Taphonomic Overprints on Phanerozoic Trends in Biodiversity: Lithification and Other Secular Megabiases

Abstract

AbstractTaphonomic biases introduce heterogeneity into the quality of the fossil record and can skew paleontologists’ perception of biodiversity. This paper reviews the temporal extent and consequences of major taphonomic biases, including lithification of sediments, skeletal replacement through silicification and phosphatization, concentration of skeletal hard-parts, and the exceptional preservation of soft-bodied faunas. The frequency of occurrence of particular biases, and their effects of fossil faunas is identified using occurrence-based datasets, such as the Paleobiology Database.Lithification of most Paleozoic and Mesozoic fossiliferous sediments has likely had a significant influence on perceptions of within-community diversity and paleoecological composition. The increased availability of unlithified sediments in rocks of late Mesozoic through Cenozoic age coincides with a two- to threefold increase in local diversity, a discrepancy that remains even after employing sampling-standardization techniques. Taxa that possess small body size and aragonitic skeletal mineralogy are preferentially lost or obscured following the cementation of host sediments. Additionally, morphological details are often obscured or not preserved in specimens obtained from lithified sediments, suggesting that taphonomic damage could hinder taxonomic practice and estimates of diversity at the global-scale. Silica replacement, which generally enhances diversity among groups composed of less stable skeletal composition, appears most frequently among Permian fossil assemblages. Phosphatic replacement, which plays a key role in the preservation of soft-bodied and small-shelly faunas, appears commonly in assemblages of Cambrian age. Konservat-lagerstätten, while providing a rich source of information on the rarely preserved soft-bodied biota, are infrequent in the fossil record, but perhaps are most notable in rocks of Cambrian age. Shell beds are well known as sources of tremendous diversity and although they are not easily defined these beds appear to increase in frequency in middle Paleozoic and Cenozoic age successions. Fossil molds, unlike previously mentioned biases, suggest lost diversity, and are most frequent in rocks of early Cambrian and early Mesozoic age.The non-random nature of the above biases raises concerns regarding the comparison of diversity or ecological complexity over the course of the Phanerozoic or between contemporaneous faunal groups. Furthermore, a number of the biases have tremendous potential to affect community-scale patterns, either degrading (e.g., lithification, aragonite dissolution) or enhancing (e.g., silicification, phosphatization) the relative quality of fossil data. A number of approaches can be undertaken to minimize these biases, including the selective filtering of datasets to remove taphonomically vulnerable groups or the use of taphonomic control taxa that indicate the appropriate preservation state of fossil assemblages.KeywordsFossil RecordAlpha DiversityFossil AssemblageTaphonomic ProcessGulf Coastal PlainThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.