"Giants of the Cambrian" survived longer

480 million year old anomalocarid fossils still show presence in the Ordovician

Model of the Cambrian Anomalocaridae Laggania, based on a fossil from the Burgess Shale. © Esben Horn
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The Anomalocarida animal group was considered extinct towards the end of the Cambrian, but probably the largest sea creatures of its time have survived at least 30 million years longer. The evidence in Morocco discovered 480 million year old fossils of these exotic-looking sea predators. As the researchers report in "Nature", these Anomalocarida with more than one meter in length for that time are true giants.

The Anomalocarida were considered the "giants" of the Cambrian: More than 500 million years ago, these 60 to 120 centimeters long multi-limbed animals populated the oceans in various forms. They had no teeth, but only soft horny plates in the mouth, but they wore two long, articulated gripper - probably to bring the food to the mouth. Little is known about their way of life beyond their scathing or predatory diet, as they are only conserved in a few fossils and - so it was thought - all died out at the end of the Cambrian. Because soft tissue and other non-ossified constituents are seldom conserved as fossils, the animal world of this early phase of evolution is still only fragmentarily known.

"The Anomalocarids are among the most iconic groups of Cambrian wildlife, " explains Derek Briggs, director of the Yale Peabody Museum of Natural History. "These invertebrate predators and scavengers have become almost symbolic of the unusual morphologies of organisms that evolved early as side branches on the animal's tree and then died out."

Fossil headgear of an anomalocarid from the Ordinary © Peter Van Roy

Ancient sea giants survived to the Ordovician

But as it turns out now, at least the Anomalocarids have apparently lasted longer than previously thought: Together with his colleague Peter Van Roy, Briggs discovered in a fossil lake bottom in Morocco fossils of this group of animals, which are only 488 to 472 million years old. Thus, this is the first evidence that the Anomalocarids survived the Cambrian era and remained at least 30 million years longer in the primeval oceans, even into the Ordovician.

The new discoveries indicate that animals that are considered typical of the Cambrian, such as the Anomalocarids, still have a significant impact on biodiversity and ecology many millions of years later marine communities, "said Van Roy. The newly discovered fossils were more than a meter long and therefore true giants for that time. On each segment of their bodies, they carried leaf-like appendages, which, according to the researchers, must have served as gills. The animals crawling about on the muddy bottom of the sea were probably so well preserved because swirling, fine sediment densely covered them, thus protecting the soft tissues from decay and decomposition. (Nature, 2011; DOI: 10.1038 / nature09920) Display

(Yale University, 30.05.2011 - NPO)