result illustrates that the Ediacara biota may not have been as bizarre as it is sometimes suggested, and provides an ecological link with the animal-dominated benthic ecosystems of the Palaeozoic era.
Rangeomorphs dominate the Ediacaran Avalonian macrofossil assemblages of Charnwood Forest, UK (~562 Ma). 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 or absence of characters of Primocandelabrum boyntoni, P. aethelfalaedia, and P. aelfwynnia on the Bed ‘B’. 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) species of Primocandelabrum 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 density areas of Primocandelabrum. 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.
Ediacaran fossil communities consist of the oldest macroscopic eukaryotic organisms. Increased size (height) is hypothesized to be driven by competition for water-column resources, leading to vertical/epifaunal tiering and morphological innovations such as stems. Using spatial analyses, we find no correlation between tiering and resource competition, and that stemmed organisms are not tiered. Instead, we find height is correlated to greater offspring dispersal, demonstrating the importance of colonization potential over resource competition.
Exceptionally preserved fossils are the product of complex interplays of biological and geological processes including burial, autolysis and microbial decay, authigenic mineralization, diagenesis, metamorphism, and finally weathering and exhumation. Determining which tissues are preserved and how biases affect their preservation pathways is important for interpreting fossils in phylogenetic, ecological, and evolutionary frameworks. Although laboratory decay experiments reveal important aspects of fossilization, applying the results directly to the interpretation of exceptionally preserved fossils may overlook the impact of other key processes that remove or preserve morphological information. Investigations of fossils preserving non-biomineralized tissues suggest that certain structures that are decay resistant (e.g., the notochord) are rarely preserved (even where carbonaceous components survive), and decay-prone structures (e.g., nervous systems) can fossilize, albeit rarely. As we review here, decay resistance is an imperfect indicator of fossilization potential, and a suite of biological and geological processes account for the features preserved in exceptional fossils.
Background
The fossil record of Plecoptera (stoneflies) is considered relatively complete, with stem-groups of each of the three major lineages, viz. Antarctoperlaria, Euholognatha and Systellognatha (and some of their families) represented in the Mesozoic. However, the family Pteronarcyidae (the salmonflies; including two genera, Pteronarcys and Pteronarcella) has no fossil record to date, and the family has been suggested to have diverged recently.
Results
In this paper, we report on a set of specimens belonging to a new fossil species of stonefly, discovered from the Middle Jurassic Daohugou locality (China). Our comparative analysis of wing venation and body characters demonstrates that the new species belongs to the Pteronarcyidae, and is more closely related to Pteronarcys than to Pteronarcella. However, it differs from all known species of the former genus. It is therefore assigned to a new genus and named Pteroliriope sinitshenkovaegen. et sp. nov. under the traditional nomenclatural procedure. The cladotypic nomenclatural procedure is also employed, with the resulting combination Pteroliriope nec Pteronarcys sinitshenkovaesp. nov.
Conclusions
The first discovery of a fossil member of the Pteronarcyidae demonstrates that the corresponding lineage is not a very recent offshoot but was already present ca. 165 million years ago. This discovery concurs with the view that divergence of most stonefly families took place very early, probably in the Triassic, or even in the Permian. This contribution demonstrates the need for (re-)investigations of the systematics of fossil stoneflies to refine divergence date estimates for Plecoptera lineages.
The Mistaken Point and Trepassey formations (Conception and St. John's groups, respectively) comprise a terminal Neoproterozoic, deep-marine succession of fine-grained turbidites and volcanogenic deposits that are part of the Avalonian Terrane. Debris-flow beds, slumped units, the low dispersion of turbidity-current paleoflow directions, and the absence of wave-generated structures together indicate that the sediment was deposited on a deep-water, southeast-facing slope. Channels were not present in the study area. The upward increase in the abundance of slump structures suggests that these units represent toe-of-slope and mid-slope environments, respectively. These units prograded over basin-floor deposits of the Drook and Briscal formations, which have (axial) paleocurrent directions that are orthogonal to the inferred downslope flow that characterized the overlying deposits. Within the Mistaken Point and Trepassey formations, a diverse assemblage of soft-bodied, non-phototrophic Ediacaran organisms is preserved beneath volcanic ash layers on more than one hundred surfaces. Individual fossiliferous surfaces can be correlated up to several kilometres. The felling orientations of frondose fossils indicate that contour currents, as well as up- and downslope currents of tidal and (or) wind-forced origin, influenced the sea floor in the intervals between event beds when the organisms lived. The contour currents may have been responsible for sustaining the organisms in this deep-water setting. The current-produced inclination of the frondose organisms at the time of ash deposition allowed their preservation by preventing the accumulation of ash beneath them.
