A Brittlestar Specimen Fossilized During Cloning

A newly discovered brittle star, fossilized during its cloning process.

Post Author - Carlin Decker

How did the complex traits and behaviors that define certain species come to be? The answers lie in hundreds of millions of years of geological time and evolutionary genealogy, but determining when exactly a trait was developed can be a significant benchmark for mapping a species’ genetic history. For a myriad of practical reasons, brittle stars have the ability to remove their legs or split themselves and grow back, and now, recent archaeological evidence shows that these stars have been behaving like this for much longer than we thought. 

Brittle stars, along with their cousins sea stars, are known for their ability to asexually reproduce via the removal of limbs to grow a new organism. These stars essentially “clone” themselves by splitting off their symmetrical half to grow new arms. These fissiparous brittle stars tend to have six legs instead of the recognizable five point star. Fissiparity is a common trait observed in many species of brittle and sea stars. Scientists have been able to familiarize themselves with how these stars have been able to reproduce as they are observed today in most major marine zones, however, there have been difficulties pinpointing the exact start of this trait in the stars’ evolutionary timeline. A new discovery in southern Germany has brought forth a fossilized brittle star specimen that had recently fissioned during the late Jurassic Period.

Brittle star evolutionary chart

The fossil was found in the Nusplingen limestone deposit in 2018, and recent publications have determined that this specimen dates back to about 155 million years ago. The deposit was a lagoonal area which was home to many prehistoric marine species, and is known to contain many well-preserved fossils. The low levels of oxygen toward the bottom of the lagoon prevented decomposers from picking away at the carcasses of deceased creatures, helping create the well preserved fossils. The star appears to have three larger legs and three smaller ones. This is one of the oldest recorded specimens with evidence of star fission. As these stars tend to have a fast post-mortem decay rate, and the window of post-fission regeneration in an observable state is rather small, a specimen this old and in this shape is a very rare find. 

Dr. Ben Thuy, a paleontologist at the Natural History Museum in Luxembourg, comments how the star has been kept so well intact that it looks almost as if it has been washed up and found on a beach today. This fossil has been categorized into the family of brittle stars Ophiactidae, and has been given the name Ophiactis Hex. Hex refers to the number of arms of the star, as well as a nod to the supercomputer character of the same name in Terry Prachett’s Discworld series. This specimen is one of the only known fossil records this old of a brittle star regenerating its limbs along a symmetrical plane.