Fossil discovery captures brittle star mid-regeneration, 155 million years old

German scientists have uncovered a fossil of a six-armed brittle star, preserved while it was in the midst of regeneration. This unique find was made in 2018 in a limestone deposit in southern Germany, an area that was once a deep lagoon rich with coral meadows and sponge beds. Today, this site is a treasure trove of fossils, including shark teeth and remnants of extinct pterosaurs, crustaceans, and crocodile-like creatures from the late Jurassic period.

This fossil represents the first and only known example of a new brittle star species, Ophiactis hex. The fossil was identified by researchers as part of this new species. Many modern brittle stars and some starfish reproduce through fissiparity, a process where the star splits in two and each half regenerates the missing parts. This method of reproduction, also known as clonal fragmentation, typically involves species with six arms to facilitate an even split.

The paper, published in the journal Proceedings of the Royal Society B: Biological Sciences, states that while the biology and ecology of clonal fragmentation are fairly well understood, its evolution and geological history remain largely unknown.

The Ophiactis hex fossil, which is 155 million years old and preserved well enough to display its hook-shaped arm spines, provides significant evidence of the ancient origins of clonal fragmentation in star-shaped echinoderms. The name “Ophiactis hex” honors a supercomputer from Terry Pratchett’s Discworld novels. This discovery demonstrates that fissiparity is an ancient asexual reproduction strategy linked to the six-armed symmetry.

The study notes that while fossils of ophiuroids (brittle stars) with regenerating arms are relatively common, finding individuals with a regenerating body half is exceedingly rare. This particular specimen is only the second known case of such regeneration and the first where it appears linked to six-fold symmetry and clonal fragmentation.

The researchers admit that it’s challenging to determine the exact appearance of the species before it split and whether it originally had six arms since only one specimen of Ophiactis hex has been found so far.