This dissertation summarizes actualistic research in the intertidal environments of northeastern Baja California, Mexico. The first project is a taphofacies analysis of three generations of cheniers that differ in age and taphonomic history. The study shows that the shells that accumulated in the cheniers are slightly affected by biological processes and moderately affected by physical processes. Only the luster features of shells vary substantially and consistently with chenier age -- a result of subaerial weathering. Taphofacies analysis successfully discriminates the three chenier generations. Chenier assemblages are distinct from assemblages formed in other marine environments by a lower frequency of bioerosion and encrustation. Taphonomic differences between the cheniers that differ in age suggest that fossil cheniers may be useful in detecting incompleteness gradients along stratigraphic boundaries (i.e., taphofacies with shells of poorer-than-average preservation indicate a longer subaerial exposure and thus a larger stratigraphic hiatus). The second project investigates the taphonomy of a Recent lingulide brachiopod Glottidia palmeri Dall. Live lingulides occur in patches across the intertidal zone. Dead specimens include in situ shells, surface shells (found on intertidal flats), and beach shells (found on the shoreface). Recent lingulides have a very low fossilization potential. Consequently, large-scale aspects of their history are poorly recorded in the fossil record, but the outcrop-scale aspects may be recorded with high fidelity. The literature survey suggests that Paleozoic lingulides had a higher fossilization potential than their post-Paleozoic relatives. The decrease in diversity and ecologic importance of lingulides after the Paleozoic may be due to a taphonomic megabias. The third project proposes a comparative use of size-frequency distributions derived from trace fossil assemblages for interpretation of ancient populations. Two examples illustrate the approach: Recent lingulide burrows (Baja California) and Cambrian Diplocraterion burrows (Arizona). They show that the approach can provide accurate data useful for paleoecology, sedimentary facies analysis and even local stratigraphic correlations. The fourth project is a theoretical essay on the concept of time-averaging and the concluding part of the dissertation discusses the pitfalls and premises of the actualistic approach in the context of my research in Baja California.

Accumulations of dead shells in both modern coastal settings and in the rock record contain valuable information on past ecosystems and environmental conditions. However, death assemblages are not simply snapshots of living communities; rather, the abundances of different species have been biased due to differential rates of postmortem destruction. In order to constrain the nature and degree of bias in modern molluscan death assemblages in a shallow marine environment, I deployed mesh-bag experiments including six species of bivalves into a natural marine environment on the Texas coast. The mesh bag design for tethering shells allowed for maximum exchange between ambient environmental conditions and the shells while the apparatus was deployed. The apparatuses were recovered after 2 weeks, 4 weeks, 8 weeks, 16 weeks, 8 months, and 12 months. Shells were examined under a Scanning Electron Microscope (SEM) to analyze integrity, document degradation, and investigate patterns of biological, chemical, and physical abrasion and destruction. SEM analysis indicates that some shells clearly degraded, while others did not, even after 12 months. In addition, epifaunal shells experienced postmortem encrustation by sessile organisms more than infaunal shells, indicating a species-level preservational bias.

Thesis (MS)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: David Varricchio. Includes bibliographical references (leaves 86-96).

No description available.

Shark attacks on humans are increasing every year, and due to this fact, it is important to understand the damage that these predators can inflict on bone. The present study examined the striation patterns that shark teeth leave behind on bones during an attack or scavenging event and determined whether they can be used to identify the species of shark involved. The present study examined twelve different species of sharks including white shark (Carcharodon carcharias), tiger shark (Galeocerdo cuvier), and bull shark (Carcharhinus leucas), as there are high incidences of attacks reported of these species. Striations were made in dental wax using the teeth of these species, as well as nine others including blue shark (Prionace glauca), tawny nurse shark (Nebrius ferrugineus), blacktip reef shark (Carcharhinus melanopterus), dusky shark (Carcharhinus obscurus), java shark (Carcharhinus amboinensis), gray reef shark (Carcharhinus amblyrhynchos), sand tiger shark (Carcharias taurus), cookiecutter shark (Isistius brasiliensis), and lemon shark (Negaprion brevirostris), to compare morphologies, their serration patterns, and what striations would be left on bone. It was hypothesized that the striations left in the impressions would be distinct to each species and would provide another method to identify species implicated in attack and scavenging events on humans. The results of this study suggest a statistically significant difference between the patterns of serrations found between some species of sharks examined. The white shark and the tiger shark can be distinguished from the other species in the present study. Further research on this method should be conducted, so future scientists can identify species involved in predation events and scavenging using striation patterns.

No description available.

Drawing on the large body of taphonomic, ethnoarchaeological, and general zooarchaeological literature currently available, the main goal of this research report is to provide the first comprehensive taphonomic account of the fauna at Kalkbank in order to establish whether humans, carnivores, or other natural processes were the major accumulators of the assemblage. Through examination of species presence and abundance, patterns of bone breakage, various surface modifications to the bones, several aspects of skeletal part representation, and mortality profiles, it has been proven that carnivores were the main agent of accumulation. Furthermore, it has been determined that the site accumulated sometime during the late Pleistocene, but closely resembles several open-air sites dated from the Acheulean.

