Division in the Jurassic period

150 million year old brittle star clone discovered

In some groups of snakes and starfish, a higher or lower number of arms is also linked to their ability to reproduce asexually.(Bild: APA/Naturkundemuseum Stuttgart/Günter Schweiger)

Like many other echinoderms (Echinodermata), brittle stars can regrow body parts. Some species also have the ability to reproduce asexually (fissiparity). This means that the animal divides and two new organisms - i.e. clones - are created from the two halves of the body. 

A team of researchers from Austria has now described a 150-million-year-old fossil of a brittle star that cloned itself shortly before its death. This was discovered in 2018 during excavations in the Nusplinger Plattenkalk in Baden-Württemberg.

Around 150 million years ago in the Jurassic period, there was an oxygen-poor lagoon of a tropical sea in the region, in which layer after layer of calcareous mud was deposited. Numerous animals were trapped in this mud after their death and eventually preserved as detailed fossils.

Non-uniform physique
The fossil of the brittle star - less than three centimetres tall with outstretched arms - is incredibly detailed. The most striking feature of the brittle star, which was assigned to the genus Ophiactis, which is still represented today, is its inconsistent body structure. While three arms are comparatively large and covered with spines, the other three arms are significantly thinner, shorter and less extended, with less pronounced spines.

The different sized arms indicate that the animal was in the middle of regenerating one half of its body at the time of death.

Asexual reproduction for 150 million years
It is difficult to say when this clonal fragmentation occurred because the ability to regenerate and grow depends on many factors, such as the availability of nutrients. The animal probably cloned itself at least a few weeks before its death, but it could also have been a few months. In any case, the researchers have succeeded in using the fossil to prove that echinoderms were already practicing this type of asexual reproduction 150 million years ago.