Fauna and ecology of the holothurian bed, Llandrindod, Wales, UK (Darriwilian, Middle Ordovician), and the oldest articulated holothurian

Abstract

Unlike Cambrian Lagerstätten, Ordovician exceptionally preserved faunas generally differ substantially from each other in taxonomic composition, suggesting a much greater diversity of palaeocommunities during this interval. It is unclear, however, how much of the Ordovician ecological diversity is due to the atypical facies or communities being represented by most of the known exceptional biotas. This paper describes a new Lagerstätte, preserved through high sedimentation rates and early pyritization, from the Middle Ordovician (Darriwilian, Hustedograptus? teretiusculus Biozone) of Wales. A preliminary analysis of the ecology of the fauna, which includes a new methodology for translating preserved abundance of different groups into estimated life abundance, has revealed that an ostensibly trilobite-dominated fauna was dominated instead by brachiopods, reticulosan and protomonaxonid sponges, and palaeoscolecidans, with carpoids and holothurians being nearly as abundant as trilobites. Under normal preservational conditions, this community would appear as a typical Ordovician mudstone fauna, implying that it represents a relatively normal open marine community. The biota does not closely resemble any of the previously described exceptional Ordovician faunas, suggesting that there is a large amount of hidden diversity in communities of this age. Among the exceptional taxa is the earliest known articulated holothurian, Oesolcucumaria eostre gen. et sp. nov., which is a small globular form with partly skeletonised ambulacrae. © Palaeontological Association March 2012.