Castle Bank
Fossil deposit in Wales
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History of research
Prior to the formal description of the locality, the Castle Bank site had been discovered by palaeontologists Joe Botting and Lucy Muir sometime during 2013, although at the time they deemed the site uninteresting, and thus left it. It wouldn't be until 2020 when they returned to the locality, primarily due to the fact that they could no longer travel to Cardiff were they worked at the Amgueddfa Cymru – Museum Wales with the onset of the COVID-19 lockdowns, and the fact it was relatively close to where they lived in the town of Llandrindod Wells. Upon closer inspection, they realised that a small area of the site contained an abundance of fossil material, although this material was far too small for them to properly study. The owners of the farm which the site was found within suggested to Dr. Botting and Muir that they should crowdfund some instruments to permit them to study said material, which they did. With this, during the period between 2020 and 2023, Dr. Botting and Muir, as well as researchers coming in from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) to help, would recover over 170 species, most of which are new to science. The site itself would be formally described and named in 2023, taking its name from Castle Bank Quarry, which it is found outcropping in.
Whilst the collection of new fossil material continues, various new fossil genera have been slowly described from the locality, such as the opabiniid-like panarthropod Mieridduryn bonniae in 2022 prior to the naming of the locality, alongside the bivalved arthropods Ffabach and Gloynia in 2026.
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Geology
The Castle Bank site can be found outcropping in the upper layers of the graptolitic siltstone Gilwern Volcanic Formation, near to Llandrindod Wells in Mid Wales, which itself is a part of the wider Builth Volcanic Group. The site itself is predominately composed of Siltstone, with substantial deposits of volcanic rock alongside ash laminae, all of which is capped by a 2 m (6.6 ft) layer of tuffaceous rocks, with the overall known thickness of the locality coming in at 10 m (33 ft).
The environment of the Castle Bank site at the time of its deposition was likely to be an open-marine along a volcanic island complex, on what was then the microcontinent of Avalonia, which was at the time occupying the temperate southern latitudes of the Middle Ordovician.
Dating
The Castle Bank site has been dated using the notably abundance of Graptolite fossils, namely Didymograptus murchisoni and D. foliaceus. This would see the locality placed in the Middle Ordovician Didymograptus murchisoni-Biozone, which would thus lithostratigraphically place the deposition of the rocks at roughly 462 Ma.
Paleobiota
The Castle Bank site contains a wealth of Burgess Shale-type fauna, rivalling even the best Cambrian deposits in the shear abundance and preservation of fossils, as well as showing major changes that occurred ecologically. The fossils themselves are preserved as carbonaceous remains, with a majority of them being notably small in size, ranging from just 1–5 mm (0–0 in) in most cases, excluding fragments of trilobites and centimetre large sponges. The small size of the fossils may be a result of the miniaturisation of organisms in order to be able to make use of equally small benthic organisms as shelter from larger animals, and thus showing that the transition to small and meiofaunal life habits likely began sometime during the Middle Ordovician and the Great Ordovician Biodiversification Event, filling in a notable gap between the Cambrian fauna and the later Ordovician faunas. The site has thus been noted to be highly important by Dr. Botting and Muir, as well as a myriad of other researchers in the field, potentially to a similar level of importance as the Burgess Shale in Canada.
The biota itself is predominately composed of arthropods, such as the opabiniid-like Mieridduryn bonniae, alongside a myriad of bivalved arthropods such as Caryocaris, Bullaeferum, and Ffabach. The locality also contains a large collection of sponges, something noted to be a common feature in Burgess-shale Type Faunas, such as Choiaella, Nectocollare, Teganiella, and a myriad of undescribed sponges.