We know that land animals today evolved from creatures that lived in water millions of years ago. To move onto land, certain barriers had to be overcome—after all, a fin or flipper is not much use on land. Let’s take a look at some of the changes that took place.
FROM FINS TO LEGS
Legs evolved from the fins of fish. The first animals to develop legs—the tetrapods—had four legs with digits at the end of each one. Some had up to eight digits.
A BIT ABOUT DIGITS
Nearly all land-dwelling vertebrates have five digits (fingers or toes) in each foot, and the same arrangement of bones in each limb. That’s because they all evolved from the same ancestor—one of the early land pioneers, which happened to have five-fingered feet.
PROTECT THE YOUNG!
One of the most important steps in freeing animals from a dependence on water was the evolution of eggs that could be laid on land. Most amphibians have to return to water to breed, but the first reptiles had eggs with lots of membranes, and later shells, to help the egg withstand dry conditions.
NO NEED FOR WATER
These fossilized tracks were found in 2010 in Canada. They are around 318 million years old and are believed to be evidence of some of the oldest reptiles.
Land animals take oxygen from air and have no need for the gills that fish use to extract oxygen from water. Lungs evolved in some early fish to help them gulp air at the water’s surface. One group of fish retained lungs, which were crucial when they began clambering onto land. Among the first fish to clamber onto land and breathe out of water were the lungfish, some 400 million years ago. Prehistoric lungfish were found all over the world in the Devonian Period, some 400 million years ago.