Fossils from a Time of Intense Biodiversification
Paleontologists have discovered a rich array of exceptionally preserved fossils of marine animals
that lived between 480 million and 472 million years ago, during the early part of a period known
as the Ordovician. The specimens are the oldest yet discovered soft-bodied fossils from the
Ordovician, a period marked by intense biodiversification. The findings, which appear in the May 13, 2010
issue of the journal Nature, greatly expand our understanding of the sea creatures and ecosystems that
existed at a crucial point in evolutionary history, when most of the animal life on the planet was found in the oceans.
Discovered in Southeastern Morocco
The team-led by Peter Van Roy, a Yale postdoctoral associate, and Derek Briggs, the Frederick William
Beinecke Professor of Geology & Geophysics and director of the Yale Peabody Museum of Natural
History-uncovered more than 1,500 fossils of soft-bodied marine animals in newly discovered sites in
southeastern Morocco during a field expedition last year. Many are complete fossils, and include sponges,
annelid worms, mollusks and horseshoe crabs-in particular, a species similar to today's horseshoe crab,
which appeared some 30 million years earlier than previously known.
The Great Biodiversification Event
The Cambrian period, known for the "Cambrian Explosion" that saw the sudden appearance of all the
major animal groups and the establishment of complex ecosystems, was followed by the "Great
Ordovician Biodiversification Event," when the number of marine animal genera increased exponentially
over a period of 25 million years.
Because hard shells fossilize and are preserved more readily than soft tissue, scientists had an
incomplete and biased view of the marine life that existed during the Ordovician period until now.
Why This Discovery is So Important
"The early Ordovician was a critical moment when massive diversification takes off, but we were
only seeing a small piece of the picture that was based almost exclusively on the shelly fossil
record," Briggs said. "Normal faunas are dominated by the soft-bodied organisms we knew were
missing, so these exceptionally well-preserved fossils have filled in much of the missing picture."
Rapid Burial and Calm Waters Preserved Fossils
The site in Morocco where the fossils were discovered was conducive to preserving even the
soft tissues of the creatures that lived in its waters so long ago, thanks to generally calm
waters, occasional rapid burial that protected the animals from scavengers, and favorable
chemical conditions within the sediment that allowed for the rapid mineralization of soft tissue as it decayed.
A Burgess Shale Connection
In addition to providing a more complete understanding of marine life at that time, the team's
discovery upends a long-held belief that so-called Burgess Shale-type faunas, which are typical
for the Early to Middle Cambrian, disappeared at the end of the Middle Cambrian epoch, some
499 million years ago.
"There was an anomaly in the fossil record. Most of these animals just seemed to disappear at
the end of the Middle Cambrian," said Van Roy, first author of the paper.
The team found that these Burgess Shale-type species survived well into the Ordovician period,
which would have had a major impact on those ecosystems and their evolution, Van Roy said.
Future Work at the Moroccan Field Site
The team expects to find even more fossils representing other species during future planned
expeditions in Morocco. "We're only scratching the surface," Van Roy said. "I'm certain there
will be more spectacular fossils coming out of this site in the near future."
Authorship and Support
Other authors of the paper include Patrick J. Orr (University College Dublin), Joseph P.
Botting (Leeds Museum Discovery Centre), Lucy A. Muir, Jakob Vinther (Yale
University), Bertrand Lefebvre (Université Lyon), and Khadija el Hariri (Université Cadi Ayyad).
The fossil sites were originally discovered by a local Moroccan collector, Mohammed Ou Said Ben Moulla.
This research was funded by an Agency for Innovation by Science and Technology (IWT)
doctoral fellowship, an Irish Research Council for Science, Engineering and Technology (IRCSET)
postdoctoral fellowship, and a National Geographic Society Research and Exploration grant.
|Researchers found more than 1500 fossils of marine creatures, such as this cheloniellid arthropod,
that lived nearly 500 million years ago. Photo: Peter Van Roy/Yale University.|
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