More than 500 million years ago, sea-dwelling invertebrates pioneered a new evolutionary experiment: skeletons. But while those tough, tube-like structures have stood the test of time as fossils, the animals’ soft bodies shriveled up and disappeared, erasing all evidence of what these ancient animals might have looked like. Now, a recent re-examination of those ancient skeletal tubes has finally revealed the identity of one of these mysterious beings.
These calcium-enhanced “skeletal” tubes date to a period known as the Cambrian Explosion (541 million to 510 million years ago) and appear to have been an effective survival strategy, appearing in multiple groups over a relatively short period of geological time (about 50 million years). During this period, everything from the segmented ancestors of earthworms to the bizarre ancient relatives of gaiters created protective tube-like structures.
However, tracing the evolutionary history of these early exoskeletons has proven difficult. “Soft tissues tend to decay,” Xiaoya MaAn invertebrate paleontologist at Yunnan University in China and co-author of a study describing the findings, told Live Science. For this reason, identifying fossil Cambrian pipes was a bit like trying to guess the contents of an empty, unclassified can based on the shape of the tin alone—most could have easily held chicken soup like whipped corn.
But scientists are shedding light on the mysterious skeleton makers. In the new study, published November 2 in the journal Proceedings of the Royal Society bAn international team of researchers has described four incredibly well-preserved Cambrian specimens from the Chinese province of Yunnan. These 514-million-year-old fossils of a tube-dwelling creature Gangtuconia aspera It includes the soft tissue prints left by the bodies of animals. By closely studying these impressions, scientists have determined that the tubes belonged, of all things, to ancient, skeleton-forming jellyfish.
Soft-bodied invertebrates are hard to find in the fossil record, and jellyfish in particular are almost never preserved. “This fossil was a double whammy in terms of rarity,” Luke BarryThe University of Oxford paleontologist and co-author of the study, told Live Science in an email.
Related: The ancient armored “worm” is the Cambrian ancestor of three major animal groups
Normally, when a marine organism dies, scavengers and bacteria make quick work of its soft tissues. But often, a wave of fine sediment covers the remains fast enough to prevent aerobic bacteria from settling. This is how the famous North American fossil deposit Burgess Shale was formed, according to Smithsonian National Museum of Natural History in Washington, D.C., and also likely how the site of Jonah was formed.
The newly discovered fossils, unearthed by lead study author Guangsu Zhang, a graduate student at Yunnan University, are preserved in such detail that paleontologists have even been able to identify the animals’ internal organs. The creatures’ mouths were surrounded by a ring of tentacles, each about 0.2 inch (5 mm) long. And they had a sac-like intestine with only one opening (as opposed to the separate mouth and anus that vertebrates are blessed with).
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These characteristics led the team to this conclusion raw g It likely belongs to the phylum Cnidaria, which includes modern jellyfish, corals, and sea anemones. He also established an ancient theory that the creature was an annelid, which is identified by its segmented body and intestine with two openings.
raw g It likely was attached in ancient oceans with one end of its tube attached to other members of its kind or by mobile creatures such as trilobites, retracting into its shell when predators swam by. It likely fed much as modern jellyfish polyps do, extending its stinging tentacles when prey was close.
Today only the larvae of one jellyfish group, Scyphozoa, create exoskeletons today. Some other cnidarians, such as corals, retain their skeletons into adulthood. However, today’s corals build their skeletons from calcium carbonate. in contrast, raw g Its tubes were made of calcium phosphate, the same hard compound that makes up tooth enamel and bone.
Why modern cnidarians switched from calcium phosphate to calcium carbonate exoskeletons remains a mystery. “One possible reason is that the environment before our era was rich in phosphorous,” Ma said. But the answer can be found in bleak genetics, too. Ma and her team hope to answer this question and others as their research continues. “We hope to have more for everyone in the near future,” she said.
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