Abstract
The Cambrian Burgess Shale-type biotas form a globally consistent ecosystem, usually dominated by arthropods. Elements of these communities continued into the Early Ordovician at high latitude, but our understanding of ecological changes during the Great Ordovician Biodiversification Event (GOBE) is currently limited by the paucity of Ordovician exceptionally preserved open-marine faunas. Here we clarify the early stages of the GOBE by describing a new open-marine Konservat-Lagerstätte from the Early Ordovician of Wales. The Afon Gam Biota includes many lineages typical of the Cambrian Burgess Shale-type biotas, but the most abundant groups were sponges, algae and worms, with non-trilobite arthropods being unexpectedly rare. Labile tissues occur abundantly in the sponges and are also present in other groups, including brachiopods and hyoliths. Taphonomic biases are considered and rejected as explanations for arthropod rarity; the preserved biota is considered to be an approximation to the original community composition. We note that other exceptionally preserved communities in the Welsh Ordovician are also sponge-dominated, suggesting a regional change in benthic ecology during the early stages of the GOBE.
Highlights
The Cambrian Burgess Shale-type biotas form a globally consistent ecosystem, usually dominated by arthropods. Elements of these communities continued into the Early Ordovician at high latitude, but our understanding of ecological changes during the Great Ordovician Biodiversification Event (GOBE) is currently limited by the paucity of Ordovician exceptionally preserved open-marine faunas
There are probably no deposits that preserve all components of the original community, some KonservatLagerstatten appear to preserve the majority of taxa within the centimetre to decimetre size range
The community composition of the Burgess Shale is strikingly similar to that seen in the Chengjiang Biota[1], which is regarded as preserving most or all of the original community
Summary
The Cambrian Burgess Shale-type biotas form a globally consistent ecosystem, usually dominated by arthropods Elements of these communities continued into the Early Ordovician at high latitude, but our understanding of ecological changes during the Great Ordovician Biodiversification Event (GOBE) is currently limited by the paucity of Ordovician exceptionally preserved open-marine faunas. The Fezouata formations were deposited near the Ordovician South Pole, and it is not known whether their communities were typical of Early Ordovician life globally, or represent non-standard communities such as cold-water refugium faunas[14] It is unclear whether many Burgess Shale-type taxa survived into the Ordovician in lower latitudes. The rocks preserving the biota were laid down at a palaeolatitude of approximately 60uS18, representing a cool temperate latitude, in contrast to the near-polar Fezouata Biota
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