Trilobites set foot on breathing

A new study found the first evidence of sophisticated respiratory organs in sea creatures 450 million years ago. Contrary to previous beliefs, trilobites were the respiratory organs of the legs, with gill-like structures hanging on the thighs.

Trilobites are a group of marine animals with half-moon-like heads that resemble horseshoe crabs and have been very successful in terms of evolution. They are now extinct, but longer than dinosaurs and have survived for over 250 million years.

Thanks to new technology and very rare fossils, scientists at the University of California, Riverside have been able to show and explain how trilobites breathe oxygen. These findings, published in the journal Science Advances, help connect the puzzles of early animal evolution.

“So far, scientists have compared the upper branches of trilobite legs to the non-respiratory upper branches of crustaceans, but our paper shows for the first time that the upper branches functioned as gills. “Jin-Bo Hou said. , UCR Paleontology PhD student who led the study.

Among the oldest animals on earth, this task places trilobites more safely on evolutionary trees, among old arthropods, large groups of animals with exoskeletons, and crustaceans. Useful for.

Studies were possible, in part, for abnormally preserved fossil specimens. There are more than 22,000 species of trilobites found, but only about 20 are visible in the soft parts of the animals.

“These were preserved in pyrite (fool’s gold), but they are more important than gold because they are the key to understanding these ancient structures,” said UCR Geology professor and paper co-author. One Nigel Hughes said.

The CT scanner was able to read the difference in density between pyrite and the surrounding rocks, helping to create a three-dimensional model of these rarely seen gill structures.

Paleontologist Melanie Hopkins, a research team member at the American Museum of Natural History, said:

“This gave us a view that was difficult to see under a microscope. It’s a very small trilobite anatomy, about 10 to 30 microns wide,” she says. For comparison, human hair is approximately 100 microns thick.

These specimens were first described in the late 1800s, and other specimens examined them using CT scans, the first study to use technology to inspect this part of the animal.

Researchers were able to see how blood was filtered through these delicately structured chambers and picked up oxygen on the way. They look much like the gills of modern marine arthropods such as crabs and red shrimp.

By comparing pyrite specimens with other trilobite species, the team was able to learn more about how the filaments are arranged with each other and with respect to the legs.

Most trilobites used lower limb spikes to clean the seabed to catch and grind their prey. Above those parts, on the branches of the upper limbs, were these additional structures that were believed to be intended to assist in swimming and digging.

“In the past, there was some debate about the purpose of these structures because the upper limbs are not the best place for the respiratory system,” Hopkins said. “You’ll find it easy for those filaments to get clogged with sediment where they are. It’s an open question why they evolved the structure of that place in their body.”

Hughes’ lab uses fossils to answer questions about how life developed in response to changes in the Earth’s atmosphere. Approximately 540 million years ago, there was an explosive diversity in the diversity and complexity of marine animals.

“We know that in theory this change must be associated with an increase in oxygen, as these animals require the presence of oxygen, but their ability to measure it is almost non-existent. There wasn’t, “Hughes said. “This makes these findings even more exciting.”

Reference: “The upper limb branch of trilobite is a well-developed gills,” Jin-bo Hou, Nigel C. Hughes, Melanie J. Hopkins,31 March,2021.

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