Even top predators weren’t safe in Cambrian seas around 520 million years ago. An extraordinary fossil shows a healed wound where one predator took a bite out of the side of another. The predator with a bite taken out of it is called Amplectobelua symbrachiata, which belonged to a long-extinct group of strange arthropods known as the radiodonts that looked a bit like a cross between squid and lobsters.
They had two vicious, grasping appendages on their heads for catching prey, and a line of swimming flaps protruding from their sides that decreased in size towards their rear. Extraordinary ichthyosaur fossil shows its last meal was a pterosaur They grew to nearly a metre long, which might be tiny compared with modern marine predators, but back in the Cambrian Period, it made them one of the biggest predators around. The swimming flaps of radiodonts were softer than their grasping appendages, resulting in very few fossils of them.
But a team recently found a single flap at a site in China called the Yu’anshan Formation, where soft tissues are exceptionally preserved. It is recognisable as a radiodont flap because of a characteristic pattern of lines on its surface. If it was the largest swimming flap, the animal would have been at least 23 centimetres long.
If it was one of the smaller flaps, it could have been much larger. The researchers noticed an odd W-shaped feature on the edge of the flap – the kind of shape typically left when two fangs tear through flesh. But is it really a bite wound?
The researchers in China got in touch with Pates because he has studied similar injuries in trilobites. X-ray fluorescence mapping shows that the chemical composition of the W-shaped part is consistent with the rest of the fossil, which means it’s not an artefact caused by flaking. What’s more, there is a black band visible around the edges of the W-shape that appears to be a sign of healing.
The team can’t be sure, but it could have been another species of radiodont, or even a member of the same species, says Pates. Palaeontologists have found new evidence that the early ancestors of amphibians, reptiles and mammals did not have a larval stage with external gills like modern frogs or salamanders Hundreds of likely predation wounds have been found on trilobites, but their fossils are much more common because of their hard exoskeletons and because they survived until 250 million years ago, whereas radiodonts were all extinct by around 480 million years ago. Trilobites were also much smaller and nearer the bottom of the food chain.
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