MULTITUBERCULATE MAMMALS FROM THE WAHWEAP (CAMPANIAN, AQUILAN) AND KAIPAROWITS (CAMPANIAN, JUDITHIAN) FORMATIONS, GRAND STAIRCASE-ESCALANTE NATIONAL MONUMENT, SOUTHERN UTAH, AND IMPLICATIONS FOR BIOSTRATIGRAPHIC METHODS

At least 18 species of multituberculate mammals are present in the Wahweap Formation, of these, only 2 are with certainty conspecific with taxa from the type fauna of the Aquilan Land Mammal "Age" (Milk River Formation) and one conferred species may be conspecific. Of 17 species of multituberculates recovered from the Kaiparowits Formation, only 2 of these are with certainty conspecific with species from the type Judithian fauna from the Judith River Formation, and 5 other conferred species may possibly be conspecific. Previous reports on therian mammals by Richard Cifelli support the correlation of the fauna recovered from the Wahweap Formation to the Aquilan Land Mammal "Age," and the fauna from the Kaiparowits Formation to the Judithian.

It is currently impossible to resolve whether the low percentage of multituberculate taxa that are conspecific with taxa from the type faunas (a minimum of 11% of the multitiberculates from the Wahweap Formation, to a possible maximum of 41% of the multituberculates from the Kaiparowits Formation) reflect differences in time (older or younger than type faunas), or latitudinal or other paleoecologic controls. This lack of resolution reflects both sampling methods and lack of intergrated Cretaceous nonmarine biostratigraphies that allow for independent assessment of age. Sampling for microfossils is highly biased by prospecting methods that result in the collection of samples from the best developed outcrops and these may not represent key stratigraphic intervals or allow for documentation of age boundaries. This can be remedied by collecting some samples for screen washing from fine-grained rocks at key intervals necessary to resolve biostratigraphic boundaries regardless of whether any surface fossils are evident. This method has produced abundant fossils at critical horizons, but most of these fossils are not mammalian. It is thus also essential to begin integrating molluscs, ostracods, palynomorphs, and lower vertebrates into Cretaceous nonmarine biostratigraphic schemes. Only then will it be possible to correlate Cretaceous nonmarine strata at a level of resolution comparable to that which can be accomplished in marine strata.