1 Natural groups
Darwin made extensive observations on a great many creatures, including mammals, and noticed that species fell into natural groups, e.g. lions, tigers and leopards have many similarities, and resemble cats. On the basis of his observations, he was able to place mammals in distinct groups.
His work has continued, and we now recognise that mammals have evolved from a common ancestor, and have branched into many different groups, or ‘Orders’. The animation below shows the different Orders of mammals.
Click on the names of the different Orders shown on the evolutionary tree of mammals to find out how many species of animals are in each Order. You will be able to see a picture of some of the mammals in that Order, and find out something about them.
What does an evolutionary tree like this really show?
To understand what the tree shows, we need to look at the different branches on the tree, and how long ago they had their origins.
It shows that Monotremes are on a separate branch of the tree, and that they branched off from the branch which led to other mammals more than 100 million years ago.
Marsupials are on a separate branch which originated between 60 and 100 million years ago.
All other mammals fall into four main groups, shown in the animation in purple, red, blue and green, and all the main Orders of mammals were already present by 60 million years ago.