326 



KNOWLEDGE. 



August. 1911. 





FiGUKE 3. 



Acpyornia iiuj.xiiniis Geoffroy (restored) from the 

 Pleistocene of Madagascar. 



allied to the grebes of tn-d:i\'. so well adapted to an 

 aquatic habitat that it i>r(>bably rarel\-, if ever, 

 walked on land. The set-back of the legs, and the 

 large knee-cap and enemial crest seem to have 

 rendered an erect position impossible. The mouth 

 was well provided with teeth, set like a lizard's in 

 a groove, not in distinct sockets. The remains of 

 other Mesozoic birds have been found which, barring 

 the possession of teeth, are not very different from 

 modern forms, e.g., Ictliynniis allied to the gulls. 



Unfortunateh- for the palaeontologist the bones of 

 birds are rarely found fossilized. Their lightness 

 prevents them in a great measure from sinking, and 

 thus being covered up b\- some sedimentary deposit. 

 a necessary step in the process of fossilization. 

 Hence it is not hard to understand win-, with the 

 important e.xception nf Archaeopfcryx. as \ct no 

 remains of an^■ intermediate forms between reptiles 

 and birds have come to light. 



In the Santa Cruz lied (? Miocene) of South 

 America we find the remains of another giant 

 flightless bird Plwrorliacos. allied probabK- to the 

 Secretary Bird of South Africa. The reason for 



the large size of many flightless birds is not hard 

 to see. .\mong the extinct pterodact}des, as well 

 as in birds, there is a strict limit to size when the 

 body has to be raised into the air. Muscular tissue 

 and general vertebrate anatom\' being what it is. \\e 

 may safelv assume that no animal much larger than 

 a swan ever tfew through the atmosphere of our 

 planet. But as soon as the necessity for tlight is 

 removed, so likewise is the embargo on any increase 

 in size, and natural selection has a free hand. Size, 

 strength, and fleetness of foot have often to make 

 up for loss of flight. A few generations, probably, 

 were sufficient to ]>roduce a marked increase in 

 weight and stature in a bird that had ceased 

 to fly. To return to P/iororhacos. The bird had 

 certainly a larger and more massive head and beak 

 than any other \et discovered, and it is not im- 

 probable that it resembled P'igure 2. It is portra\ed 

 killing a lizard, but there can be little doubt that 

 it would have made short work of anv living snake 

 if its habits and mode of attack were the same as 

 those of its smaller modern relati\'e. 



Figures j and 4 are those of Acpyornis and 



Figure 4. 



hiiKirnis inii.\:iiiiiis (Jweii (restoredl from the Sand-hills 

 of New Zealand. 



