Taphonomic processes in modern freshwater molluscan death assemblages: Implications for the freshwater fossil record

AbstractBiologic asymmetry is present in all bilaterally symmetric organisms as a result of normal developmental instability. However, fossilized organisms, which have undergone distortion due to burial, may have additional asymmetry as a result of taphonomic processes. To investigate this issue, we evaluated the magnitude of shape variation resulting from taphonomy on vertebrate bone using a novel application of fluctuating asymmetry. We quantified the amount of total variance attributed to asymmetry in a taphonomically distorted fossil taxon and compared it with that of three extant taxa. The fossil taxon had an average of 27% higher asymmetry than the extant taxa. In spite of the high amount of taphonomic input, the major axes of shape variation were not greatly altered by removal of the asymmetric component of shape variation. This presents the possibility that either underlying biologic trends drive the principal directions of shape change irrespective of asymmetric taphonomic distortion or that the symmetric taphonomic component is large enough that removing only the asymmetric component is inadequate to restore fossil shape. Our study is the first to present quantitative data on the relative magnitude of taphonomic shape change and presents a new method to further explore how taphonomic processes impact our interpretation of the fossil record.

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On the benefits of being redundant: low compositional fidelity of diatom death assemblages does not hamper the preservation of environmental gradients in shallow lakes

Paleobiology ◽

10.1017/pab.2014.10 ◽

2015 ◽

Vol 41 (1) ◽

pp. 154-173 ◽

Cited By ~ 9

Author(s):

Gabriela S. Hassan

Keyword(s):

Shallow Lakes ◽

Environmental Gradients ◽

Taxonomic Composition ◽

Community Response ◽

Data Sets ◽

Intrinsic Properties ◽

Structural Redundancy ◽

Data Set ◽

Death Assemblages ◽

Taphonomic Processes

AbstractComparisons between death assemblages and their source living communities are among the most common actualistic methods of evaluating the preservation of compositional and environmental information in fossil assemblages. Although live-dead studies have commonly focused on marine mollusks, the potential of diatoms to preserve ecological information in continental settings has been overlooked. Thus, little is known about the nature and magnitude of the taphonomic biases affecting live-dead agreement of diatom assemblages, despite their extensive application as modern and fossil bioindicators in paleoecological and paleoenvironmental reconstructions. In this study, I analyzed three live-dead data sets in order to evaluate the compositional and environmental fidelity exhibited by diatom death assemblages in shallow lakes. I find that diatom death assemblages (DAs) do differ significantly in their taxonomic composition from living assemblages (LAs), mainly as a consequence of (1) differences in the temporal resolution between time-averaged DAs and non-averaged LAs, and (2) differential preservation of diatom taxa related to the intrinsic properties of their valves. Despite compositional dissimilarities, DAs were able to capture the same environmental gradients as LAs, with high significance. This decoupling between live-dead agreement in community composition and community response to gradients can be related to the existence of at least two mutually exclusive subsets of species that significantly captured compositional dissimilarities based on the full set of the species in the three lakes. This functional redundancy implies that the between-sample relationships of living assemblages can be significantly preserved by DAs even if some taxa are removed by taphonomic processes. The preservation of environmental gradients thus does not require good preservation of all living taxa. Structural redundancy compensates for the loss of compositional fidelity caused by postmortem processes in the diatom data set.

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Procesos tafonómicos en una encrinita regional pensilvánica (Atokano), Sonora, México

Revista de Biología Tropical ◽

10.15517/rbt.v65i1-1.31676 ◽

2017 ◽

Vol 65 (1-1) ◽

pp. 147

Author(s):

Catalina Gómez-Espinosa ◽

Blanca Estela Buitrón-Sánchez

Keyword(s):

North America ◽

Debris Flow ◽

Fossil Record ◽

High Energy ◽

Marine Communities ◽

Storm Wave ◽

Energy Environment ◽

Taphonomic Processes

Taphonomic processes in a Pennsylvanian regional encrinite (Atokano), Sonora, Mexico. Crinoids have an extensive fossil record and were a major component in Paleozoic marine communities; encrinites are common crinoid accumulations where specimens are totally disarticulated from the Ordovician to the Jurassic. In Sonora, Mexico, the crinoid skeleton was altered during diagenesis and replaced by silica. The corrasion was high; the incrustation low and there is evidence of dissolution and compaction. This is a sedimentological type accumulation in a high energy environment of allochthonous organism transported in a debris flow, deposited below the storm wave base in an outer ramp. Our results can be correlated with regional encrinites prevalent in the Pennsylvanian cyclothems of North America. Rev. Biol. Trop. 65(Suppl. 1): S147-S159. Epub 2017 November 01.

