32 THE THEORY OF EVOLUTION 



orders (Turtles, Crocodiles, Snakes, and Lizards) nothing 

 is known. 1 



The first birds, Archseopteryx, have toothed beaks, 

 the vertebrae of the long tail remain separated, the 

 free digits of the front limb (= hand or wing) carry 

 claws. These are characters which occur now in 

 reptiles. This bird has, furthermore, many other 

 peculiarities confined to itself. 



From this it was concluded that birds were descended 

 from reptiles. But all attempts failed to trace a con- 

 nection with any particular reptile. 2 The nearest birds 

 (Cretacean) can by their habit be assigned to quite 

 definite bird families Laornis, for example, to the 

 Geese so that Steinmann can say ' each of the three 

 well-recognized types of Cretaceous birds represents a 

 separate ancestry. ' 3 



The Mammalia show from the beginning ' two 

 groups of lower mammalia quite clearly differentiated/ * 

 Then they almost disappear during the immense Mesozoic 

 period (= Secondary formation group), and appear 

 again at the commencement of the Tertiary (Eocene) 



1 J. Bumiiller : Die EntwicTdungslJieorie und der Mensch, p. 23 (according 

 to Zittel's investigations). 



2 Steinmann : Die Geologischen Grundlagen der Abstammung&lelire, p. 222 : 

 ' From the older strata of the Jura and from the Trias (which come next into 

 consideration) we know practically nothing of small, long-legged reptiles 

 of such a habit as the Archeeopteryx demands as ancestor.' Deperet- 

 \Vegner : Die Umbildung der Tierwelt, p. 231 : ' The Archseopteryx is, 

 however, a true bird in its entire construction, and possesses beyond doubt 

 a long line of ancestors which at present eludes our knowledge.' 



3 Steinmann : Die Geologischen Grundlagen der Abstammungslehre, 

 p. 225. 



4 Deperet-Wegner : Die Umbildung der Tierwdt, p. 281. 



