14 DAY TRIAL // At the end of the Paleozoic era, in the final stages of the Permian period, about 250 million years ago, the Earth experienced the biggest mass extinction in its history, when 95% of marine species and 70% of land species perished. This extinction, in the dawns of the Dinosaur era, did more than eliminate species: it fundamentally changed the basic ecology of the world's oceans, as a new study showed.
Ecologically simple marine ecosystems were largely displaced by complex communities, and the new pattern has continued till now ever since. Complex communities (photo above) are dominated by higher-metabolism, mobile organisms (such as snails, fish, squids, starfish and crabs) that actively forage for food or just more complex (clams) and simple ecosystems (photo bellow) are dominated by older groups of low-metabolism, stationary organisms, like lamp shells (Brachiopoda) and sea lilies (Crinoidea) that filter nutrients from the water.
Until now, previous studies research relied on counting the number of species alive at one particular time to track the diversity of marine life and the scientists missed the ensemble picture. But the new approach examined the proportion of marine groups in communities over the past 540 million years. This time, they could consult data from the new Paleobiology Database, a huge repository of fossil occurrence.
This study has measured for the first time at a large scale changes in the complexity of marine ecosystems over the Phanerozoic (since first fossils of macroorganisms appeared in the seas). "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. "They show that the end-Permian mass extinction permanently altered not just taxonomic diversity but also the prevailing marine ecosystem structure." The data were introduced in analyses models concerning relative fossil abundance in communities throughout the Phanerozoic.
In simple marine ecosystems the bottom-dwelling organisms partitioned their resources similarly, but in complex marine communities, interactions among different species, like competition, predation, symbiosis, parasitism, as well as a greater variety of ways of life, affected abundance distributions.
Before the Permian mass extinction, both types of marine communities (complex and simple) were equally common, but after the mass extinction the complex communities were three times more abundant than the simple communities. "Tracing how marine communities became more complex over hundreds of millions of years is important because it shows us that there was not an inexorable trend towards modern ecosystems," Wagner said. "If not for this one enormous extinction event at the end of the Permian, then marine ecosystems today might still be like they were 250 million years ago."
"Studies by modern marine ecologists suggest that humans are reducing certain marine ecosystems to something reminiscent of 550 million years ago, prior to the explosion of animal diversity. The asteroid that wiped out the dinosaurs couldn't manage that." added Wagner.
"We had little idea of just how profoundly this one mass extinction--but not the others like it--changed the marine world." said Scott Lidgard, Associate Curator of Fossil Invertebrates at The Field Museum.
