A Tournaisian (earliest Carboniferous) conglomerate-preserved non-marine faunal assemblage and its environmental and sedimentological context

Abstract

A conglomerate bed from the Tournaisian Ballagan Formation of Scotland preserves a rich array of vertebrate and other nonmarine fossils providing an insight into the wider ecosystem and paleoenvironment that existed during this pivotal stage of Earth history. It challenges hypotheses of a long-lasting post-extinction trough following the end-Devonian extinction event. The fauna recovered includes a wide size range of tetrapods, rhizodonts, and dipnoans, from tiny juveniles or small-bodied taxa up to large adults, and more than one taxon of each group is likely. Some fauna, such as actinopterygians and chondrichthyans, are rare as macrofauna but are better represented in the microfossil assemblage. The fauna provides evidence of the largest Carboniferous lungfish ever found. The specimens are preserved in a localized, poorly-sorted conglomerate which was deposited in the deepest part of a river channel, the youngest of a group of channels. In addition to the fossils (micro- and macro-), the conglomerate includes locally-derived clasts of paleosols and other distinctive elements of the surrounding floodplains. Charcoal fragments represent small woody axes and possible larger trunk tissue from arborescent pteridosperms. Preservation of the fossils indicates some aerial exposure prior to transport, with abrasion from rolling. The findings presented here contrast with other published trends in vertebrate size that are used to interpret a reduction in maximum sizes during the Tournaisian. The richness of the fauna runs counter to the assumption of a depauperate nonmarine fauna following the end-Devonian Hangenberg event, and charcoal content highlights the occurrence of fire, with the requisite levels of atmospheric oxygen during that stage.

The early diversification of ray‐finned fishes (Actinopterygii): hypotheses, challenges and future prospects

“…This sharp rise is especially notable because the early Carboniferous (Tournaisian and early Visean) coincides with ‘Romer's Gap’, an apparent hiatus in the fossil record of tetrapods (and other animals) variably explained as either a period of poor sampling (Romer, 1956 ), low atmospheric oxygen (Ward et al ., 2006 ) or recovery following the EDME (Sallan & Coates, 2010 ). Recent concerted efforts have begun to populate Romer's Gap, indicating that poor sampling accounted for most of the apparent paucity of the record (Clack et al ., 2019 ; Otoo et al ., 2019 ). The diversification of actinopterygians immediately following the EDME likely represents an adaptive radiation seeded by very few – or perhaps just one – actinopterygian lineages (Sallan & Friedman, 2012 ; Sallan, 2014 ; Giles et al ., 2017 ), although this hypothesis has not been explicitly tested.…”

Systematics and description of the lungfish genusSagenodusfrom the Carboniferous of the UK

“…A similarly shaped lungfish anocleithrum from the Tournaisian of Scotland is figured in Clack et al . (2019, fig. 8D).…”

Xiphosurid from the Tournaisian (Carboniferous) of Scotland confirms deep origin of Limuloidea

“…2). Recent studies exploring the first terrestrialisation of tetrapods have furthered the understanding of the sedimentology, palynology, stratigraphy, and palaeoenvironment of the Ballagan Formation, which consists of a thick succession of red and grey siltstones, fine sandstones, ferroan dolostones, and over 200 separate palaeosol horizons 39,40,42–44 (Figs 1, 2). These likely record a seasonal climate with a mosaic of closely packed distinct habitats from both coastal floodplain and marginal marine environments 39 .…”