Theses and Dissertations at Montana State University (MSU)
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Item A critical evaluation of our understanding of bone transport and deposition in fluvial channels(Montana State University - Bozeman, College of Letters & Science, 2015) Evans, Thomas Vincent; Chairperson, Graduate Committee: David VarricchioForensic scientists, archaeologists, and paleontologists are interested in understanding fluvial bone transport respectively to find human remains, determine if human behavioral information persists in skeletal assemblages, or to estimate the temporal and spatial resolution of fossil assemblages. This dissertation reviews what we think we understand about fluvial bone transport, then tests the hypotheses that: 1. Elongate and concave bones adopt preferred orientations relative to flow, 2. There is a relationship between bone shape and relative transportability, and 3. There is a relationship between bone density and relative transportability. Generally two research techniques prevail, 1. Flume observations, and 2. Fluvial seeding trials. Flume data are often poorly reported, have small sample sizes, and the conditions within the flume are usually incompletely reported. Fluvial seeding trial results are characterized by a series of well documented anecdotes, largely due to specimen loss causing small sample sizes. The results from these techniques are contradictory so research to clarify what conclusions are valid is needed. Three techniques were utilized to address these problems, river surveys, river seeding trials, and river seeding trials using bone casts. No correlation between elongate bone orientation (N=157) and flow direction was observed, though concave bones (N=89) oriented ~70% concave down, while flat bones lay flat against the bed. Similarly, there was no association between bone shape and transportability. Denser bones were less transportable than less dense bones however there was substantial overlap in transportability between dense and less dense bone casts. These results suggest our understanding of bone transport is simplistic and incomplete. This is probably because most research has utilized flumes which provide unrealistically uniform conditions, so flume results are a poor analog for the heterogeneous natural environment. Moreover, bones are constantly changing density which is a variable previous authors have more or less assumed was constant. This simplifying assumption is violated so frequently that this assumption has led the scientific community to assume bone transport behaviors that are not frequently observed in natural systems. Ultimately the analytical tools based on this incomplete understanding of bone transport should be discontinued or validated to avoid spurious conclusions when interpreting skeletal assemblages.Item Sedimentological analyses of eggshell transport and deposition : implication and application to eggshell taphonomy(Montana State University - Bozeman, College of Letters & Science, 2013) Imai, Takuya; Chairperson, Graduate Committee: David VarricchioThe interpretation of fossil eggshell assemblages in the absence of nesting structures is problematic because eggshells can be transported by hydraulic flows in fluvial environments. Failure to recognize transported eggshells may lead to erroneous interpretation of the reproductive behavior and ecology of those animals. An inconsistent array of evidence has been used in past studies to assess eggshell transport. Here, a series of flume studies was conducted to establish analytical techniques for assessing eggshell hydraulic transport in the fossil record. Using modern eggshells in a flume, I investigated preferred eggshell orientation after transport, the relationship of flow competence with eggshell shape and size, and size of clastic sediment expected to be associated with transported eggshells. Emu, goose, and ostrich eggshell fragments were released in a rectangular flume with decelerating flow. The transport of each eggshell was observed five times on each of four substrates (coarse sand, sparse gravel, dense gravel, and polyvinylchloride). At eggshell deposition, eggshell orientation and flow depth were recorded. Critical bed shear stress for eggshell deposition was estimated based on the flow depth at the point of eggshell deposition. The probability of concave-down orientation for deposited eggshells was estimated for each eggshell type transported on each substrate. The relationship of the critical bed shear stress for eggshell deposition with eggshell shape and size was tested. Size of clastic grains deposited under the critical bed shear stress for eggshell deposition was estimated. The probability of concave-down orientation after transport was > 85% regardless of eggshell types and substrates. The bed shear stress at eggshell deposition was most closely related to eggshell height and volume. Estimated size of clastic sediment associated with transported eggshell was coarse sand or coarser sediment. One may consider a high proportion of concave-down oriented eggshells in fossil assemblages as indicative of transport regardless of eggshell types. In addition, eggshells may be sorted according to their height and volume. Coarse sand or larger particles observed in matrix of fossil eggshells may be used as evidence of eggshell transport. Further studies are necessary to test reliability of those techniques and broaden their applicability.