NEARING THE END: REEF BUILDING CORALS AND BIVALVES IN THE LATE TRIASSIC AND COMPARING CORALS AND BIVALVES BEFORE AND AFTER THE END-TRIASSIC MASS EXTINCTION USING A TAXONOMIC DATABASE

Hannah Morgan Elliott Shepherd, The University of Montana

Abstract

One of the most important tenants in geology is that the present is the key to the past, but it can also be said that the past is the key to the present. The five great extinction events are some of the key events that can help us to understand how changes in climate and sea chemistry can cause great changes in the ecology of our planet. Today the increase in atmospheric CO2 is causing ocean acidification, which has also been proposed as part of the system that caused the end-Triassic mass extinction. Ocean acidification can be greatly detrimental to the skeletal structures of marine invertebrate such as reef building corals and bivalves. During the Norian and Rhaetian (Late Triassic), corals and bivalves had high diversity and abundance, but like many organisms involved in the mass extinction, quickly disappeared at the end of the Triassic. In the early Jurassic, very few surviving species of corals can be found, and almost no reefs. If this ‘reef gap’ was caused by a change in ocean chemistry, then how did these few species of corals survive? Were bivalves also affected by the changes? On Vancouver Island, rock units containing corals and bivalves can be found that represent both Norian and Rhaetian time intervals, but early Jurassic sedimentary units are found rarely, if ever. This creates a difficulty in looking for patterns in changes that happened after the mass extinction, but does allow for analysis of what reef communities looked like shortly before the end of the Triassic. In addition, by building upon data from the Paleobiology Database, changes in the global reef communities after the end-Triassic mass extinction can be examined.