COMPARATIVE PALEOECOLOGY OF PALEOGENE AND NEOGENE MAMMALIAN FAUNAS - TROPHIC STRUCTURE AND COMPOSITION

Trophic structure and composition are examined in two important biotic records, one the Paleogene of Wyoming and Montana, and the other from the Neogene of Pakistan. The Paleogene sequence spans approximately 10 million years and encompasses four North American Land Mammal Ages (Torrejonian, Tiffanian, Clarkforkian, and Wasatchian). The Neogene sequence spans approximately 17 m.y. and includes most of the Miocene and Pliocene with the best documented interval spanning from 16 to 7 Ma. Five basic trophic categories (primary consumers: herbivores, frugivores, omnivores; secondary consumers: insectivores, carnivores) are recognized for Paleogene and Neogene mammals based on tooth morphology, body size, and analogy with modern mammalian groups. The Paleogene mammalian biota is characterized as one in which both trophic structure and taxonomic composition change through the history of the record. The Neogene mammalian biota maintains a relatively consistent trophic structure through most of the record, although taxonomic composition changes substantially through time. Based on comparisons of trophic structure from the Paleogene and Neogene records with that of selected modern mammalian faunas, Paleogene habitats fluctuated between closed, humid forests and more open, drier woodlands. Neogene trophic structure indicates that savanna woodlands were the typical habitat present through most of the sequence. Only after 7 Ma did these woodlands give way to more open grasslands in Pakistan.