162 LIVING FOSSILS. 



brouglit to liglit the existence of the remains of a large 

 number of more or less nearly allied reptiles in the 

 Secondary rocks of Europe and other parts of the world. 

 Accordingly the tuatera, which, although not generically 

 identical with any one of these extinct forms, has every 

 right to be regarded as a " living fossil " ; while it enjoys 

 the further distinction of being, with the exception of 

 the lancelet, the only vertebrate animal which can be 

 definitely regarded as the sole living representative of a 

 distinct order. 



Since birds have no species witli any very great claim to 

 l)e mentioned here, we pass on to mammals, of which our 

 notice must necessarily be brief. In a previous chapter 

 it has been stated that certain remarkable Secondary 

 Eurojiean and American mammals apjDcar to be related 

 to the egg-laying mammals of Australia and New Guinea ; 

 and we may, therefore, assume that the latter, as their 

 structure indicates, are very ancient types, although their 

 direct ancestors have not yet been discovered. The banded 

 anteater (Myrmecohius) and the bandicoots (Peramelei) of 

 Australia seem to be the nearest relatives of another great 

 group of Secondary mammals, and are therefore probably 

 some of the oldest tyjDes with which we are yet acquainted, 

 although here again their exact genealogy is at present 

 unknown. No other groups of living mammals are j^et 

 definitely known to have existed before the Tertiary period, 

 and the pedigree of the class in general is consecjuently 

 brief as compared with that of many of the animals 

 discussed above. The opossums (DidelpJnjs) are, however, 

 perhaps those mammals best entitled among the Tertiary 

 groups to the appellation of "living fossils," as they have 

 existed without generic modification since the period of 

 the Eocene, and have now entirely vanished from their 

 old European haunts to maintain an existence in America, 

 where they are mainly characteristic of the southern half 

 of the continent. Although the insectivores and the 

 lemurs are evidently iirimitive types, but few of their 

 existing genera date far back in the Tertiary jjeriod, while 

 in the latter group not a single existing genus is known 

 before the present epoch. None of these mammals 



