ABSTRACT: Dinosaur Dusk-Mammalian Dawn; Changes in Vertebrate Community Structure During the Late Cretaceous and Paleogene

Richard K. Stucky

Late Cretaceous and Paleogene vertebrate communities show marked differences in structure because of the extinction at approximately 66 MYA of all large-bodied obligatory herbivore and carnivore guilds (dinosaurs) and reduction in the small-bodied terrestrial/scansorial omnivore guild (marsupials). Not until ca. 45 MYA did Paleogene vertebrate communities "recover" to the extent that they resemble those of the Late Cretaceous with the reoccurrence (through in situ evolution and immigration) of large-bodied obligatory carnivores and herbivores. Major differences also existed between late Cretaceous and early Paleogene plant habitats with the former being more open savanna-like and the latter more closed tropical forest-like. Vertebrate species richness in local habitats wa reduced by about one-third as a result of dinosaur extinction but, within several hundred thousand years after that event, recovered to previous levels. By a few million years after dinosaur extinction, species richness achieved levels of 50 to 100% greater. Major differences (and factors) to be considered in the analysis of vertebrate community structure from the Late Cretaceous through the Paleogene include: (l) body size; (2) trophic range (dental function); (3) physiological constraints; (4) reproductive strategies; and (5) population structure. The major controlling axis for Paleocene through middle Eocene vertebrate communities appears to have been vegetation structure. In Late Cretaceous and late Eocene vertebrate communities, large-bodied vertebrate herbivores and carnivores wer additional controlling factors.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990