A team of paleobiologists from UC Riverside University in California (USA) has found the first evidence of sophisticated respiratory organs in trilobites, those alien-looking sea creatures with crescent-shaped heads – and indeed with a certain resemblance to the horseshoe crabs – that inhabited the Earth 450 million years ago. Contrary to previous beliefs, researchers have discovered that trilobites breathed through their legs, bearing gill-like structures hanging from their thighs.
Trilobites are well known from an extensive fossil record. Due in part to their enormous diversity and tough exoskeletons, some 20,000 fossilized species of these arthropods have been discovered and described. And while they are now extinct, they survived for more than 300 million years in Earth’s ancient oceans, much longer than the popular dinosaurs. They appeared in the early Cambrian period, about 540 million years ago, yes, long before life emerged on our planet, and they disappeared about 252 million years ago during the mass extinction at the end of the Permian period, known as the Great Dying. . The greatest extinction that has ever taken place on Earth. Approximately 95% of marine species and 70% of terrestrial vertebrate species disappeared (and the cause of which is still involved in various hypotheses).
They are among the oldest animals on Earth
Now, thanks to new technologies and an extremely rare but incredibly well-preserved set of fossils, UC Riverside scientists have shown that trilobites breathed oxygen and their curious method of doing so, something that again helps us to continue to complete the puzzle. of this animal that had great evolutionary success (in fact, its fossil exoskeletons can be found all over the world).
“Until now, scientists have compared the upper limb of the trilobite leg to the non-respiratory upper limb in crustaceans, but our article shows, for the first time, that the upper limb functioned as gills,” says Jin-Bo Hou, PhD student in paleontology at the UCR who directed the research published in the journal Science Advances .
The researchers examined the pyritized remains of two trilobite species : Olenoides serratus from Burgess Shale and Triarthrus eatoni from Beecher’s Beds. Triarthrus eaton i lived approximately 450 million years ago (Ordovician period); Olenoides serratus lived during the Cambrian period, about 500 million years ago.
“They were preserved in pyrite, fool’s gold, but it is more important than gold to us, because it is key to understanding these ancient structures,” said Professor Nigel Hughes, a paleontologist in the University’s Department of Earth and Planetary Sciences. . of California and leader of the work.
A computerized axial tomography scanner was able to read the density differences between the pyrite and the surrounding rock, which made it possible to create three-dimensional models of these rarely seen gill structures , so they did not have to drill and polish the rock covering the specimens. and therefore see the fossil without damaging the preserved structure in the pyrite.
“This way we could get a view that would even be difficult to see with a microscope – really tiny trilobite anatomical structures on the order of 10 to 30 microns wide, ” he said. For comparison, a human hair is approximately 100 microns thick.
The researchers were able to see how blood had filtered through chambers in these delicate structures of the legs, picking up oxygen on its way as it moved. They closely resemble the gills of modern marine arthropods such as those found in crabs and lobsters.
“In the past, there was some debate about the purpose of these structures because the upper part of the leg does not seem like a good location for the respiratory apparatus,” he clarifies. Hopkins. “You’d think it would be easy for those filaments to get clogged with sediment where they are. It is an open question of why they developed the structure in that place of their bodies “, concludes the expert.
An exciting find without a doubt.
Referencia: Jin-bo Hou, Nigel C. Hughes, Melanie J. Hopkins. The trilobite upper limb branch is a well-developed gill. Science Advances, 2021; 7 (14): eabe7377 DOI: 10.1126/sciadv.abe7377
