The first apex predator on Earth is likely to have been better suited to feasting on soft-bodied prey than pursuing hard-shelled creatures, new biomechanical analysis of the creature’s appendages shows.
Anomalocaris canadensis was a 60-centimetre-long arthropod (the group of animals that includes insects, spiders, crabs and scorpions), making it one of the largest animals to live during the Cambrian period which lasted from 541 million to about 484 million years ago.
The Cambrian witnessed an “explosion” of life leading to the formation of all the major body structures of animals that we see today: the first eyes and back-boned animals emerged during this period as did Anomalocaris, discovered in Canada’s Burgess Shale in the 1800s.
The creature’s scientific name means “weird shrimp from Canada.” Palaeontologists theorise that this bizarre animal’s strange arachnid-like front “legs” would have been used for capturing prey and directing it into its ring-shaped mouth.
While probably fast and agile, new biometric analysis of Anomalocaris published in the Proceedings of the Royal Society B suggests it was weaker than previously thought.
Previous fossil findings of crushed trilobite exoskeletons have been associated with Anomalocaris feeding.
“That didn’t sit right with me,” says Dr Russell Bicknell, a researcher in the American Museum of Natural History who conducted the study while at the University of New England in Australia.
Bicknell is lead author of the paper.
“Trilobites have a very strong exoskeleton, which they essentially make out of rock, while this animal would have mostly been soft and squishy.”
Recent research cast doubt over the animal’s armour-plated mouthparts to process hard food. The new study aimed to find out if the long, spiny front appendages could do the job instead.
The international research team built a three-dimensional reconstruction of Anomalocaris. Using modern whip scorpions and whip spiders as biomechanical analogues, the team found that the segmented appendages would have been good at stretching out, flexing and grabbing prey.
But modelling showed that the stress and strain on the appendages would have led to damage when handling hard prey like trilobites.
The study suggests Anomalocaris was maybe a fast-swimming predator zipping after soft prey with outstretched front appendages.
“Previous conceptions were that these animals would have seen the Burgess Shale fauna as a smorgasbord, going after anything they wanted to, but we’re finding that the dynamics of the Cambrian food webs were likely much more complex than we once thought,” Bicknell adds.
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