Published on May 1st, 2023 | by David Marshall

Episode 153: Castle Bank

A new Ordovician lagerstätte (site of special fossil preservation) has just been described from Llandrindod Wells, Wales. The site contains the remains of well over 150 different species, most of which are entirely new to science. It is dated to around 461 million years old, placing it at a critical point in life’s evolution: the Great Ordovician Biodiversification Event. This is even more significant, considering the relative sparsity of lagerstätten of this time.

We are joined in this interview by Drs Joe Botting and Lucy Muir, who discovered the Castle Bank site a short walk from their house whilst fossil collecting during covid lockdown in 2020. From them, we’re able to learn what it’s like to discover a new site of international significance and we question why the fossil from this site are so small.

The Castle Bank site in Llandrindod, mid-Wales is newly-described lagerstätte from the Ordovician period, some 461 million years ago.
The site was discovered by husband and wife team Joe Botting and Lucy Muir, who are experts in sponges and graptolites respectively. Both have a keen interest in sites of special preservation.
The exact location of the site is being kept a closely-guarded secret and visitors are under constant surveillance [by sheep].
The rocks in the quarry are a mix of volcanic ashes and mica-rich siltstones. Surprisingly, the best fossils are actually preserved in the coarser siltstone.
This area of Wales was the birthplace of biostratigraphy and so the dating of these sediments is incredibly accurate. This is thanks to index fossils such as the graptolite Didymograptus murchisoni that provides an an age of around 461 million years.
The preservation of fossils can vary between layers, attesting to the complexity of the site. Here, Proclimacograptus angustatus shows a lot more infilling of pyrite than the last graptolite figured.
The first thing to note about the Castle Bank fauna is the preservation of soft tissues. This is incredibly rare under most circumstances. This means that entirely soft-bodied organisms, such as this priapulid worm, can be preserved. But even more than that, internal details such as gut traces are also sometimes visible.
Excitingly, details such as the eyes, optic nerves and neural tissues can be seen in the head of this unknown arthropod. The dark spot on the left of the head is the eye and from there, the dark lines represent the optic nerve and then some of the neural tissue. Whilst this is fairly difficult to see in this picture, other such eyes, nerves and brains have similarly been documented in fossils from Chengjiang.
The second thing is that these fossils rarely get above 1mm long. Why these fossils are all so small is a mystery, especially why not even a fragment of any larger animal has ever been discovered. This fauna, it seems, is just tiny.
In fact, the fossils were so small that, Joe and Lucy had to crowd-fund a microscope to analyse them. Here Lucy uses a ‘camera lucida’ which allows her to draw what she sees whilst looking down the microscope.
Whilst many groups are present throughout the section, by far the most diverse are sponges with around 35-40 different species. In terms absolute numbers of specimens, graptolites, brachiopods, sponges and trilobites dominate. Sponges such as the reticulosan Cyathophycus sp. (pictured) can have soft tissues preserved.
Fossils such as this conulariid-like animal really demonstrate just how detailed these fossils can be, with its very fine-scale detail. This fossil is only about 1cm in length.
This problematic tube-dwelling animal is one of the most commonly encountered fossils with soft tissue preservation. Out of the end of the tube extend two tentacles.
One of the most exciting finds is this unknown arthropod. At the bottom, three legs seem to be visible, making the case that it could actually be a hexapod. IF confirmed, this could be of massive significance since it would be the oldest hexapod discovered and the first from a marine environment.
Reconstruction of Castle Bank by Yang Dinghua.
Even though the outcrop of rocks is limited, there is still the potential to discover many more specimens since the fossils are so small. Joe and co-author Stephen Pates in the field.
Therefore Castle Bank will probably play a huge role in research into the Ordovician for decades to come.

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