SKULL OF PTERANODON INGENS Marsh. 13 



crocorax, the occipital style or " xiphoid bone " has attained such size that it can no 

 longer be overlooked in a hasty examination of the skull. Finally, in Chelydra and 

 Chamaeleo, the crest occupies about one-third the entire length of the cranium, and the 

 muscles that are attached to it are the most prominent in the anatom}- of the head. With 

 the exception of Chamaeleo, these animals are all noted for their skill in capturing fish. 



To quote from a letter in which Dr. R. W. Shufeldt has kindly expressed his views, 

 there is at present no doubt on the matter of the physiology of the occipital style : 

 ' Owing to the character of the food (living, struggling fish) and the mode of feeding of 

 such birds as Cormorants, Plotus, etc., it is undoubtedly a structure that has been devel- 

 oped in time, to afford an increased surface for the origin of the temporal muscles upon 

 either side. The seizing and prehensile power of the jaws is thus manifestly increased." 



This statement applies equally well to the development of the crest in Chelydra and 

 other chelonians, e. g., the quasi-marine Toxochelys from the Upper Cretaceous of 

 Kansas, whose skull in this respect is similar to that of Chelydra. 



In all these examples, the relation of the crest to the temporal muscles is regarded 

 as simple, and the function of the crest is supposedly limited to satisfying the need of 

 increased muscular origin ; the earlier stages of the development which culminated in the 

 crest of Pteranodon may well have been similar to the developmental stages through which 

 the ancestors of Phalacrocorax among birds and of Chelydra among reptiles have passed. 



In Pteranodon, the temporal muscles must have extended from their mandibular inser- 

 tions through the pterygo-jugal vacuities and so upward and backward to the large 

 supratemporal fossae. How far their origins spread posteriorly is not shown by the fossil 

 remains ; but in the absence of large bladelike pterygoids, such as are present in the 

 Crocodilia, it is evident that the temporal muscles were the principal elevators of the 

 lower jaws, just as in the genera of recent birds and reptiles referred to above. And. 

 as in these recent animals, the size and power of the temporal muscles could best be 

 increased by extending their origins posteriorly along the sides of a median crest. Such 

 a modification would have been strictly in accord with the general change of form which 

 the skull of Pteranodon had undergone during its specialization. 



The occurrence of Pteranodon remains in the chalk deposited in a shallow sea and 

 at a distance of not less than one hundred miles from the probable shore line, also the 

 shape and proportionate size of the jaws, have given rise to the supposition that this 

 pterodactyl lived principally upon small fish taken at the surface in a manner somewhat 

 similar to that adopted by the Skimmer, Rhynchops, which is said to feed as it skims 

 low over the water with the fore parts inclined downward, the under mandible grazing 

 or cutting the surface. If this were true, it would add greatly to the probability that 

 Pteranodon originally developed a crest in the same way that certain piscatorial birds 

 have developed theirs. It is scarcely imaginable, however, that the temporal muscles of 

 the pterodactyl extended backward along the entire length of the fully developed crest, 

 as in Phalacrocorax, Chelydra, and Chamaeleo ; and in order to account for the complete 

 development of this part it seems necessary to fall back upon the general theory that 

 growth along certain lines may be initiated through the exercise of one function, while 

 further development is dependent upon another totally distinct function. Of what use 

 the posterior part of the crest was to Pteranodon remains largely conjectural. The high 

 crest carried by the head of the male Basilicus, to which in regard to form and direction 

 Professor Marsh compared the Pteranodon crest, is strictly exoskeletal, and therefore 

 is of little assistance in the present case. The weight of the crest would appear not to 



