DINOSAURS. 107 
shield or carapace of certain extinct armadillos known as Glypto- 
donts (see Chapter XII.). A specimen of such a shield is to be 
seen in the collection at South Kensington (Wall-case 4). It is to 
be hoped that, some day, further remains of the Polacanthus will 
be brought to light, so that a restoration may become possible. 
Dr. Mantell had already pointed out certain analogies between 
Iguanodon and the huge extinct sloths of the South American 
continent, that flourished in the much more recent Pleistocene 
period ; and this idea is now considerably strengthened by the 
later discoveries of armoured Dinosaurs. ‘These are his words: 
‘In fine, we have in the Iguanodon the type of the terrestrial 
herbivora which, in the remote epoch of the earth’s physical 
history termed by geologists the age of Reptiles, occupied the 
same relative position in the scale of being, and fulfilled the same 
general purposes in the economy of nature, as the Mastodons, 
Mammoths, and Mylodons (extinct sloths) of the Tertiary period, 
and the existing pachyderms.” 
It is, perhaps, one of the most interesting discoveries of modern 
geology, that certain races of animals now extinct have in various 
ways assumed some of the characteristics presented by animals 
much higher in the scale of being, that flourish in the present day. 
It seems as if there had been some strange law of anticipation at 
work, if we may venture so to formulate the idea. It has already 
been shown how the great saurians Ichthyosaurus and Plesiosaurus 
presumed to put on some of the characters of whales, and to play 
their 7é/e in nature, though they were only reptiles ; how the 
carnivorous Dinosaurs acquired teeth like those now possessed by 
lions and tigers, which also are mammals; and now we find 
herbivorous Dinosaurs imitating the Glyptodon, an armadillo 
that lived in South America almost down to the human period. We 
shall not lose sight of this very interesting and curious discovery, 
for other cases will present themselves to our view in future 
chapters. The reader might ask, ‘“‘If reptiles were able in these 
and other ways to imitate the mammals of to-day, or of yesterday, 
