AN ICHTHYOSAUEIAN SKULL FSOM QUEENSLAND.— LONGMAN. 255 



Etheridge gave details of these species with actual localities and records of other 

 fragments, and queried the identity of the two species. '^^ In 1897 he made a further 

 note on precaudal vertebra as being Ichthyosaurus australis^^ Direct comparison 

 between the type fragment of /. marathonensis and the present skull shows too 

 great a similarity, so far as this region is concerned, to warrant the introduction of 

 a new specific name ; indeed the type fragment, except for the slightly smaller 

 teeth, could almost be placed as a section of the rostrum of our fairly complete 

 skull without doing violence to its contours. 



Unfortunately, McCoy's material was too inadequately described to perm't 

 Etheridge to make a satisfactory comparison. The teeth were compared with those 

 of /. campf/Iodon, and the antero-posterior diameter of the orbit was given as five 

 and a-half inches. Chapman figured a cranial fragment and a paddle of the type 

 material in his useful handbook. ^^ McCoy's species has priority, and in the present 

 state of our knowledge it is deemed inadvisable to ignore it in connection with the 

 Queensland skull, with which its sectional dimensions fairly agree. Our specimen 

 has therefore been catalogued as Ich'kyosaurus australis McCoy. 



/. marathonensis is regarded as a synonym. There is evidence, however, 

 of another species occurring in Queensland, distinguished by smaller teeth, but 

 this awaits further material before elucidation. 



The relationships of the Ichthyosaurs have been the suljject of recent 

 research by such prominent authorities as Sollas, Andrews, Williston, Merriam, 

 van Huene, and Broom, and partly centre around the homologies of the temporal 

 elements. It is now generally agreed that the Ichthyosaurs are descended from the 

 primitive Permian Carboniferous Cotylosaurs. This primitive reptilian group exhibits 

 ordinal characters which, in the words of W. K. Gregory, are " structurally ancestral 

 to all the higher vertebrates. "^^ This fascinating problem, with its wealth of litera- 

 ture illustrating very numerous forms, is too intricate to be dealt with here. From 

 the standpoint of popular interest it may be mentioned, however, that an outstanding 

 characteristic of most Ichthyosaurs, an elongated rostrum, is a common feature in 

 very diverse vertebrates. Among the large present-day reptiles the prolonged 

 snout of the gavials is remarkable. There are commonplace examples amongst 

 birds and fishes. The Ziphoid Cetaceans, such as species of Mesoplodon, are 

 mammalian types which rival the Ichthyosaurs in the extreme development of the 

 anterior elements. This elongated rostrum is evidently a characteristic associated 

 with special feeding habits, and is a demonstration of the mobility of vertebrate 

 structure. Fortunately the specialised forms in these groups are not isolated, in 

 this respect, but can now be studied in conjunction with allied genera and families 



^^ Jack & Etheridge, Geology and Palaeontology of Queensland, 1892, pp. 505-508. 

 26 Etheridge, Rec. Austr. Mus., Ill, 1897, pp! 66-68. 

 2' Chapman, Australasian Fossils, 1914, fig. 13.3, p. 277. 



-* W. K. Gregory, " Origin and Evolution of Human Dentition,'' Jr. Dent. Res., II, 1920, 

 p. 100. 



