There seems to be an incongruity between the posterior nostrils and the heavy flat ribs, the former suggesting free swimming and diving habits, the latter shallow water and bottom habits. Possibly the position of the nostrils has been the result of the great elongation of the face in front of the nostrils; and we know that their posterior position in the phytosaurs (Figs. 95 and 96) has not been due to swimming habits only. Nothing has been discovered to indicate the nature of the external covering of the body. Possibly, even probably, the skin was more or less covered by horny scales or plates, though it may have been quite bare, as in the salamanders. To which other reptiles the proganosaurs are nearest related has long been a subject of dispute, and still is. The more probable view, however, is that they were a very early branch of the most primitive stock of reptiles, the Cotylosauria, one that soon perished, leaving no descendants, unless possibly the ichthyosaurs were their progeny. Some writers have thought that they were the early ancestral stock of the plesiosaurs, and they are often classified with the Sauropterygia. Still others have believed that they were an early side-branch of the great group of Rhynchocephalia. And this doubt has been chiefly due to our imperfect knowledge of the bones of the cranium. As has been explained, very much stress in the classification of reptiles has been laid by students on the possession of one, two, or no openings on the side of the skull back of the eyes. And this part of the skull of the Proganosauria has not yet been satisfactorily made out. Dr. McGregor thought that there are two openings in the temporal region, allying the group with the Rhynchocephalia. Dr. Huene is more positive that there is but one, like that of the ichthyosaurs. In this state of indecision, the proganosaurs may be dignified by giving them an ordinal position by themselves. CHAPTER X PROTOROSAURIA PROTOROSAURUS