Postcranial stem tetrapod remains from the Devonian of Scat Craig, Morayshire, Scotland



The postcranial stem tetrapod remains from Scat Craig include a neural arch, humerus, tibia, femur, and incomplete pectoral girdles and ilia. These elements are all large or very large compared with the corresponding bones of other stem tetrapods. They correlate well in size with the proportions of Elginerpeton, the known stem tetrapod from Scat Craig, and probably belong to this genus. The neural arch has weak zygapophyses, and the ilia and shoulder girdles resemble those of Ichthyostega. The femur is strongly twisted, with the intercondylar fossa facing anteroventrally, so the hind limb probably functioned as a paddle. The tibia is broad, as in Acanthostega and Ichthyostega. The humerus is approximately intermediate in shape between those of osteolepiforms and later stem tetrapods, but seems to have a ventral radial facet like Ichthyostega. Overall, the postcranial bones combine apparent synapomorphies with Ichthyostega and characters which are uniquely primitive among stemgroup tetrapods. This character combination is incongruent. A recently discovered postorbital bone from the site is, strictly speaking, indeterminable but may belong to Elginerpeton; it broadly resembles the postorbitals of Ichthyostega and Acanthostega, and demonstrates that the typical stem tetrapod facial morphology had evolved before the end of the Frasnian.