INTENSIVE GEOCHEMICAL ANALYSES OF SPATIALLY- AND TEMPORALLY-CONSTRAINED SITES TO FACILITATE HIGH-RESOLUTION PALEOCOMMUNITY AND PALEOENVIRONMENTAL RECONSTRUCTION: A CASE-STUDY FROM THE CRETACEOUS

There is a growing consensus in vertebrate paleontology that database meta-analyses examining biodiversity and macroecology at coarse spatial (i.e. continental to global) and temporal (i.e. formation to Stage-level) scales must be augmented by more intensive smaller-scale studies of individual assemblages. Such studies, with greater spatial and temporal resolution, and more control over preservational and sampling biases, are necessary for testing ecological hypotheses regarding changes in environments, biodiversity, and their interactions. Vertebrate microfossil bonebeds can offer a useful source of data for such intensive studies as a result of being spatially- and temporally-constrained, highly fossiliferous, depositionally-consistent, and abundant stratigraphically. When data from these sites are analyzed using a suite of isotopic and other geochemical proxies, high resolution reconstructions of paleoenvironmental and paleocommmunity structure are possible, as are the coordinated testing of multiple interrelated ecological hypotheses.

To illustrate this, I provide a case-study based on data field-sampled from a vertebrate microfossil bonebed in the Upper Cretaceous (Campanian) Oldman Formation of Alberta, Canada, and resultant data from stable C, O, and Sr isotope and elemental analyses of bioapatite, organic C isotope analyses from sediments, as well as XRD and FTIR tests of diagenetic alteration. These analytical data are used, alongside fossil occurrence/abundance data and comparative studies from modern near-analogue environments, to reconstruct paleocommunity structure, temperature, and other environmental conditions. From this, hypotheses of dietary physiology, habitat and dietary preferences, as well as niche partitioning among the sampled taxa are tested, and aquatic-terrestrial resource interchange in this Cretaceous greenhouse system assessed. Taken together, these constrained multi-proxy datasets provide the resolution necessary to meaningfully reconstruct community ecology in these ancient systems, their responses to changing environmental conditions, as well as facilitate the rigorous testing of hypotheses of the paleobiology of the taxa within, while underscoring the importance of intensive site-based studies in community paleoecology.