Friday, November 24, 2006
Chicago, Illinois - The earth experienced its biggest mass extinction about 250 million years ago, an event that wiped out an estimated 95% of marine species and 70% of land species. New research shows that this mass extinction did more than eliminate species: it fundamentally changed the basic ecology of the world's oceans.
Ecologically simple marine communities were largely displaced by complex communities. Furthermore, this apparently abrupt shift set a new pattern that has continued ever since. It reflects the current dominance of higher-metabolism, mobile organisms (such as snails, clams and crabs) that actually go out and find their own food and the decreased diversity of older groups of low-metabolism, stationary organisms (such as lamp shells and sea lilies) that filter nutrients from the water.
So says embargoed research to be published in the journal Science on November 24, 2006. An accompanying article suggests that this striking change escaped detection until now because previous research relied on single numbers--such as the number of species alive at one particular time or the distribution of species in a local community - to track the diversity of marine life. In the new research, however, scientists examined the relative abundance of marine life forms in communities over the past 540 million years.
One reason they were able to do this is because they tapped the new Paleobiology Database, a huge repository of fossil occurrence data. The result is the first broad objective measurement of changes in the complexity of marine ecology over the Phanerozoic.
'We were able to combine a huge data set with new quantitative analyses,' says Peter J. Wagner, Associate Curator of Fossil Invertebrates at The Field Museum and lead author of the study. 'We think these are the first analyses of this type at this large scale. They show that the end-Permian mass extinction permanently altered not just taxonomic diversity but also the prevailing marine ecosystem structure.'
Based on "Abundance Distributions Imply Elevated Complexity of Post-Paleozoic Marine Ecosystems"
Likelihood analyses of 1176 fossil assemblages of marine organisms from Phanerozoic (i.e., Cambrian to Recent) assemblages indicate a shift in typical relative-abundance distributions after the Paleozoic. Ecological theory associated with these abundance distributions implies that complex ecosystems are far more common among Meso-Cenozoic assemblages than among the Paleozoic assemblages that preceded them. This transition coincides not with any major change in the way fossils are preserved or collected but with a shift from communities dominated by sessile epifaunal suspension feeders to communities with elevated diversities of mobile and infaunal taxa. This suggests that the end-Permian extinction permanently altered prevailing marine ecosystem structure and precipitated high levels of ecological complexity and alpha diversity in the Meso-Cenozoic.