Dickinsonia is a Neoproterozoic, Ediacaran fossil, variously considered a polychaete, turbellarian or annelid worm, jellyfish, polyp, xenophyophoran protist, lichen or mushroom. Its preservation as unskeletonized impressions in quartz sandstones has been attributed to a Neoproterozoic regime of aerobic decay less effective than today, microbial pyritization much nearer the surface than today, or agglutinate-mineralization as in xenophyophorans. However, the great variation in thickness independent of width or length of South Australian Dickinsonia is evidence of decay like the wilting of a fossil leaf, lichen or mushroom, but unlike clotting and distortion during decay, wilting or osmotic shrinkage of modern and fossil worms and jellyfish. Decayed specimens of Dickinsonia arrayed in arcs have been interpreted as slime trails or tumble tracks, but can also be interpreted as rhizinous bases of decayed crustose lichens or mushrooms arranged in fairy rings. Dickinsonia is interpreted to be sessile because adjacent specimens show reaction rims indicative of competitive interaction, and because no overlapping well-preserved specimens have ever been found. Folded and bent Dickinsonia reveal firm attachment and limited flexibility, but no brittle deformation indicative of pyritic, sideritic or calcitic 'death masks' or xenophyophoran agglutinate skeletons. Dickinsonia was resistant to compaction by overburden, like fossil lichens such as Spongiophyton and Thucomyces, and more compaction-resistant than fossil logs, jellyfish or worms. Dickinsonia also shows indeterminate growth like lichens, fungi, plants, xenophyophorans and colonial animals. Growth, decay and burial compaction of Dickinsonia were more like those of plants, lichens and fungi, than of worms, jellyfishes or anemones.
Ediacaran fossils are taphonomically similar to impressions of fossil plants common in quartz sandstones, and the relief of the fossils suggests that they were as resistant to compaction during burial as some kinds of Pennsylvanian tree trunks. Fossils of jellyfish are known from siderite nodules and fine-grained limestone, and even in these compaction-resistant media were more compressed during burial than were the Vendobionta. Vendobionta were constructed of materials that responded to burial compaction in a way intermediate between conifer and lycopsid logs. This comparative taphonomic study thus falsifies the concept of Vendobionta as thin soft-bodied creatures such as worms and jellyfish.
Lichens, with their structural chitin, present a viable model for the observed preservational style of Vendobionta, as well as for a variety of other features that now can be reassessed from this new perspective. The diversity of Ediacaran body plans can be compared with the variety of form in fungi, algae, and lichens. The large size (ca. 1 m) of some Ediacaran fossils is reasonable for sessile photosynthetic symbioses, and much bigger than associated burrows of metazoans not preserved. Microscopic tubular structures and darkly pigmented cells in permineralized late Precambrian fossils from Namibia and China are also compatible with interpretation as lichens. The presumed marine habitat of Ediacaran fossils is not crucial to interpretation as lichens, because fungi and lichens live in the sea as well as on land.
