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The axial skeleton of the Devonian tetrapod Ichthyostega

Abstract

Ichthyostega was the first Devonian tetrapod to be subject to a whole-body reconstruction1,2,3. It remains, together with Acanthostega4, one of only two Devonian tetrapods for which near-complete postcranial material is available. It is thus crucially important for our understanding of the earliest stages of tetrapod evolution and terrestrialization. Here we show a new reconstruction of Ichthyostega based on extensive re-examination of original material and augmented by recently collected specimens. Our reconstruction differs substantially from those previously published and reveals hitherto unrecognized regionalization in the vertebral column. Ichthyostega is the earliest vertebrate to show obvious adaptations for non-swimming locomotion. Uniquely among early tetrapods, the presacral vertebral column shows pronounced regionalization of neural arch morphology, suggesting that it was adapted for dorsoventral rather than lateral flexion.

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Acknowledgements

We thank the Geological Museum and University of Copenhagen for access to their Ichthyostega material, and G. Cuny and D. Harper for their help and support during our visits. We would also like to acknowledge the late E. Jarvik and S. Bendix-Almgreen, both of whom gave us access to specimens then in their care. Preparation of MGUH f.n. 300 was carried out by S. Finney. M. Coates kindly permitted us to use one of his unpublished Acanthostega reconstructions for part of Fig. 1c. Most of our project was supported by an NERC grant with additional funding for H.B. provided by the Isaac Newton Trust Fund and by a project grant and salary from Vetenskapsrådet (the Swedish Research Council) for P.E.A.

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Competing interests

Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Correspondence to Per Erik Ahlberg.

Supplementary information

Supplementary Notes

Discussion on preservation and taphonomy of the Ichthyostega material. (DOC 30 kb)

Supplementary Figure Legend

Text to accompany Supplementary Figure S1. (DOC 27 kb)

Supplementary Figure S1

This illustrates three thoracic and three lumbar neural arches from different Ichthyostega specimens. (JPG 124 kb)

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Further reading

Figure 1: Reconstructions of Ichthyostega and Acanthostega.
Figure 2: Specimens of Ichthyostega.
Figure 3: MGUH VP 6054, vertebral column, pelvis and hindlimb of Ichthyostega.
Figure 4: MGUH VP 6139, skull, shoulder girdle, thoracic and presacral region of Ichthyostega.

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