It is a dog-eat-dog world on the market. However earlier than there have been canine — and even dinosaurs — there have been trilobites brutally biting one another on the Cambrian seafloor. New analysis has revealed that these armored predators did not solely hunt smaller and weaker animals for meals, however would often take bites out of their trilobite comrades of the identical species. This discovering represents the earliest proof of cannibalism in the fossil report up to now.
Trilobites are now-extinct marine arthropods that first appeared in the fossil report round 541 million years in the past. They have been stout creatures with thick exoskeletons, which is probably going one of the explanations so many trilobite fossils remained preserved all these years; exoskeletons fossilize a lot simpler than softer tissues.
Russell Bicknell, a paleontologist on the College of New England in Australia, spent 5 years inspecting trilobite fossils from the Emu Bay Shale formation on Kangaroo Island in South Australia. There are two trilobite species from the identical genus discovered in this formation: Redlichia takooensis, a deposit feeder (opens in new tab) that ate particles on the ocean ground, and the bigger, predatory R. rex.
Many of the R. takooensis fossils have been discovered with what seemed to be chunk marks, totally on their hind ends. This was anticipated, as paleontologists already knew that R. rex made meals of R. takooensis. Within the Emu Bay formation, fossilized feces, referred to as coprolites, left behind by R. rex comprise trilobite shell remnants. This implies that R. rex had the potential of consuming the smaller trilobite species. What was sudden, although, have been indicators of related chunk marks on R. rex. These accidents, the researchers concluded, have been seemingly the consequence of cannibalism.
Associated: Why did trilobites go extinct?
“There’s not much else in this deposit that has the toolkit, is biomechanically optimized for this kind of thing, and could willingly crunch down on something hard,” Bicknell advised Stay Science. Whereas not a lot is known about trilobite mouthparts, Bicknell is for certain that these accidents weren’t “bites” in the standard sense. As a substitute, the underside of a trilobite featured two rows of legs, and on these legs have been little inward-facing spines. You probably have ever eaten crab legs or lobster, then think about an animal with legs just like the software trendy cooks use to crack open these shells. R. rex was born to hunt trilobites, and apparently it did not matter a lot which species.
Most of the accidents seen on the Emu Bay fossils have been accidents to the stomach and never the pinnacle. Bicknell believes it is because the injured animals have been making an attempt to get away from their predator’s clutches, however he additionally suggests there could have been a bit of survivorship bias at play too. The injured fossils are from the animals that obtained away — they weren’t eaten. Trilobites that sustained head accidents seemingly ended up as coprolites.
Whereas that is the earliest documented instance of cannibalism for any animal in the fossil report, Bicknell mentioned it is seemingly that cannibalism is way older and extra widespread than even these fossils recommend.
“I would go as far as to say that arthropods have been eating arthropods since the dawn of arthropods becoming arthropods,” Bicknell mentioned. Nevertheless, direct proof of such historical cannibalism has not been accessible in the fossil report, till now.
Whereas it’s tough to show that cannibalism came about, Bicknell and his colleagues have been capable of systematically take away all different explanations for the accidents discovered in R. rex fossils. “What you’re left with is this almost demonstrable record of cannibalism, just short of going back in time and watching it happen,” mentioned Bicknell.
This analysis was printed April 1 in the journal Palaeogeography, Palaeoclimatology, Palaeoecology (opens in new tab).
Initially printed on Stay Science.