When tetrapods first ventured onto the land, what new selection pressures did they face? What characteristics might have fostered the success of these animals as they made the transition from aquatic to terrestrial habitats?

Step 1 of 2

Tetrapods originated from osteolepiforms, a group of fleshy-finned fishes in the late Devonian period. They were the first animals in evolution to show the presence of four limbs. Since the ancestors of tetrapods were first and foremost fishes in the water, they met severe pressure when they first risked the land. The difference in density of water and air, loss of body water due to evaporation in air, and diminished sensory functions in the air proved to be a struggle for the first tetrapods.

However, the land provides abundant food sources such as soft invertebrates, arthropods, and plants. The absence of predators and a high oxygen supply in the air was found to be convenient.