New starfish-like fossils suggest evolution is in action

Cambridge University researchers have uncovered the earliest fossils of starfish-like animals that help us understand the origins of these mobile weapons. New starfish-like fossils suggest evolution is in action.

The starfish prototype, which is common to modern water lilies and starfish, is the missing link in the chain for scientists trying to piece together their early evolutionary history.

A very well preserved fossil called Cantabrigiaster fezouataensis has been found in the Anti-Atlas Mountains of Morocco. Its intricate design - with hairy hands like the ends - has been frozen in about 480 million years.

This new species is unusual in that it lacks many of the basic features of its modern relatives and loses about 60% of the body shape of modern starfish.

Instead, the fossil's properties are a mixture of starfish and lotuses or crinoids - not plants, but food filters with wavy arms attached to the seabed by cylindrical "rods".

The findings, reported in Biology Letters, capture the early steps of animal evolution at a time in Earth's history when life suddenly developed, a period known as the Ordovician Biodiversification Event.

The discoveries also mean that scientists can now use new discoveries as a template for understanding how they evolve from these more basic forms to the complexity of their contemporaries.

"It's very interesting to find a lack of connection with your ancestors. If you go back in time and put your head underwater in the Ordovician, you won't recognize any marine organisms - other than starfish, they were one of the first modern animals." said lead author Dr. Aaron Hunter, a visiting PhD student in the Department of Earth Sciences.

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Modern starfish and brittle stars belong to the echinoderm family called echinoderms. Although they do not have a backbone, they are closest to vertebrate animals. Crinoids and otherworldly creatures such as sea urchins and sea cucumbers are echinoderms.

The origin of sea stars has been unnoticed by scientists for decades. But this new species is so well preserved that its body can eventually be mapped in detail and its evolution understood. "The level of detail in the fossil is incredible - the structure is so complex that it took us a while to figure out what it means," said Hunter.

Jäger's work on life and fossils of echinoderms helped him see their hybrid nature. "I looked at modern crinoids in one of the collections at the Western Australian Museum and found that the hands were very familiar, reminiscent of an unusual fossil I found in Morocco a few years ago, but it was difficult for me to work," he said.

Fezouata in Morocco is a holy grail for paleontologists - the new fossil is just one of the many well-preserved soft-bodied animals found at the site.

Hunter and co-author Dr. Javier Ortega-Hernandez, who previously worked in the Department of Zoology at Cambridge and now works at Harvard University, named the species Cantabrigiaster in honor of the long history of echinoderm research at their respective institutions.

Hunter and Ortega-Hernandez explore their new species along with a catalog of hundreds of starfish. They index all the structures and features of their bodies by creating a road map of the echinoderm skeleton that will allow them to assess how the Cantabrigaster relates to other family members.

Modern echinoderms come in all shapes and sizes, so understanding how they are connected can be difficult. The new analysis, using extraaxial theory - a biological model generally only applied to living species - means Hunter and Ortega-Hernandez can identify similarities and differences between modern echinoderm body designs and then understand how each member of the echinoderm could be related to their Cambrian ancestors.

They found that in the Cantabrigiaster there were only keys, or axial parts of the body, the food pathways that lead food into each starfish's hand. Anything beyond that, extra-axial body parts, was added later.

The authors plan to expand their work to search for early echinoderms. "One thing that we hope to answer in the future is why starfish are developing all five of their arms," ‹‹said Hunter. "It seems they can take a stable form - but we still don't know why. We still have to look for the fossils that give us that special connection, but when we return to early ancestors like the Cantabrigiaster we will be much closer."  Reuters