Evolution of the anuran assemblages during the Cretaceous in western part of North America; comparisons with the anuran fossil record in Eurasia

The Upper Cretaceous (Cenomanian through Campanian) sedimentary rocks of Southern Utah in the USA yielded, during the past 15 years, a great number of disarticulated skeletal remains of small vertebrates, including frogs. The mentioned stratigraphic sequence represents a nearly uninterrupted sequence of strata deposited during almost 30 million years, in a relatively restricted geographic area. Abundance of fossil anuran remains is comparatively high in washing samples, and although traditional separation techniques (i.e., screen washing of matrix) caused partial destruction of the fragile anuran bones, the amount and kind of preserved bones make their sufficiently precise taxonomic determination possible. Preliminary analysis of the material recovered until now suggests that anuran samples from various localities represent taxonomically diversified assemblages that can be compared with each other not only in geographical, but in geochronological context as well.