THE EVOLUTION OF THE HORSE (Equus) Przewalski's horse (Equus ferus przewalski) © WWF-Canon / Hartmut JUNGIUS

© 2016 Paul Billiet ODWS

The odd-toed ungulates

Horses belong to the Perissodactyla, the odd-toed ungulates

This group includes horses, rhinos and tapirs today White Rhinoceros (Ceratotherium simum) © KHW

© 2016 Paul Billiet ODWS

The genus Equus includes horses, zebra and asses

The last remaining branch of a diverse group of equids

Similar to the status of Homo sapiens, the last remaining species of a once diverse group of Hominids

The evolution of the horse is much better documented than ours

The fossil record is very complete

Equus

© 2016 Paul Billiet ODWS

Trends in the evolution of the horses

Increased size Reduced number of toes and longer legs A stiffer back

EquusMerychippus

20Ma© 2016 Paul Billiet ODWS

Teeth for grazing

Larger teeth and a larger skull to hold them

© 2016 Paul Billiet ODWS

Teeth for grazing

Teeth with bands of hard (enamel) and soft (dentine) material on the crown

Open tooth roots permitting continuous growth

© 2016 Paul Billiet ODWS

Trends in the evolution of the horses

The trends correspond to changes in the climate and vegetation of the Earth over the past 55 million years,

combined with the 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.

© 2016 Paul Billiet ODWS

From ladders to bushes

The view of evolution in Darwin’s day was that of Gradualism

One species slowly transforming into another

Equus

Pliohippus

Merychippus

Mesohippus

Hyracotherium(aka Eohippus)

Orohippus

© 2016 Paul Billiet ODWS

From ladders to bushes

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© 2016 Paul Billiet ODWS

© 2016 Paul Billiet ODWS