Chris L. Schneider

EFFECTS OF DATA CATEGORIZATION ON PALEOCOMMUNITY ANALYSIS: A CASE STUDY FROM THE PENNSYLVANIAN FINIS SHALE OF TEXAS

Abstract Paleocommunity research efforts have explored a multitude of faunal assemblages using a wide range of sampling and analytical methods to infer a paleoecological signal. Here, we derive six secondary datasets from a single stratigraphic series of faunal assemblages in the Finis Shale (Pennsylvanian) of Jacksboro, Texas, USA, using a variety of data categorization decisions (i.e., abundance versus calcified biomass, all taxa versus selected indicator taxa, and generic versus higher clade resolution). Biomass- and abundance-derived datasets were not significantly different in terms of evenness, Shannons information index, or Simpsons diversity index. Using Bray-Curtis and nonmetric multidimensional scaling ordinations, with Sorenson and relative Sorenson distance measures, ordination axis scores of the six derived datasets were all significantly correlated with one another, suggesting little difference in their respective paleoecological signals. Three potential explanations for this consistent paleoecological signal, regardless of which data categorizations are employed, include: (1) the dominance of a few brachiopod taxa overwhelmingly influenced the community structure, (2) relatively constrained environmental conditions limited community variation, and (3) low variation in specimen size minimized potential differences among abundance and calcified biomass categorizations. We suggest that other datasets with greater diversities, greater evenness, or from a wider range of paleoenvironments might not show this consistency. Thus, to the degree possible and appropriate, paleoecological investigators should test the effects of these data categorization decisions on a paleoecological signal, regardless of the analytical method employed.

Categorization of shell fragments provides a proxy for environmental energy and predation intensity

Shell fragments are extremely abundant in many marine environments; the origins of these fragments can largely be attributed to either crushing by predators or post-mortem processes such as transport. We present and test a new approach to identifying the origin of shell fragments in marine environments by examining modern mollusc assemblages from three wave-exposed, low-predation and three wave-sheltered, high-predation intertidal localities in Bamfield, British Columbia. We hypothesized that fragments with all-rounded edges (AR) or a combination of rounded and sharp edges (R&S) are indicative of taphonomic processes such as transport and so should occur more often in wave-exposed, low-predation localities whereas fragments with all sharp edges (AS) or a combination of intact and sharp edges (I&S), indicative of predation, should be more common in wave-sheltered, high-predation settings. In keeping with the prediction, All-Rounded (AR) and Rounded and Sharp (R&S) fragments are more abundant at the wave-exposed localities than at wave-sheltered localities whereas Intact and Sharp (I&S) and All-Sharp (AS) fragments are more abundant at high-predation localities than at low-predation localities. The two types of localities were statistically distinguishable for either gastropod or bivalve fragments. This supports the hypothesis that I&S and AS result from predation, whereas AR and R&S have a taphonomic genesis.

Breaking the mold: using biomechanical experiments to assess the life orientation of dorsibiconvex brachiopods

Abstract. Understanding the life orientation of fossil organisms, such as brachiopods, is not only important for understanding the biology of the organism in question, but it also can be used to interpret paleoecological information about the assemblages from which the specimens were derived. The dorsibiconvex brachiopod morphology is particularly common, especially among the Order Atrypida, yet there have been few independent, biomechanical studies to assess the life orientation of these brachiopods. In this study, we assess potential orientations of two end-member morphologies of a dorsibiconvex brachiopod, Pseudoatrypa lineata, from the Mid-Late Devonian of North America by placing realistic models in a flume. Using materials with the specific gravity of calcium carbonate, we modeled two well-preserved Pseudoatrypa lineata from the Waterways Formation (Givetian—Frasnian, Alberta, Canada) to represent the original shell. The hydrodynamic stability of the models was assessed by placing the models in a recirculating flume in one of three initial orientations: (1) anterior commissure upstream, (2) umbo upstream, and (3) lateral (specimen perpendicular to flow), each with the dorsal and ventral valve topmost. The entire process was conducted both on a Plexiglas substrate and on well-sorted, medium-grained sand. All scenarios were repeated five times for a total of sixty trials per specimen (120 total). Flume trials indicate that neither brachiopod had a true hydrodynamically stable orientation. Reorientations occurred at low velocities (∼0.2 m/s), with transport occurring soon after (∼0.3 m/s). Assuming that a juvenile, pedunculate, dorsibiconvex brachiopod would initially have been oriented with its ventral valve topmost, our results suggest two outcomes: the brachiopods either (1) were attached via pedicles throughout their lives or (2) lived in quiet, undisturbed waters. Given the abundance of dorsibiconvex brachiopods in observed high-energy environments, our results indicate it is more conservative to assume dorsibiconvex brachiopods retained pedicles throughout their lives.

