Article: Taxonomic revision of the Late Devonian tetrapod Ichthyostega from East Greenland
Two morphologically distinct assemblages of the Late Devonian tetrapod Ichthyostega from East Greenland are described on the basis of a large collection of skulls and postcranial elements. Skull specimens collected on Gauss Halvo show that the assemblage from the lower Aina Dal Formation has proportionally narrower skulls and finer skull roof sculpture than the assemblage from the higher Britta Dal Formation. The assemblages are compared with the stratigraphically unconstrained type material from the north side of Celsius Bjerg on Ymer O, allowing a taxonomic revision. From the original description of seven taxa, three species are recognized and related to the assemblages from Gauss Halvo. I. stensioei is comparable with the Aina Dal Formation assemblage while I. eigili and I. watsoni are valid for specimens found in the Britta Dal Formation. Ichthyostegopsis wimani is not a valid genus or species and may be regarded as a juvenile I. eigili. This example of species-level variability is the earliest known from the fossil record of early tetrapods.