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Tuesday, September 27, 2022

*Yorchycystis*, a 500-million-year-old relative of the starfish that lost its skeleton

Four years after excavating fossils in a churchyard in York, Pennsylvania, amateur paleontologist Chris Hafner made an interesting discovery. “I knew it was worth keeping,” he said. He posted his discovery on Facebook.

I saw his post, and realized it was a great discovery: I study fossil invertebrates at the Spanish Research Council. When I contacted Hefner, he agreed to donate the fossil to the Natural History Museum in London.

Working with colleagues in the US and UK, we determined that it was a 510 million year old relative of today’s starfish and sea urchins. It is extremely unique, new to science, and has only a partial skeleton. we named it yorkystis hefneriAfter its finder.

yorkcystis has revealed new information about how early life on Earth was developing at the time when most of today’s animal groups first appeared.

sea ​​urchins are yorkcystis‘ Living relatives.
Samuel ZamoraCC BY-ND

Cambrian explosion

yorkcystis Lived during the “Cambrian Explosion” between 539 million and 485 million years ago. Before this time, bacteria and other simple microbes lived alongside Ediacaran organisms, mysterious, soft-bodied creatures about which scientists know little.

The Cambrian brought a great proliferation of species that emerged from the seas. They included the groups of organisms that would eventually dominate the planet and representatives of most animal groups today.

Within a few million years, complex animals with skeletons and hard shells appeared. Why this happened is unclear, but a major change in ocean chemistry, with higher concentrations of calcium carbonate, likely played an important role.

Echinoderms were not the first of these to be found in the geological record. Brachiopods – marine animals that lived protected within seaweeds – predated them. So did arthropods, a group that had well-rounded calcite exoskeletons, including trilobites.

For context, dinosaurs appeared 294 million years after the dawn of the Cambrian.

first echinoderms

There are over 30,000 extinct echinoderm species, but they are very rare in places with exceptional Cambrian conservation, such as the Burgess Shale in Canada and Chengjiang in China.

Some of the first primitive echinoderms were quite different from their current relatives, with five arms extending out from the center of the body, a structure known as “pentamerous symmetry”.

Cambrian echinoderms had a wide range of body structures. Eocrinoids had vase-shaped bodies protected by geometrically patterned plates and numerous armalike structures. The thick cigar-shaped helicoplakoids were plated in calcite armor with a “mouth” that wrapped around its body. The blastoid species took on various shapes, often resembling exotic flowers.

Edrioasteroidea looked similar to today’s sea star, and with five arms protruding from its mouth, it is the creature that yorkystis hefneri Most similar. So we classified it on the evolutionary tree within this group.

yorkcystisEchinoderm without skeleton

While many Cambrian creatures built sophisticated skeletons and defense structures to protect them from predators, yorkcystis did the opposite. It “demineralized” its skeleton. It was a partially soft animal, with no protection on most of its body.

To understand this creature’s anatomy, we partnered with a paleoillustrator to visualize this creature from fossil evidence. Hugo Salas first modeled each part of the skeleton in 3D and then used it to create a reconstruction, a high-resolution replica.

From this replica, we saw that only its arms, or ambulacra, were calcified, protecting its “food grooves”—its feeding parts, which are yellow in the fossil. A series of plates covered its mesh and opened and closed during the meal. The rest of its body was soft, represented by a dark, carbon-rich film in the fossil.

Most extant echinoderms, found from the world’s coastline to deep ocean depths, have an internal skeleton. The exceptions are sea cucumbers and some species that remain buried under the ocean floor. their skeletons, like yorkcystisFormed by porous calcite plates.

Black And White Image Of Fossils Of Six Extinct Creatures
Representative of the Cambrian echinoderm with a mineralized calcite skeleton. A. Ctenocystoid. B Sinta. C helicoplakoid. D dissolve. E. eocrinoids. F Adriasteroid.
Samuel ZamoraCC BY-ND

Bring in yorkcystis For life

As paleontologists, we want to understand extinct organisms. yorkcystis presented a major challenge, as no similar animal is known, neither alive nor extinct.

Little is known about why and how some echinoderms lost parts of their skeletons. But advances in molecular biology have shown that echinoderms have a specific set of genes responsible for skeletal formation. All living echinoderms carry these genes; We believe that extinct groups did too.

but in yorkcystis, there is a marked difference between the calcification of its rays, or arms, and the lack of it on the rest of its body. This gives rise to the hypothesis that genes involved in skeletal formation may have acted independently in different parts of the yorkcystis‘ Body. This is a mystery that only molecular biologists will be able to solve.

Our study has allowed us to make some guesses about this animal, although many questions remain. We believe that without a skeleton in a significant part of its body, yorkcystis Was able to conserve energy for other metabolic processes such as eating or breathing. It also increased flexibility, allowing for more active respiration through pumping.

There is another intriguing possibility: the lack of skeleton may be related to some sort of stinging defense system, such as that used by present-day anemones that paralyze prey with stinging cells on tentacles around their mouths. gives. However, and many other questions cannot be answered with just one fossil.

but the wonderful discovery of yorkcystis The dawn of the Cambrian explosion has provided more insight into periods of distinct evolutionary history, a time when some organisms adopted skeletons to escape predators – and others adapted in very different ways.

World Nation News Desk
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