Diverse and durophagous: Early Carboniferous chondrichthyans from the Scottish Borders

Abstract

Chondrichthyan teeth from a new locality in the Scottish Borders supply additional evidence of Early Carboniferous chondrichthyans in the UK. The interbedded dolostones and siltstones of the Ballagan Formation exposed along Whitrope Burn are interpreted as representing a restricted lagoonal environment that received significant amounts of land-derived sediment. This site is palynologically dated to the latest Tournaisian–early Viséan. The diverse dental fauna documented here is dominated by large crushing holocephalan toothplates, with very few, small non-crushing chondrichthyan teeth. Two new taxa are named and described. Our samples are consistent with worldwide evidence that chondrichthyan crushing faunas are common following the Hangenberg extinction event. The lagoonal habitat represented by Whitrope Burn may represent a temporary refugium that was host to a near-relict fauna dominated by large holocephalan chondrichthyans with crushing dentitions. Many of these had already become scarce in other localities by the Viséan and become extinct later in the Carboniferous. This fauna provides evidence of early endemism or niche separation within European chondrichthyan faunas at this time. This evidence points to a complex picture in which the diversity of durophagous chondrichthyans is controlled by narrow spatial shifts in niche availability over time.

Feeding structures in the ray-finned fishEurynotus crenatus(Actinopterygii: Eurynotiformes): implications for trophic diversification among Carboniferous actinopterygians

“…2011; Friedman & Sallan 2012; Sallan & Friedman 2012; Richards et al . 2018). It is clear that the extinction did not result in a complete taxonomic shift, as members of the dominant Devonian and Carboniferous durophagous fish groups overlapped to varying degrees in the Late Devonian and early Carboniferous (Sallan et al .…”

A fish and tetrapod fauna from Romer's Gap preserved in Scottish Tournaisian floodplain deposits

“…; Richards et al . ) and lungfish (Smithson et al . ) during the Tournaisian and Visean has been noted previously.…”

“…Few Tournaisian fish localities have been known until recently (Clarkson ; Long ; Sallan & Coates ; Mansky & Lucas ; Sallan & Galimberti ; Mickle , Richards et al . ), and these, too, appear impoverished relative to subsequent Visean faunas.…”

Fossils, function and phylogeny: Papers on early vertebrate evolution in honour of Professor Jennifer A. Clack – Introduction

“…This funded a four-year multi-institutional and cross-disciplinary study led by Jenny of the fauna, flora, stratigraphy, and sedimentology of the new sites. The TW:eed Project (Tetrapod World: early evolution and diversification) began in 2012 and has produced a series of important multi-authored papers (e.g., Otoo et al 2018;Richards et al 2018;, which have shown that, far from being an impoverished hiatus in the fossil record, Romer's Gap had a rich and diverse fauna that quickly recovered from the end-Devonian extinction event and contained the foundations of the modern vertebrate fauna (Fig. 7).…”