(MENAFN – The Conversation) The discovery of a beautifully preserved fossil find in the desert landscape of Morocco has solved one of the great mysteries of biology and palaeontology: how stars developed their arms.
Stars are one of the most recognizable animals on our planet. Most people probably associate them with trips to the beach, walking in rock pools or swimming in the sea. They may feature simple creatures, but until now it has not been known how the specific biology of these animals evolved.
Our new study, published in the journal Biology Letters, sheds light on how the stars developed their unique shape.
Star Mystery
Stars, and their close relatives with the brutal stars, belong to a group called echinoderms. These are sharp-skinned animals, including sea urchins, sea lilies and sea cucumbers, with strange biological characteristics. They have no head or brain, and have a special circulatory system called the water vascular system, which uses seawater instead of blood. They even have the power to regenerate more than 75% of their body mass if it is lost.
Stars have always had the same five-armed body shape. This has not changed for nearly 480 million years, through the five major survivors.
Other echinoderms use their arms to filter bait or catch food from the water and, unlike stars, face up with their arms outstretched to feed them. But there are no stars, and the unique shape of their body appeared in the fully formed fossil record. So for years scientists have been concerned with how it evolved and how stars are connected to their close relatives, the brutal stars.
Am Pompeii de palaeontology
The Fezouata formations of sedimentary rock deposits in Morocco date back to the early Ordovician, a critical stage in the evolution of life, which ended about 460 million years ago. Palaeontologists believe that life has multiplied rapidly during this period, in a program called the Ordovician Biomedical Big Event, when animals we may recognize today first appeared.
The Fezouata forms are somewhat similar to the Pompeii of palaeontology. The conditions on the seabed meant that even soft cloth, which would normally be destroyed over time, could be preserved. Because of this, the forms provide a window into what happened at a pivotal moment in the history of life on Earth.
Am Pompeii de palaeontology. Aaron Hunter, Author awarded
Although stars may appear very strong animals, they are usually made up of many hard parts connected by ligaments and soft tissue which, when they die, shrink sharply. This means that we rely on places like the Fezouata forms to provide images of their growth.
The starfish fossil record is inconsistent, especially at the critical time when many of these animal groups first appeared. Solving how each of the different old star types are alike is like putting together a puzzle when many of the parts are missing.
The oldest star
[Cantabrigiaster](https://www.biorxiv.org/content/10.1101/216101v1.full.pdf ‘) the most star-like primary animal found in the fossil record. It was discovered in 2003, but it took more than 17 years to realize its importance.
What makes Cantabrigiaster unique is that it lacks the features we find in crumbs and stars.
Stars and traps belong to the Asterozoa family. Their ancestors, the Somasteroids were particularly fragile – before Cantabrigiaster we only had a handful of samples. Renowned Moroccan palaeontologist Mohamed Ben Moula and his local team were instrumental in the discovery of these amazing fossils near the town of Zagora, in Morocco.
The break
Our positive moment came when I compared Cantabrigiaster’s arms with today’s sea lily arms, seed feeders with long feather arms that tend to be attached to the seabed with gas or starch.
Because of the striking resemblance between these modern seed foods and the old stars, our team from Cambridge University and Harvard University conducted a new analysis. We applied a biological model to the characteristics of the existing Asterozoa early fossils, along with a sample of their closest relatives.
Cantabrigiaster is the most star-like animal found in the fossil record. Aaron Hunter, Author awarded
Our results show that Cantabrigiaster is the most important of the Asterozoa, and probably came from ancient animals called crinoids that lived 250 million years before dinosaurs. The five arms of stars are a memorial left over from these ancestors. As for Cantabrigiaster, and his star descent, he came forward with an upside-down squat so that his front arms were down on the sediment for feeding.
Although we sampled relatively small numbers of these ancestors, one of the unexpected results was that it suggested how they might be related to each other. Palaeontologists who study echinoderms are often missed in detail because the different groups are so different from each other, so it is difficult to tell what came up first.
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