The recent discoveries come from a pristine site in southern China's Yunnan province.  (Source: University of Bristol)

A mid-Triassic ichthyosaur, a predatory aquatic reptile, was among the 20,000 fossils recovered by the recent dig.  (Source: University of Bristol)

The saurichthys was another fearsome sea predator identified.  (Source: University of Bristol)

Newly evolved sea urchins (left) and horseshoe crabs (right) looked much like their modern counterparts do today.  (Source: University of Bristol)
Collection of 20,000 fossils reveal that life almost recovered within 10 million years

A vast body of paleontological evidence points to the Permian-Triassic period transition, which occurred approximately 250 million years ago, was the largest extinction event in history, surpassing even the extinction of the dinosaurs at the end of the Cretaceous period.  The extinction event is the only known extinction event to feature a mass extinction of typically hard insects.  And the extinction in total encompassed 96% of all marine species, 70% of terrestrial vertebrate species, 57% of all families, and 83% of all genera.

Mike Benton, professor of vertebrate palaeontology in the School of Earth Sciences at the University of Bristol, and a team of researchers at the Chengdu Geological Center in China have published a study from the middle Triassic (235 mya) that reveals how evolution allowed for a surprisingly quick biotic recovery and yielded new kinds of species (like the dinosaurs and early mammals).

Describes Professor Benton in a university news release, "The Luoping site dates from the Middle Triassic and contains one of the most diverse marine fossil records in the world.  It has yielded 20,000 fossils of fishes, reptiles, shellfish, shrimps and other seabed creatures. We can tell that we're looking at a fully recovered ecosystem because of the diversity of predators, most notably fish and reptiles. It's a much greater diversity than what we see in the Early Triassic -- and it's close to pre-extinction levels."

The study is one of the most important works to come out about the extinction event since a 2000 study which used uranium/lead ratios of zircons from rock sequences near Meishan, Changxing, Zhejiang Province, China (located in Western China) to definitively show when the event occurred -- approximately 251.4 ±0.03 mya (with elevated extinction rates for some time thereafter).

The scientific community has been desperate to discover more about the causes and impact of this world changing event.  Among the key questions is how the Earth's climate changed and what kind of disaster struck to cause the extinction.  Some speculate that volcanism contributed to the extinction, with geological evidence pointing to the Siberian Traps eruption which covered 2,000,000 square kilometers (772,204.3 sq mi) in lava.  Others point to a meteor impact, anoxia (lack of atmospheric oxygen), and/or hydrogen sulfide emissions from deep sea bacteria as play a role in the extinction.

While the debate about the event's causes continues, another critical question is how life evolved in response to the event.  That's where the new study really shines.

The new study uses fossil evidence extracted from a site in the Luoping in Yunnan Province, a souther Chinese province.  The site was in pristine condition and thus yielded an incredible amount of intact fossils, which allowed paleontologists to identify various specimens and begin analyzing the period's biodiversity.

The study unveils early versions of a number of infamous marine predators, including members of the bony fish genus Saurichthys (similar to today's sturgeon), the ichthyosaur genus Mixosaurus (which played a role similar to today's dolphins), the sauropterygian genus Nothosaurus (an ancestor to the larger plesiosaurs).

But the wealth of fossil evidence covers far more than these iconic predators.  It also showcases a variety of lower lifeforms, including the crustaceans, fishes and bivalves that the predators thrived upon.  Many of these creatures appear to have evolved key new features, not present in their Permian-survivor ancestors.

What is clear from the study, published in the journal 
Proceedings of the Royal Society B, is that the ever-flexible genome was able to allow diversity to rebound to pre-extinction levels in only 10 million years.  Previously it was far less certain exactly how quickly that recovery occurred.

States Professor Benton, "The fossils at Luoping have told us a lot about the recovery and development of marine ecosystems after the end-Permian mass extinction.  There's still more to be discovered there, and we hope to get an even better picture of how life reasserted itself after the most catastrophic global event in the history of our planet."

Professor Shixue Hu of the Chengdu Group cheered the discovery, stating that it will offer many decades to come of fruitful research.  He comments, "It has taken us three years to excavate the site, and we moved tonnes of rock. Now, with thousands of amazing fossils, we have plenty of work for the next ten years!"

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