THE EVOLUTION OF THE HORSE Equus Przewalskis horse

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

The odd-toed ungulates n Horses belong to the Perissodactyla, the odd-toed ungulates n This group includes horses, rhinos and tapirs today © 2008 Paul Billiet ODWS White Rhinoceros (Ceratotherium simum) © KHW

Equus n n n 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 © 2008 Paul Billiet ODWS

Evolution of the Horse ¡ Did not occur in a straight line ¡ Many horse like animals branched off ¡ Now one genus is the only surviving branch of a once large evolutionary bush n Equus

© 2008 Paul Billiet ODWS

Evolution of the Horse n What is the earliest known ancestor of the horse? ¡ Eohippus n a. k. a. Hyracotherium or dawn horse n ~ the size of a fox (8 -18” at shoulder) n Four functional toes on each front foot n Three toes on hind feet

Eohippus n Structure of teeth suggest ¡ n Earliest remains found in ¡ n North America Thought to have lived ¡ n Browser ~54 million years ago Remains also found in ¡ Europe dating 50 million years old

Eohippus n Alert ears, doglike, furry coat, swishing tail n Long face w/ 44 teeth ¡ Unlike today’s horse n n 36 -42 Both front and back toes replaced by tiny hooves

Evolution of the Horse n Mesohippus ¡ Lived ~ 35 million years ago ¡ Earth’s temperature and climate had changed ¡ Forest thinned and grass became more prevalent ¡ Mesohippus appeared

Mesohippus n A. k. a. “Middle Horse” n Larger than Eohippus ¡ 24” at shoulder n Teeth had further evolved but 44 remained intact n Only had three toes on front ¡ n Was better suited to outrun predators Lateral supporting toes decreased in size ¡ Middle toe strengthened

Mesohippus n Toes now ended in little hooves ¡ n Still had a pad behind them Became extinct in Europe and North America ~ 7 million years ago

Merychippus ¡ Lived ~ 20 million years ago ¡ Completely new type of horse ¡ Evolved in North America ¡ Adapted to hard grasses of plains ¡ Beginning of grazing horse of today

Merychippus n Stood ~35” n Increasingly gregarious n Developed complicated grinding teeth similar to present day horses n Lateral toes diminished ¡ n No longer touched the ground Main toe thickened and hardened

Pliohippus ¡ Developed ~5 million yrs ago ¡ Branch of horses crossed into Asia ¡ Quickly multiplied ¡ Spread to Europe ¡ North America n Horse developed into the final model

Pliohippus n First true monodactyl ¡ One-toed animal n Used speed to flee from predators n Further evolution of teeth and limbs n Spread into ¡ South America, Asia, Europe, and Africa

Equus caballus n ~2 million years ago n Modern day horse n Became extinct in N. America ¡ n ~8, 000 yrs ago Was not to return until ¡ Spanish arrived in 1400’s

How Evolution Works n Common evolutionary trends are ¡ n On the whole, horses ¡ ¡ n Not seen in all horse lines Progressively larger Some then grew smaller Many evolved ¡ Complex facial pits

Trends in the evolution of the horses n n n Increased size Reduced number of toes and longer legs A stiffer back Merychippus 20 Ma © 2008 Paul Billiet ODWS Equus

Trends in the evolution of the horses n n 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. © 2008 Paul Billiet ODWS

Teeth for grazing n Larger teeth and a larger skull to hold them © 2008 Paul Billiet ODWS

Teeth for grazing n n Teeth with bands of hard (enamel) and soft (dentine) material on the crown Open tooth roots permitting continuous growth © 2008 Paul Billiet ODWS