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An early tetrapod from ‘Romer's Gap’

Abstract

The fossil record of early tetrapods has been increased recently by new finds from the Devonian period1 and mid–late Early Carboniferous period2. Despite this, understanding of tetrapod evolution has been hampered by a 20-million-year gap (‘Romer's Gap’3) that covers the crucial, early period when many key features of terrestrial tetrapods were acquired. Here I describe the only articulated skeleton of a tetrapod, Pederpes, yet found from the Tournaisian epoch (354–344 million years ago (Myr)). The new taxon includes a pes with five robust digits, but a very small, possibly supernumerary digit preserved on the manus suggests the presence of polydactyly. Polydactylous early tetrapods may have survived beyond the end of the Devonian and pentadactyly cannot be assumed for the pes. However, the pes has characteristics that distinguish it from the paddle-like feet of the Devonian forms and resembles the feet of later, more terrestrially adapted Carboniferous forms. Pederpes is the earliest-known tetrapod to show the beginnings of terrestrial locomotion and was at least functionally pentadactyl. With its later American sister-genus, Whatcheeria4,5, it represents the next most primitive tetrapod clade after those of the Late Devonian, bridging the temporal, morphological and phylogenetic gaps that have hitherto separated Late Devonian and mid-Carboniferous tetrapod faunas.

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Figure 1: Holotype specimen of Pederpes finneyae.
Figure 2: Close-up of the skull of Pederpes showing the stapes.
Figure 3: Manus and pes of Pederpes.
Figure 4: Reconstruction of pedes of various taxa.
Figure 5: Single most parsimonious tree showing the whatcheerids to be the next most crownward stem tetrapod clade after the Devonian forms.

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Acknowledgements

I thank J. Richardson at the Natural History Museum, London, for spore-analysis dating the specimen, J. Jeffery for bringing the specimen to my notice, and E. Lombard and J. Bolt for access to the specimens of Whatcheeria. I also thank M. Coates, M. Ruta, P. Upchurch and A. Warren for discussion and analysis of the phylogeny, and the NERC for funding the research project, including the preparation and photography by S. M. Finney.

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Clack, J. An early tetrapod from ‘Romer's Gap’. Nature 418, 72–76 (2002). https://doi.org/10.1038/nature00824

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