rare fossil helps solve the puzzle of weapon development

January 22, 2021 1:17:48 PM

The accidental discovery of a beautifully preserved fossil in the Moroccan desert landscape solved one of the great mysteries of biology and paleontology: how starfish developed their arms.

Starfish are one of the most famous animals on our planet. Most people likely associate them with trips to the beach, walks in rock pools, or swimming in the ocean. They appear to be just creatures, but how the characteristic biology of these animals developed was unknown until recently.

Our new study, published in the magazine Biology letters, highlights how the starfish developed its distinctive shape.

Although starfish appear to be very robust animals, they are usually made up of many hard parts connected by ligaments and soft tissues that decompose quickly when they die. Photo credit: Unsplash

The secret of the starfish

Starfish and their close relatives, the fragile stars, belong to a group called Echinoderms. They are thorn-skinned animals, including sea urchins, water lilies, and sea cucumbers, with bizarre biological characteristics. They have no heads or brains and a unique circulatory system called the liquid vasculature that uses seawater instead of blood. They even have the power to regenerate if they lose more than 75% of their body mass.

Starfish almost always have the same five-armed body shape. This has not changed in the Big Five in nearly 480 million years mass extinction they survived.

Other echinoderms filter food with their arms or take food out of the water and, unlike starfish, look up with their arms spread outward to feed. However, starfish are not, and their distinctive body shape is contained in the fully developed fossil record. For years scientists have been confused about its evolution and the relationship between starfish and their close relatives, the fragile stars.

The Pompeii of paleontology

The Fezouata Formations are deposits of sedimentary rocks in Morocco from the early Ordovician period. a critical phase in the development of lifethat ended about 460 million years ago. Paleontologists think about life quickly diversified during this time, in what has been dubbed the Great Ordovician Biodiversity Event, when the animals we might recognize today first appeared.

The formations of Fezouata are a bit like the Pompeii of paleontology. Conditions on the ocean floor even meant soft tissue what would normally be destroyed over timeremain. For this reason, the training courses offer an insight into what happened at a crucial point in the history of life on earth.

Although starfish appear to be very robust animals, they usually consist of many hard parts connected by ligaments and soft tissues and after death dismantle quickly. This means that we rely on places like the formations of Fezouata to provide snapshots of their evolution.

The fossil record of starfish is inconsistent, especially at the critical time when many of these animal groups first appeared. Figuring out how the different types of ancient starfish relate to one another is like putting a puzzle together when many pieces are missing.

The oldest starfish

Cantabrigiaster is the most primitive starfish-like animal discovered in the fossil record. It was discovered in 2003, but it took over 17 years to determine its true meaning.

What does Cantabrigiaster The peculiarity is that it lacks almost all properties that can be found in fragile stars and starfish.

Starfish and brittle stars are part of the family Asterozoa. Your ancestors who Somasteroids were particularly fragile – before Cantabrigiaster We only had a handful of copies. The famous Moroccan paleontologist Mohamed Ben Moula and his local team contributed to the discovery these amazing fossils near the city of Zagora, Morocco.

discovery

Our defining moment came when I compared the arms of Cantabrigiaster along with those of modern water lily filter feeders with long, feathery arms that tend to be attached to the ground with a stem or pole.

The remarkable similarity between these modern filter filters and the ancient starfish prompted our team at Cambridge University and Harvard University to do a new analysis. We applied a biological model to the properties of all of the earliest asterozoan fossils today, as well as a sample of their closest relatives.

Our results show Cantabrigiaster is the most primitive of all asteroids and likely evolved from ancient animals called crinoids, which lived 250 million years before dinosaurs. The five starfish arms are a relic of these ancestors. In case of Cantabrigiasterand its offspring of starfish evolved by turning over so that its arms were face down on the sediment for food.

Although we interviewed a relatively small number of these ancestors, one of the unexpected results was that we had some idea of ​​how they might relate to one another. Paleontologists studying echinoderms often get lost in detail because the various groups differ so drastically from one another that it is difficult to tell which came into existence first.

Aaron W Hunter, Scientific Guide and Tutor, Department of Earth Sciences, Cambridge University

This article is republished by The Conversation under a Creative Commons license. Read the original article.

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