An amniote-like skeleton from the Early Carboniferous of Scotland

The origin of tetrapods occurred in the Late Devonian period1, and the earliest known taxa were aquatic2. A gap of 30 million years has separated these early forms from the first record of terrestrial tetrapods, in the Late Viséan (Early Carboniferous)3. Here we report the discovery of a small, highly ossified, postcranial skeleton of a terrestrially adapted, amniote-like tetrapod from the Mid Viséan; this specimen shows the earliest known pentadactyl manus. The skeleton is associated with a gracile humerus that has a constricted shaft and exhibits torsion between proximal and distal articulations. These features are associated with the maintenance of postural support and are strong evidence of locomotion on land4. The specimen pushes back the known occurrence of terrestrial vertebrates closer to the origin of tetrapods. Phylogenetic analysis places this new animal close to undisputed amniotes occurring in the Westphalian, indicating that, by the Mid–Late Viséan, amniotes already had a long, but previously unrecorded, history. The origin of amniotes seems to have occurred early in the Carboniferous and was part of a rapid diversification of tetrapods at this time3,5,6.