Excavation reveals sponge dominance in wake of end-Ordovician crisis

Feb. 10 (UPI) -- Scientists in China have unearthed a treasure trove of sponge fossils, their fragile skeletons and soft tissues neatly preserved. The find offers a rare glimpse of life as it was 445 million years ago in the second-largest mass extinction.

Roughly 85 percent of all species disappeared during the end-Ordovician crisis. An ice age and then rapid warming, accompanied by dramatic changes in the chemistry of the ocean, followed. Little is known about life in the immediate aftermath of the crisis.

The only other post-crisis deposit is South Africa's Soom Shale, a Late Ordovician strata showcasing life as it existed in a glacial lagoon.

The new fossil fauna, dubbed Anji Biota, showcases life in the deep ocean. It consists of a thin layer of mudstone found in the forests of China's Zhejiang Province. So far, scientists have identified 100 different species.

Analysis of the Soom Shale has suggested most post-extinction survivor species were small and stunted. The Anji sponge fauna feature larger, more complex species. Though it appears sponges dominated, scientists also identified a few conical-shelled nautiloids and one sea scorpion.

"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 increased enormously by the death and destruction all around them," researcher Joe Botting said in a news release.

The discovery was detailed in the journal Current Biology.