Credit: Günter Schweigert
Phys.org has an article about starfish. In 2018, workers with the State Museum of Natural History Stuttgart discovered a brittle star fossil in a 150 million year old Jurassic limestone from a German deposit. The animal was named Ophiactis hex. It was preserved while in the process of regenerating three of its arms. Many species of echinoderms can reproduce by splitting off parts of their body. The main and the part can then regenerate into separate animals. This process is called fissiparity or clonal fragmentation. The findings were published in the journal Proceedings of the Royal Society B: Biological Sciences.
The work was based mostly on luck—the ancient brittle star was found during a random dig. But finding it was important, they note, because it shows that the evolutionary history of clonal fragmentation in brittle stars goes back at least 150 million years.
The research team determined that the creature had been in the middle of regenerating arms because the three new ones were much thinner and clearly less mature than the other three as evidenced by the difference in the growth of sharp spines.
They also note that it is the first such fossil evidence of its kind ever found. Brittle stars are known to live in dense colonies, suggesting that more specimens may be found at the same dig site.