Biomechanics reveal 508-million-year-old sea monster was surprisingly weak

A new study employs biomechanical modeling to challenge old beliefs about one of Earth's earliest apex predators, Anomalocaris canadensis.
Sade Agard
An illustration of Anomalocaris
An illustration of Anomalocaris

Katrina Kenny 

The ancient marine predator Anomalocaris canadensis, known for its large size during the Cambrian era, was weaker than previously believed, according to new research published in Proceedings of the Royal Society B on July 4.

Scientists conducted biomechanical studies on A. canadensis, "legs," resembling arachnids— think spiders and scorpions. Their findings indicate that the sea monster was more of a 'softy,' preferring to chase soft prey in open water. This challenges the common notion of it pursuing hard-shelled creatures on the ocean floor.

Was Anomalocaris the first predator on Earth?

Discovered in the late 1800s, Anomalocaris canadensis, or "weird shrimp from Canada," had flaps for swimming, large compound eyes, and grasping appendages to catch prey. It's among the largest animals of the Cambrian era and considered an early apex predator. However, others have been found in older Cambrian rocks. 

Significantly, A. canadensis has been viewed as the cause behind damaged trilobite exoskeletons discovered by paleontologists in fossils.

"That didn't sit right with me because trilobites have a very strong exoskeleton, which they essentially make out of rock, while this animal would have mostly been soft and squishy," said lead author Russell Bicknell in a press release, a postdoctoral researcher in the American Museum of Natural History's Division of Paleontology.

Recent research on the armored, ring-shaped mouthparts of A. canadensis casts doubt on its capacity to process hard food. With this in mind, the new study explored whether the predator's long, spiny front appendages might have played that role instead.

Biomechanical modeling challenges old sea monster beliefs

An international team of scientists from Germany, China, Switzerland, the United Kingdom, and Australia constructed a 3D model of A. canadensis to begin their research. They used remarkably well-preserved, albeit flattened, fossils discovered in Canada's Burgess Shale, which date back 508 million years.

The team drew upon modern whip scorpions and whip spiders as comparisons. It demonstrated that the predator's segmented appendages could seize and manipulate prey. Additionally, they could extend and retract, providing flexibility for capturing and handling food.

Biomechanics reveal 508-million-year-old sea monster was surprisingly weak
A pair of Anomalocaris canadensis appendages

That said, when applying a modeling technique called finite element analysis to show the stress and strain points on this grasping behavior of A. canadensis, it was revealed that the appendages would have been damaged while grabbing hard prey like trilobites. 

The researchers then employed computational fluid dynamics to simulate the predator's movements in a virtual current. This enabled them to predict the most probable body position the creature assumed while swimming.

These advanced biomechanical modeling techniques, employed together for the first time in a scientific paper, have revealed a fresh perspective on A. canadensis.

Contrary to earlier assumptions, this ancient creature was probably a swift swimmer, zipping through the water with its front appendages stretched out in pursuit of soft prey within the water column.

"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 concluded.

If you're not familiar, a smorgasbord is a Swedish meal featuring a diverse selection of buffet-style dishes. In this context, the ancient sea monster might have needed to be more selective in its food choices.

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