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EVOLUTION

Powerpoint Presentation: Evolution of the Horse

THE EVOLUTION OF THE HORSE (Equus)

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Horses belong to the Perissodactyla, the odd-toed ungulates. This group includes horses, rhinos and tapirs today but it was a much more diverse group 50 million years ago.

The genus Equus includes horses, zebra and asses, are themselves the last remaining branch of a diverse group of equids. This is similar to the status of Homo sapiens being the last remaining species of a once diverse group of Hominids.

The evolution of the horse, however, is much better documented than ours. The fossil record is very complete.

In the evolution of the horses we can see a number of trends:

Increased size
Reduced number of toes and longer legs
A stiffer back
Larger teeth and a larger skull to hold them
Teeth with bands of hard and soft material on the crown
Open tooth roots permitting continuous growth

The trends correspond to changes in the climate and vegetation of the Earth over the past 55 million years, combined with an arms race between predators and prey.

From…….. rich rainforest which covered most of the Earth in which the horses ancestors browsed on leaves and hid from predators.

To ……. open savannah grassland where the modern horses grazed grass and had to run from predators.

The view of evolution in Darwin’s day was that of Gradualism. One species slowly transforming into another.

The modern fossil record reveals a different picture.

Periods of radiation where species diversify and fill different niches.
Species giving rise to new species whilst they still thrive. Species do not "turn into" new species and completely disappear.
The result is a more bushy appearance of the pathway of evolution not a linear ladder.
An irregular rate of evolution.

References

Stephen J Gould (1991) Bully for Brontosaurus Penguin Books

The case of the creeping terrier clone.	The use and abuse of school text books.
Life’s little joke	The changing views on the evolution of the horse.
Bully for Brontosaurus	The principle of precedence in scientific names.

Web sites

Talks Origin Archive exploring the Creation/Evolution Controversy Horse Evolution Katheleen Hunt Copyright 1995

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