Mapping sclerobiosis: a new method for interpreting the distribution, biological implications, and paleoenvironmental significance of sclerobionts on biotic hosts

Abstract. The use of sclerobiosis as a tool for paleoenvironmental and paleoecological research is undermined by a lack of comparable methods for sclerobiont data collection and analysis. We present a new method for mapping sclerobiont distributions across any host, and offer an example of how the method may be used to interpret sclerobiont data in relation to host orientation. This approach can also be used to assess the suitability of beds and fossil material for paleoenvironmental reconstruction. A sample of 150 encrusted dorsibiconvex atrypide brachiopods were selected from six beds in the Waterways Formation (latest Givetian — Early Frasnian; Alberta, Canada). The dorsal and ventral valves of each brachiopod were photographed. Sclerobiont taxa were mapped onto the photographs, and the maps were used to create stacked images with each of the 25 brachiopod specimens from each bed. Based on the life orientation of dorsibiconvex atrypides, three zones were designated on the host: the post mortem zone, (only available to sclerobionts after death and reorientation of the host); the shaded zone (brachial valve, excluding the post mortem zone); and the exposed zone (ventral valve). Randomization simulation results indicate that all beds likely exhibit non random encrustation patterns, and corroborate the hypotheses that: (1) much of the encrustation occurred while the hosts were alive, and (2) these beds and fossils have experienced little physical reworking or transport and would be suitable for paleoenvironmental analysis. Mapping sclerobionts across hosts can serve as a unifying method to increase the recognition and use of sclerobiosis in paleontological studies.

An Overview of Conservation Paleobiology

The field of conservation paleobiology was formally established in the early 2000s, as a growing body of literature substantiating the fidelity of paleontological data on a variety of spatial and temporal scales emerged, and paleontologists became increasingly aware of the potential insights that the fossil record could provide into the current biodiversity crisis. Conservation paleobiology contributes a temporal scope and historical perspective lacking from the relatively short time spans covered by modern ecological studies, progressively in demand in the face of changing climate and environmental degradation. The increasing number of conservation paleobiology studies in the past decade validates the potential contributions of this field to conservation efforts, and fall within a range of temporal categories (e.g., “near-time” and “deep-time”). Data are not restricted to fossils, but can also include historical reports and archeological evidence (conservation archeobiology). Although temporal resolution often declines with increased assemblage age, ancient ecosystems document responses to, and recoveries from, global crises. Thus, the field of conservation paleobiology, when considered in concert with historical ecology and conservation biology, has the potential to positively affect future ecosystems and biodiversity.

Marine Refugia Past, Present, and Future: Lessons from Ancient Geologic Crises for Modern Marine Ecosystem Conservation

Refugia are one means of species survivorship during a global crisis. As the Earth is facing a major crisis in the marine biosphere, the study of refugia through past extinctions and other global crises is relevant to creating and maintaining effective marine reserves (including marine protected areas and other formally established havens for conservation). A synthesis of previous studies identifies the following properties common to most definitions of a refugium: (1) During a global crisis, a species can persist in a refugium, which can include a range shift, habitat shift, or migration or contraction to an isolated geographic area. Subsets of isolated geographic refugia include life history refugia (areas necessary for breeding), cryptic refugia (small areas, must remain connected for populations to remain viable), and harvest refugia (defined from the modern literature to escape overfishing pressure). (2) In the refugium, the habitat may remain stressed but is sufficiently habitable for the species to maintain sufficient albeit small populations (relative to pre-crisis population size) over many generations. (3) After the crisis ends, the species emerges from the refugium and expands during the recovery interval. Otherwise, the refugium will become a refugial trap in which the species remains a relict population or ultimately becomes extinct.