The Ediacaran Period takes its name from the fossils of the Ediacara biota, which represent the first appearance of large and diverse assemblages of organisms in the fossil record. Although the global record of these distinctive body fossils is now well known, a previously unrecognized megascopic organic record of textured organic surfaces (TOS) occurs in the Ediacara biota. However, TOS is also a feature over a wider range of paleoenvironmental settings, where body fossils are unknown, in Ediacaran siliciclastic successions that have been studied in Australia, Namibia and western North America.Paleoecological analysis of successive bedding planes of strata from the late Ediacaran Rawnsley Quartzite in the Flinders Ranges of South Australia, reveals that TOS represent the most common organic features in bedding-surface assemblages of the Ediacara biota. The TOS consist of preserved, patterned assemblages of textured organic mats, fibers and simple tubular body fossils. Complex Ediacara body fossils while striking for their distinctive body plans, and dominating some of the beds, are relatively minor components of combined overall surface area. Many elements of TOS have previously been miss-diagnosed as trace fossils, which are in practice limited to two or at most three morphotypes that indicate the presence of Bilateria. Although TOS represent a simpler grade of organismic construction than discrete and more complex Ediacara body fossils, they were preserved in a similar manner. Marked variability in all components of the biota between successive surfaces suggests that Ediacara ecologies fluctuated at short intervals despite an apparently consistent sedimentary regime.
The Ediacara biota of the late Neoproterozoic is justly famous as a biological puzzle. Studies of Ediacaran biology have commonly used analogy with living organisms as a cipher for the decoding of biological affinity, and consequently the life mode and habit. Here, we discuss the problems of using such analogous reasoning and put forward our alternative approach, that of using Morphospace Analysis for the study of growth, form and phylogeny. This tool, we suggest, has the potential to be used for testing the unity of an evolutionary clade, such as 'rangeomorphs' and 'dickinsoniomorphs'. Preliminary data from the members of the Ediacara biota do indeed show such a unity within our preliminary morphospace model (all k values are low). This method reveals no clear relationships, between these forms and more recent biological groups such as the sea pens or the Foraminifera.
Study of historical and fresh collections from the Longmyndian Supergroup sheds new light on Ediacaran microbial communities and taphonomy. First reported by Salter in 1856, and noted by Darwin in the Origin of Species in 1859, a range of macroscopic bedding plane markings are already well known from the Longmyndian supergroup. Here we report filamentous and sphaeromorph microfossils, variously preserved as carbonaceous films, by aluminosilicate permineralization and as bedding plane impressions. This supports a long-suspected link between wrinkle markings and microbes, and draws further attention to our hypothesis for a taphonomic bias towards high-quality soft tissue preservation in the Ediacaran Period.
Charnia from the Ediacara biota is here examined in terms of its growth and development. The Ediacara biota comes from the critical period of evolution just before the Cambrian Explosion and is key to our understanding of the origin of animal life. We show that Charnia cannot be related to the modern cnidarian group the sea pens (Pennatulacea) with which it has for so long been compared, as generative zones cannot be homologized between these forms.
Epifaunal tiering, the subdivision of vertical space within a community, is a fundamental attribute of Phanerozoic suspension-feeding communities. This paper documents tiering, including the presence of meter-tall organisms, in Neoproterozoic Ediacaran communities. Ediacaran tiering was studied from three exceptionally preserved deep-water communities at Mistaken Point, Newfoundland, which contain in situ census populations of hundreds to thousands of organisms. Tiering consists of overlapping populations of dominant organisms and is characterized by gradational, rather than abrupt, tier boundaries. At least three tiers are apparent: a lower level 0–8 cm above the seafloor, an intermediate level between 8–22 cm above the seafloor, and an upper level that extends as high as 120 cm. Tier boundaries are relatively consistent between communities, but the constituent organisms in each level are variable, suggesting that some Ediacaran taxa could fill different tiers interchangeably. Development of a tiered epifaunal structure is consistent with suspension feeding or absorbing dissolved nutrients directly from seawater. Despite the common occurrence of tall organisms, all communities share a similar population structure in which biomass is concentrated in the basal 10 cm above the seafloor. Comparison with shallow-water Ediacaran localities suggests that the observed tiering structure is typical of Ediacaran communities. Ediacaran tierers also show the fundamental subdivision between organisms and/or colonies that fed along their entire length and those that developed a specialized feeding apparatus, implying that the features of Phanerozoic tiered skeletal ecosystems were first initiated in soft-bodied communities in the late Neoproterozoic.
