RESTRUCTURING OF MARINE COMMUNITIES DURING LATE PALEOZOIC CLIMATE CHANGE IN BOLIVIA

Studies of modern ecological communities demonstrate that climate change may trigger changes in diversity and taxonomic composition; however, these studies are fundamentally limited to short timescales and therefore cannot demonstrate the full impact of major climate change. Understanding the ecological response of marine invertebrate communities to the Late Paleozoic Ice Age (LPIA), the last complete transition from icehouse to greenhouse, can establish a more complete picture of the climate-faunal relationship. The Copacabana Formation of Bolivia contains fossiliferous carbonates spanning the LPIA, allowing community structure from pre-glacial, glacial, and post-glacial conditions to be analyzed. Samples ranging in age from the Moscovian to the Artinskian, spanning the greatest extent of the LPIA, were collected from four localities of the Copacabana Fm.: Ancoraimes, Yaurichambi, Cuyavi, and Yampupata. Cluster analysis reveals three general groups: 1) Moscovian samples from before the main LPIA glaciation that include Gypospirifer and Linoproductus, 2) Asselian/Sakmarian samples from the P1 glacial and (possibly) interglacial characterized by Rhipidomella, Quadrochonetes, Hustedia, and Stenoscisma, and 3) Artinskian samples from the end of the P2 glacial, which lack the group 2 suite. The richness of samples is relatively stable through time with an average of 10 genera, including taxa mostly indicating a warm-water faunal association. Moscovian samples have a high proportion of cosmopolitan genera whereas those from the Permian are characterized by a high proportion of genera typical of Panthalassa (particularly west Texas). Unexpectedly, the majority of samples from the Permian that coincide with the greatest extent of glaciation have a more tropical character and unchanged diversity, though a few samples, mainly from Yaurichambi, have a high percent of characteristically Gondwanan taxa. These results indicate that community composition changed with the waxing and waning of the main Asselian/Sakmarian glacial, but diversity and the tropical character did not, perhaps related to the slow rate of climate change and ability of organism to adapt.