84 ME. C. W. ANDEEWS ON THE SKULL AND 



Concluding Remarks. 



In the preceding pages only a few of the types to which the fossils have been compared 

 are mentioned, they being the only types to which any resemblances pointing to possible 

 affinities could be made out. And even among these there are some to which the 

 similarity is so slight that they also might perhaps have been omitted. For instance, 

 in the case of Diomedea, it is only in the structure of the palate and one or two other 

 points in the skull that any similarity with Phororhacos can be detected, the rest of 

 the skeleton being strongly against any such relationship. In fact, it seems to the writer 

 that the only groups that really come into question are the Falconiformes and aberrant 

 Gruiformes, Cariama, Chunga, and to a less degree Psophia. 



It is to a relationship with the former group that the general appearance of the skull 

 and feet of Phororhacos seems to point ; but, as above shown, the general structure of the 

 skeleton, particularly of the pelvis and hind limb, is opposed to this, while, on the other 

 hand, it is strongly in favour of affinity with the Gruiformes. In this, however, the 

 skull at first sight seems to oppose a number of serious difficulties, differing widely 

 from the skull of the typical Crane both in general appearance and in many points of 

 structure, e. g. in its holorhinal nares and desmognathous palate ; but it is precisely in 

 these points that the Cariamidse also differ from the typical members of the group and 

 therefore resemble the fossil. Still the differences between the skull of Phororhacos and 

 that of Cariama are so great that some explanation of them is necessary if the close 

 affinity of the two forms is to be maintained. This explanation seems to be found in 

 the extraordinary size of the beak in the fossil, a specialization that has led to great 

 modifications in several regions of the skull. Thus the size and weight of the upper 

 jaw have led to changes in the palate in the direction of greater rigidity, resulting in 

 the extensive union in the middle line of the maxillo-palatine plates and their 

 complete fusion with the anterior ends of the palatines (this occurs also in Toucans 

 and Hornbills). Moreover, the development of the peculiar prominent ridges formed 

 by these combined elements, and, as already described, projecting below the tomium on 

 either side the middle line, also tends greatly to increase the rigidity of the beak, and 

 possibly the modes of union of the pterygoids with the basis cranii may still further 

 add to it. 



Again, with the great massiveness of the mandible is correlated the large size of 

 the temporal fossae, and the weight of the skull as a whole has led to an increase 

 in the area of the occipital surface by the extension of the lambdoidal and paroccipital 

 crests, to which the muscles supporting the head are attached. The characters thus 

 accounted for give the skull of Phororhacos its peculiar form, so different from that 

 of Cariama, and would be evidence of a high degree of specialization even if the 

 rest of the skeleton were unknown. 



It was no doubt this high degree of specialization that brought about the extinction 

 of this giant bird as soon as the conditions to which it was adapted underwent some 



