Following another landslide at Seatown over the last few days (in Summer 2021), it is intriguing to wonder what new discoveries will be waiting for us when it is safe to visit once more. Of course, this is not the first landslide movement we have seen on this stretch of coast in the last year, and the massive cliff fall that occurred in April provided a fantastic opportunity to investigate some of the Site’s rarer fossil interests.

The cliffs east of Seatown contain Early Jurassic marine rocks; at their base is the Eype Clay Member and above this is the Down Cliff Sand Member, both of the Dyrham Formation – apologies for the scientific terms! This boundary marks the transition from clay-rich muds and shales to the sandstones and limestones that continue around the coastline to Thorncombe Beacon and beyond.

 

Brittlestar Eype

A large brittle star (Palaeocoma egertoni) found at Eype, Dorset. The delicate arms were carefully revealed from the rock using hand tools over many hours to conserve this
exceptional level of detail.

 

The cause of this shift in the dominant rock type was a fall in global sea levels that led to the establishment of shallow, topical seas. The Mesozoic was subject to several of these sea level fluctuations and they are responsible for producing the diverse fossil record we see today; notable examples include a major rise in sea level at the end of the Triassic that resulted in a transition from terrestrial red-rocks to marine mudrocks at the base of the Jurassic as well as the boundary between the Kimmeridge Clay and Portland Limestone formations where dark, organic-rich shales deposited in deep, oxygen-poor waters were replaced by limestones laid down in warm, tropical seas.

By far the most exciting section of this cliff, at least for palaeontologists, is a layer of rock positioned between the Eype Clay and Downcliff Sands known as the Eype Starfish Bed. This name is actually a little deceptive since by far the most common fossils of note found in this layer are brittlestars – delicate creatures with five slender arms that are closely related to starfish.

 

Palaeocoma JC 1 - for website

Palaeocoma, a type of brittlestar. © Mark Witton.

 

Brittlestars are one of nature’s great survivors and still exist today; they can be found in a range of different environments, including in UK rock pools! The name brittlestar is a hint at their primary defence strategy, which is to shed arms if they feel threatened by a predator. We even have evidence of this in fossil brittlestars from the Jurassic Coast, with a particularly fine example currently on display in Bridport Museum.

Because these fossils are preserved in such exquisite detail, unique depositional conditions must have protected them from being broken apart or scavenged on the seafloor. Whilst the exact cause is unclear, it is likely that they were caught up in a big storm event that buried the abundant benthic community in one catastrophic instance.

Despite their unique story and fantastic appearance, brittlestars and other echinoderms from the Dyrham Formation were not named as a scientifically important feature of the Jurassic Coast when the Site was inscribed for World Heritage status; as a result, we hope to use the Jurassic Coast Collection to re-evaluate their significance and understand their context within our local fossil record.

 

Brittlestar Dyrham

A range of echinoderms from the Dyrham Formation including brittlestars and crinoids
(Balanocrinus sp.).

 

Unfortunately, the big issue with these fossils is that they are really REALLY difficult to collect. Because the Eype Starfish Bed is composed of a thick, hard sandstone, it often falls to the beach in large pieces up to 10 foot in length! Fossil collectors have special permission to remove brittlestars from these fallen blocks using stone saws because even the gentlest seas can quickly wear away these delicate fossils and the most extreme storms can destroy a perfect brittlestar in a matter of days. Instead of searching for your own, we recommend you take a look at some examples that have been cleaned and prepared by experienced fossil collectors and are now on display.

Bridport Museum has a small, but nonetheless exceptional geology gallery crowded with fantastic fossils from the beaches between Seatown and West Bay, Dorset. Their collection of brittlestars is magnificent and will help you appreciate the delicate nature and exceptional process behind their survival.

 

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Exploring Jurassic Coast fossils at Bridport Museum.