Many animals produce mating-calls and more complex sequences of sounds that may be termed "love-songs." Insects, for instance, generate involved musical sequences and many water-living creatures produce sounds, some of which are outside the range of human hearing. Amphibians first produced love-songs that could have been heard by human beings had there been any alive at the time. Amphibians first started singing to each other on dry land, somewhere between two hundred and three hundred and fifty million years ago, in the Carboniferous Period. Thus Wendt - ". . . we can scarcely imagine that the as yet unknown ancestors of frogs who lived in the earlier Paleozoic Era did not jump and croak. How otherwise would they have met for mating?" Perhaps the argument is not conclusive but it is oddly romantic to think of animals first beginning to communicate by sound.