PARIS: Scientists have discovered the beautifully preserved fossils of a huge arthropod — the group that includes crabs, scorpions, insects, spiders, centipedes and more — that lived 480 million years ago in what is now Morocco.
It was Earth’s largest animal at the time, at least double the size of anything else, says Peter Van Roy, palaeontologist at Yale University, who led the research published in the journal Nature.Despite its size, it was a gentle giant that ate only plankton.
The creature, called Aegirocassis benmoulae, was at least 2.1 metres long. It is the last known member of a group called anomalocaridids that included some of the first top predators near the dawn of animal life.
Almost all the group’s members were active predators, grabbing prey with appendages sprouting from their heads. Aegirocassis adopted another feeding strategy. Its appendages acted as a sieve, capturing oodles of plankton.
Periodically during Earth’s history, large predatory animal groups have produced exceptionally big species that were filter-feeders, not active hunters. Exploiting a plankton explosion during the Ordovician Period, Aegirocassis represents the beginning of this trend, foreshadowing today’s baleen whales and whale sharks.
“Given the huge size of Aegirocassis and its very alien appearance, I assume most people would probably be terrified if they’d encounter it while swimming. However, contrary to almost all other anomalocaridids which were active predators, our animal would have been a very peaceful guy,” Van Roy says.Aegirocassis possessed a torpedo-shaped head, an elongated body with 11 segments and two sets of flaps, considered precursors to the limbs of more advanced arthropods, along the side of each segment.
The lower flaps were used for swimming, with rhythmic undulations. The upper flaps stabilised the animal in the water and helped steer at higher speeds.
Ribbon-like structures, probably functioning as gills, covered its back. Two appendages near its mouth were specialised for filter-feeding, with a series of spines lined with bristle-like structures to sweep up small animals and particles.
