Philip M. Novack-Gottshall

Effects of sampling standardization on estimates of Phanerozoic marine diversification.

Global diversity curves reflect more than just the number of taxa that have existed through time: they also mirror variation in the nature of the fossil record and the way the record is reported. These sampling effects are best quantified by assembling and analyzing large numbers of locality-specific biotic inventories. Here, we introduce a new database of this kind for the Phanerozoic fossil record of marine invertebrates. We apply four substantially distinct analytical methods that estimate taxonomic diversity by quantifying and correcting for variation through time in the number and nature of inventories. Variation introduced by the use of two dramatically different counting protocols also is explored. We present sampling-standardized diversity estimates for two long intervals that sum to 300 Myr (Middle Ordovician-Carboniferous; Late Jurassic-Paleogene). Our new curves differ considerably from traditional, synoptic curves. For example, some of them imply unexpectedly low late Cretaceous and early Tertiary diversity levels. However, such factors as the current emphasis in the database on North America and Europe still obscure our view of the global history of marine biodiversity. These limitations will be addressed as the database and methods are refined.

Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity

The maximum size of organisms has increased enormously since the initial appearance of life >3.5 billion years ago (Gya), but the pattern and timing of this size increase is poorly known. Consequently, controls underlying the size spectrum of the global biota have been difficult to evaluate. Our period-level compilation of the largest known fossil organisms demonstrates that maximum size increased by 16 orders of magnitude since life first appeared in the fossil record. The great majority of the increase is accounted for by 2 discrete steps of approximately equal magnitude: the first in the middle of the Paleoproterozoic Era (≈1.9 Gya) and the second during the late Neoproterozoic and early Paleozoic eras (0.6–0.45 Gya). Each size step required a major innovation in organismal complexity—first the eukaryotic cell and later eukaryotic multicellularity. These size steps coincide with, or slightly postdate, increases in the concentration of atmospheric oxygen, suggesting latent evolutionary potential was realized soon after environmental limitations were removed.

The multidimensionality of the niche reveals functional diversity changes in benthic marine biotas across geological time

Despite growing attention on the influence of functional diversity changes on ecosystem functioning, a palaeoecological perspective on the long-term dynamic of functional diversity, including mass extinction crises, is still lacking. Here, using a novel multidimensional functional framework and comprehensive null-models, we compare the functional structure of Cambrian, Silurian and modern benthic marine biotas. We demonstrate that, after controlling for increases in taxonomic diversity, functional richness increased incrementally between each time interval with benthic taxa filling progressively more functional space, combined with a significant functional dissimilarity between periods. The modern benthic biota functionally overlaps with fossil biotas but some modern taxa, especially large predators, have new trait combinations that may allow more functions to be performed. From a methodological perspective, these results illustrate the benefits of using multidimensional instead of lower dimensional functional frameworks when studying changes in functional diversity over space and time.

Scale-dependence of Cope's rule in body size evolution of Paleozoic brachiopods.

The average body size of brachiopods from a single habitat type increased gradually by more than two orders of magnitude during their initial Cambrian–Devonian radiation. This increase occurred nearly in parallel across all major brachiopod clades (classes and orders) and is consistent with Copes rule: the tendency for size to increase over geological time. The increase is not observed within small, constituent clades (represented here by families), which underwent random, unbiased size changes. This scale-dependence is caused by the preferential origination of new families possessing initially larger body sizes. However, this increased family body size does not confer advantages in terms of greater geological duration or genus richness over families possessing smaller body sizes. We suggest that the combination of size-biased origination of families and parallel size increases among major, more inclusive brachiopod clades from a single habitat type is best explained by long-term, secular environmental changes during the Paleozoic that provided opportunities for body size increases associated with major morphological evolution.

