Fossil catches the starfish’s cousin in the process of cloning itself

Some brittle stars give an arm and a leg (and another appendage) to propagate. When mating is infrequent, these starfish-like marine creatures divide themselves in half. Each side then regrows the missing half, creating two identical copies of the original animal.

This process, known as clonal fragmentation, is practiced by approximately 50 extant species of brittle stars and their sea star relatives. However, scientists have found it difficult to pinpoint when brittle stars, a long-standing group of echinoderms, began to reproduce in this way.

A recently discovered fossil from Germany pushes the origin of sea star cloning back more than 150 million years. In a paper published on Wednesday in Proceedings of the Royal Society Ba team of scientists describes the fossil of a brittle star that fossilized while regenerating three of its six limbs.

“It is the first fossil evidence of this phenomenon,” said Ben Thuy, a paleontologist at the National Museum of Natural History in Luxembourg and author of the new study. He added that the sample shows that “clonal fragmentation is actually much older than people previously thought.”

The brittle star fossil was discovered in limestone deposits at Nussblingen in southern Germany. In the late Jurassic period, 155 million years ago, this area was a quiet lagoon home to marine crocodiles. Sharks And Pterosaurs. When some of these creatures died, they sank to the bottom and were buried in mud. Low oxygen levels slowed their decomposition, preventing garbage collectors from picking up the bodies.

These conditions preserved the fossils in incredible detail, capturing minute structures such as Dragonfly wings And even a Dinosaur feather. The newly described brittle star is another treasure imprinted on limestone slabs at the site. “You have this brittle star with every piece in its original place, just as if it washed ashore a day ago,” Dr. Thuy said.

The brittle star fossil was discovered during 2018 excavations conducted by researchers from the State Museum of Natural History in Stuttgart, Germany. Dr. Thuy collaborated with researchers from across Germany and Austria to study the fossil.

The mismatched anatomy of the brittle star stood out. Three of its arms were thin, sinuous compared to its other three arms, which were larger and studded with thorns.

Scientists placed the fragile star inside a CT scanner to examine its structure. They also compared the animal’s anatomy with other types of brittle stars.

The researchers concluded that the fossil is the oldest known member of a family of still-living brittle stars called Ophiactidae. They placed the brittle fossil star in the genus Ophiactis and added the species name Hex, in reference to its six arms, and as a nod to Hex, a magical supercomputer created by fantasy writer Terry Pratchett. In Pratchett’s “Discworld” books, Hex can imagine the unimaginable.

For scientists, discovering a fossilized creature cloning itself was unthinkable.

In the past, researchers have discovered fossils of starfish regenerating single limbs. A brittle star from Jurassic sediments in Switzerland regrew multiple limbs when it fossilized. But the irregular growth patterns in these earlier fossils appear to represent sea stars regaining limbs lost to injury. In contrast, O. hex appears to regenerate its limbs along a symmetrical plane, making it the only known fossil echinoderm to have been immobilized following cloning.

The new fossil provides evidence that brittle stars have been splitting into two since at least the late Jurassic. According to Gordon Hendler, curator of echinoderms at the Natural History Museum of Los Angeles County, about half of living Ophiactis brittle stars are capable of cutting themselves in two. Asexual reproduction helps scavengers quickly colonize environments such as spongy meadows and moss patches.

Since they usually live in densely populated groups, it may be possible to find more fragile star clones in the Nussblingen limestone. But Dr. Hendler says finding a fossil like the O. hex specimen was fortunate.

“The chances of finding another discovery like this ‘ancient link’ seem very slim,” he said in an email. “I hope I’m wrong!”