Giants were predators of ancient deep

YALE (US) — Fossils discovered in Morocco show that a group of prehistoric sea predators grew more than a foot longer and lived for 30 million years longer than previously thought.

The creatures, known as anomalocaridids, were already thought to be the largest animals of the Cambrian period.

The period was known for the “Cambrian Explosion” that saw the sudden appearance of all the major animal groups and the establishment of complex ecosystems about 540 to 500 million years ago.

Scientists previously thought that the animals—which had long spiny head limbs presumably used to snag worms and other prey, and a circlet of plates around the mouth—grew to be about two feet long and died out at the end of the Cambrian.

Researchers have since discovered a giant fossilized anomalocaridid that measures one meter (more than three feet) in length with a series of blade-like filaments in each segment across the animal’s back, which may have functioned as gills.

In addition, the creature dates back to the Ordovician period, a time of intense biodiversification that followed the Cambrian, meaning these animals existed for 30 million years longer.

Details of the research are published in the journal Nature.

“The anomalocaridids are one of the most iconic groups of Cambrian animals,” says Derek Briggs, professor and director of Peabody Museum of Natural History at Yale University.

“These giant invertebrate predators and scavengers have come to symbolize the unfamiliar morphologies displayed by organisms that branched off early from lineages leading to modern marine animals, and then went extinct. Now we know that they died out much more recently than we thought.”

The specimens are just part of a new trove of fossils from Morocco that includes thousands of examples of soft-bodied marine fauna dating back to the early Ordovician period, 488 to 472 million years ago.

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 before the recent discoveries in Morocco.

The animals found in Morocco inhabited a muddy sea floor in fairly deep water, and were trapped by sediment clouds that buried them and preserved their soft bodies.

“The new discoveries in Morocco indicate that animals characteristic of the Cambrian, such as the anomalocaridids, continued to have a considerable impact on the biodiversity and ecology of marine communities many millions of years later,” says former Yale researcher Peter Van Roy (now at Ghent University in Belgium.

This research was supported in part by a National Geographic Society Research and Exploration grant.

The anomalocaridid sea predator existed longer and grew to much larger sizes than previously thought. (Credit: Peter Van Roy)

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