AORTIC ARCHES OF BIRDS — GLENNY 613 



its exact relationships, for it may well be a monotypic form, not 

 properly placed among the Loriinae, since the carotid arrangement is 

 of the A-2-s type, while all other members of this subfamily, thus far 

 examined, have the A-1 carotid arrangement. Other similarities to 

 the Loriinae may be instances of paramorphogenesis and, as a relict 

 evolutant, it may constitute a monotypic subfamily, or be reassigned 

 to the Psittacinae. 



Certain phyletic relationships may be ascertained reasonably well 

 on the basis of the carotid artery arrangement, and the arterial ar- 

 rangement-patterns appear to have a phylogenetic significance. 

 The constancy of occurrence of the basic bicarotid condition and the 

 progressive developmental steps that lead to several modifications 

 of the system tend to point to this conclusion and to substantiate, 

 in part, the theory that ontogeny recapitulates phylogeny. 



As a result of early dispersal movements of birds and mammals 

 from their center (s) of origin, a large number of fossil forms might 

 well be expected in many parts of the land areas. Few of these 

 fossils can well be considered as true ancestral forms which led to the 

 present-day species, but strong similarities in structure might show 

 their affinities with extant species. 



Occurrence of relict species and families of birds and mammals 

 in Australia, New Zealand, and South America tends to support the 

 view that birds and mammals may well have originated in Antarctica, 

 and that as a result of protective isolation in these localities they 

 were able to survive and undergo considerable speciation. 



Evolution of both birds and mammals must have been from reptilian 

 forms which had a reasonably well developed sternum, since this 

 structure is found in both classes but is more highly developed in 

 birds than in mammals. This tends to preclude any relationship 

 between the Neornithes and the so-called Archaeornithes (Arch- 

 aeopteryx and Archaeornis) . Simpson (1946) has summarized Lowe's 

 views with respect to Archaeopteryx and Archaeornis: In most respects 

 they are purely reptilian, in all respects they are as reptilian as avian, 

 and in some respects they are too specialized to be ancestral to birds. 

 It is suggested, therefore, that the forms now placed in the Arch- 

 aeornithes be placed in the Sauropsida with the Reptilia, since mere 

 presence of feathers is not sufficient grounds for placing them in close 

 association with modern birds and cannot be construed as sufficient 

 evidence for a closer phyletic relationship. The presence of scales 

 on birds and some mammals is as sound single evidence for placing 

 both of these classes of vertebrates in the Sauropsida as the presence 

 of feathers on reptUes is for placing them among the bu*ds. 



During the earliest stages of avian and mammalian evolution, a 

 rapidly evolving group of profamily types probably took place, with 



