tetrapods. As would be expected from a fin, there are numerous lepidotrichia (long and thin fin rays). Panderichthys has many features that can be considered an intermediate form during the fish-tetrapod evolution and displays some features that are more derived than its phylogenetic position indicates, while others that are more basal. The body form of Panderichthys and Tiktaalik represents a major step in the transition from fish to tetrapods and they were even able to haul out on land. According to Shultze and Trueb, Panderichthys shares ten features with tetrapods: The skull roof is flat compared to fish skulls. The orbits are more dorsal and closer together. The external naris is close to the margin of the upper jaw. Paired frontals. External intracranial joint is absent. Parietal located between the orbits and main portion posterior to orbits. In P. rhombolepis, the squamosal touches the maxilla (varies among specimens though). Teeth have complex polyplocodont structure. Lack of median fins. In panderichthyids and Ichthyostega ribs are attached to the neural arch and there is an intercentrum. Humerus One of the key transitional features of Panderichthys is its humerus. During the transition from fish to tetrapods the limbs began to move and became located at a right angle to the body rather than being oriented toward the posterior end. As a result, the muscles became perpendicular to the body and caused the limbs to move in a more anteroposterior and dorsoventral pattern. This in turn affected the shape of the humerus and as a result early tetrapods have an L-shaped humerus. Due to a recent discovery of a humerus of Panderichthys that was not flattened, the specimen could be analyzed in much greater detail. The humerus of Panderichthys displays a variety of features including ones that are both primitive and derived. Despite being placed as basal to Tiktaalik, the humerus of Panderichthys has features that are more derived, but overall is very similar. Both Panderichthys and Tiktaalik have humeri that are dorsoventrally flattened with a blade like entepicondyle curving ventrally, separated epipodial facets, a latissimus dorsi process and ectepicondule process that is parallel to the preaxial margin. The humeri of both species are considered transitional forms because they are almost L-shaped, have a low latissimus dorsi process, a low entepicondyle, and an intermediate entepicondylar canal. The humerus of Panderichthys is more derived than that of Tiktaalik because of the presence of a more