Lucy A. Muir

Welsh gold: A new exceptionally preserved pyritized Ordovician biota

Few Konservat-Lagerstatten are known from the Ordovician, and most preserve atypical marginal marine communities. Thus, we have little idea of how animals with a low preservation potential evolved during the Great Ordovician Biodiversification Event. Here we report the newly discovered Llanfawr Mudstones Lagerstatte from the basal Sandbian (Late Ordovician) of central Wales, UK. This biota, which has been studied through X-ray radiography and microtomography, is dominated by sponges. It also includes cnidarians (the oldest known solitary hydroid), arthropods, priapulids, various worm-like forms, entoproct-like organisms, and a variety of enigmatic fossils. The fauna includes taxa that are rarely preserved even in exceptional fossil biotas, and offers the potential for a new perspective on Ordovician ecosystems. The dominantly filter-feeding assemblage resembles modern abyssal sponge-dominated communities, although it was formed in much shallower water. The unusual Llanfawr Mudstones fauna shows that Ordovician ecological development was considerably more advanced in offshore environments than the mineralized fossil record implies.

Relationships of the Cambrian Protomonaxonida (Porifera)

The Protomonaxonida consist of a heterogeneous group of early fossil sponges traditionally assigned to the demosponges. However, an affinity to the hexactinellid-like Reticulosa has also been suggested, and their relationships are potentially critical to understanding the origins of the extant sponge classes. In this paper, the relationships of the protomonaxonid sponges to each other and to other sponge groups have been reassessed, using previously described specimens as well as new material from the Burgess Shale of Canada and the Hetang Biota of South China. The sponges fall into two coherent groups, one consisting of taxa with long, mostly sub-longitudinal spicules, and the other with complex arrays composed of tracts of minute (millimetre-scale) monaxons, which grade into aspiculate taxa such as the Vauxiidae. Previous ideas relating the Protomonaxonida to extant demosponge lineages are supported in the case of the second group, whereas the first group confirms the view of derivation from a hexactinellid-like ancestor. Whether the two groups were directly related or evolved monaxonid spiculation in parallel is currently uncertain. Joseph P. Botting. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China acutipuerilis@yahoo.co.uk Lucy A. Muir. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China lucy@asoldasthehills.org Jih-Pai Lin (corresponding author). State Key Laboratory of Palaeobiology and Stratigraphy, and Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, CAS, 39 East Beijing Road, Nanjing 210008, China jplin@nigpas.ac.cn

Chapter 8 Cambrian, Ordovician and Silurian non-stromatoporoid Porifera

Abstract The Cambrian, Ordovician and Silurian distributions of non-stromatoporoid sponges are reviewed. The earliest Cambrian faunas contain mostly hexactinellids, with protomonaxonids dominating middle Cambrian assemblages. There are no obvious palaeobiogeographical patterns, with many genera being found widely. Vauxiids, lithistids and heteractinids are apparently confined to low latitudes, but this may be due to a poor fossil record. Most known Ordovician faunas are from low latitudes, although some high-latitude faunas are known, which contain reticulosan hexactinellids and protomonaxonids. There is some division of faunas within Laurentia, into eastern and western provinces, with the western assemblage extending across low northern latitudes during the Late Ordovician. During the Silurian Period, sponge diversity was very low during the Llandovery Epoch, probably partly owing to lack of habitat for taxa restricted to carbonate facies, and also because of sampling bias. There was a dramatic increase in diversity through the Silurian Period, mostly owing to an apparent diversification in the demosponges; however, there are many ghost lineages, indicating that their fossil record is poorly known. Non-lithistid sponges are very poorly known, with few recorded outside Euramerica. The currently available data for Early Palaeozoic sponges are too incomplete to allow any reliable palaeobiogeographical inferences. Supplementary material: the compilation of Silurian sponge occurrences is available at: http://www.geolsoc.org.uk/SUP18666.

An enigmatic, possibly chemosymbiotic, hexactinellid sponge from the early Cambrian of South China

Six specimens of a strongly curved, cylindrical hexactinellid sponge have been recovered from the TommotianAtdabanian Hetang Biota of South China, and are described as Decumbispongia yuani gen. et sp. nov. The robust, thick-walled sponge shows no evidence of an osculum or basal structures, and the body form is inconsistent with an upright, filter-feeding life position. Interpretations as a detritivore feeding by amoeboid extensions, or as a facultative chemosynthetic symbiosis of sponge and bacteria are considered. The latter interpretation is preferred due to the highly constrained body shape, and the body form is interpreted from this perspective. The species indicates that Cambrian sponges occupied at least some autecological niches that appear to have been vacant since that time.