MESOZOIC TIME — CRETACEOUS. 871 



There are grounds enough., therefore, for the conclusion that the class of 

 E.eptiles culminated in the latter half of the Reptilian age. The reality of 

 the Reptilian feature of the era comes out strongly on comparing the great 

 Reptiles in the Wealden as to size and numbers with those of the present 

 time. 



l^ow, in India, or the continent of Asia, there are but two species of 

 Reptiles over 15 feet long ; in Africa, but one ; in all America, but three ; 

 and not more than six in the whole world ; and the length of the largest 

 does not exceed 25 feet. During the Wealden there lived in England alone 

 16 large Dinosaurs and 12 Crocodiles, besides a Plesiosaur and three Ptero- 

 saurs. The Reign of Reptiles becomes more strongly pronounced when 

 the little Marsupial Mammals of the era are brought into view by way of 

 contrast. 



Birds. — Since Birds are so poorly represented among fossils, little can 

 be said as to progress in the Cretaceous period beyond the fact that part of 

 the Cretaceous Birds, as known first from Marsh's discoveries, retained the 

 teeth of the Jurassic Birds ; and some, even the low character of biconcave 

 vertebrae. They had lost the Reptile-like bones and fingers of the fore limb, 

 and the long tail existing in the Jurassic species, and had, in general, the 

 style of vertebrae characterizing modern Birds, besides modern features in 

 most other respects. 



It is also a fact of interest that already degenerate forms were in exist- 

 ence under the Bird-type ; for such is the Hesperornis, as shown in its 

 obsolescent wing-bones and wings, a feature that reduced it to the meros- 

 thenic condition of an Ostrich and a Dinosaur. Thus, between the Middle 

 Jurassic and Middle Cretaceous the Bird-type reached essential perfection, 

 though not advanced to its highest stage ; and also it passed along at least 

 one line downward to Ostrich-like imperfection. The presence of teeth is 

 not a structural imperfection. Their absence looks much more so ; but it 

 is not inconsistent with a high and advancing grade of structure in all other 

 respects. 



Progress in Mammals. — The Monotremes and Marsupials from the Creta- 

 ceous formation show little progress in Mammals beyond the condition in the 

 Jurassic period — nothing, up to the present time, that bears the decided 

 character of a placental Mammal. As the known fossils are mainly teeth 

 and jaws, full comparisons are not yet possible, and certainty of conclusion 

 as to the question, Marsupial or not, is not yet, in all cases, possible. 



Contrast of the European and North American marine faunas. — The 

 contrast between the marine species of Europe and North America, which 

 characterizes the Early and Middle Mesozoic (page 792), continues, but in 

 diminished degree, into the Cretaceous period. The following table gives 

 the number of species that have been described from the Cretaceous beds of 

 Great Britain and North America, under the tribes mentioned in the first 

 column; the former from Etheridge, as enumerated by him in 1885; the 

 latter, by Whitfield, in 1894. 



