When the first mammals appeared, all the continents were locked together in one large landmass. Over millions of years, they gradually drifted apart. This meant that the mammals were split up on to large “islands”, where they evolved into many different groups.
North and South America eventually drifted back together again, and mammals from the two continents found themselves competing for food and territory with unfamiliar “relatives”. They also faced new predators. Some kinds died out altogether. The marsupials suffered in most parts of the world, but in Australasia, which was still isolated, many were able to thrive.
Around the world, each kind of mammal adapted to its environment. Giraffes evolved a very long neck to browse from the tallest trees which other mammals could not reach. Whales and dolphins lost the fur and four legs of their ancestors and developed tails and fins to move more easily through the water.
Picture Credit : Google