These form the decades spent crossing the ocean on Jurassic Sea rafts. Such

The English city of Lyme Regis is part of the Jurassic Coast World Heritage Site. It was here in the 1830s, William Buckland, formerly known for his discovery of dinosaurs, Megalosaurus, Collected fossils with another leading paleontologist, Mary Anning.

One of his discoveries was the remains of fossil crinoids, sometimes referred to as “sea lilies”. Close relatives of sea urchins and starfish, these flower-like animals have a series of plates linked together in branches with a stem.

The specimens of Lyme Regis, dating back 180 million years to the Jurassic period, look like polished brass because they have been fossilized with pyrite (fool’s gold).

Buckland observed that these crinoid fossils were associated with small pieces of driftwood that we call lenses, which were turned into coal. He hypothesized that crinoids were associated with drift during vivacity, and probably for the rest of their lives, possibly living lives suspended below it.

Modern crinoids do not usually make such trips, but we have since discovered fossil examples of clusters of floating crinoids. However it was not clear whether these were actually colonies inhabited by driftwood or just short-term travelers.

Now I and my colleagues have shown that such rafts can last up to 20 years, with plenty of time for crinoids to mature and become full-time marine sailors.

Buckland’s idea was initially seen as imaginative and the scientific world remained skeptical. Till, it is, discovered in the 1960s, not far from Stuttgart, Germany, a very magnificent group of fossils of Holzmäden.

Crinoid fleet fossils have now been found. (R. Houde / University of Göttingen)

Among marine reptiles, crocodiles and ammonites, there were huge colonies that included hundreds of complete cover of fully preserved rhinoids.

German Professor Adolf Silacher and his then student (now Professor) Reimund Houde solve the mystery of Buckland. These floating rafts of crinoids were present.

This view was reinforced by evidence that, in the Jurassic period, what was now Holzmden was a seabed that was uninhabitable due to low oxygen levels. The crinoids are glued to life in these logs because there was no seabed to live on them.

However, not all scientists agreed. One of the major questions asked was whether these log rafts could survive long enough for the crinoids to grow until they matured. It can take up to ten years depending on the modern growth rate of its living relatives which can still be found at a depth of about 200 meters.

A team of scientists from Britain and Japan decided to tackle the problem themselves. We were inspired by research conducted by Professor Tatsuo Oji on Japanese crinoids, which were kept alive in laboratories at the University of Tokyo.

One of the major parts of the original theory was that any floating colony of crinoids developed until the population became too heavy to support the wooden fetters. The log will sink into an oxygen-free seafloor where the crinoid will then become fossilized.

However, research on crinoid populations living off the coast of Japan has shown that even in large mature colonies, animals will become very light, causing logs to overburden and drown.

Model breakup

Our research then turned to wood. We established that the way to understand how long a colony could live was to develop a “diffusion model”. It is estimated how long it will take for the logs to become saturated with water and fail.

In Crinoid fleet fossils, wood is not sufficiently preserved for us to know from which species it comes. We therefore represented it in the model with an overall estimate of trees that we know exist in the Jurassic, such as trees of conifer, cycad, and ginkgo.

We found that floating wood and its crinoid cargo could last at least 15 years and probably begin to sink or break logs until 20 years ago. There is evidence from the museum’s collection of fully grown fully developed chronoids, associated with them that can only result in such a collapse.

In the end, we took Dr. Used a technique known as spatial point analysis, developed by Emily Mitchell, to plot spaces between fossils and to find out if the position pattern is ecological, environmental, or both. This enabled us to speculate on how this crinoid community might have looked on the log.

We found that the crinoid actually hangs under the driftwood, but is tufted toward one end of it. Although difficult to observe in the original fossils, the pattern resembles that of other modern rafting species such as swan barnacles.

They inhabit the area behind a fleet, where there is minimal resistance, which can tell us the direction of the colony’s travel across the ocean.

This research has now put beyond doubt that crinoid fleet colonies can survive for many years to grow and mature and travel vast distances in the Jurassic oceans. They are a deep time example of similar structures that we see in today’s oceans.

These exciting techniques are now being used by a new team to compare populations living on the ocean floor to their Jurassic precursors.

This can help explain how past changes in climate have shaped marine communities and will help scientists understand how such communities can respond to future challenges in a changing world. chit chat

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

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