How Jurassic sea creatures spent years crossing oceans on rafts
Model breakup
Our research then turned towards the wood itself. We established that the way to understand how long the colony could have lasted was to develop a “diffusion model.” This estimated how long it would take before the log would become saturated with water and fail.
The wood in crinoid raft fossils hasn’t been preserved well enough for us to know what species it comes from. So we represented it in the model with a composite estimate of trees we know existed in the Jurassic, such as conifers, cycads, and ginkgo trees.
We foundthat the floating wood and its crinoid cargo would have been able to last for at least 15 years and maybe up to 20 years before the log would begin to sink or break up. There is evidence from museum collections of fragments of wood with entire, fully grown crinoids attached to them that could only have resulted from this kind of collapse.
Finally, we utilized a technique known asspatial point analysisdeveloped by Dr. Emily Mitchell, to plot the spaces between the fossils and work out whether the position pattern is ecological, environmental, or both. This enabled us to estimate how this crinoid community might have looked on the log.
We found that the crinoids do indeed hang suspended underneath the driftwood, but clustered towards one end of it. Although difficult to observe in the original fossils, the pattern resembles that of other modern rafting species such as goose barnacles. They tend to inhabit the area at the back of a raft where there is the least resistance, which can tell us the direction of travel of the colony across the ocean.
This research has now put beyond doubt that crinoid raft colonies could exist and survive for many years to grow to maturity and travel the vast distances across the Jurassic oceans. They are a deep-time example of similar structures we seein today’s oceans.
These exciting techniques are now being usedby a new teamto compare living populations on the seafloor to their Jurassic forebears. This could reveal how past changes in climate have shaped marine communities and will help scientists understand how such communities might respond to future challenges in an ever-changing world.
This article is republished fromThe ConversationbyAaron W Hunter, Science Guide & Tutor, Dept. of Earth Sciences,University of Cambridgeunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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