We can see why, in islands, there should be some relation between the presence of mammals, in a more or less modified condition, and the depth of the sea between such islands and the mainland.
Horrelaxe uler dezakegu zergatik izan behar duten batak bestearekin zerikusiren bat, irletan eraldaketa maila handiago edo txikiagoko ugaztunak bizitzeak eta irlon eta lehorburuaren arteko itsas sakonerak.