Taphonomy and paleobiology

Abstract

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 biological 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 variations through time in preservational regimes (megabiases), caused by the evolution of new bodyplans and behavioral capabilities, and by broad-scale changes in climate, tectonics, and geochemistry 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, equalizing samples via rarefaction, inferences about preservation probability, isotaphonomic comparisons, taphonomic control taxa, and modeling of artificial fossil assemblages based on modern analogues. All of this work is yielding a more quantitative assessment of both the positive and negative 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.

Secondary Cartilage Revealed in a Non-Avian Dinosaur Embryo

“…It may be that additional mineralized SC nodules existed at this embryonic stage but were removed by some post-mortem process without leaving a trace of their former presence (e.g. see [28]). However, given the excellent microstructural preservation, and the absence of abrasion on the edges of the bones (where SC would be found if it were present), our biological interpretation is that the SCs of locations 1 and 2 had not yet arisen (Figure 1C,E), or had arisen but had not yet calcified.…”

Nonstochastic Variation of Species-Level Diversification Rates Within Angiosperms

“…The origination and extinction dates of a lineage observed in the fossil record (based on the oldest and youngest known fossil occurrences of the lineage) rarely if ever reflect the true temporal range of a taxon because the range is degraded by gaps in which the taxon has not been preserved. Preservation rates are heterogeneous among different groups of organisms and often are correlated with morphological and ecological attributes such as abundance, resistance to decay and physical degradation, and proximity in life to environments where they will be covered in accumulating sediments prior to decay (e.g., lakes, swamps, and deltas; Behrensmeyer et al 2000). Just as the empirical support for nodes within a phylogenetic hypothesis can be assessed using resampling metrics such as the bootstrap or jackknife, similar resampling approaches can be applied to fossil data of the temporal distribution of occurrences within clades to quantify preservation rates and compute error bars on observed dates of oldest occurrence (e.g., Strauss and Sadler 1989;Marshall 1994;Foote et al 1999a).…”

Measuring Past Biodiversity

“…The answer is so simple that it is commonly overlooked in studies of biases in the fossil record, which emphasize factors like outcrop area, taxonomic effort, and the poor preservation of fossils in older rocks (3,6,23). There are pitifully few modern, extensive monographic studies of tropical Cenozoic (much less Pliocene) corals, cheilostome bryozoans, bivalves, or gastropods because Europe and North America (the sources of almost all collections in the global database) had largely moved out of the tropics by Cenozoic time (24).…”

“…About 300,000 living species of marine macroinvertebrates have been described, but estimates that account for inadequate sampling range from ~0.5 to 5 million (5). Only onethird contain hard parts likely to be preserved as fossils (6). Furthermore, fossil species are often unnamed.…”