Scientists discovered something surprising in the fossilized embryo from a worm-like creature of the Cambrian period. The remains of a small, doughnut-shaped brain were found 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). Researchers have found hundreds of embryos that capture the different stages of the animal’s early development, but scientists have not yet found any fossils of these worm-like weirdos. Each embryo measures approximately half a millimeter (0. 02 inch) across.
“The great thing about Markuelia is that it looks like an adult — it actually looks like the penis worm of a small penis worm.” This gives scientists a better idea of what a mature M. Hunanensis likely looks like, Philip Donoghue of Live Science, a professor of paleobiology, at the University of Bristol, in England.
Donoghue and his collaborator Xi-ping Dong, a professor in the School of Earth and Space Sciences at Peking University in Beijing, have examined many of these embryos over the years, but this is the first time they’ve found one with preserved brain tissue hidden inside. They reported their discovery Oct. 4 in the journal Royal Society Open Science(opens in new tab).
Historically, reports of scientists finding fossilized brain tissue have been controversial because it was once thought that nervous tissue couldn’t fossilize, Live Science previously reported. The evidence in this case is convincing, according to Nicholas Strausfeld (a regents professor at the University of Arizona in Tucson) who was not involved with the study.
“That seems to me, inescapably, a tissue that is not muscle — and it’s not gut either, so what could it be?” Strausfeld told Live Science. He said that he would say they are neurons and that brain cells were arranged in a circle around what would have been once the animal’s stomach.
The exceptional embryo was taken from the Wangcun Lagerstatte fossil deposit in western Hunan. The tiny fossil was enclosed in a large slab made of limestone. Dong and his colleagues at Peking University carefully disintegrated the limestone rock with acid. Then, they manually sorted the microfossils from the residue.
” You can picture each one of these [embryos] weighing fractions of agram but he was literally reducing tons, metric tons of rock,” Donoghue stated about Dong’s efforts over the years to find these embryos. He said, “It’s beyond the ‘needle-in-a haystack’ territory.”
Once liberated from the limestone, the embryos were shipped to the Paul Scherrer Institute in Villigen, Switzerland, which houses a particle accelerator measuring about 1,300 feet (400 meters) in diameter. Donoghue stated that the machine generates radiation at a speed that is similar to light by hurling electrons at the speed of light. In this case, the team used high-powered X-rays produced by the accelerator to take snapshots of their tiny M. hunanensis embryos.
“The specimen rotates through 180 degrees within the beam, and it takes 1,501 X-rays as it goes,” Donoghue said. These individual X-rays can be combined into a 3D model that allows the team to view each embryo without needing to physically break it open.
” Normally, we don’t get preservation of an organism’s original anatomy; we just get the “cuticle” which refers to the animal’s tough outer shell. Donoghue explained about X-rayed embryos. Scientists often see thin lines that crosshatch the embryo’s interior. These lines are believed to be evidence that microbes grew over the animal before it was fossilized.
The embryo with traces of nervous tissue looked very different to what the team usually observed. The embryo had a clear, well-organized structure in its head that the team believed was the animal’s ring-shaped skull. The fossil also had a distinctive structure in its tail that the team interpreted to be remnants muscle.
” In this specimen, both the head as well as the tail, we have an entirely distinct, structured and organized mineralization fabric. It’s very unlike anything we’ve seen in any other specimen,” Donoghue stated. “That’s why it’s an intrinsic biological structure to the original organism and then it’s up to us to figure out .”
what it was.
Based on the relationship of M. Hunanensis to animals like penisworms and muddragons, scientists can reasonably expect its brain would be ring-shaped. Strausfeld explained that Strausfeld’s interpretation of the fossil makes sense. “Leaving aside the possibility of the brain’s fossilization, it would not be surprising if it displayed a different morphology,” Strausfeld explained in his report.
The authors noted that this fossilized nervous tissue is the first to be found in an Orsten-style fossil. These fossils usually have a length of 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 produces a tiny but detailed 3D fossil. It usually preserves only the animal’s cuticle and not its internal organs.
” The most fascinating thing about our paper, Donoghue stated, is what it tells us regarding the potential for future discoveries.” “Nobody could have predicted that calcium phosphate could preserve brains and nervous tissues. It’s possible to do so, but it’s only a matter of looking in museum drawers .”
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