Ediacara-type fossils represent a group of soft-bodied organisms, mainly known from imprints in Proterozoic coarse-grained siliciclastic sedimentary rocks. Circular compressions of Beltanelliformis brunsae and remains related to Ediacara-type fossils, such as Cucullus fraudulentus, and Mucuplagum primitivum are reported here in an organic mode of preservation from the Neoproterozoic Doushantuo and Liulaobei Formations of China. They can be interpreted as prokaryotic colonies. A charnid fossil with circular attachment disc and stalk, but torn-off frond, is documented in a three-dimensional and partly organic mode of preservation from the Neoproterozoic Ust-Pinega Formation (White Sea coast, Russia). According to their morphology and structure, the Charniidae are not regarded by us as pennatulaceans. Modern Myxobacteria illustrate that macroscopic size, complexity, and even compartmentalization can also be developed by prokaryotic colonies. Part of the Ediacara-type fossils may therefore represent prokaryotic colonies or symbiotic organisms involving prokaryotes. Finally, direct evidence indicates that biofilms with associated prokaryotic sheaths, preserved in both organic and pyritic fashion, form the wrinkled surfaces (``elephant skin'') that were preferentially colonized by Ediacara-type fossils. This finding supports previous interpretations, based on comparative morphological and sedimentological approaches, that ancient wrinkle structures were microbial mats.
The Ediacaran Global Stratotype Section and Point has now been defined at the base of the Nuccaleena Formation in the Flinders Ranges National Park, South Australia. This GSSP marks the end of a major glacial epoch. In the absence of definitive biozones marking the base of the Ediacaran, the utility of this "cap carbonate' for correlation will depend on the verification of a global fingerprint based on the stratigraphic pattern, stable isotope trends and magnetostratigraphy. Even though the fossil record for the Ediacaran System is relatively sparse, it clearly characterizes this period on all continents except Antarctica. The task facing the Ediacaran Subcommission of the ICS is the correlation of the GSSP horizon around the globe and to foster biostratigraphic subdivision of the Ediacaran System. In the Flinders Ranges National Park, the well exposed, structurally uncomplicated, 3.5-km- thick Ediacaran succession is capped with a 2-km-thick, fossiliferous Early Cambrian succession (Fig. 1). The Flinders Ranges Ediacaran succession preserves an apparently primary palaeomagnetic record, distinctive stratigraphic events, and fossils of the Ediacara biota at three well-separated levels. • The palaeomagnetic record of the Elatina Formation, immediately below the Ediacaran GSSP, indicates that the Adelaide geosyncline experienced a protracted interval of glaciogenic sedimentation when the region was straddling the palaeomagnetic equator (Schmidt and Williams, 1995; Sohl, et al., 1999). New approaches to palaeomagnetic analysis promise a magnetostratigraphy for the Ediacaran succession in the Flinders Ranges.
We report new high-resolution laser scanning of the type material for the earliest, complex Ediacaran genera Charnia, Bradgatia, Charniodiscus and Ivesheadia from Charnwood, UK, and compare these with Beothukis mistakensis gen. et sp. nov. and the recently described taxa Charnia wardi, Charnia antecedens and Fractofusus spp. from broadly coeval strata in Newfoundland. We use the laser and other techniques to map the similarities and differences in morphology between these Ediacaran rangeomorphs. Key features are suggested to include the number of growth axes, the number and placement of growth tips, the presence of radiating or subparallel axes for the first- and higher-order branches, the extent of displayed or undisplayed leaf-like 'rangeomorph' architecture, and the extent of furling of the margins of these leaf-like elements. These features are then used to propose suggested homologies between these taxa, leading to a preliminary phylogenetic hypothesis for the evolution of the Avalonian Ediacara biota.
