Now researchers believe the site could help plug gaps in scientific understanding of how evolution proceeded after the Cambrian explosion – the period when the ancestors of most modern animals are believed to have evolved. It could even prove to be as important as the Burgess Shale in Canada that preserves one of the world’s first complex marine ecosystems, experts say.

The Welsh site, known as Castle Bank, dates from the Middle Ordovician period, about 460m-70m years ago. It represents a community of diverse and mostly diminutive (1mm to 5mm in body length) marine organisms that existed at a time when ocean covered what is now mid-Wales.
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The site is important because it gives us a new window into how life was evolving at the time. The Cambrian explosion, which occurred between 540m and 485m years ago, was a period when many new and complex life forms arose. But by 400m years ago, almost all of these creatures had disappeared, eventually replaced by the ancestors of many modern animals. The Castle Bank fossils could help to bridge that gap, providing an insight into how life was evolving at a time when there was virtually no life on land, but animals and algae were thriving in the seas.
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Although other Ordovician fossil sites exist, most are older and preserve only a limited fauna, with few entirely soft-bodied animals. “Here, it seems, we’ve got everything,” said Botting.

https://www.theguardian.com/science/2023/may/01/couple-unearths-one-of-worlds-greatest-fossil-finds-in-mid-wales

A Middle Ordovician Burgess Shale-type fauna from Castle Bank, Wales (UK)

Burgess Shale-type faunas are critical to our understanding of animal evolution during the Cambrian, giving an unrivalled view of the morphology of ancient organisms and the ecology of the earliest animal-dominated communities. Rare examples in Lower Ordovician strata such as the Fezouata Biota illustrate the subsequent evolution of ecosystems but only from before the main phase of the Great Ordovician Biodiversification Event. Later Ordovician Konservat-Lagerstätten are not directly comparable with the Burgess Shale-type faunas as they do not represent diverse, open-shelf communities, limiting our ability to track ecological development through the critical Ordovician biodiversification interval. Here we present the Castle Bank fauna: a highly diverse Middle Ordovician Burgess Shale-type fauna from Wales (UK) that is directly comparable with the Burgess Shale and Chengjiang biotas i n p al ae oe nv ir onment and preservational style. The deposit includes animals with morphologies similar to the iconic Cambrian taxa Opabinia, Yohoia and Wiwaxia, combined with early examples of more derived groups such as barnacles. Many taxa such as kinorhynchs show the small sizes typical of modern faunas, illustrating post-Cambrian miniaturization. Castle Bank provides a new perspective on early animal evolution, revealing the next chapter in ecosystem development following the Chengjiang, Burgess Shale a n d F ez ou ata biotas.

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