Using a theoretical ecospace to quantify the ecological diversity of Paleozoic and modern marine biotas

Abstract The process of evolution hinders our ability to make large-scale ecological comparisons—such as those encompassing marine biotas spanning the Phanerozoic—because the compared entities are taxonomically and morphologically dissimilar. One solution is to focus instead on life habits, which are repeatedly discovered by taxa because of convergence. Such an approach is applied to a comparison of the ecological diversity of Paleozoic (Cambrian–Devonian) and modern marine biotas from deep-subtidal, soft-substrate habitats. Ecological diversity (richness and disparity) is operationalized by using a standardized ecospace framework that can be applied equally to extant and extinct organisms and is logically independent of taxonomy. Because individual states in the framework are chosen a priori and not customized for particular taxa, the framework fulfills the requirements of a universal theoretical ecospace. Unique ecological life habits can be recognized as each discrete, n-dimensional combination of character states in the framework. Although the basic unit of analysis remains the organism, the framework can be applied to other entities—species, clades, or multispecies assemblages—for the study of comparative paleoecology and ecology. Because the framework is quantifiable, it is amenable to analytical techniques used for morphological disparity. Using these methods, I demonstrate that the composite Paleozoic biota is approximately as rich in life habits as the sampled modern biota, but that the life habits in the modern biota are significantly more disparate than those in the Paleozoic; these results are robust to taphonomic standardization. Despite broadly similar distributions of life habits revealed by multivariate ordination, the modern biota is composed of life habits that are significantly enriched, among others, in mobility, infaunality, carnivory, and exploitation of other organisms (or structures) for occupation of microhabitats.

Comparative geographic and environmental diversity dynamics of gastropods and bivalves during the Ordovician Radiation

Abstract Bivalves and gastropods, prominent members of the Modern Evolutionary Fauna, are traditionally noted for sharing remarkably similar global diversity trajectories and environmental distributions throughout the Phanerozoic. By comparing their fossil occurrences at several scales within a finely resolved geographic, environmental, and temporal framework, it is possible to evaluate whether such similarities are caused primarily by intrinsic macroevolutionary factors or extrinsic ecological factors. Using a database of 7779 global gastropod and bivalve genus occurrences, we investigate the geographical and environmental attributes of bivalves and gastropods during the Ordovician Period at scales ranging from global, to a comparison among five paleocontinents, to an intracontinental comparison of four regions within Laurentia. Although both classes shared statistically indistinguishable global diversity trajectories and broadly similar environmental distributions during the Ordovician, their environmental distributions differed in several significant features. Furthermore, the diversity trajectories and environmental distributions of these classes differed significantly among paleocontinents and among regions within Laurentia. Bivalves were consistently most diverse in deeper water, siliciclastic-rich settings in higher-latitude paleocontinents whereas gastropods were consistently most diverse in shallower, carbonate-rich settings in more-equatorial paleocontinents. Notably, these environmental differences were robust to changing physical parameters within paleocontinents, with each class consistently tracking its preferred environmental setting. These results suggest that environmental factors played significant, albeit distinct, roles in the Ordovician diversifications of gastropods and bivalves. However, their similar global diversity trajectories suggest that shared, intrinsic macroevolutionary attributes also may have played an important role in the evolution of these classes during the Ordovician Radiation.

Using Simple Body-Size Metrics to Estimate Fossil Body Volume: Empirical Validation Using Diverse Paleozoic Invertebrates

Abstract Body size is one of the most significant organismal characteristics because of its strong association with nearly all important ecological and physiological characteristics. While direct body mass measurement (or estimation from other size metrics) is not feasible with most extinct taxa, body volume is a measurable and general proxy for fossil size. This study explores the reliability of several metrics that can be used to estimate the body volume of Paleozoic invertebrates of various sizes, shapes, taxonomic affinities, and ecological habits. The ATD model, based on the product of lengths of the three major body axes (anteroposterior, transverse, and dorsoventral), is simple and widely applicable. Models specific to particular morphological and taxonomic groups are slightly more accurate than this ATD model, but the advantages are minor. The ATD model is consistent with previous studies demonstrating widespread shape allometry—that is, small taxa tend to have globose geometries while large ones tend to be conical, even within the same taxonomic group. The ATD model successfully predicts the volume of 10 validation samples that were excluded from development of the original model. Because the linear measurements used to estimate volume are easy to obtain from specimens in the field or from published work, estimates of body volume can be incorporated into paleontological analyses, even those spanning multiple phyla.

