Benjamin K. A. Otoo, Jennifer A. Clack, Timothy R. Smithson, Carys E. Bennett, Timothy I. Kearsey & Michael I. Coates (2018)
A fish and tetrapod fauna from Romer's Gap preserved in Scottish Tournaisian floodplain deposits.
Palaeontology (advance online publication)
Data archiving statementData for this study, including faunal diversity datasets and micropalaeontological data, are available in the Dryad Digital Repository:
https://doi.org/10.5061/dryad.j5t58j4
The endâDevonian mass extinction has been framed as a turning point in vertebrate evolution, enabling the radiation of tetrapods, chondrichthyans and actinopterygians. Until very recently 'Romer's Gap'' rendered the Early Carboniferous a black box standing between the Devonian and the later Carboniferous, but now new Tournaisian localities are filling this interval. Recent work has recovered unexpected tetrapod and lungfish diversity. However, the composition of Tournaisian faunas remains poorly understood. Here we report on a Tournaisian vertebrate fauna from a wellâcharacterized, narrow stratigraphic interval from the Ballagan Formation exposed at Burnmouth, Scotland. Microfossils suggest brackish conditions and the sedimentology indicates a lowâenergy debris flow on a vegetated floodplain. A range of vertebrate bone sizes are preserved. Rhizodonts are represented by the most material, which can be assigned to two taxa. Lungfish are represented by several species, almost all of which are currently endemic to the Ballagan Formation. There are two named tetrapods, Aytonerpeton and Diploradus, with at least two others also represented. Gyracanths, holocephalans, and actinopterygian fishes are represented by rarer fossils. This material compares well with vertebrate fossils from other Ballagan deposits. Faunal similarity analysis using an updated dataset of DevonianâCarboniferous (GivetianâSerpukhovian) sites corroborates a persistent Devonian/Carboniferous split. Separation of the data into marine and nonâmarine partitions indicates more DevonianâCarboniferous faunal continuity in nonâmarine settings compared to marine settings. These results agree with the latest fossil discoveries and suggest that the DevonianâCarboniferous transition proceeded differently in different environments and among different taxonomic groups.
Alexander J. Krause, Benjamin J. W. Mills, Shuang Zhang, Noah J. Planavsky, Timothy M. Lenton & Simon W. Poulton (2018)
Stepwise oxygenation of the Paleozoic atmosphere.
Nature Communications 9, Article number: 4081Â
Free pdf:
Oxygen is essential for animal life, and while geochemical proxies have been instrumental in determining the broad evolutionary history of oxygen on Earth, much of our insight into Phanerozoic oxygen comes from biogeochemical modelling. The GEOCARBSULF model utilizes carbon and sulphur isotope records to produce the most detailed history of Phanerozoic atmospheric O2 currently available. However, its predictions for the Paleozoic disagree with geochemical proxies, and with non-isotope modelling. Here we show that GEOCARBSULF oversimplifies the geochemistry of sulphur isotope fractionation, returning unrealistic values for the O2 sourced from pyrite burial when oxygen is low. We rebuild the model from first principles, utilizing an improved numerical scheme, the latest carbon isotope data, and we replace the sulphur cycle equations in line with forwards modelling approaches. Our new model, GEOCARBSULFOR, produces a revised, highly-detailed prediction for Phanerozoic O2 that is consistent with available proxy data, and independently supports a Paleozoic Oxygenation Event, which likely contributed to the observed radiation of complex, diverse fauna at this time.
====