A PRELIMINARY ASSESSMENT OF DIVERSITY PATTERNS OF NONMARINE VERTEBRATES IN THE CRETACEOUS WESTERN INTERIOR OF NORTH AMERICA

Abstract

The ranges of more than 500 orders, families, and genera of nonmarine vertebrate taxa were compiled from the literature for the Cretaceous of the Western Interior of North America. This record currently includes the Barremian through Maastrichtian stages, a span of approximately 60 million years. In this preliminary attempt to assess the patterns of diversity of nonmarine vertebrates we recognize that there are many limitations on the data. Diversity curves were compared to eustatic curves, and stable-isotope and paleobotanical-based paleotemperature curves over the same time interval. No strong correlation was found between patterns of nonmarine vertebrate diversity and any of the curves, but there is a weak correlation between diversity and the overall first-order pattern of sea-level fluctuation. Although some diversity changes appear to correlate with the third-order eustatic changes, they may not represent cause and effect phenomena as many other large-scale eustatic fluctuations in the Cretaceous are not accompanied by significant changes in diversity. Perhaps the most marked event in terrestrial vertebrate diversity is an almost doubling of genera in the late Campanian accompanied by only a modest rise in sea level. Even this apparently dramatic change in diversity may represent nothing more than a sampling bias resulting from the extent of outcrop and the fossiliferous nature of late Campanian strata in the Western Interior relative to older Cretaceous strata. This analysis suggests that diversity curves for North American Cretaceous nonmarine vertebrates reflect incomplete sampling. It is also considered likely that patterns of diversity result from complex interactions of the environment and may not be directly correlated to any single cause. KEY WORDS. Nonmarine. Vertebrate. Diversity. Cretaceous. Eustacy. North America