PALEOECOLOGY OF THE CLOVERLY FORMATION (LOWER CRETACEOUS) VERTEBRATE FAUNA FROM MICROVERTEBRATE SITES IN THE BIGHORN BASIN, WYOMING

The terrestrial Early Cretaceous (121-98.9 Ma) of western North America is represented by several formations that record a wide temporal and geographic range of environments and document major faunal changes between the Late Jurassic and the Late Cretaceous; however, relatively little is known about the paleoecology of these Early Cretaceous terrestrial communities. Vertebrate microfossil assemblages offer a promising means of quantifying paleoecology by offering large, diverse samples of parautochthonous taxa. In this study, four newly discovered microvertebrate sites from the Cloverly Formation are used to assess the composition and structure of the assemblage.

Cloverly vertebrate specimens were identified to the lowest possible taxonomic level, and grouped into successively higher taxonomic categories. General anatomical and phylogenetic data were used to infer diet and habitat for each taxon, allowing a broad qualitative examination of the paleoecology of each site. Rarefaction of the Cloverly Formation bulk samples indicate that repeated sampling is not likely to produce significantly more taxa than the 31 taxa identified thus far. Principle coordinates analysis was applied to the taxon presence-absence data from the four Cloverly microsites, and non-metric multidimensional scaling was used to quantify taxon abundance differences.

Specimen identifications from our sample of Cloverly microvertebrates greatly increased the known taxonomic diversity of the Cloverly Formation, especially with respect to aquatic forms. Preliminary paleoenvironmental and paleoecological reconstructions reveal both predominantly terrestrial and predominantly aquatic sites within the formation, although several aquatic and terrestrial taxa are ubiquitous. Continued study of such microvertebrate sites will allow a more comprehensive analysis of the Cloverly Formation's vertebrate fauna and their paleoenvironment.