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Taphonomic Signature and the Imprint of Taphonomic History: Discriminating Between Taphofacies of the Inner Continental Shelf and a Microtidal Inlet

The Paleontological Society Special Publications ◽

10.1017/s247526220000558x ◽

1990 ◽

Vol 5 ◽

pp. 370-390 ◽

Cited By ~ 10

Author(s):

George M. Staff ◽

Eric N. Powell

Keyword(s):

Continental Shelf ◽

Chemical Processes ◽

Paleoenvironmental Reconstruction ◽

Shell Material ◽

Wide Range ◽

Death Assemblages ◽

Taphonomic Analysis ◽

Inner Continental Shelf ◽

Taphonomic Processes

Although taphonomic processes alter or destroy much of the preservable portion of the original community, many of these processes also imprint valuable paleoecological information about the fauna and the environment of deposition which might be employed in paleoenvironmental reconstruction (Brett and Baird, 1986; Speyer and Brett, 1986, 1988). Accordingly, taphonomic analysis of modern and ancient death assemblages has received much attention recently (Powell et al., in press; Parsons et al., 1988; Kidwell and Behrensmeyer, 1988) and a new concept, that of the taphofacies, has been developed (e.g., Speyer, 1988). Taphofacies are based on distinct suites of taphonomic characteristics, taphonomic signatures, imprinted on the shell material and on its relationship to the sedimentary fabric by mixtures of physical, biological and chemical processes, which potentially are unique for a given environment. Ideally, if unique taphonomic signatures can be identified and the formative processes understood in a wide range of modern environments, this baseline can be employed to make more accurate reconstructions of equivalent paleoenvironments.

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Fidelity of variation in species composition and diversity partitioning by death assemblages: time-averaging transfers diversity from beta to alpha levels

Paleobiology ◽

10.1666/08024.1 ◽

2009 ◽

Vol 35 (1) ◽

pp. 94-118 ◽

Cited By ~ 52

Author(s):

Adam Tomašových ◽

Susan M. Kidwell

Keyword(s):

Species Composition ◽

Temporal Variation ◽

Temporal Resolution ◽

Beta Diversity ◽

Fossil Record ◽

Time Averaging ◽

Data Sets ◽

Diversity Partitioning ◽

Preservation Potential ◽

Death Assemblages

Despite extensive paleoecological analyses of spatial and temporal turnover in species composition, the fidelity with which time-averaged death assemblages capture variation in species composition and diversity partitioning of living communities remains unexplored. Do death assemblages vary in composition between sites to a lesser degree than do living assemblages, as would be predicted from time-averaging? And is the higher number of species observed in death relative to living assemblages reduced with increasing spatial scale? We quantify the preservation of spatial and temporal variation in species composition using 11 regional data sets based on samples of living molluscan communities and their co-occurring time-averaged death assemblages. (1) Compositional dissimilarities among living assemblages (LA) within data sets are significantly positively rank-correlated to dissimilarities among counterpart pairs of death assemblages (DA), demonstrating that pairwise dissimilarity within a study area has a good preservation potential in the fossil record. Dissimilarity indices that downplay the abundance of dominant species return the highest live-dead agreement of variation in species composition. (2) The average variation in species composition (average dissimilarity) is consistently smaller in DAs than in LAs (9 of 11 data sets). This damping of variation might arise from DAs generally having a larger sample size, but the reduction by ∼10–20% mostly persists even in size-standardized analyses (4 to 7 of 11 data sets, depending on metric). Beta diversity expressed by the number of compositionally distinct communities is also significantly reduced in death assemblages in size-standardized analyses (by ∼25%). This damping of variation and reduction in beta diversity is in accord with the loss of temporal resolution expected from time-averaging, without invoking taphonomic bias (from differential preservation or postmortem transportation) or sample-size effects. The loss of temporal resolution should directly reduce temporal variation, and assuming time-for-space substitution owing to random walk within one habitat and/or temporal habitat shifting, it also decreases spatial variation in species composition. (3) DAs are more diverse than LAs at the alpha scale, but the difference is reduced at gamma scales because partitioning of alpha and beta components differs significantly between LAs and DAs. This indicates that the effects of time-averaging are reduced with increasing spatial scale. Thus, overall, time-averaged molluscan DAs do capture variation among samples of the living assemblage, but they tend to damp the magnitude of variation, making them a conservative means of inferring change over time or variation among regions in species composition and diversity. Rates of temporal and spatial species turnover documented in the fossil record are thus expected to be depressed relative to the turnover rates that are predicted by models of community dynamics, which assume higher temporal resolution. Finally, the capture by DAs of underlying variation in the LA implies little variation in the net preservation potential of death assemblages across environments, despite the different taphonomic pathways suggested by taphofacies studies.

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A review of preservational variation of fossil inclusions in amber of different chemical groups

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s1755691017000391 ◽

2016 ◽

Vol 107 (2-3) ◽

pp. 203-211 ◽

Cited By ~ 4

Author(s):

Victoria E. McCoy ◽

Carmen Soriano ◽

Sarah E. Gabbott

Keyword(s):

Fossil Record ◽

Wide Spectrum ◽

Published Data ◽

Fossil Preservation ◽

A Site ◽

Chemical Groups ◽

The Impact ◽

The Relationship ◽

Taphonomic Processes

ABSTRACTFossils in amber are a particularly important and unique palaeobiological resource. Amber is best known for preserving exceptionally life-like fossils, including microscopic anatomical details, but this fidelity of preservation is an end-member of a wide spectrum of preservation quality. Many amber sites only preserve cuticle or hollow moulds, and most amber sites have no fossils at all. The taphonomic processes that control this range in preservation are essentially unknown. Here, we review the relationship between amber groups and fossil preservation, based on published data, to determine whether there is a correlation between resin type and aspects of preservation quality. We found that ambers of different chemistry demonstrated statistically significant differences in the preservational quality and the propensity of a site to contain fossils. This indicates that resin chemistry does influence preservational variation; however, there is also evidence that resin chemistry alone cannot explain all the variation. To effectively assess the impact of this (and other) variables on fossilisation in amber, and therefore biases in the amber fossil record, a more comprehensive sampling of bioinclusions in amber, coupled with rigorous taphonomic experimentation, is required.

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