Thelodonts and distribution of associated conodonts from the Llandovery–lowermost Lochkovian of the Welsh Borderland

Abstract

ABSTRACT. Thelodont scales from the Middle Llandovery±lowermost Lochkovian of southern Britain are described with three new taxa, Loganellia? unispinata sp. nov., Nethertonodus prodigialis gen. et sp. nov. and Paralogania tarranti sp. nov. established, and Paralogania kaarmisensis Ma Èrss identi®ed for the ®rst time from Britain. Thelodonts are rare in the Llandovery and Wenlock series where predominantly Loganellia cf. aldridgei Turner, Loganellia scotica (Traquair) and Thelodus sp. are accompanied by coniform conodonts Panderodus Ethington, Decoriconus Cooper and Dapsilodus obliquicostatus (Branson and Mehl). The majority of the material has been recovered from the Ludlow and Pr Ïõ Âdolõ Â series. Thelodus laevis (Pander) and Paralogania martinssoni (Gross) occur in the lower Gorstian. Paralogania kaarmisensis and Phlebolepis elegans Pander come from the Upper Gorstian±Lower Ludfordian and are associated with the zonal conodont Polygnathoides siluricus Branson and Mehl in the upper Gorstian. Thelodus parvidens Agassiz and T. trilobatus Hoppe dominate in the Upper Ludfordian in association with the rarer zonal conodonts Ozarkodina snajdri (Walliser), O. crispa (Walliser) and O. remscheidensis eosteinhornensis (Walliser). The basal Pr Ïõ Âdolõ Â Series indicates a change to a thelodont fauna dominated by Paralogania ludlowiensis (Gross) and including Nethertonodus prodigialis. Higher in the Pr Ïõ Âdolõ Â Series, a succession in faunas includes Katoporodus cf. timanicus (Karataju Åte-Talimaa), Paralogania tarranti, Loganellia? unispinata and Goniporus alatus (Gross). In the highest Pr Ïõ Âdolõ Â beds Paralogania kummerowi (Gross) and Loganellia cuneata (Gross) can be traced before the incoming of the lowermost Devonian taxon Turinia pagei (Powrie) along with Nikolivia gutta Karataju Åte-Talimaa. Correlations with the Baltic are suggested from the Lower Ludlow, Upper Silurian, up to the Lower Lochkovian, Lower Devonian. Gross (1967) studied and described scales from the Ludlow and Temeside Bone Beds and the Psammosteus Limestone, and also scales from some other Devonian outcrops he obtained from O. Walliser of Go Èttingen and T. érvig (1917±1994). Gross (1967) also suggested that British thelodonts were useful for biostratigraphy and correlations with the Baltic and Oslo Region. Turner (1973) gave the distribution of thelodonts from a large number of localities in Britain, recognized a succession of assemblages, and suggested correlations with the Baltic, Scandinavia, Podolia, North Timan, Spitsbergen and Canada. As a result of this study, the distribution of thelodonts was considered when correlating Upper Silurian boundaries in Britain and the Siluro-Devonian boundary in particular (Turner 1977;White and Coppack 1977; Bassett et al. 1982). Thelodonts have been identi®ed from some British borehole studies and used in biostratigraphy (Turner 1973(Turner , 1984(Turner , 2000White and Coppack 1977). New thelodonts were [Palaeontology, Vol. 47, Part 5, 2004 q The Palaeontological Association described during collabo...

Revision of Silurian vertebrate biozones and their correlation with the conodont succession

“…However, later research revealed that the scales from these two regions possess several different features; as a result, two species, L. einari (Märss 1996), which occurs in the Tagavere Beds of the Jaagarahu Stage in Estonia (see below), and L. avonia (Turner 2000), which occurs in the Brinkmarsh Beds, lower Sheinwoodian, Lower Wenlock of Tortworth Inlier, Avon, were established. Because of the restricted distribution of L. avonia (found only in one locality), the zone was removed from the zonal scheme (Märss & Miller 2004).…”

“…References. Märss 1982aMärss , 1982bMärss , 1990Karatajūtė-Talimaa & Brazauskas 1995;Vergoossen 1999;Talimaa 2000;Märss & Miller 2004.…”

“…All the Silurian vertebrate-bearing localities in northwestern Canada (the Selwyn Basin) were revised (Soehn et al 2000), biostratigraphically valuable thelodonts were described, a faunal succession scheme for the Avalanche Lake region (Mackenzie Mountains) was developed and correlations were made (Soehn et al 2001). Additionally, studies of vertebrates from southern Britain (Turner 2000;Märss & Miller 2004) and Belarus (Plax & Märss 2011) have provided further taxonomical and biostratigraphical information about that group.…”

“…That paper also presented the first carbon isotope data from the region and correlated δ 13 C variations with those in the Baltic area. The taxonomy and distribution of agnathans and fishes in southern Britain have been investigated, the regional vertebrate zonal scheme has been updated and characteristic vertebrate assemblages have been correlated with the conodont zonation (Miller & Märss 1999;Turner 2000;Märss & Miller 2004). …”

Biostratigraphy of the Ludlow chitinozoans from East Baltic drill cores; pp. 170–184

“…The distribution of all three microfossil groups is facies controlled, as was proved by the integrated study of the Ohesaare, Ventspils, and Pavilosta cores (Kaljo et al 1986). Although many samples lack chitinozoans in the Ludlow strata of the Ohesaare core, this section still offers the best opportunity for comparison of the zonal successions of vertebrates (Märss 1986;Märss & Miller 2004), conodonts (Viira 1982;Viira & Aldridge 1998), and chitinozoans (Fig. 11).…”