DISTRIBUTION OF AVES IN TIME. 505 



Order VIII. SaururiE. — This order includes only the 

 extinct bird, the Archceopteryx macrura, a single specimen of 

 which — and that but a fragmentary one — has been discovered 

 in the Lithographic Slates of Solenhofen (Upper Oolites). 

 This extraordinary bird appears to have been about as big as a 

 Rook ; but it differs from all known birds in having two free 

 claws belonging to the wing, and in having a long lizard-like 

 tail, longer than the body, and composed of separate vertebrae. 

 The tail was destitute of any ploughshare-bone, and each ver- 

 tebra carried a single pair of quills. The metacarpal bones, 

 also, were not anchylosed together as they are in all other 

 known birds, living or extinct. 



CHAPTER LXXI. 



DISTRIBUTION OF AVES IN TIME. 



As regards the geological distribution of Birds, there M^e many 

 reasons why we should be cautious in reasoning upon merely 

 negative evidence, and more than ordinarily careful not to 

 infer the non-existence of birds during any particular geological 

 epoch, simply because we can find no positive evidence for 

 their presence. As Sir Charles Lyell has well remarked, " the 

 powers of flight possessed by most birds would insure them 

 against perishing by numerous casualties to which quadrupeds 

 are exposed during floods/' and " if they chance to be drowned, 

 or to die when swimming on water, it will scarcely ever happen ' 

 that they will be submerged so as to become preserved in 

 sedimentary deposits," since, from the lightness of the bones, 

 the carcass would remain long afloat, and would be liable to 

 be devoured by predacious animals. As, with a few utterly 

 trivial exceptions, all the deposits in which fossils are found 

 have been laid down in water, and more especially as they are 

 for the most part marine, these considerations put forward by 

 Sir Charles Lyell afford obvious ground against the anticipa- 

 tion that the remains of birds should be either of frequent 

 occurrence or of a perfect character in any of the fossiliferous 

 rocks. In accordance with these considerations, as a matter 

 of fact, most of the known remains of birds are either frag- 

 mentary or belong to forms which were organised to live a ter- 

 restrial life, and were not organised for flight. 



The earliest remains which have been generally referred to 



