The Bothriolepis (Placodermi, Antiarcha) material from the Valentia Slate Formation of the Iveragh Peninsula (middle Givetian, Ireland): Morphology, evolutionary and systematic considerations, phylogenetic and palaeogeographic implications

Abstract

Material of the antiarch placoderm Bothriolepis from the middle Givetian of the Valentia Slate Formation in Iveragh Peninsula, Ireland, is described and attributed to a new species, B. dairbhrensis sp. nov. A revision of the genus Bothriolepis is proposed, and its taxonomic content and previous phylogenetic analyses are reviewed, as well as the validity of morphologic characteristics considered important for the establishment of the genus, such as the shape of the preorbital recess of the neurocranium. A series of computerised phylogenetic analyses was performed, which reveals that our new species is the sister taxon to the Frasnian Scottish form B. gigantea. New phylogenetic and biogeographic analyses of the genus Bothriolepis together with comparisons between faunal assemblages reveal a first northward dispersal wave from Gondwana to Euramerica at the latest in the mid Givetian. Other Euramerican species of Bothriolepis seem to belong to later dispersal waves from Gondwana, non-excluding southward waves from Euramerica. Questions remain open such as the taxonomic validity and stratigraphic constraints for the most ancient forms of Bothriolepis in China, and around the highly speciose nature of the genus.

Non-tetrapod sarcopterygians from the Valentia Slate Formation (Givetian, Devonian) of the Iveragh Peninsula, south-western Ireland: systematic reappraisal and palaeobiogeographic implications

“…Holoptychius and the rhizodont (if correctly identified) represent both the earliest examples of these taxa in Euramerica. Bothriolepis, the most abundant member of the Valentia Slate fauna, is also the earliest from Euramerica but is known from earlier deposits in Gondwana and South China (Dupret et al, 2023). The lungfish shows a derived tooth-plate morphology with procumbent teeth, otherwise only known from Late Devonian and later examples.…”

“…This age assignment has been significantly refined by the Isotopic dating of the Keel Tuff, that stratigraphically occurs 800 m above the main Bothriolepis fauna (FB1) in St Finan's Bay. The Keel Tuff has yielded an isotopic age of 385 My (Williams, 2000) which unequivocally demonstrates that Valentia Slate Formation is Givetian in age, and makes the Bothriolepis material the earliest record of the genus in Laurussia (Dupret et al, 2023). The present study is primarily based on the re-examination of material originally described by Russell (1978) and stored in the fossil vertebrate collections of the Natural History Museum of London.…”

“…The fauna recorded from Valentia Slate Formation presents a biogeographic and stratigraphic puzzle that is rendered all the more important by the occurrence in the same formation of some of the earliest known tetrapod trackways (Stössel, 1995;Stössel et al, 2016). The most common faunal component of the Valentia Slate Formation is the antiarch Bothriolepis, which represents the earliest record of this genus in Euramerica, though still older representatives are known from Gondwana and South China (Dupret et al, 2023). The record of Holoptychius is possibly the earliest in the world, and the lungfish and probable rhizodont both resemble Late Devonian taxa.…”

“…This deformation produced significant crustal shortening and a strong tectonic cleavage in the rocks, which has had a pronounced effect on the preservation of the fossil material. The metamorphism INTRODUCTION AND GEOLOGICAL SETTING Dupret, V. et al -Non-tetrapod sarcopterygians from the Givetian of SW Ireland -Spanish Journal of Palaeontology 38 (1), [37][38][39][40][41][42][43][44][45][46]2023 has led to zones of mineralization around the bones, as well as elemental exchange between bone and matrix (Dupret et al, 2023) of the fossil material. The Valentia Slate Formation on Valentia Island is of great palaeontological importance as it contains the second oldest record of tetrapod trackways in the world (Clack, 1997;Stössel, 1995;Stössel et al, 2016).…”

“…The Valentia Slate Formation on Valentia Island is of great palaeontological importance as it contains the second oldest record of tetrapod trackways in the world (Clack, 1997;Stössel, 1995;Stössel et al, 2016). The Formation also contains a fauna of disarticulated non-tetrapod vertebrate remains (Dupret et al, 2023;Russell, 1978). Russell recorded five vertebrate fossil horizons (FB1-FB5) in the Valentia Slate Formation at St Finan's Bay.…”