BIRDS OF THE PAST— WETMORE 389 



period, one of diver form, and the other of flying habit that ap- 

 parently fed on the wing over water. These are both so specialized 

 that we may expect that other toothed birds existed though their 

 possible presence is now indefinitely indicated by fragments of a 

 few species of uncertain status. The Tertiary should give many 

 more species than now known, particularly in its Miocene and 

 Pliocene beds, and finally from the Pleistocene we may expect many 

 forms in addition to those already discovered. From cavern and 

 other deposits we may hope for more extinct species related tO; 

 modern birds, some peculiar and some with relatives living to-day 

 in South America. 



It has been already intimated that the number of extinct species 

 of birds now known from North America is far less than is to be 

 expected. As the forms described by earlier students are passed 

 under review it is evident that much remains to be done to decide 

 their proper status. Many have been named from such insufficient 

 material that their systematic position is doubtful, while there are 

 a few in which the type material is a composite of fragments that 

 may contain remains from two or more families, so that selection 

 must be made to properly apply the name. Some that have been 

 called birds probably are not avian and eventually will be rejected 

 from our list. Progress is being made steadily in these matters, 

 and yearly the condition improves, so that our uncertainties become 

 fewer and fewer. Such glimpses as our few fossils give us of the 

 life of the past are fascinating and promise high return for the 

 most painstaking study. At the present rate with which new ma- 

 terial comes to hand we may possibly expect to see our knowledge 

 of palaeornithology in North America doubled in the next 20 years. 

 24034—29 26 



