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 1 0 million years and encompasses four North American Land Mammal Ages ( Torrejonian, Tiffanian, Clarkforkian, and Wasatchian). The Neogene seq uence 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, frugivor es, omnivores; secondary consumers: insectivores, carnivores) are reco gnized for Paleogene and Neogene mammals based on tooth morphology, bo dy size, and analogy with modern mammalian groups. The Paleogene mamma lian biota is characterized as one in which both trophic structure and taxonomic composition change through the history of the record. The N eogene mammalian biota maintains a relatively consistent trophic struc ture through most of the record, although taxonomic composition change s substantially through time. Based on comparisons of trophic structur e 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 indi cates 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.