The specimens hitherto known give no evidence of such a change being in progress. But just as the division of Mammals termed Edentata usually wants only the teeth which characterise the front of the jaw, yet others, like the Great Ant-eater of South America named Myrmecophaga, have the jaws as free from teeth as the toothless Pterodactyles or living Birds, and show that in that order the teeth have no value in separating these animals into subordinate groups any more than they have among the Monotremata, where one type has teeth and the other is toothless. The following table gives a summary of the Geological History and succession in the Secondary Rocks of the principal genera of Flying Reptiles. -----------------------+---------------------------------------------- | NAMES OF THE GENERA. GEOLOGICAL FORMATIONS. +-----------------------+---------------------- | British and European. | North American. -----------------------+-----------------------+---------------------- Upper Chalk | |} Ornithostoma | |} (_Pteranodon_) Lower Chalk |} Ornithocheirus |} Nyctodactylus Upper Greensand |} | Ornithostoma | Gault | | | -----------------------+ | | Lower Greensand | | | Wealden | Ornithodesmus | Purbeck | Doratorhynchus | -----------------------+ | Portland |{ Pterodactylus | |{ Ptenodracon | Kimeridge Clay and |{ Cycnorhamphus | Solenhofen Slate |{ Diopecephalus | |{ Rhamphorhynchus | Coralline Oolite |{ Scaphognathus | | | Oxford Clay | | -----------------------+ | Great Oolite and | | Stonesfield Slate | Rhamphocephalus | | | Inferior Oolite | | -----------------------+ | Upper Lias |{ Campylognathus | |{ Dorygnathus | Lower Lias | Dimorphodon | -----------------------+ | Rhætic | bones | | | Muschelkalk | ? bones | -----------------------+-----------------------+---------------------- CHAPTER XVI CLASSIFICATION OF THE ORNITHOSAURIA