This happened with the species of Mesohippus found from 40 to 30 million years ago. Successive fossils show the change over time of teeth shapes and foot and leg anatomy to a grazing habit with changes for escaping predators.
The series of fossils shows the change in anatomy that came from a drying trend over time that changed the landscape from a forest to a prairie. The record goes back to a dog-like ancestor some 55 million years ago that gave rise to the first horse-like species 55 to 42 million years ago in the genus Eohippus. These show anatomy in between earlier and later forms.
The fossil record of horses in North America is quite rich. The fossil record that comes from this is made up of all the fossils scientists have found to tell a story of the past and show the evolution of form over millions of years.įor example, fossil records with a lot of detail have been found for sequences of species in the evolution of whales and modern horses. Scientists figure out the age of fossils and sort them all over the world to decide when the organisms lived in relationship to each other. This causes entire groups of living things to change because the parents pass on what helped them live to their children.įossils give strong evidence that livings things from the past are not the same as those found today because they show a progression of evolution. Evolution is when organisms adapt over time to their environments in ways that help them live long enough to reproduce.
A large part of Darwin's book, On the Origin of Species, found patterns in nature that were consistent with evolution, and since Darwin, what we know has become clearer and broader. Looking at every level of organization in living systems, biologists see the mark of past and present evolution. The evidence for evolution is deep and far-reaching.
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