IT MAY have had a face only a mother could love, but it was the ocean’s top predator 500 million years ago.
It also persisted in those ancient oceans for much longer than palaeontologists realised thanks to a Yale University research team led by Irish scientist Prof Derek Briggs.
He and Dr Peter Van Roy recovered fossil remains of an animal that first emerged 525 million years ago; a sea creature that ruled the oceans for about 15 million years before disappearing.
Scientists believed that the animal, an invertebrate predator known as an anomalocaridid, must have died out. But then the Yale group recovered a much bigger and younger anomalocaridid from rocks in southeastern Morocco. They published their findings this morning in Nature.
The fossils are near complete examples of these animals, including their unusual front appendages as seen in the accompanying image.
Prof Briggs is famous for being among a group who recovered these and other exotic fossil animals from the Burgess Shale site in the Canadian Rockies of British Columbia.
Only partial anomalocaridid fossils were found, but they were so unusual that the two appendages were originally assumed to be the animal’s dinner, two prawn-like creatures trapped in the predator’s jaws, Prof Briggs said.
However, subsequent discoveries in Utah and Germany showed that the curved-back shapes were actually part of this predator’s feeding machinery. The assumption is that the “grasping appendages” were used to trap or hold prey, then pass it on to the animal’s jaws and mouth which were positioned underneath, he said.
The earliest discoveries are dated to 525 million years ago during a time known as the Cambrian period. This was an important episode for life on our planet because the simple worms and shelled animals delivered after millions of years of evolution suddenly developed into myriad forms during the “Cambrian explosion”.
The anomalocaridid rose to the apex of the food chain, becoming the top marine predator, said Prof Briggs, who is the director of Yale’s Peabody Museum of Natural History. Then the fossil trail ended for this animal by about 510 million years ago – at least until the discovery by the Yale researchers. They also discovered that the creature had changed.
“The extraordinary thing about this is we have found the largest species of this animal yet discovered,” he said. While the earlier finds were about 50cm (20in) or 60cm long, the Moroccan fossil was more than a metre long.
“This is the largest complete animal yet discovered and it is also 30 million years younger,” he said. “They persisted a lot longer than we realised and must have been an important component of the marine environment. They were still the top predators at that time.”
The Moroccan fossils date to about 480 million years ago, putting them into a more recent period, the Ordovician, he said.
There has been some discussion among palaeontologists about how “efficient” they were as the lions or killer whales of their environment, he said.
“These things went for the easy things, worms and soft bodied animals. The fact that they got to such a large size means that there was plenty of nutrients around.”
There is limited evidence that they went for hard shelled animals as well however. Some hard-bodied fossils show signs of bite marks and damage that matches the unusual jaw of this giant anomalocaridid.
He believes that the Moroccan find will be from the same genus but will prove to be a different species of these animals given the 30 million year difference between them.
