As well as Acanthostega and Ichthyostega, I have worked on a number of other Devonian tetrapod taxa, in collaboration with colleagues.

Published with Per Ahlberg, Henning Blom and Sarah Finney (Clack et al. 2012), Ymeria is a new taxon of tetrapod from the Devonian of East Greenland. It is similar in some ways to Ichthyostega, but is distinguishable mainly on dentition. Its tooth shape is quite different from Ichthyostega, and it has areas of dense denticulation on its lower jaw, hence the specific name.

It was found in 1947 by a Swedish-Danish expedition, and Jarvik did not think it was a specimen of Ichthyostega. Our studies showed his instinct was correct. The name derives from Ymer Ø (Ymer Island) and also refers to the ancient Norse god Ymer, the giant from whose body the world was created in Scandinavian mythology. (The journal would not let us include this in the etymology because Ymer is male and Ymeria is female.)

In 2008, I contributed to the description of new and exquisite material of the Famennian tetrapod Ventastega curonica from Latvia (Ahlberg et al. 2008). This new material showed that Ventastega retained a number of primitive features not seen in other tetrapods, and that its spiracular region and posterior skull roof were most closely similar to the near-tetrapod Tiktaalik rosea. It appeared to be the most primitive known tetrapod at the time of its publication.

With colleagues, Ted Daeschler and Neil Shubin ( Daeschler et al. 2009) I studied some of the isolated bones recovered from the Famennian site of Red Hill, from which specimens of Hynerpeton and Densignathus were found. Several taxa appear to be represented among these elements, including a lacrimal bone that most closely resembles that of the whatcheeriid Pederpes. If this is indeed the case, the whatcheeriids are the only clade known so far to cross the Devonian/Carboniferous boundary.

Ongoing discovery, collection, preparation and description is taking place of beautiful new material from northern Russia of a tetrapod that may be even more primitive than Ventastega. Funding has been secured from the National Geographic Society for enlarged excavations of the riverside site during the summer of 2012 or 2013. Per Ahlberg and I are working on this with our Russian colleague Pavel Besnosov.

Per Ahlberg and I are working on yet another new Devonian tetrapod from Greenland, again a lower jaw, but very much smaller than any previous finds, although to judge by the degree of ossification, apparently an adult.