The British town of Lyme Regis is part of the Jurassic Coast World Heritage Site. Here in the 1830s, William Buckland, who is better known for discovering the first dinosaur, Megalosaurus, having collected fossils with another pioneering paleontologist, Mary Anning.
One of their discoveries was the remains of fossilized crinoids, sometimes referred to as the “sea lilies”. A close relative of sea urchins and starfish, these flower-like animals consist of a series of interconnected plates in stem branches.
The specimens from Lyme Regis, dating back to the Jurassic more than 180 million years ago, look like polished brass because they have been fossilized with pyrite (cheater gold).
Buckland found that these fossils were attached to small pieces of driftwood that we call lenses, which have turned into coal. He hypothesized that the crinoids had stuck to the log while alive and perhaps throughout their lives, could live below it.
Modern crinoids do not usually make such journeys, but since then we have discovered fossil examples of groups of floating crinoids. However, it is not clear if these are truly thriving colonies living on driftwood or just short-term passengers.
Now, my colleagues and I have proven that such rafts can last up to 20 years, plenty of time for the crinoids to mature and become full-time ocean sailors.
Buckland̵7;s idea was initially seen as fiction, and the scientific community remained skeptical. Until the discovery of a truly spectacular group of fossils in the 1960s from Holzmaden, a village not far from Stuttgart, Germany.
Among marine reptiles, crocodiles and whales, are giant flocks comprised of complete logs covered with hundreds of perfectly preserved crinoids.
German professor Adolf Seilacher and then student (now professor) Reimund Haude seem to have solved Buckland’s mystery. Floating rafts of crinoids used to exist.
This idea is underpinned by evidence that, during the Jurassic period, today’s Holzmaden was an uninhabitable seabed due to its low oxygen content. The crinoids will linger for life on these logs because there is no seabed for them to live on.
However, not all scientists agree. One of the key questions to be asked is whether these wooden rafts can survive long enough for the crinoids to grow to maturity. This process could take up to ten years, given the modern rate of development of their surviving relatives can still be found at a depth of about 200 meters.
A group of scientists from the UK and Japan led by me decided to solve this problem. We were motivated by Professor Tatsuo Oji’s groundbreaking study of critical diseases in Japan, which was kept in a laboratory at the University of Tokyo.
One of the key parts of the early theory was that any floating crinoids would grow until the population became too heavy for the raft to support it. The log will sink to the bottom of the sea without oxygen, where the crinoids will then become fossils.
However, research on wild populations living off the coast of Japan shows that these animals are so light, even in large adult herds, that a log becomes overwhelmed and sinks.
Our research then focused on wood itself. We determined that the way to understand how long the colony could last was to develop a “diffusion model”. This is estimated how long it will take before the log is water-saturated and spoiled.
The wood in the freckle raft fossils has not been well preserved so that we know what species it comes from. So we represented it in the model with a composite estimate of plants we know existed during the Jurassic period, such as conifers, marijuana, and ginkgo trees.
We found that the floating wood and its dangerous goods could last for at least 15 years and possibly up to 20 years before the log begins to sink or break. There is evidence from museum collections of wood fragments with intact, fully grown pieces attached to them that could only have been the result of this collapse.
Finally, we use a technique called spatial point analysis developed by Dr. Emily Mitchell, to plot the space between fossils and find out whether site morphology is ecological or environmental. or both. This allows us to estimate what this disabled community might look like on the log.
We found that the tabs were actually hanging below the driftwood log, but focused on one end of it. Although difficult to observe in early fossils, this pattern resembles other modern rafting species such as the roast geese.
They tend to reside in the back area of a raft, where there is the least amount of resistance, which can tell us the direction of the flock’s movement across the ocean.
This study now suspects that dinosaur raft colonies can survive and persist for many years to mature and travel large distances across the Jurassic oceans. They are a profound example of similar structures that we see in the oceans today.
These interesting techniques are currently being used by a new team of researchers to compare undersea populations with their Jurassic ancestors.
This can reveal how past changes in climate shaped marine communities and will help scientists understand how those communities can cope with future challenges. an ever-changing world.
Aaron W Hunter, Science Instructor & Tutor, Department of Earth Science, University of Cambridge.
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