Copyright ( 2000, The Paleontological Society Taphonomy and paleobiology Anna K. Behrensmeyer, Susan M. Kidwell, and Robert A. Gastaldo Abstract.ÐTaphonomy 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 ®delity; that is, the degree to which different types of assemblages re¯ect the species composition and abundance of source faunas and ¯oras; 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 arti®cial 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. Anna K. Behrensmeyer. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, MRC 121, Washington, D.C. 20560. E-mail: [email protected] Susan M. Kidwell. Department of Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637. E-mail: [email protected] Robert A. Gastaldo. Department of Geology, Colby College, Waterville, Maine 04901-4799. E-mail: [email protected] Accepted: 30 June 2000 What is Taphonomy? characterize more generally as ``the study of The fossil record is rich in biological and processes of preservation and how they affect ecological information, but the quality of this information in the fossil record'' (Behrens- information is uneven and incomplete. The meyer and Kidwell 1985). Since the 1950s, the same might be said for many types of neo- analysis of postmortem bias in paleobiologic biological information, but in such cases, sam- data has been one of the prime motivations of pling biases are imposed by scientists and are the ®eld, but taphonomy has always been a explicable as part of a research design. With multi-tasking science (e.g., see historical re- fossils, natural processes have done the sam- views in Behrensmeyer and Kidwell 1985; Ca- pling and created the biases before research deÂe 1991), and this remains true today. States begins. Taphonomy seeks to understand these of preservation of biotic remains are not only processes so that data from the fossil record (1) indicators of how faithfully biological his- can be evaluated correctly and applied to pa- tory has been recorded (issues of paleobiolog- leobiological and paleoecological questions. ic data ®delity and resolution), but are also (2) Efremov (1940: p. 85) ®rst de®ned taphon- testaments to environmental conditions (the omy as ``the study of the transition (in all its aegis of ``taphofacies''), and (3) evidence of details) of animal remains from the biosphere important aspects of biological evolution into the lithosphere,'' naming a ®eld that we (skeletal and biochemical novelties, live/dead q 2000 The Paleontological Society. All rights reserved. 0094-8373/00/2604-0005/$1.00 104 ANNA K. BEHRENSMEYER ET AL. interactions and feedbacks), because organ- nipulative experiments, analyses of synoptic isms not only produce potential fossils but data sets, probabilistic models) and scienti®c also are highly effective recyclers of plant and disciplines (tools and expertise from biogeo- animal material. Strictly speaking, the logical chemistry, geomicrobiology, isotope geo- limits of taphonomy are de®ned by its focus chemistry, geochronology, ecology, biome- on processes and patterns of fossil preserva- chanics, archeozoology, anthropology, sedi- tion1, but in practice, taphonomy serves a mentology, sequence stratigraphy; see recent broader role in stimulating research on all reviews and syntheses in Wilson 1988a; Al- types of biases affecting paleontological infor- lison and Briggs 1991a; Donovan 1991; Gif- mation, including those introduced by collect- ford-Gonzalez 1991; Lyman 1994; Brett 1995; ing, publication, and curation methods on the Briggs 1995; Haglund and Sorg 1997; Claas- one hand, and stratigraphic incompleteness sen 1998; Martin 1999). on the other (see also Lyman 1994; Donovan Taphonomy still is strongly oriented to- and Paul 1998; Holland this volume). ward modern analogues as a means of iden- Taphonomy today is focused ®rst and fore- tifying and quantifying processes, but in- most on a geobiological understanding of the creasingly exploits the stratigraphic record earth, grounded on the postmortem process- for hypothesis testing. Reliance on the fossil es that recycle biological materials and affect record to ``bear its own witness'' is an abso- our abilityÐpositively and negativelyÐto lute necessity for some facies and taxa, but reconstruct past environments and biotas. constitutes a powerful independent method The classic ¯owchart of taphonomic transfor- even for environments and groups that are mations (Fig. 1) is now underpinned by a well represented in the Recent world. Re- much fuller and quantitative understanding gardless of subject, however, most taphono- of interim states and pathways of fossiliza- mists remain determinedly empirical in ap- tion, owing to an explosion of interest in the proach, dedicated to assembling baseline in- ®eld since the early 1980s. Some of the most formation on taphonomic patterns and pro- notable advances have been in (1) microbial, cesses. Such work usually targets individual biogeochemical, and larger-scale controls on fossil assemblages or modern analogues for the preservation of different tissue types; (2) particular groups of organisms (protists to processes that concentrate biological re- vertebrates) and types of environments (gla- mains; (3) the spatio-temporal resolution and cial to abyssal plain). This fact-gathering fo- ecological ®delity of species assemblages; cus is typical of a relatively new ®eld of and (4) the outlines of ``megabiases'' (large- study, but a theoretical component also is be- scale patterns in the quality of the fossil rec- ginning to develop, with proposals for gen- ord that affect paleobiologic analysis at pro- eral models for organic preservation (e.g., Ly- vincial to global levels and at timescales usu- man 1994; Kowalewski 1997). There have ally exceeding ten million years). These ad- been a number of forays into the realm of vances are highlighted in this review because taphonomic theory by paleobiologists seek- of their impact on paleobiologic analysis and ing to distinguish sampling biases from bio- their promise as research themes in the com- logical patterns. These include attempts to ac- ing decades. Such advances re¯ect an in- count for preservational biases using as- creasingly ecumenical approach in terms of sumptions of random preservation and ``hol- scienti®c methods (®eld measurements, ma- low curve'' models for original taxonomic abundance as well as models that test the ef- fects of incomplete fossilization, stratigraphic 1 It often falls to Taphonomy to answer the most basic of incompleteness, nonrandom distributions of paleontological questions, ``What is a fossil?'' Material de®nitions concerning degree of mineralization and cri- facies and hiatuses, and blurring of genera- teria based on age considerations are problematic for tions by time-averaging on our ability to eval- Holocene to sub-Recent organic remains. Hence, we pre- uate phylogenies, rates of evolution, and tem- fer a more ¯exible de®nition: ``A fossil is any nonliving, biologically generated trace or material that paleontol- po and mode of speciation (Marshall 1990, ogists study as part of the record of past life.'' 1994; Gilinsky and Bennington 1994; Foote TAPHONOMY AND PALEOBIOLOGY 105 FIGURE 1. The main pathways for organic remains from death to paleobiological inference. Each path is af- fected by taphonomic processes and circumstances that ®lter the information as it passes to the next stage. Taphonomy is the study of how biological, chemical, and physical processes operating between each stage preserve