102 Paleontology (Posters) III - Diversity and Paleoecology

Monday, 1 November 2010
8:00 AM - 6:00 PM
Hall D

LONG-TERM TRENDS IN THE RICHNESS OF FRESHWATER ACTINOPTERYGIANS FROM THE LATE CRETACEOUS (CENOMANIAN-MAASTRICHTIAN) OF THE WESTERN INTERIOR OF NORTH AMERICA

Paper number: 102-16
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Nonmarine boney fish assemblages from the Late Cretaceous of the Western Interior of North America have traditionally been regarded as being dominated by basal actinopterygians. This is likely a bias resulting from the ease with which isolated elements of these fish can be identified. Teleosts have largely gone unstudied, even though they are abundant throughout the Late Cretaceous and represent an important component of freshwater ecosystems during that time interval. The goal of this study was to address this issue, by quantitatively characterizing changes in teleost community composition for the entire Late Cretaceous of the Western Interior of North America. Changes in community composition were assessed based on the abundance of teleost centra recovered from microvertebrate localities in southern Utah, northeastern Montana, and southern Alberta. The localities from these regions represent nine stratigraphic intervals extending from the late Cenomanian to the latest Maastrichtian.

Cenomanian boney fish assemblages are dominated by pycnodonts, amiids, and Lepidotes and at least seven kinds of teleosts present, including an elopomorph, an osteoglossomorph, and a hiodontid. A major restructuring of freshwater communities occurred between the Cenomanian and Turonian, marked by decreased abundance of pycnodonts and Lepidotes and the first occurrence of Lepisosteus, the amiid subfamily Vidalamiinae, and an indeterminate ostariophysan. Acanthomorphs first occur in the Coniacian, but do not become common until the middle Campanian. There is also a significant faunal turnover between the middle and late Campanian, with over seven new taxa appearing in the late Campanian. This increase in origination rates occur both in the northern (Alberta) and southern region (Utah).

Latitudinal differences between the northern and southern co-eval faunal assemblages do exist. Coriops and an unnamed semionotiform dominate the northern assemblage and Vidalamiinae and the indeterminate ostariophysan dominate the southern assemblages. These differences are considered to reflect latitudinal climatic conditions as opposed to differences in local environment sampling, because the taxa that occur in Alberta have been sampled from a wide range of freshwater environments.