Ancient worm burrows offer insights into early 'ecosystem engineers'

July 18 (UPI) -- Newly discovered fossils have offered scientists fresh insights into the role worms played in transforming the seabed during the Cambrian Period.

Fossilized burrows recovered in China deliver a snapshot of a subtle seabed change with significant ecological ramifications.

Prior to the Cambrian explosion, a period of accelerated speciation and biological diversity some 500 million years ago, the seabed was dense and oxygen-deprived. Organisms larger than bacteria couldn't survive there.

That changed with the arrival of the first bioturbators, species capable of moving and reworking sediment -- the first "ecosystem engineers."

The newest fossils showcase this important shift. Similar fossils have been found previously, but they revealed only shallow, horizontal burrows. The newest Cambrian fossils reveal deeper, more complex branching burrows.

"Here we see animals that were really able to go down into the sediment -- sometimes they went more than 30 centimeters, which is a lot -- and they were able to produce these branching systems," Luis Buatois, a professor of geological sciences at the University of Saskatchewan, said in a news release. "So in terms of locomotion and behavior, this was a much more advanced type of creature than the ones we have seen before."

Researchers believe their burrows were dug by some sort of early sea worm species. Their tunneling unlocked buried nutrients and allowed water and oxygen to penetrate deeper into the seabed, making the microhabitat more hospitable to an array of new species.

This newly livable acreage offered fresh space for evolution to run its course. New creatures adapted to the new environs, further altering the seabed.

"What we expect to see in a case like this is a kind of feedback loop," said Buatois. "The activity of these animals would have resulted in other animals exploiting the resources they generated, so the final product was one of increased complexity."

The findings of Buatois and his colleagues -- detailed in the journal Scientific Reports -- suggest bioturbation may have played an important role in facilitating the Cambrian explosion.