Conquering Land

By | September 9, 2016

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.

PROTEROGYRINUS

PROTEROGYRINUS

This amphibian enjoyed a diet of fish, but did not spend its life submerged in water. It used lungs to breathe, and was one of the first animals to do so.

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!

fossilized-eggs

Fossilized eggs

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

turtle-egg

A tortoise’s eggs do not dry out due to their shells and internal membranes.

SURVIVAL

 from-egg-to-tortoise1

Turtle and tortoise young spend about 6–8 weeks in their egg. All the moisture they need is contained inside the egg.

ANCIENT

turtle-fossil

Turtles and tortoises date back some 220 million years.

FIRST TRACKS

old-trackThese 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.

Breathing air

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.

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