THE JURASSIC PERIOD. 253 



able peculiarities of its structure from all existing members of 

 the class of Birds. This extraordinary Bird (fig. 182) appears 

 to have been about as big as a Rook the tail being long and 

 extremely slender, and composed of separate vertebrae, each 

 of which supports a single pair of quill-feathers. In the flying 

 Birds of the present day, as before mentioned, the terminal 

 vertebrae of the tail are amalgamated to form a single bone 

 (" ploughshare-bone "), which supports a cluster of tail-feathers ; 

 and the tail itself is short. In the embryos of existing Birds 

 the tail is long, and is made up of separate vertebrae, and the 

 same character is observed in many existing Reptiles. The 

 tail of Arch&opteryx\ therefore, is to be regarded as the per- 

 manent retention of an embryonic type of structure, or as an 

 approximation to the characters of the Reptiles. Another 

 remarkable point in connection with Arcfuzopteryx, in which 

 it differs from all known Birds, is, that the wing was furnished 

 with two free claws. From the presence of feathers, Archce- 

 opteryx may be inferred to have been hot-blooded ; and this 

 character, taken along with the structure of the skeleton of the 

 wing, may be held as sufficient to justify its being considered 

 as belonging to the class of Birds. In the structure of the 

 tail, however, it is singularly Reptilian ; and there is reason to 

 believe that its jaws were furnished with teeth sunk in distinct 

 sockets, as is the case in no existing Bird. This conclusion, 

 at any rate, is rendered highly probable by the recent discovery 

 of "Toothed Birds" (Odontornithes) in the Cretaceous rocks 

 of North America. 



The Mammals of the Jurassic period are known to us by 

 a number of small forms which occur in the " Stonesfield 

 Slate" (Great Oolite) and in the Purbeck beds (Upper 

 Oolite). The remains of these are almost exclusively sepa- 

 rated halves of the lower jaw, and they indicate the existence 

 during the Oolitic period in Europe of a number of small 

 " Pouched animals " {Marsupials}. In the horizon of the 

 Stonesfield Slate four genera of these little Quadrupeds have 

 been described viz., Amphilestes, Amphitherium, Phascolo- 

 therium, and Stereognathus. In Amphitherium (fig. 183), the 

 molar teeth are furnished with small pointed eminences or 

 " cusps ; " and the animal was doubtless insectivorous. By 

 Professor Owen, the highest living authority on the subject, 

 Amphitherium is believed to be a small Marsupial, most 

 nearly allied to the living Banded Ant-eater (Myrmecobius) of 

 Australia (fig. 158). Amphilestes and Phascolotherium (fig. 

 184) are also believed by the same distinguished anatomist 

 and palaeontologist to have been insect-eating Marsupials, and 

 13 



