1 8 REPTILES 



published by Professor H. F. Osborn in the American Natural- 

 ist for 1898 may be quoted :— 



"Important, also, among the resemblances between the 

 Theriodontia and Mammalia is the general bodily form, so 

 far as it is known in the former, the proportions of the limbs to 

 the back, and the apparent elevation of the body considerably 

 above the ground. This, taken together with the peculiar special- 

 isation of the teeth into carnivorous and herbivorous types, 

 indicates that the Theriodontia filled somewhat the same role 

 in the economy of nature as is filled by the Mammalia at the 

 present time. The most striking general difference is the very 

 large size of several of these animals, such as Cynognathus. We 

 had rather anticipated from our knowledge of the earliest Stones- 

 field (Lower Jurassic) mammals that their reptilian ancestors 

 would have been very small. The large size of these Permian 

 (or Triassic) theriodonts is, however, not incompatible with the 

 hypothesis that smaller and less specialised members of the 

 group may have constituted a persistent phylum (or branch)." 



Passing on to a proportionately brief survey of the probable 

 evolutionary history of the numerous ordinal groups included 

 in the subclass Ornithomorpha, it may be repeated that the 

 most primitive and at the same time the most ancient of these 

 orders is undoubtedly the Rhynchocephalia, which includes the 

 Permian Protorosaurus, and may have sprung directly from the 

 microsaurian amphibians. The Rhynchocephalia, now surviv- 

 ing only in the form of the New Zealand tuatera {SpJienodon 

 punctatus, Plate II.), are characterised, among other features, by 

 the presence of complete upper and lower temporal arcades to 

 the skull, which also shows a large parietal foramen, by the 

 bodies of the vertebrae being cupped at both ends, by the pres- 

 ence of intercentra between many of the vertebrae, and of 

 chevron-bones attached to the lower surface of those of the tail, 

 by the fully developed shoulder-girdle and five-toed limbs, the 

 firmly fixed quadrate bone, the acrodont teeth, and the presence 

 of a foramen (entepicondylar) on the inner side of the lower end 

 of the humerus, and of a system of abdominal ribs, forming an 

 incipient plastron on the lower surface of the body. Of the 

 numerous divergent branches which have been given off from 

 the rhynchocephalian stock, one has apparently culminated in 

 the birds. Among the fossil representatives of the group may be 



