Conodonts in the Upper Ordovician Keisley Limestone of northern England: taxonomy, biostratigraphical significance and biogeographical relationships

Abstract

The classical fauna from the Keisley Limestone, one of the first Upper Ordovician conodont faunas described from the UK, is re-evaluated based on relatively abundant collections of well-preserved conodont elements representing 20 multielement taxa. Common taxa are representatives of Amorphognathus duftonus, Birksfeldia circumplicata, Eocarniodus aff. E. gracilis, Hamarodus brevirameus, Scabbardella altipes, Strachanognathus parvus and several coniform species. These occur with more rare specimens of, among others, Aphelognathus nudus, Amorphognathus aff. A. ordovicicus, Dapsilodus mutatus, Icriodella prominens, Icriodella rhodesi sp. nov. and Protopanderodus liripipus. One new species is proposed, and the concepts of Birksfeldia, Gamachignathus, Icriodella and Notiodella are discussed. It is proposed that Birksfeldia is a senior synonym of Gamachignathus and Notiodella a junior synonym of Icriodella. The described Keisley species association, which represents the A. ordovicicus Zone and is of late Katian (Ka4) age, is closely similar to those of the Boda Limestone of south-central Sweden and some other European faunas, but coeval shallow-water faunas from eastern North America differ in several respects from these European faunas. Biostratigraphy and carbon isotope chemostratigraphy indicate that most of the Keisley Limestone is of late Katian age

Two new early balognathid conodont genera from the Ordovician of Oman and comments on the early evolution of prioniodontid conodonts

“…places all these taxa within the Icriodontidae (Fig. 10) as well as suggesting that the third P element in Notiodella is an M element and that Icriodella and Notiodella are synonymous (see also discussion in Bergström and Ferretti 2015). Our…”

“…Details and results of a re-run of Donoghue's analysis including these newly described taxa is included in the next section. Above we suggest that Omanognathus has similarities with Notiodella, Icriodella and Gamachignathus (Birksfeldia according to Bergström and Ferretti, 2015). places all these taxa within the Icriodontidae (Fig.…”

Trans-Atlantic application of the Baltic Middle and Upper Ordovician carbon isotope zonation

“…The upper box shows the δ 13 C curve through the upper Vauréal and Ellis Bay formations of Anticosti Island, Québec as reported by Young et al (2010). Note that Birksfeldia was recently interpreted to be a senior synonym of Gamachignathus (Bergström & Ferretti 2014). The right column (with Baltic stages along its right margin) shows the excursions and the isotope zones recognized in the reference section in the Jurmala R-1 drillcore in Latvia (after Ainsaar et al 2010, fig.…”

Conodonts in Ordovician biostratigraphy

“…Bergström , ; Orchard ; Savage & Bassett ; Ferretti et al . ,b; Bergström & Ferretti ) contain several species that are common in Baltoscandia, these faunas have their own distinctive provincial character with the presence of some taxa of North American affinities, such as species of Plectodina , Ozarkodina and Icriodella , which are absent, or very rare, in coeval faunas from the East Baltic. Several late Darriwilian–Sandbian faunas from outcrops near Girvan and Tweeddale in South Scotland (Bergström ; Armstrong ) show close affinities with coeval faunas from eastern North America, particularly Newfoundland, but are also very similar to equivalent Baltoscandic faunas.…”