A total of 5065 specimens (5018 valves of bivalve and 47 gastropod shells) have been identified and classified into 27 species from 55 samples collected from raised glaciomarine and estuarine sediments, and glacial tills. The bivalves <i>Hiatella arctica</i>, <i>Mya truncate</i>, <i>Astarte borealis</i>, and <i>Serripes groenlandicus</i> are the most common species. Our samples record the dominance of infaunal suspension-feeders that are most abundant on soft substrates typically occurring in nearshore environments. The dominance of bivalves with respect to gastropods reflects an averaged record of the fossil assemblages inhabiting the high latitude nearshore environments. Six unique associations, which are comparable to the composition of modern communities inhabiting in fiords and on continental shelf from Canadian high arctic, and three distinctive taxa groups (deposit feeders, suspension-feeders, and rare taxa) are recognized by cluster analysis and Multidimensional Scaling conducted on presence-absence data. The trophic composition of paleocommunities in this study is as follows: suspension-feeders > deposit feeders > carnivores > browsers. The occurrence of <i>Mya pseudoarenaria</i> in fossil assemblages indicates an age of the fossils around early Holocene. <p>Most of the samples are not substantially transported nor significantly reworked. Shell disarticulation and fragmentation can result from sea ice scouring of the seafloor and the development of permafrost in raised marine sediments. The degree of shell disarticulation for the four most common taxa is generally low which likely reflects high sedimentation rates and rapid burial in nearshore environments, especially those from glaciomarine silts and estuarine deposits. Four common species exhibit different preservation potential based the degree of fragmentation and disarticulation (Serripes < Mya < Hiatella < Astarte). Shells with high (or low) degree of fragmentation for single species (i.e. Hiatella) also correspond to different energy conditions of the associated sediments facies from which the shells are recovered. The general absence of strongly bioeroded or encrusted shells among samples suggests rapid burial of the shells with only limited exposure on the sediment surface, or the absence of grazing, boring or encrusting taxa in the environment that is dominated by infaunal habit of most of the taxa represented in the shell assemblages. <p>Four taphofacies are recognized by cluster analysis on the basis of four taphonomic variables (fragmentation, corrasion, bioerosion, and encrustation) characterized by poor preservation, fair preservation, fair-good preservation, and fair preservation with poor corrasion respectively. Faunal succession and paleo-marine environments during the deglaciation in early Holocene are reconstructed from the seven sedimentation facies (glacial, beaches, shallow marine, proglacial, shallow marine or estuarine - pebbly sand and gravel with algal debris, shallow marine or estuarine - pebbly silt with algal debris, shallow marine or estuarine - interbedded silt and sand).

A total of 5065 specimens (5018 valves of bivalve and 47 gastropod shells) have been identified and classified into 27 species from 55 samples collected from raised glaciomarine and estuarine sediments, and glacial tills. The bivalves <i>Hiatella arctica</i>, <i>Mya truncate</i>, <i>Astarte borealis</i>, and <i>Serripes groenlandicus</i> are the most common species. Our samples record the dominance of infaunal suspension-feeders that are most abundant on soft substrates typically occurring in nearshore environments. The dominance of bivalves with respect to gastropods reflects an averaged record of the fossil assemblages inhabiting the high latitude nearshore environments. Six unique associations, which are comparable to the composition of modern communities inhabiting in fiords and on continental shelf from Canadian high arctic, and three distinctive taxa groups (deposit feeders, suspension-feeders, and rare taxa) are recognized by cluster analysis and Multidimensional Scaling conducted on presence-absence data. The trophic composition of paleocommunities in this study is as follows: suspension-feeders > deposit feeders > carnivores > browsers. The occurrence of <i>Mya pseudoarenaria</i> in fossil assemblages indicates an age of the fossils around early Holocene. <p>Most of the samples are not substantially transported nor significantly reworked. Shell disarticulation and fragmentation can result from sea ice scouring of the seafloor and the development of permafrost in raised marine sediments. The degree of shell disarticulation for the four most common taxa is generally low which likely reflects high sedimentation rates and rapid burial in nearshore environments, especially those from glaciomarine silts and estuarine deposits. Four common species exhibit different preservation potential based the degree of fragmentation and disarticulation (Serripes < Mya < Hiatella < Astarte). Shells with high (or low) degree of fragmentation for single species (i.e. Hiatella) also correspond to different energy conditions of the associated sediments facies from which the shells are recovered. The general absence of strongly bioeroded or encrusted shells among samples suggests rapid burial of the shells with only limited exposure on the sediment surface, or the absence of grazing, boring or encrusting taxa in the environment that is dominated by infaunal habit of most of the taxa represented in the shell assemblages. <p>Four taphofacies are recognized by cluster analysis on the basis of four taphonomic variables (fragmentation, corrasion, bioerosion, and encrustation) characterized by poor preservation, fair preservation, fair-good preservation, and fair preservation with poor corrasion respectively. Faunal succession and paleo-marine environments during the deglaciation in early Holocene are reconstructed from the seven sedimentation facies (glacial, beaches, shallow marine, proglacial, shallow marine or estuarine - pebbly sand and gravel with algal debris, shallow marine or estuarine - pebbly silt with algal debris, shallow marine or estuarine - interbedded silt and sand).

Thesis (Ph. D.)--University of Washington, 1991. / Vita. Includes bibliographical references (leaves [193]-209).