Comparative Taxonomic Richness and Abundance of Late Ordovician Gastropods and Bivalves in Mollusc-rich Strata of the Cincinnati Arch

Abstract Using a field analysis of Upper Ordovician mollusc-rich faunas of the Cincinnati Arch, this study tests whether the large-scale patterns of Ordovician gastropods and bivalves observed in a companion study are maintained at the finer scales of individual strata and localities, and when utilizing abundance data in addition to taxonomic richness. Non-metric multidimensional scaling and several statistical analyses show that the taxonomic richness and abundance of these classes within samples were significantly negatively correlated, such that bivalve-rich settings were only sparsely inhabited by gastropods and vice versa. There also were important environmental differences between these classes. Gastropods were most dominant in shallow, carbonate-rich, and generally low-turbidity settings. Gastropods also occurred in restricted lagoons, where bivalves were only minor elements. In contrast, bivalves were most dominant in deep subtidal, siliciclastic shales with high levels of turbidity. Both in terms of abundance and taxonomic richness, these results strongly support those observed at the larger scales of paleocontinents and the globe. Taken together, these results argue that, despite similar taxonomical diversification patterns of these classes at the global scale and heterogeneous patterns among paleocontinents and among regions within Laurentia, gastropods and bivalves had quite different, yet unchanging, environmental distributions throughout the Ordovician, and that these classes did not co-occur to a significant degree, either in terms of taxonomic richness or abundance.

Ecosystem-wide body-size trends in Cambrian–Devonian marine invertebrate lineages

Abstract Fossil marine lineages are generally expected to exhibit long-term trends of increasing body size because of inherent fitness advantages or secular changes in environmental conditions. Because empirical documentation of this trend during the Paleozoic has been lacking for most taxonomic groups, the magnitude, timing, and taxonomic breadth of the trend have remained elusive. This study uses the largest existing database of fossil invertebrate sizes from four faunally important phyla to document ecosystem-wide size trends in well-preserved biotas from deep-subtidal, soft-substrate assemblages during the Cambrian through Devonian. Size of type specimens was measured along standard body axes from monographic plates and converted to body volume by using a broadly applicable empirical regression. Results demonstrate that mean body size (herein volume) of individual genera doubles during this interval, especially from the Late Ordovician through Early Devonian. The timing is gradual in spite of major radiations and extinctions, and the increase is primarily attributable to a net increase in the three-dimensionality of genera. The overall increase is not caused by replacement among clades because increases are widespread among arthropods, brachiopods, and echinoderms, at the phylum and class levels; in contrast, mollusks do not display a net size change at either taxonomic level. The increase is also more pronounced in microbivores than in carnivores. Combined with known environmental changes during this interval, and especially records of carbon dioxide, these trends provide support for the claim that primary productivity increased during the early to mid Paleozoic.

CRITICAL ISSUES OF SCALE IN PALEOECOLOGY

In mid-September 2007, 32 paleontologists gathered at the Smithsonian Institution to spend four days discussing research frontiers in paleoecology, particularly at the interface with neoecology. They represented expertise throughout the Phanerozoic and in all major groups of fossilizable organisms. This meeting was timely, given the increasing evidence of the impact of climate change on ecosystems in our modern world. The vast repository of paleoecological data on past environmental change and concomitant ecological responses, observed at many different spatial, temporal, and taxonomic scales, is of potentially great value for understanding and predicting how modern ecosystems will respond to climate change. Of particular interest to the participants of this meeting were questions of how ecological data collected at different scales could be reconciled so that our knowledge of ecological change in the past can better inform our understanding of the present and our predictions of how ecosystems will change in the future. Certainly, this is one of the most exciting research frontiers in paleoecology. Data collected for different ecological studies (both paleoecological and neoecological) encompass a wide range of spatial, temporal, and taxonomic scales. Understanding the scales inherent in an ecological research question is critical to designing a sampling protocol that will yield data capable of resolving that question, yet these scales are often not adequately evaluated or presented in published paleoecological reports. Furthermore, for any body of paleoecological research to be rescued from isolation and integrated with other studies, the various scales encompassed by the research questions and data must be understood and reported. The greatest barrier to communicating and collaborating with neoecologists is not that data collected from extant ecosystems are necessarily different or more complete than paleoecological data but, rather, that these two data sets commonly represent or are collected at different scales. If such differences of scale can …