We present two alternative sets of global palaeogeographical reconstructions for the time interval 615-530 Ma using competing high and low-latitude palaeomagnetic data subsets for Laurentia in conjunction with geological data. Both models demonstrate a genetic relationship between the collisional events associated with the assembly of Gondwana and the extensional events related to the opening of the Tornquist Sea, the eastern Iapetus Ocean (600-550 Ma), and the western Iapetus Ocean (after 550 Ma), forming a three-arm rift between Laurentia, Baltica, and Gondwana. The extensional events are probably plume-related, which is indicated in the reconstructions by voluminous mafic magmatism along the margins of palaeo-continents. The low-latitude model requires a single plume event, whereas the high-latitude model needs at least three discrete plumes. Coeval collisions of large continental masses during the assembly of Gondwana, as well as slab pull from subduction zones associated with those collisions, could have caused upper plate extension resulting in the rifted arm that developed into the eastern Iapetus Ocean and Tomquist Sea but retarded development of the western Iapetus Ocean. As a result, the eastern Iapetus Ocean and the Tornquist Sea opened before the western Iapetus Ocean.
New specimens of Precambrian fossils have been found in the Charnian of Leicestershire, at two fossil localities previously described by Boynton and Ford (1995).
Microbial biofilms in marine environments are dynamic systems exhibiting spatial and temporal heterogeneity. Their species composition may range from low to high diversity and change over time. Within the biofilm, populations of individual species are clustered together in microcolonies or bundles of filaments and can be organized into distinct layers. These communities are faced with fluctuating environmental conditions that may change diurnally, tidally, seasonally, and episodically. These changes may be reflected in the overall structure of the biofilm, especially in cases where sedimentary deposits result. In hypersaline lagoons and sabkhas this results in laminated sediments. In carbonate rich waters, where sediment trapping and binding, as well as lithification occur, the end result of these processes is a stromatolite. In this study, two different marine microbial mat systems were compared and contrasted using light and transmission electron microscopy: a flat laminated microbial mat from Laguna Figueroa, Baja California, Mexico, and lithified marine stromatolites from Highborne Cay, Bahamas. This approach, including preliminary image analysis has revealed several unique features.
Siliciclastic depositional systems like sandy tidal flats or shelf environments are predominantly governed by erosion, deposition and deformation (Pettijohn & Potter 1964). But also microbiological parameters influence the sedimentary dynamics, because the sediments are widely colonized by a variety of epibenthic microorganisms like cyanobacteria. Epibenthic microbes attach to the surfaces of depositional grains by adhesive mucous secretions that are known as ‘extracellular polymeric substances (EPS)’ (Decho 2000 and literature therein). Such organic coatings around grains are termed ‘biofilms’ (see Charaklis and Wilderer 1989, Decho 2000; Stolz 2000; also Paterson and Black 2000). At sites of favorable ecological conditions, biofilms continue to grow to form thick and significant organic layers that are known as ‘microbial mats’ (compare Krumbein 1983, also Gerdes & Krumbein 1987, Cohen et al. 1984, or Cohen & Rosenberg 1989, Neu 1994, Stolz 2000, Noffke in press b). Microbial mats can cover large areas of a sedimentary surface. Within shallow-marine depositional environments, the sedimentary dynamics controlls abundance and distribution of epibenthic microorganisms, and also the formation of biofilms and mats (Noffke et al. 200la, b, Noffke et al. 2002).
The Ediacaran fauna of Charnwood Forest is reviewed and several new forms are formally named and described, including a complex colonial form Bradgatia linfordensis and three new medusoid genera and species, Ivesia lobata, Shepshedia palmata and Blackbrookia oaksi. A new medusoid species Cyclomedusa cliffi is described. The frondose fossil Charnia grandis is recorded from Charnwood Forest for the first time. Three trails are also noted. -Authors
The strange biota of Neoproterozoic sea bottoms become more understandable if we assume that otherwise soft sediments were sealed by firm and erosion-resistant biomats. This allowed 'mat encrusters' (vendobionts; trilobozoan and other sponges) to get attached to sandy bottoms, and molluscan 'mat scratchers' to scrape off an algal film, as if they were living on rocks. Minute conical 'mat stickers' (Cloudina) probably required a sticky substrate to become stabilized in upright position. Horizontal burrows are interpreted as the works of worm-like 'undermat miners.' Only the latter lifestyle appears to go back to the Mesoproterozoic; the others emerged in Vendian times and virtually disappeared when matgrounds became restricted to hostile environments in the wake of the Cambrian ecological revolution.
