Browsing by Author "Reese E. Barrick, Committee Member"

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    Predators and Dangerous Prey in the Fossil Record: Evolution of the Busyconine Whelk-Mercenaria Predator-Prey System.
    (2002-08-09) Dietl, Gregory Paul; Reese E. Barrick, Committee Member; James A. Rice, Committee Co-Chair; Patricia H. Kelley, Committee Co-Chair; Brian M. Wiegmann, Committee Member
    Escalation is enemy-driven evolution. This top-down view of a predator-prey evolutionary arms race downplays the role of prey in driving the predator's evolution. In the related process of coevolution, species change reciprocally in response to one another; prey are thought to drive the evolution of their predator, and vice versa. In the fossil record, the two processes are distinguished most reliably when the predator-prey system is viewed within the context of other species that may influence the interaction. I examined the interaction between busyconine whelks and their bivalve prey Mercenaria to evaluate whether reciprocal adaptation (coevolution) was likely to occur in this predator-prey system. Species of busyconines either employ a wedging or a chipping mode of predation when feeding on bivalve prey that often results in breakage to the predator's own shell. Prey in this interaction have been hypothesized to be 'dangerous' because they are able to inflict damage to the predator as a consequence of the interaction; such damage may lead to decreased growth, reproduction and increased probability of mortality for individual whelks. Asymmetry in selection pressure (which is thought to preclude reciprocity of adaptation) is reduced when predators interact with damage-inducing prey. The likelihood of a reciprocal selection response of the predator in the interaction involving the shell-chipping whelk Sinistrofulgur sinistrum and the bivalve Mercenaria mercenaria was viewed by regressing the frequency of shell breakage in encounters with prey (an index of predator fitness) on prey phenotype (a function of size). Experimental results indicate interaction with Mercenaria has strong highly significant and predictable selective consequences for Sinistrofulgur, suggesting that evolutionary response of the predator to prey adaptation is likely in this system. The late Oligocene to Recent fossil record of whelk predation traces on shells of Mercenaria species was analyzed to determine the temporal window of possible coevolution between shell-chipping whelks and Mercenaria. Based on the fossil record of successful and unsuccessful whelk predation traces, chipping behavior evolved in the Busycon-Sinistrofulgur clade in the early late Pliocene, which constrains tests of reciprocal adaptation to the Pliocene to Recent record of the interaction. Temporal trends in the frequency of successful and unsuccessful whelk predation traces on Mercenaria suggest predation intensity, and the likelihood of prey adaptation in response to whelk predation, increased through the Plio-Pleistocene record of the interaction in Florida. Mercenaria evolutionary size increase is best explained as coevolutionary response to whelk predators. Temporal trends in decreased prey effectiveness (ratio of unsuccessful to total predation attempts) and increase in minimum boundary of a size refuge from predation suggest that, although prey responded evolutionarily to whelk predation pressure, whelk predators also were increasing their prey capture capabilities. Sinistrofulgur evolutionary size increase is best explained as reciprocal coevolutionary response to prey adaptation (which decreased the likelihood of shell breakage when encounters with damage-inducing prey occur) coupled with (or reinforced by) an escalation response to the whelk's own enemies, such as fasciolariid gastropods and durophagous crabs. Coevolution between predator and dangerous prey best explains temporal behavior-related changes in the predator that led to a decrease in frequency of chipping-induced damage to the predator when encounters with prey occur, and an increase in predator site-selective stereotypy of attack position.
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    Stratigraphic Distribution, Taphonomy, and Isotope Paleoecology of the Dinosaurian Fauna in the latest Campanian lower Horseshoe Canyon Formation, Alberta, Canada
    (2003-06-02) Straight, William Herbert; Elana Leithold, Committee Co-Chair; Dale A. Russell, Committee Chair; Reese E. Barrick, Committee Member; Elisabeth Wheeler, Committee Member; David Eberth, Committee Member
    Vertebrate fossils in the lower Horseshoe Canyon Formation are remains of dinosaurs, crocodilians, champsosaurs, turtles, and fish supported during the last ~2 m.y. of the Campanian by a coastal lake-strewn wetland occupying what is now south-central Alberta, Canada. Bones accumulated on the floodplain through attritional mortality and are preserved unweathered except for surface polish, scratches, and mottling characteristic of bioturbation during rapid burial in fine-grained sediment. Fossil-bearing sites cluster stratigraphically in laterally extensive horizons between thicker less fossil-rich intervals of similar fluvial strata. These horizons, formed by a long-term balance between bone supply, accommodation, and depositional rate, result from a newly recognized 'floodplain fill' mode of preservation for vertebrate fossils and are analogous to marine condensed sections. Like condensed sections, these fossiliferous horizons lie adjacent to lithostratigraphic surfaces created by stillstands in base-level. Together, hiatal surfaces and fossiliferous horizons reveal repeating rhythms in the facies distribution and fluvial architecture. These rhythms, 'packages' of strata bounded by hiatal surfaces, arose through two scales of variation in base-level: a grand-scale base-level cycle reflecting tectonic control during the construction of the clastic wedge, and a smaller 'package'-scale cycle reflecting Milankovitch control over local climate and precipitation. Both the fluvial architecture and the accumulations of fossils are a consequence of this change in accommodation and sediment supply through time. Fossil evidence does not indicate a faunal change through time, but changes in climate through time resulted in a reduction in organic-rich mudrocks and coal, an increase in soil development, and changes in the dominant configuration for fossil preservation from sparse bonebeds to microsites. Climate change was also investigated through stable oxygen isotopes in tyrannosaur tooth enamel phosphate, which daily recorded the response of surface (drinking) water to changes in humidity and temperature. The enamel isotopic record shows a transition from highly variable, seasonal climate to relatively constant conditions, consistent with the interpretation of change in the stratigraphy and taphonomy. This combined application of architectural stratigraphy, vertebrate taphonomy, and stable isotope paleoecology represents a new approach for paleontologists interested in evaluating changes through geologic time in paleoenvironment and animal communities in a fluvial succession.