Friday, 17 February 2017

Sponges Ruled the World After Second-Largest Mass Extinction

By Laura Geggel, Senior Writer | February 13, 2017 10:15am ET 
Sponges may be simple creatures, but they basically ruled the world some 445 million years ago, after the Ordovician mass extinction, a new study finds.

Roughly 85 percent of all species died in the Ordovician mass extinction, the first of the world's five known mass extinctions. (The other mass extinctions are the Late Devonian, End Permian, End Triassic and End Cretaceous.) However, while the Ordovician mass extinction wiped out many of these ancient creatures, one group actually prospered: sponges.

"We think the sponges thrived because they can tolerate changes in temperature and low oxygen levels, while their food source (organic particles in the water) would have been increased enormously by the death and destruction all around them," lead study author Joe Botting, a paleontologist at Nanjing Institute of Geology and Palaeontology in China, said in a statement.

Chinese and British researchers discovered the fossils of some of these sponges in the newfound Anji Biota, a fossil deposit in the bamboo forests of Zhejiang province, in eastern China. The scientists uncovered nearly 100 species during their first excavation at Anji, and 75 of these species were sponges, many with preserved soft tissues, they said. 

The diversity of sponges is impressive given that the end-Ordovician event is the second-largest mass extinction on record, the researchers said.

The extinction occurred when a sudden, intense ice age was followed by an equally rapid warming period, which changed the ocean's chemistry and circulation, the researchers said. Earlier studies show that plankton quickly recovered after the extinction, but there are few fossils from that time period that show how other organisms fared, they said. In fact, until the discovery of the Anji Biota, the only known, well-preserved fossil deposit from that era was South Africa's Soom Shale.

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