It is generally accepted that the extraordinary preservation of fossils in the Burgess Shale is at least partly due to the exclusion of large metazoan scavengers through rapid burial in an inimical environment. Disruption of individual organisms appears to have been largely the result of mechanical processes and/or microbial decay. The absence of bioturbation through much of the classic section, including Walcott's Phyllopod Bed, supports these arguments. However, macroscopic traces are known from other horizons within the Burgess Shale section and from lateral equivalents in the Stephen Formation a short distance south of the main locality.

The sparse ichnoassemblage includes bedding-plane exposures of portions of compacted, parallel-sided burrows containing skeletal debris comprising fragmented and disarticulated hyoliths, small trilobites, and bracniopods. Walcott originally figured one such trace as Planolites sp. ? and noted, but offered no evidence for, an association with the archaeopriapulid Ottoia prolifica. This notion was subsequently rejected by Conway Morris.

A recently collected specimen, from talus south of the main locality, contains a poorly preserved but recognizable body fossil of Ottoia within the outline of a “Planolites”. Although this juxtaposition may be accidental, a number of features of the association, and a consideration of the burrowing behaviour of modern priapulids, suggest that Ottoia could have been the generator of “Planolites”-like traces.

The Bilk Creek Limestone of the Black Rock Terrane in northwestern Nevada and the McCloud Limestone of the Eastern Klamath Terrane in northern California contain a diverse and abundant Permian brachiopod fauna currently under study. The composite rock record of both limestones spans the Wolfcampian and Leonardian stages of the Permian, during which both terranes were part of a volcanic arc separated from the North American continent by a marginal basin of unknown dimension. Brachiopods of this volcanic arc provide important evidence bearing on current hypotheses of Permian paleobiogeography and paleogeography.

The Bilk Creek/ McCloud brachiopods are best characterized as an endemic fauna of a unique province and not as a mixed, “Tethyan” and North American fauna. The central problem of these arc faunas is not how similar they are to faunas of the Tethyan basin but why they are so dissimilar from North American faunas. Overlying rock units in both terranes contain Guadalupian brachiopod faunas that are North American in character. The paleobiogeographic pattern is one of decreasing levels of endemism throughout the Wolfcampian and Leonardian, to ultimate deprovincialization during the Guadalupian. This is not consistent with a pantropic dispersal hypothesis.

The temporal pattern is consistent with a paleogeographic hypothesis of initial, long-distance separation of arc and continent with convergence of the arc toward the North American continental margin. The dissimilarity of the arc brachiopod faunas to coeval, same-environment faunas of North America suggests that the marginal basin that separated the two must have been several thousand kilometers wide during the Early Permian, producing the endemic fauna. A Japan-style model, with arc and continent in close proximity is not supported.

The Pliocene uplift of the Panamanian isthmus isolated previously contiguous Caribbean and eastern Pacific marine faunas, and initiated the development of different selective regimes on opposing sides of the barrier. Contrasting environmental conditions provided the context for different rates and kinds of evolutionary change on either side of the isthmus. The goal of our study is to characterize the rates and types of these paleoenvironmental changes; we employ stable isotopic profiles of venerid bivalve shells from the Miocene-Recent deposits of Panama and Costa Rica.

We analyzed geographic and depth variation in Recent shells as a means of calibrating the fossil analyses. Results from Recent venerids highlight the differences between the Caribbean and eastern Pacific shallow marine environments. Pacific shells typically exhibit strong annual fluctuations in δ18O, associated with seasonal upwelling and its associated cool waters. In shallow, near-shore habitats, freshwater runoff during the rainy season also contributes significantly to annual δ18O cycles. Caribbean shells exhibit negligible annual cyclicity.

We analyzed fossil shells from the Miocene Gatun Formation, and the Pliocene Cayo Agua, Escudo de Veraguas, and Rio Banano Formations from the Caribbean coast, and the Plio-Pleistocene Charco Azul Group from the Pacific coast. Results from fossil shells indicate that annual cycles are well-preserved, and not obscured by diagenesis or other alteration. A strong annual signal in δ18O (amplitude >1.5‰) is found back at least to the Early Pleistocene along the Pacific coast. Some post-uplift Caribbean samples exhibit stronger seasonality than that observed in similar habitats today.