PALEOECOLOGICAL CONSIDERATIONS REGARDING THE IRVINGTONIAN BIOTA FROM EL GOLFO DE SANTA CLARA, NORTHWESTERN SONORA, MEXICO

Ancient Colorado River fluvio-deltaic deposits are exposed in northwestern Sonora, Mexico along the upper Gulf of California from which a diverse Irvingtonian paleobiota has been recovered. Fossils have been found in badlands that developed in response to late Pleistocene doming along the Cerro Prieto Fault. To date, over 7000 mapped vertebrate fossil localities are documented and over 120 species have been identified. The entire preserved paleobiota suggests the existence of four ecologic communities: freshwater aquatic, riparian galleria forest, shrub and brush woodland, and savannah-like grassland. A suite of specific species suggests that the Irvingtonian climate was quite different from the temperate desert that prevails in the area today. The recovery of fan palm (Washingtonia sp.), giant tortoise (Hesperotestudo sp.), crocodile (Crocodylus sp.), boa constrictor (Constrictor constrictor), crested guan (Penelope sp.), flamingo (Phoenicopterus sp.), capybara (Neochoerus dicroplax), giant anteater (Myrmecophaga tidactyla), and prehensile-tailed porcupine (Coendou sp.) remains implies that the annual regional temperature supported tropical to subtropical climates, and that areas existed within the region where at least partial shade prevailed.