afrol News, 14 May - The discovery of a rich fossil site in south-eastern Morocco provides knowledge of a geological era that so far mostly has been in the dark, the Ordovician. The Fezouata find, still only sparsely mapped, could define the era.
Palaeontologists this week report that they 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 bio-diversification. "The findings 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," the researchers say.
The team, led by Yale palaeontologists Peter Van Roy and Derek Briggs, uncovered more than 1,500 fossils of soft-bodied marine animals in newly discovered sites in south-eastern Morocco during a field expedition last year. The sites are located in the Drâa Valley, north of Zagora, south-east of Ouarzazate, and are part of the Fezouata geological formation.
Many are complete fossils, and include sponges, annelid worms, molluscs and horseshoe crabs, in particular a species similar to today's horseshoe crab, which appeared some 30 million years earlier than previously known.
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 Bio-diversification Event," when the number of marine animal genera increased exponentially over a period of 25 million years.
Because hard shells fossilise 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.
"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," Mr 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."
The Fezouata site in Morocco 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 favourable chemical conditions within the sediment that allowed for the rapid mineralisation of soft tissue as it decayed.
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 Mr Van Roy.
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, the Yale researcher added.
The team expects to find even more fossils representing other species during future planned expeditions in Morocco. "We are only scratching the surface," Mr Van Roy said. "I am certain there will be more spectacular fossils coming out of this site in the near future."
The well-known Burgess Shale-type faunas are named after a famous fossil site in British Columbia, Canada, which has defined the geological era of the Middle Cambrian period. Fezouata in Morocco could equally define the Ordovician if the sites continue yielding the fossils anticipated by Mr Van Roy.
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