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Phylogenetic and environmental context of a Tournaisian tetrapod fauna

Abstract

The end-Devonian to mid-Mississippian time interval has long been known for its depauperate palaeontological record, especially for tetrapods. This interval encapsulates the time of increasing terrestriality among tetrapods, but only two Tournaisian localities previously produced tetrapod fossils. Here we describe five new Tournaisian tetrapods (Perittodusapsconditus, Koilopsherma, Ossiraruskierani, Diploradusaustiumensis and Aytonerpetonmicrops) from two localities in their environmental context. A phylogenetic analysis retrieved three taxa as stem tetrapods, interspersed among Devonian and Carboniferous forms, and two as stem amphibians, suggesting a deep split among crown tetrapods. We also illustrate new tetrapod specimens from these and additional localities in the Scottish Borders region. The new taxa and specimens suggest that tetrapod diversification was well established by the Tournaisian. Sedimentary evidence indicates that the tetrapod fossils are usually associated with sandy siltstones overlying wetland palaeosols. Tetrapods were probably living on vegetated surfaces that were subsequently flooded. We show that atmospheric oxygen levels were stable across the Devonian/Carboniferous boundary, and did not inhibit the evolution of terrestriality. This wealth of tetrapods from Tournaisian localities highlights the potential for discoveries elsewhere.

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Figure 1: New tetrapod taxa from Willie’s Hole.
Figure 2: Ossirarus kierani gen. et sp. nov. (UMZC 2016.3) from Burnmouth Ross end cliffs.
Figure 3: Diploradus austiumensis gen. et sp. nov. (UMZC 2015.30) from Burnmouth Ross end cliffs.
Figure 4: Aytonerpeton microps gen. et sp. nov. (UMZC 2015.46b) from Burnmouth Ross end shore exposure.
Figure 5: Phylogenetic analysis of early tetrapods.
Figure 6: Burnmouth sedimentary log showing palaeosol and tetrapod fossil distribution.

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Acknowledgements

We acknowledge funding from NERC consortium grants NE/J022713/1 (Cambridge), NE/J020729/1 (Leicester), NE/J021067/1 (BGS), NE/J020621/1 (NMS) and NE/J021091/1 (Southampton). We thank the following for their support and contributions: the late S. Wood and M. Wood for discovery of and access to collections; O. Kieran and B. Kieran and the Burnmouth community for support for the project; M. Browne for field assistance and information on stratigraphy; M. Lowe for access to UMZC collections; S. Finney for field assistance, conservation advice and preparation of Koilops; V. Carrió for conservation and preparation of NMS specimens; J. Sherwin for stratigraphy and field assistance; and S. Akbari (Southampton) for contribution to palynological processing. T.I.K. and D.M. publish with the permission of the Executive Director, British Geological Survey (NERC). A. Brown and C. MacFadyen of Scottish Natural Heritage gave permission to collect at sites in their care and P. Bancks, from The Crown Estates Office in Edinburgh, gave permission to collect on Crown land. PRISM, the Isaac Newton Trust Fund (Trinity College, Cambridge), the Crotch Fund (UMZC) and an anonymous donor provided funding for the purchase of specimens. This is a contribution to IGCP project 596.

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J.A.C. was lead principal investigator. T.R.S., J.AC., B.K.A.O. and K.Z.S. collected, described and analysed the tetrapod specimens. C.E.B., T.I.K., S.J.D. and D.M. contributed to the stratigraphical, sedimentological and environmental studies. J.E.A.M., D.K.C., and E.J.R. contributed to the charcoal, palynological and stratigraphical studies. M.R. and J.A.C. contributed to the phylogenetic analysis. A.J.R. contributed information on the arthropods. S.A.W. provided additional work on micro-CT scan data. A.J.R., S.A.W. and N.C.F. organized the Willie’s Hole excavation that provided the sedimentological information. All authors contributed to discussion, preparation and writing of the paper.

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Correspondence to Jennifer A. Clack.

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Supplementary Figures 1–9, Supplementary Data and Supplementary Table 1 (PDF 7070 kb)

Supplementary Video 1

Video of an Aytonerpeton whole specimen (MOV 5858 kb)

Supplementary Video 2

Video of an Aytonerpeton skull (MOV 12360 kb)

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Clack, J., Bennett, C., Carpenter, D. et al. Phylogenetic and environmental context of a Tournaisian tetrapod fauna. Nat Ecol Evol 1, 0002 (2017). https://doi.org/10.1038/s41559-016-0002

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