A variety of sedimentary structures and patterns in Proterozoic siliciclastic sedimentary rocks cannot be explained by known inorganic processes. In particular, certain bed-surface textures, and domed and disrupted sand lamination, are demonstrably the mechanical products of microbially bound sediment and microbial mats. In all but the most wave and current active marine environments of the terminal Proterozoic, the absence of effective grazing and burrowing allowed mat-communities of cyanobacteria to colonize sedimentary surfaces. The resultant microbial mats inhibited sediment erosion, formed partings when buried between sand beds, and restricted vertical migration of pore fluid and gas in both exposed and subaqueous environments. Distinctive 'petee' laminations, known from modern mat-bound, tidal-flat sediments, are recorded for the first time in the rock record from the terminal Proterozoic Rawnsley Quartzite of South Australia. The preservation of external molds of soft-bodied Ediacaran organisms is interpreted as a function of the early diagenesis of a sole veneer. A form of 'death mask' resulted from bacterial precipitation of iron minerals in the sand that smothered decaying microbial mats and megascopic benthic organisms. The appearance of three-dimensional trace fossils in Early Cambrian strata signaled a behavioral revolution; the evolution of efficient grazing reduced the development of benthic mat communities in all but the most extreme environments, while bioturbation disrupted buried mats and closed a taphonomic window of preservation for soft-bodied organisms.
Up to the 1950s, the Precambrian was regarded as unrewardingly unfossiliferous, records of fossils being isolated, few in number and dubious. The change came with the discovery by Reg Sprigg of body fossils in latest Proterozoic sediments in South Australia. Although there had been descriptions of isolated fossils (now recognised as Ediacaran) from rocks of this age in the nineteenth century and at the start of the twentieth century, in Newfoundland and Namibia, respectively, the Ediacara finds stimulated researches and now, at the start of the twenty-first century, diversified fossil assemblages are known, all over the world, from the period 600–543 Ma, known formerly as the Vendian and now officially as the Ediacaran. In this account, a brief description of the history of these finds is given, followed by descriptions of the most important provinces [South Australia, Leicestershire, Namibia, Russia (Podolia, the White Sea Coast, Urals and Siberia), Newfoundland (Avalon Peninsula) and Northwest Canada]: then of 27 other known occurrences of this dominantly soft-bodied and perplexing fauna(?)–it seems certain that some, at least of the fossils, are animal fossils, although some, even the greater part, could be a unique form of life, not animals or plants (“Vendobionta”). These descriptions, derived in the course of a literature search lasting over a year, are followed by discussions of important special aspects: trace fossils; geochronology and correlation; geotectonics; glaciation (the “Snowball Earth” concept applied to the Varangian/Laplandian/Marinoan glaciation, which ushered in this last subdivision of the Proterozoic); the evidence for Ediacaran and other life forms existing in the Proterozoic prior to its last, Ediacaran, chronological subdivison; the Vendozoa concept. The last section consists of short summary of conclusions. This text essentially constitutes an objective record of what has been published to 2005 on the Ediacaran System.
Hapsidophyllas flexibilis new genus and species and Frondophyllas grandis new genus and species are rare Ediacaran (ca. 565 Ma) rangeomorph forms, herein termed "hapsidophyllids," which are endemic to Mistaken Point, Newfoundland, Canada. These two taxa are highly disparate in overall morphology, the former being a low-level, multibranched "network of leaves" and the latter a meter-long frond. Despite their dissimilarity in gross morphology, the two genera share a unique flexible, leaflet-type structure with a fine-scale branching structure that resembles that of charnid rangeomorphs. These leaflet structures are unknown from any other rangeomorph or Ediacaran group, and are herein termed "hapsidophyllid leaflets." Hapsidophyllids grew by an iteration or structural units, with small rangeomorph modules making up the larger hapsidophyllid leaflets, which in turn composed the larger hapsidophyllid organism. The presence of hapsidophyllid leaflets in both Hapsidophyllas and Frondophyllas Suggest the two genera were related taxonomically, with their very different gross morphologies reflecting ecological adaptations to exploit different suspension-feeding tiers.
