The Tradeoff That Helped Some Trilobites Survive Mass Extinctions – Ars Technica

Hundreds of millions of years before anthropogenic climate change became a thing at all, life on Earth suffered mass extinctions due to climate change caused by natural causes. However, there are still organisms that have survived and adapted to survive a fatal lack of oxygen. Trilobites have survived two devastating mass extinctions and still elude any surviving predators.

Paleontologists Jorge Esteve of the University of Madrid and Nigel Hughes of the University of California Riverside also found one species of trilobite, Auracopleura koninckii, It was particularly successful when ocean oxygen reached dangerously low levels. This creature persevered due to an unusual adaptation. Like most trilobites, a. Koninki It curled its fragmented body into a tight ball to avoid being devoured. But it also kept growing more segments with extra legs that doubled as gills.

Although the extra segments couldn’t fully roll over, more legs meant more opportunities for breathing, which gave this species an advantage when oxygen levels were low.

Keep rolling

fossils a. konicii They were actually found in a curled up position which is thought to have deterred predators from trying to take a bite. Trilobites can pull this off because their thoracic parts fit snugly against their heads when twisted, much like modern pills. The problem is that many a. Knoki The fossils have also been flattened by sediment that accumulated on the sea floor, making it difficult to interpret their anatomy. However, there are a few specimens that have preserved their shape after about 250 million years. Esteve and Hughes studied a particular specimen, named NMP-L12807, which was meticulously preserved in its reclining position.

When comparing Hughes and Esteve a. Koninki Sample others at different developmental stages saw that younger individuals with up to 17 segments could roll into a perfect ball with their heads under the tips of their tails. However, when cooked, the trilobites add slices with each corn. By the time they were 18 to 22, they could no longer do that tuck. Simulations of longer-twisted trilobites showed that part of the tail should extend over the head.

Our analysis indicates that in a. koninki, A transition in the recording pattern occurred at the point where the number and size of trunk segments exceeded potential [rolling into a perfect ball]Scientists said in a Stady Recently published in Proceedings of the Royal Society B.

From the bottom up

why would a. Koninki It evolves to add more segments to its body if that can make it vulnerable to attack? What would have been a disadvantage was actually an adaptation to declining oxygen levels near the sea floor on which it lived. Each segment on trilobites has two legs that act as gills that help them breathe by absorbing oxygen from the water and releasing carbon dioxide. More legs means more oxygen. Esteve and Hughes think a dwindling oxygen supply may be the reason these trilobites started adding extra segments once they reached maturity.

There is still the topic of predators, however a. konicii Much fewer encounters may have been with things with large mouths and many teeth. The mass extinctions that survived by adding thoracic segments, which augmented their breathing capabilities, meant a grim fate for creatures that couldn’t adapt to a lack of oxygen, and predators were no exception. Another way to look at its evolution, at least as suggested by the scientists, is that fewer predators meant this trilobite could afford to evolve more breathing equipment because it wasn’t in danger of snapping jaws.

Above a certain size, the predatory pressure threshold a. Koninki [possibly] Decline, thus alleviating the need to [tight rolling] And it succeeded by a clear discrepancy in the numbers of torso pieces,” the researchers said at the same time Stady.

This may have been a trade-off, but it seems to have worked in favor of the trilobites. Organisms sometimes evolve in a way that protects them from the greatest of many dangers. a. Koninki They must have been more threatened by a lack of oxygen than predators when they started adding extra segments, and the added gills gave those segments an advantage when it came to survival.

Proceedings of the Royal Society B, 2023. DOI: 10.1098/rspb.2023.0871 (about DOIs).