THE INVASION OF THE LAND
The beginning of limbs
The first fish may have crawled onto land during Devonian times (350 million years ago) and probably did so, in response to drying swamps. This required that two problems must be overcome, how to move without the support of water and how to obtain oxygen from air rather than water. The mud skipper (eg Periophthalmus sobrinus which occurs in our mangrove swamps) suggest adaptations that ancestral fish may have developed in their quest to colonize land. Each pair of front flippers has a fleshy base supported internally by bones and is able to be used to lever the animal forward. Another animal which showed the beginnings of limbs is the coelacanth Latimeria chalumnae (order Crossopterygii), the living fossil that was thought to have been extinct for 70 million years.
Periophthalmus modestus (Mudskipper)