The rarity of transitional forms is interesting. It suggests the new forms are not yet dominant in the ecology of their time, and their populations are relatively small. It follows that their fossils would be scarce. In the Solnhofen limestone where "Archaeopteryx" was found, there are more examples of pterosaurs of several genera than there are of the proto-bird. In the Jurassic, the pterosaurs were dominant in the air.