Cambrian Explosion: early form with definite brain (Introduction)

by David Turell , Wednesday, October 05, 2022, 19:21 (780 days ago) @ David Turell

This speciman definitely has a brain:

https://www.livescience.com/cambrian-fossil-embryo-with-brain?utm_campaign=368B3745-DDE...

"Scientists uncovered something unexpected in the fossilized embryo of a worm-like creature from the Cambrian period: the remains of a tiny, doughnut-shaped brain in the primordial animal's head.

"The roughly 500 million-year-old fossil is an example of the marine species Markuelia hunanensis, an ancient cousin of penis worms (priapulids) and mud dragons (Kinorhyncha). To date, scientists haven't found fossils of the worm-like weirdos in their adult form, but researchers have uncovered hundreds of pristine embryos that capture different stages of the animals' early development. Each of these embryos measures only about half a millimeter (0.02 inch) across.

"'The thing about Markuelia is, it looks like a mini-adult — it actually looks like a miniature penis worm," which gives scientists an idea of what a mature M. hunanensis likely looked like, Philip Donoghue, a professor of paleobiology at the University of Bristol in England, told Live Science.

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"The exceptional embryo was collected from a fossil deposit known as the Wangcun Lagerstätte in western Hunan, China. There, the teeny-tiny fossil had been encased in a large slab of limestone. Back at their lab at Peking University, Dong and his colleagues carefully dissolved this limestone rock with acid and then manually sorted through the microfossils in the residue.

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"'Normally, we don't get preservation of the original anatomy of the organism; we just get the cuticle," meaning the animal's tough outer shell, Donoghue said of the X-rayed embryos. In addition, scientists often see thin lines of mineralization crosshatching the inside of each embryo; such lines are thought to be evidence of microbes that grew over the animal prior to its fossilization.

"Compared with what the team typically observed, the embryo that contained traces of nervous tissue looked starkly different. That embryo bore a clear, organized structure in its head, which the team interpreted to be the animal's ring-shaped brain. What's more, the fossil carried another distinctive structure in its tail, which the team took to be remnants of muscle.

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"Based on the known relationship of M. hunanensis to animals like penis worms and mud dragons, scientists could reasonably expect its brain to be ring-shaped, so the authors' interpretation of the fossil makes sense, Strausfeld told Live Science. "Setting aside the improbability of [the brain's] fossilization, it would be surprising were it to exhibit a different morphology," the study authors noted in their report.

"Notably, this is the first time fossilized nervous tissue has been found in a so-called Orsten-style fossil, the authors added. Such fossils are usually less than 0.08 inch (2 mm) long, are found locked in nodules of limestone and are preserved through a mineralization process whereby the animals' tissue is replaced by calcium phosphate. This process produces a minuscule but highly detailed 3D fossil that typically only preserves the animal's cuticle, not its internal organs.

"'The most interesting thing about our paper is perhaps what it tells us about the potential for future discoveries," Donoghue said. "Nobody had foreseen that you could preserve brains or nervous tissues in calcium phosphate, and maybe it's just a matter of going back and looking for it in museum drawers.""

Comment: not closing any gap but confirming a brain in a Cambrian organism. A huge physiological leap from the Edicarans.