Fossil brains are found in ancient beetle-like creatures

Scientists have discovered these marks in fossilized Alalcomenaeus arthropods, an animal that shares phylum with modern insects, spiders and crustaceans.

The animals lived during the Cambrian period, which occurred between 543 million and 490 million years ago, and created a good fossil hard skeleton. But the soft tissues of the organism's brain and nerves often decay and thus disappear from the fossil record.

Now, a new study, published in December 11 in the journal Proceedings of the Royal Society B, describes not one but two Alalcomenaeus fossils complete with brains and all their decorations.

"What we are dealing with in the fossil record is special cases. This is uncommon but super rare," said co-author Javier Ortega-Hernández, a paleontological paleontologist at Dai. Harvard University and curator of the Harvard Zoological Museum. Previously, biologists had only identified another Alalcomenaeus specimen that was thought to have nerve tissue, but this finding was met with skepticism. With two specimens in hand, scientists can now believe that neural tissue can in fact be fossilized and found in special animal fossils Cambri, Ortega-Hernández said.

A newly discovered Alalcomenaeus fossil from the western United States contains the remains of a nervous system (black spot).

The debate is long

Besides Ortega-Hernández and his team, only a handful of researchers have reported fossil nerve tissue in Cambrian arthropods. In a 2012 paper, scientists described the first evidence of a fossil arthropod's brain in a tiny creature called Fuxianhuia protensa . Despite the widespread coverage in the media, the report has attracted critics.

Nicholas Strausfeld, professor of neuroscience at the University of Arizona and co-author of the 2012 study, as well as a number of others talking about brain-like features. arthropods. Some paleontologists argue that, based on our understanding of how animals decompose, Strausfeld stained specimens and others excavated cannot contain nerve tissue, Strausfeld said. Some people hypothesize that the black spots in the brain must be a strange stream of fossils or layers of fossilized bacteria, called biofilms.

Ortega-Hernández and co-authors have discovered a new Alalcomenaeus fossil buried in Utah in a geologically depressive region called the Great American Basin. The authors note that symmetrical black spots along the midline of the organism resemble the nervous system structures found in some modern arthropods, including horseshoes, spiders and scorpions."The nervous system and the intestines cross each other, which is really interesting but common in arthropods today," Ortega-Hernández told Live Science.

The dark spots also contain carbon content, a major factor in nerve tissue. Dark debris also plugged into the animal's four eyes. After examining all these criteria, Ortega-Hernández said that he could confidently report the discovery of fossil nerve tissue in the newly discovered specimen.

But to check their findings, the authors also tested a second Alalcomenaeus fossil from the Great American Basin. Originally dug up in the 1990s, the specimen has black spots and carbon traces similar to newly discovered fossils. Moreover, both Great Basin fossils fit the description of another specimen Strausfeld found in China. All three fossils have been found buried in similar mines, indicating that a unique preservation process allows all of their fossilized brain problems, Ortega-Hernández said.

Although Ortega-Hernández and colleagues reviewed their research, the authors "often have to be cautious when claiming to have found a true fossil brain," said Jianni Liu, a professor at the Institute of Life. Live early in the Department of Geology of Northwestern University in Xi'an, China, told Live Science in an email. Liu argues that the traces seen in the Cambrian fossils may be a "somewhat random effect of decay" rather than a remnant of brain matter.

In a 2018 study, Liu and colleagues examined about 800 fossil specimens and found that nearly 10% contained traces in the head. The authors looked at previous studies of animal tooth decay and found that nerve tissue tends to decay quickly, but intestinal bacteria can stick around and "create these."

Several paleontologists, including Strausfeld, have shown that Liu failed to examine fossils containing brain tissue and the lack of key evidence marked a "major flaw" in the study, the The tested sample contained asymmetrical black spots rather than symmetry, meaning they would not be interpreted as brain tissue, Strausfeld said.

In addition, decay studies often measure tissue decomposition in water, while buried fossils interact with countless chemicals carried in the sediments surrounding them, Ortega-Hernández said. For example, some studies suggest that the combination of clay and jumping water starts a process of hardening soft tissues in the body, similar to the way special chemicals can turn flexible cowhide into skin, Ortega-Hernández said.

Much work must be done to clarify the role of sediments in fossil conservation, but so far, ample evidence suggests that arthropods are under intense pressure to harden over time, Strausfeld said. The brain and nerves in animals slough off during this process, and because nerve tissue is high in fat, the structures repel water and "have some resistance to tooth decay , " he said.

Despite supporting evidence, Ortega-Hernández, Strausfeld and their colleagues may need to dig a lot more of the brain parts of arthropods to convince those unaware that ancient brains could. fossil.

"We appreciate the efforts of the authors to prove their results to be true neural tissue, but remain skeptical while the data only comes from two fossils , " Liu said. "New data is always welcome, but as we noted before, we will be more convinced if the anatomical features appear in consistent form on some independent samples."