Pectinifrons abyssalis new genus and species is an early Ediacaran (ca. 565 Ma) rangeomorph from the Avalon Peninsula of Newfoundland. It is known from more than 200 specimens from the Mistaken Point and Trepassey formations, and is typically preserved as a comb-shaped ridge on the top of mudstone beds beneath volcanic ashfall tuffs. Morphologic and taphonomic features suggest that the living organism consisted of two parallel series of soft rangeomorph fronds, alternately branching in an opposite arrangement from an elongate, tubular pedicle rod. The pedicle rod and the struts that represent the central stalks of the fronds were originally composed of resistant material that did not decompose until after lithification of the overlying ash bed. The fronds themselves were originally composed of a soft, non-resistant material that readily degraded, resulting in their extremely rare preservation as impressions on the bedding surface. Biometric analysis implies that Pectinifrons grew primarily by strut/frond addition, with later inflation of these elements. Pectinifrons is one of the first rangeomorph taxa to display evidence of possible age cohorts comparable to those observed in modern macrobenthic organisms.
The occurrence of any organism in those ancient sediments which have been so often called Azoic is of sufficient interest for an account of it to be laid before the Society. We have hitherto been acquainted with but one genus—and that doubtfully an animal or a plant—in the oldest Cambrian schists of Ireland. No fossils from rocks of this age have been recorded from England except the forms which I now describe, and of which a brief notice was sent to the last meeting of the British Association. They are a new Sea-weed, or Zoophyte, traces of marine worms, and a Crustacean of the Trilobite group.
When, a few years back, I crossed the Longmynd with Prof. Ramsay and Mr. Aveline, the unaltered and flat-bedded sandstones which abound on the eastern side, and which are quite unaffected by cleavage, appeared most promising for fossil remains, if any organisms existed at the time when these rocks were deposited. Some of these beds were ripple-marked, and the sandstones and flaggy beds of greenish-grey stone were evidently not deposits from very deep water. I hoped, therefore, that at least Oldhamia or Fucoids might be found in them, if not more highly organized fossils; and in the summer of the past year, I was able to devote three or four weeks to the search.
The Ediacaran frond Charnia, known mainly from fragmentary leaf-like fronds from around the world, is represented by completely preserved specimens with holdfasts in the Mistaken Point biota of Newfoundland. Previous reconstructions of Charnia from two-dimensional impressions were significantly oversimplified, resulting in three-dimensional reconstructions which highlighted a sheet-like morphology. Overlapping relationships and internal structures are rarely (if ever) preserved, and only through detailed photography together with both landmark and traditional morphometric analyses of numerous complete Charnia specimens can the preservational biases be removed. Charnia is reinterpreted here as having a series of individual overlapping primary branches attached to an internal central stalk, and with individual branches constrained by an internal, organic skeleton and/or attachments between adjacent branches. Three species, C. masoni Ford 1958, C. wardi Narbonne & Gehling 2003, and C. antecedens sp. nov. can be distinguished on the basis of length/width ratios and the degree of attachment of adjacent branches. Morphological, taphonomical, and ecological studies at Mistaken Point imply that Charnia was a sessile, epibenthic frond that fed from suspension in this deep-water volcaniclastic setting. Evolution of more rigorous connections between the primary branches allowed Charnia to migrate into more turbulent, shallower-water habitats by the late Ediacaran.
The non-availability of biomineralized skeletons and low levels of predation led Vendian evolution along strange avenues. The Ediacara-type Vendobionta appear to represent a kingdom, in which foliate shapes, large sizes and the necessary compartmentalization were achieved by quilting of the skin rather than by multicellularity. Psammocorallia, in contrast, are interpreted as coelenterates that constructed an internal sand skeleton. Both were immobile soft-bottom dwellers that had high population densities, and both became preserved by obrutional accidents; thus they render "fossil snap shots', in which the original distributional patterns, age structures and standing biomasses of populations are accurately recorded. -Author