Abstract
Abstract 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 ofElginerpeton, 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 ofIchthyostega. 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 inAcanthostegaandIchthyostega. The humerus is approximately intermediate in shape between those of osteolepiforms and later stem tetrapods, but seems to have a ventral radial facet likeIchthyostega. Overall, the postcranial bones combine apparent synapomorphies withIchthyostegaand characters which are uniquely primitive among stem-group tetrapods. This character combination is incongruent. A recently discovered postorbital bone from the site is, strictly speaking, indeterminable but may belong toElginerpeton; it broadly resembles the postorbitals ofIchthyostegaandAcanthostega, and demonstrates that the typical stem tetrapod facial morphology had evolved before the end of the Frasnian.
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