Irish study fills gap in evolution

 

Fossil research by leading Irish scientists is the cover story today in a prestigious science journal, writes DICK AHLSTROM

IRISH SCIENTISTS have opened up a new window on the history of life on earth. Their analysis of fossils discovered in Morocco fills in a 30-million-year gap in the evolution of early life.

Teams based in Yale University in New Haven, Connecticut and University College Dublin found fossils of marine floor animals thought to have died out 510 million years ago. Instead their study shows that they persisted for at least another 30 million years.

Their research and images of the fossils are on the front cover of the prestigious journal Naturethis morning, an indication of the work’s importance.

Palaeontologists are excited about the findings because the fossils are of soft-bodied organisms such as worms, sponges molluscs and soft-shelled horse shoe crabs.

Fossils of soft-bodied animals are exceptionally rare in the fossil record compared to animals that leave behind hard shells and other tough tissues, explains lead author Prof Derek Briggs, director of the Yale Peabody Museum of Natural History and professor of geology and geophysics. Briggs is from Dublin and won the 2001 RDS/Irish Times Boyle Medal for Scientific Excellence.

The fossils are only preserved in the most ideal conditions, such as in the Burgess Shale in Canada, one of the world’s best fossil deposits of soft-bodied marine animals. These date back to about 510 million years ago and Briggs was part of a team that did ground-breaking work there.

Unfortunately the rich collection of early organisms discovered in the Burgess Shale had no later match. Scientists speculated that they might have gone extinct, but many believed that the exceptional preservation that took place at the Burgess Shale was so rare that it would be difficult to duplicate.

But it was duplicated, at the Fezouata Formations in the Draa Valley north of Zagora in southeastern Morocco. The region used to be part of an ancient sea floor that later formed into mudstone and siltstone.

Importantly, this rock was at least 30 million years younger than the Burgess Shale. And many of the soft-bodied organisms seen in the shales are also to be found in the Fezouata Formations.

The valley has provided a rich harvest of fossils. So far, it has delivered 1,500 soft-bodied specimens from at least 50 animal groups and, says Briggs, “this is probably just the tip of the iceberg”.

First author Dr Peter Van Roy is currently in the Draa Valley collecting fresh fossil material. It is difficult work, with team members either sitting in pits breaking off chunks of stone or searching for fossils where flash floods have cut into river beds.

Van Roy has spent 10 years searching for and studying fossils from the Moroccan site, according to Dr Patrick Orr of UCD’s School of Geological Science. From Belgium, Van Roy spent two years at UCD as a post-doctoral research fellow with funding from the Irish Research Council for Science, Engineering and Technology.

He then moved to Yale to work with Briggs, with expeditions to Morocco funded by National Geographic.

“We know the fossil record is an important record of life, but it is an incomplete record,” says Orr. It makes interpretation of the progress of evolution very difficult, akin to trying to assemble the plot of a film using only intermittent still images, he suggests.

There was an explosion of new life forms during the Cambrian Period, with the shales revealing soft-bodied animals, according to Orr, “and then the record went blank.”

Now the evolutionary story continues with the Moroccan fossils showing that many of these Cambrian animals survived and multiplied into the next period, the Ordovician.

The original animals were there but the Ordovician Period saw a rapid diversification of related species and so the mix is much more varied, Orr says.

Briggs and Van Roy worked with colleagues in Yale and UCD to make connections between the two fossil locations. “We were able to compare directly the Ordovician with the Cambrian soft-bodied animals,” Orr explains.

The find is incredibly important because details of soft-bodied fossils can now be added to the fossil record of hard-shell animals during the Great Ordovician Biodiversification Event. This came long before the first land-dwelling animals, when marine animals diversified faster than at any previous time, with new species of animals arising rapidly.

The research is important on a number of levels, Orr believes. “It forces a reshaping of a lot of the models of what happened. It fills in a major gap and throws open a new window on the history of life,” he says.“The fact that Naturehas taken it and put it on the front cover is indicative of its importance. It is a landmark.”