12 small teeth in the latter. Teeth on the vomers, palatines, and pterygoids are the norm in early archosauromorphs and reptiles as a whole. The lower jaw is slender, and most of its length is devoted to the toothed dentary bone. The dentary is downturned at its tip and its outer surface is dotted with a row of prominent foramina (blood vessel pits). There are up to 19 teeth in the dentary. Most commonly, the first six teeth are prominent conical fangs, akin to the premaxilla, while the remainder are small and tricuspid, akin to the maxilla. There is some variation in the number of each tooth shape, and some individuals may have up to 11 conical teeth. The inner surface of the dentary is joined by a splint-shaped bone, the splenial, at its lower edge. The splenial was most likely not visible in lateral view. At its rear, the dentary seems to be partially overlapped by the surangular, a bone which comprises much of the rear part of the jaw. Although it is plausible that a small coronoid bone could be present in front of the surangular, evidence is ambiguous at best for all Tanystropheus species. A sheathe-like bone, the angular, is well-exposed under the dentary and surangular, though sutures between these bones are difficult to interpret with certainty. The joint at the back of the jaw lies on the articular, a lumpy rectangular bone which is floored and reinforced by a similar bone: the prearticular. In Tanystropheus species with known skull material, both the articular and prearticular contribute equally to a segment of the jaw extending back beyond the level of the jaw joint. This feature, known as a retroarticular process, is enlarged to a similar degree to that of early rhynchosaurs. Skull of Tanystropheus hydroides The skull of Tanystropheus hydroides is broader and flatter than that of T. longobardicus. The first five of six teeth in the premaxilla are very large and fang-like, forming an interlocking “fish trap” similar to Dinocephalosaurus and many sauropterygians such as plesiosaurs and nothosaurs. All teeth in the skull have a single cusp which is sharp, curved, and unserrated. They have an oval-shaped cross section and shallow subthecodont implantation. Like T. longobardicus, T. hydroides has a single central narial opening. Unlike T. longobardicus, T. hydroides has a nearly vertical rear edge of the premaxilla, without a postnarial process. The maxilla is low,