ORIGIN, PHYLOGENY AND PALAEOBIOLOGY OF EARLY PALAEOZOIC BRACHIOPODSMain Ph.D projects in progress (original) (raw)

Organophosphatic brachiopods:Patterns of biodiversification and extinction in the Early Palaeozoic

Geobios, 1999

From a database of 226 Cambrian - Ordovician genera of organophosphatic-shelled brachiopods comprisingthe Subphylum Linguliformea, 11 sets of morphological characters typify all orders and superfamilies. Seven sets of these large-scale evolutionary novelties were established already by the end of the mid Cambrian, 2 more by the end of the late Cambrian, and the remaining 2 before the end of the Arenig. The earliest linguliformeans are of Tommotian age and represent some of the oldest known benthic organisms with a mineralised skeleton. Major diversification at the generic level took place during the mid and late Cambrian, by which time members of the Order Lingulida spread from near-shore to deep-water environments and became dominant in low diversity benthic assemblages that inhabited mobile sandy bottoms. There was a significant decline in diversity of linguliformeans during the latest Cambrian. Following recovery in the late Tremadoc-early Arenig, they then became one of the most distinctive components of benthic assemblages inhabiting marginal environments, e.g. eutrophic basins, shallow mobile sands, and abyssal depths. During the Llanvirn, there was a significant, worldwide turnover in linguliformean brachiopod faunas, when the majority of epibenthic lingulides of the families Obolidae, Zhanatellidae and Elkaniidae became extinct and were replaced, in shallow marine biofacies, by assemblages dominated by bivalved molluscs and burrowing lingulides. There is no trace until the mid Ashgill of a significant decline of micromorphic taxa in linguliformean assemblages characteristic of outer shelf environments. However, all siphonotretides, paterinides and most acrotretide genera disappeared towards the end of the late Ordovician pre-Hirnantian Dicellograptus anceps Biozone.D'après une base de données de 226 genres de brachiopodes à coquille organophosphatée du Cambro-Ordoviciencomprenant le subphylum Linguliformea, 11 ensembles de caractères morphologiques distinguent tous les ordres et superfamilles. Sept ensembles de ces innovations évolutives à grande échelle étaient déjà établies à la fin du Cambrien moyen, 2 autres à la fin du Cambrien supérieur et les 2 restantes à la fin de l'Arenig. Les premiers linguliformes sont du Tommotien et représentent quelques-uns des plus anciens organismes benthiques connus à squelette minéralisé. Une diversification majeure au niveau générique se produisit au cours du Cambrien moyen et supérieur alors que des représentants de l'ordre Lingulida s'étendaient des milieux côtiers à des environnements plus profonds et devenaient dominants dans les assemblages benthiques à faible diversité qui occupaient les fonds sableux mobiles. Il y eut un déclin significatif de la diversité des linguliformes au cours du Cambrien terminal. A la suite de la reconquête au Tremadoc supérieur-Arenig inférieur, ils devinrent l'un des constituants les plus marquants des communautés benthiques des environnements marginaux, c'est-à-dire de bassins eutrophiques, des sables mobiles peu profonds et des profondeurs abyssales. Au Llanvirn intervint un changement mondial important des faunes de brachiopodes linguliformes quand la plus grande partie des lingulides épibenthiques des familles Obolidae, Zhanatellidae et Elkaniidae disparurent et furent remplacées, dans les faciès marins peu profonds, par des assemblages dominés par des mollusques bivalves et des lingulides fouisseurs. Il n'y a pas trace jusqu'à l'Ashgill moyen d'un déclin significatif des taxons micromorphes dans les assemblages de linguliformes caractéristiques des environnements de la plateforme externe. Cependant, tous les genres de siphonotrétides, patérinides et la plupart de ceux des acrotrétides disparurent vers la fin de la biozone pré-hirnantienne à Dicellograptus anceps de l'Ordovicien supérieur.

Frontiers in Palaeontology Brachiopods: Origin and Early History

2017

Despite many major advances in recent years, three key challenges remain in bringing clarity to the early history of the phylum: (1) identifying the origin, morphology and life modes of the first brachiopods; (2) understanding the relationships of the major groups to each other and higher sister taxa; and (3) unravelling the roles of the Cambrian and Ordovician radiations that set the agenda for much of subsequent brachiopod evolution. Since some 95% of all brachiopod taxa are extinct, the fossil record is the primary source of data to frame and test models for the evolution of the phylum. The acquisition of new, and the redescription of existing faunas, in precise spatial and temporal frameworks, using new and well-established analytical and investigative techniques, are as impor-

Early Middle Cambrian (Ordian) brachiopods of the Coonigan Formation, western New South Wales

Alcheringa: An Australasian Journal of Palaeontology, 1990

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The oldest brachiopods from the lower Cambrian of South Australia

T. 2013. The oldest brachiopods from the lower Cambrian of South Australia. Acta Palaeontologica Polonica 58 (1): 93-109. The morphology and organophosphatic shell structure of the paterinate brachiopod Askepasma is documented using new and previously collected specimens from the lower Cambrian of South Australia. Lack of adequately preserved material has seen the majority of paterinate specimens previously reported from South Australia referred to the genus Askepasma and treated under open nomenclature. Large collections of paterinates from the lower Cambrian Wilkawillina, Ajax, and Wirrapowie limestones in the Arrowie Basin, South Australia have prompted redescription of the type species Askepasma toddense and the erection of a new species, Askepasma saproconcha sp. nov. Askepasma saproconcha sp. nov. currently represents the oldest known brachiopod from the lower Cambrian successions in South Australia with a FAD in pre−trilo− bitic (Terreneuvian, Cambrian Stage 2, lower Atdabanian) strata in the basal part of the Wilkawillina and Wirrapowie limestones. Askepasma toddense predominantly occurs in Abadiella huoi Zone equivalent strata (Unnamed Cambrian Se− ries 2, Stage 3, middle-upper Atdabanian) in the upper part of the lower Wilkawillina, Wirrapowie, and Ajax limestones.