Castle Bank is a Middle Ordovician aged fossiliferous deposit, which is found outcropping within the Gilwern Volcanic Formation of the wider Builth Volcanic Group, near to Llandrindod Wells in Mid Wales. Considered to be a Konservat-Lagerstätte, it contains an abundance of Burgess Shale-type fauna, such as the opabiniid-like panarthropod Mieridduryn bonniae, which is notably rare in the Ordovician.
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.
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 layer of tuffaceous rocks, with the overall known thickness of the locality coming in at .
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 .
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 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.
Arthropoda
ArthropodaGenusSpeciesNotesImagesMieriddurynM. bonniaeOpabiniid-like arthropod, likely expending the temporal range of the opabiniids into the Ordovician. OgyginusO. corndensisAsaphid trilobite. CaryocarisCaryocaris sp.Caryocaridid arthropod. Lack of diagnostic features precludes species level assignment, though it is noted to likely be C. wrightii. The singular specimen was also found long before any other material was found from here, and also has an arrow scratched into the carapace.Ivocaris (?)Ivocaris (?) sp.Caryocaridid arthropod. Poor preservation precludes species level assignment, and makes the genus level assignment tentative. If the genus level assignment can be further confirmed with better material, this would extend the geographical range of Ivocaris.BullaeferumB. llandeiloensisBolliid podocope.LaterophoresLaterophores sp.Bolliid podocope.PariconchoprimitiaPariconchoprimitia sp.Aechminid podocope.GloyniaG. jonesiBivalved arthropod of uncertain affinities.FfabachF. peryglusBivalved arthropod of uncertain affinities.
Hemichordata
Hemichordata GenusSpeciesNotesImagesDidymograptus D. murchisoniGraptolite.Dictyonema Dictyonema sp.Callograptid graptolite.
Annelida
AnnelidaGenusSpeciesNotesImagesLlwygaruaL. suzannaeThalassematid annelid.
Lophotrochozoa
LophotrochozoaGenusSpeciesNotesImagesMonobolinaM. ramsayiBrachiopod.SchizocraniaS. multistriataTrematid brachiopod.
Cnidaria
CnidariaGenusSpeciesNotesImagesSphenothallusSphenothallus sp.Conulariid cnidarian.ParaconulariaParaconularia sp.Conulariid cnidarian.
Porifera (Sponges)
PoriferaGenusSpeciesNotesImagesCyathophycusCyathophycus sp.Reticulosan sponge.TeganiellaTeganiella sp.Hexactinellid sponge, first record outside of the Americas.TeganiumT. avalonensis Teganium sp.Hexactinellid sponge.NectocollareN. zakdoueliAmphidiscophoran sponge, with probable affinities to the hexactinellids.ChoiaellaC. hexactinophoraAscospongid sponge. Species showed that choiid sponges contained hexactins, something previously only known to the hexactinellids, thus seeing a proposal to replace the order Protomonaxonida with the new class Ascospongiae.
Undescribed
UndescribedGenusSpeciesNotesImagesConulariid-like fossil (NMW.2021.3 G.93)???A fossil with a similar appearance to the Conulariida.Unidentified acrotretid brachiopod (NMW.2021.3 G.90)???An unidentified acrotretid brachiopod.Undescribed fenestellid bryozoan (NMW.2021.3 G.62)???An undescribed fenestellid bryozoan, found attached to a poorly preserved orthocone nautiloid.Probable sipunculan-like worm (NMW.2021.3 G.84)???An worm-like fossil, which bears similarities to the sipunculans.Probable priapulid-like worm (NIGP175887)???An worm-like fossil, which bears similarities to the priapulids.Unidentified spinose worm (NMW.2021.3 G.94) ???A spinose worm of uncertain affinities with a complex jaw apparatus.Probable priapulid worm (NMW.2021.3 G.97) ???A probable priapulid worm.Archaeopriapulid worm (NMW.2021.3 G.19) ???An Archaeopriapulid worm with a complex proboscis.Kinorhynch-like worm fossils ???An myriad of worm fossils, bearing similarities to the Kinorhynch.Palaeoscolecid worm with transverse plates (NMW.2021.3 G.88) ???A Palaeoscolecid worm, with transverse rows of large plates.Palaeoscolecid worm with minute plates (NMW.2021.3 G.89) ???A Palaeoscolecid worm, with notably minute plates.Hexpod-like arthropod (NMW.2021.3 G.11)???An arthropod fossil, which bears features similar to the Hexapoda.Yohoiid-like arthropod (NMW.2021.3 G.83)???An arthropod fossil, which bears similarities to the yohoiids.Unidentified arthropod (NMW.2021.3 G.34i)???Unidentified arthropod, which has a bilobed tail fan, alongside a head-region preserving preserving eyes and presumed neural tissue.Stem-group xiphosuran (NMW.2021.3 G.9)???Stem-group xiphosuran.Cephalocarid-like arthropod (NMW.2021.3 G.14)???An arthropod fossil, which bears features similar to the cephalocarids.Undetermined podocope ostracode A (NMW.2021.3G.162)???Undetermined podocope.New bivalved euarthropod (NMW.2021.3G.162)???A new bivalved euarthropod, poor preservation precludes formal description and naming.Undetermined bivalved arthropod A - I???Multiple undetermined bivalved arthropods.Undetermined bivalved carapaces without spines ???Multiple undetermined bivalved arthropods without spines.Barnacle-like fossil (NMW.2021.3 G.66)???An arthropod fossil, which bears features similar to barnacles.Small complex Hexactinellid sponge (NMW.2021.3 G.35)???A small, complex Hexactinellid sponge of uncertain affinities.Complex Hexactinellid sponge (NMW.2021.3 G.40)???A complex Hexactinellid sponge of uncertain affinities.Cylindrical Hexactinellid sponge (NIGP175889)???A tall, cylindrical Hexactinellid sponge of uncertain affinities.Complex conico-cylindrical Hexactinellid sponge (NIGP175889)???A complex, conico-cylindrical Hexactinellid sponge of uncertain affinities.Rossellid-like sponge (NMW.2021.3 G.39ii)???Rossellid-like sponge.Stalked ascosponge (NIGP175889)???A stalked ascosponge.Conical ascosponge (NMW.2021.3 G.39i)???A small, conical ascosponge.Multi-branch graptolite (NMW.2021.3 G.43) ???A multi-branched, benthic graptolite.Lophophore-bearing hemichordate (NMW.2021.3 G.44) ???A hemichordate with a notable lophophore.Dendrocystites-like solutans (NMW.2021.3 G.45) ???Two Dendrocystites-like solutan fossils.Undescribed Asterozoan (NMW.2021.3 G.67) ???A complete asterozoan fossil.Conodont fossils ???A myriad of conodont fossils.Tubicolous problematic fossil (NIGP175892)???A tubicolous fossil of problematic affinities.
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