Taphonomy and time-averaging of marine shelly faunas

Taphonomy plays diverse roles in paleobiology. These include assessing sample quality relevant to ecologic, biogeographic, and evolutionary questions, diagnosing the roles of various taphonomic agents, processes and circumstances in generating the sedimentary and fossil records, and reconstructing the dynamics of organic recycling over time as a part of Earth history. Major advances over the past 15 years have occurred in understanding (1) the controls on preservation, especially the ecology and biogeochemistry of soft-tissue preservation, and the dominance of bi- ological versus physical agents in the destruction of remains from all major taxonomic groups (plants, invertebrates, vertebrates); (2) scales of spatial and temporal resolution, particularly the relatively minor role of out-of-habitat transport contrasted with the major effects of time-averaging; (3) quantitative compositional fidelity; that is, the degree to which different types of assemblages reflect the species composition and abundance of source faunas and floras; and (4) large-scale var- iations through time in preservational regimes (megabiases), caused by the evolution of new bod- yplans and behavioral capabilities, and by broad-scale changes in climate, tectonics, and geochem- istry of Earth surface systems. Paleobiological questions regarding major trends in biodiversity, major extinctions and recoveries, timing of cladogenesis and rates of evolution, and the role of environmental forcing in evolution all entail issues appropriate for taphonomic analysis, and a wide range of strategies are being developed to minimize the impact of sample incompleteness and bias. These include taphonomically robust metrics of paleontologic patterns, gap analysis, equal- izing samples via rarefaction, inferences about preservation probability, isotaphonomic compari- sons, taphonomic control taxa, and modeling of artificial fossil assemblages based on modern an- alogues. All of this work is yielding a more quantitative assessment of both the positive and neg- ative aspects of paleobiological samples. Comparisons and syntheses of patterns across major groups and over a wider range of temporal and spatial scales present a challenging and exciting agenda for taphonomy in the coming decades.

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Taphonomy and paleobiology

Ichnology is the study of traces created in the substrate by living organisms. This is the first book to systematically cover basic concepts and applications in both paleobiology and sedimentology, bridging the gap between the two main facets of the field. It emphasizes the importance of understanding ecologic controls on benthic fauna distribution and the role of burrowing organisms in changing their environments. A detailed analysis of the ichnology of a range of depositional environments is presented using examples from the Precambrian to the recent, and the use of trace fossils in facies analysis and sequence stratigraphy is discussed. The potential for biogenic structures to provide valuable information and solve problems in a wide range of fields is also highlighted. An invaluable resource for researchers and graduate students in paleontology, sedimentology and sequence stratigraphy, this book will also be of interest to industry professionals working in petroleum geoscience.

Ichnology: Organism-Substrate Interactions in Space and Time

Palaeoecology and evolution of marine hard substrate communities

The stratigraphy of shell concentrations.

Different degrees of transport and reworking impart different physical characteristics to fossiliferous assemblages (= different taphonomic grades) and reflect different time scales of deposition and accumulation. Well-preserved fossil assemblages (= high taphonomic grade) generally reflect accumulation over short time spans; as taphonomic grade decreases, the time represented by the accumulation of the fossiliferous assemblage increases. The taphonomic grade of a fossil assemblage changes in one direction (high to low) with time, and provides a measure against which paleoecologists can evaluate other aspects of the fauna that may fluctuate through time. Beds of the same taphonomic grade reflect similar depositional histories. Characterizing faunas in terms of their taphonomic grade provides a means by which temporally and spatially disparate faunas may be compared.

https://www.jstor.org/stable/info/3514554

Taphonomic grades as a classification for fossiliferous assemblages and implications for paleoecology

Ecdysis in sea scorpions (Chelicerata: Eurypterida)

A comparison of ecdysial patterns between trilobites and other macrobenthic marine arthropods (crabs, shrimp, lobsters, horseshoe crabs) reveals differences that may have evolutionary consequences. Limulus and many malacostracans apparently have a signature ecdysial style; conversely, a range of moult configurations characterized trilobite ecdysis, and this variation is evident even within individual species. A canalised ecdysial habit may be safer or metabolically more efficient and therefore, summed over the history of the class, evolutionarily advantageous. Some trilobite clades show evolutionary trends toward morphologies that would have facilitated ecdysis (e.g. reduction in the number of thoracic segments, reduction in the number and prominence of spines), but co-adaptation or multiple-use effects complicate the evolutionary signal of ecdysial selection. Survivorship analysis supports a possible link between ecdysial habit and evolutionary success: genera with fewer thoracic segments (= easier ecyds...

Ecydsial efficiency and evolutionary efficacy among marine arthropods: implications for trilobite survivorship

http://www.cornellcollege.edu/geology/courses/Greenstein/Paleoecology/readings/Brandtetal-1995.pdf

Isotelus (Trilobita) "hunting burrow" from Upper Ordovician strata, Ohio

Rusophycus is an ichnogenus comprising shallow burrows generally attributed to trilobites and other arthropods. The paleoethological interpretation of these structures is not conclusively known; workers variously have attributed the ichnogenus to feeding, resting, hiding/escape, hunting or nesting behaviors. Rusophycus morphology varies from unornamented, bilobed forms to forms that preserve details of ventral anatomy of the trace maker. Rusophycus occurs as single or multiple impressions. Some examples of multiple-Rusophycus assemblages are clearly the result of the activity of a single animal (e.g., serially arranged impressions of the same size), but others represent the activity of several individuals. Associated traces representing multiple individuals are especially interesting, for they may give evidence of complex behavior, for example, interactions between the trace makers. Some of the multiple-trace assemblages show alignment (congruent anterior-posterior orientation of the individuals) suggesti...

Danita S. Brandt

Papers

Taphonomic grades as a classification for fossiliferous assemblages and implications for paleoecology

Ecdysis in sea scorpions (Chelicerata: Eurypterida)

Ecydsial efficiency and evolutionary efficacy among marine arthropods: implications for trilobite survivorship

Isotelus (Trilobita) "hunting burrow" from Upper Ordovician strata, Ohio

Multiple-Rusophycus (Arthropod Ichnofossil) Assemblages and Their Significance