Do you know how have mammals evolved? As you know the group of animals known as mammals are successful, widespread, and very diverse. Modern mammals range in size from animals such as the lesser shrew of Britain at a total length of a little over six centimeters and weighing little more than 4.5 grams to the giants of the oceans such as the blue whale weighing in at up to 150 tonnes.
Modern mammals occupy a range of different habitats: they can live in deserts, as does the polar bear, in jungles where many species abound, in temperate woodlands like the European badger and so on. These are the mammals that live on land. As we have seen, there are those that roam the oceans such as the whales.
How have mammals evolved?
Ocean dwelling mammals have more problems than their counterparts on land because they still have to maintain their body temperature. Obviously hair would be useless to help them retain heat. Consequently, they have evolved thick layers of fat usually known as blubber.
On the other hand, because the salt water helps them to support their body weight, they have been able to grow to these enormous sizes. In fact, the largest whales are the largest animals that have ever lived, larger even than the mighty, vegetarian dinosaur, Brontosaurus.
Mammals have also conquered the air, perhaps not as efficiently as birds, but nevertheless bats could still be considered to be successful animals in the struggle for survival.
How, then, has this great diversity been achieved? In Triassic times, some 200 million years or so ago, mammal-like reptiles had developed at least partial control of their body temperature and may have been covered in fur or hair rather than scales.
It is difficult to say with certainty from fossil evidence, exactly when the first true mammals appeared, but it was certainly not for another thirty or forty million years, when at the end of Triassic times animals, not unlike modern shrews, were alive.
The most primitive mammals probably still laid eggs rather than giving birth to living young, and today there are still mammals surviving which are also egg-laying. The duck-billed platypus of Australia, for example, lays its eggs at the bottom of a burrow.
It has been able to survive (it could be described as a living fossil) because the Australian continent has been cut off by the drifting apart of the continents for at least 100 million years. Marsupials, also found mainly in Australia, represent a kind of intermediate stage of evolution with the young being born alive at a very early stage and remaining in the mother’s pouch.
From Tertiary times until today, in geologic terms, the evolution of mammals has been very rapid with the development of animals has been very rapid with the development of animals such as the horse and the elephant being the easiest to trace.
You may like also:
- Which Animals are among the Tiniest that have ever Lived?
- What are the Simplest Animals?
- How do the Bivalves move Around ?
- What is a cuttlefish ?
- What are the worms of the seashore ?
- How does peripatus link the worms and the animals with jointed legs ?
- Which animals live on their heads and kick food into their mouths ?
- Can a lobster swim backwards?
- Why are there so many insects?