1. Evolution of the Horse: From the Swamps to the Sweeps
By Dr. Jenifer Nadeau
Dept. of Animal Science
College of Agriculture and Natural Resources, UConn

2. Lecture Objectives Define evolution Describe the horse family tree
Describe the horse’s anatomical changes and why they came to be

3. What is evolution?
A gradual process in which something changes into a different and usually more complex or better form
Change in the genetic composition of a population during successive generations

4. 3 Mechanisms of Evolution
Genetic Drift
Mutation
Natural Selection

5. Horses are a Classic Example of Evolution

6. Scientific Classification of the Horse
Kingdom
Phylum
Class
Order
Family
Genus
Species

7. The earliest ancestors of the horse appeared over 50 million years ago.

8. Time Line

9. Horse Family Tree Recent: 10,000 years ago to present
Pleistocene: million years ago
Pliocene: million years ago
Miocene: million years ago
Oligocene: million years ago
Eocene: million years ago

11. Eohippus or Hyracotherium 50 million years ago
About size of a fox, 2 feet long, 8 inches tall at withers
Long skull with 44 low crowned even teeth without cement
Originated in
N. America

12. Eohippus 50 million years ago
Carried its weight on central pad like a dog
Well adapted to living in forested and swampy environment

13. Miohippus or Mesohippus 35 Million Years Ago
“Middle horse”
Larger (2 x size of Eohippus)
3 hoofed toes on the front and hind, side toes on each leg touching the ground
Splint of 2nd digit

14. Miohippus or Mesohippus
Low crowned teeth without cement
Teeth suitable for grazing on the prairie
Greater speed, endurance for finding forage, water, protection, survival

15. Merychippus 25 million years ago
Gave way to at least 19 new grazing horse species – “Merychippine Radiation”
The 3 major groups included: Hipparions, Protohippines, true Equines
Gave rise to the first burst of diversity in the horse family

16. Merychippus Over 2 feet tall (35 inches)
Long crowned teeth with cement
Eye socket position changes

17. Merychippus 25 Million Years Ago
3 hoofed toes on each leg with smaller side toes touching the ground
Bones of the leg began fusing together

18. Pliohippus 10 Million Years Ago
Body equipped for savanna type conditions
Higher crowned molars develop for grinding grasses
1st single-hoof equine
No recognizable side toes
12 hands tall

19. Pliohippus One toe on front and hind legs
Splints of 2nd and 4th digits
Long crowned teeth with cement
Grandfather of the modern horse

20. Equus 6 Million Years Ago
Develops into modern day horse after 15 million generations

21. Equus’ Evolutionary Changes
Increase in body size
Reduction in toe number
Increase in size of cheek teeth
Longer face

23. Evolutionary Changes in Horse Body Size

24. During the Ice Age, Equus migrated from North America throughout the world over the Bering Strait

25. Equus One toe on front and hind legs Splints of 2nd and 4th digits
Long crowned teeth with cement
Found all over Asia, Africa, Europe, and North America

26. Extinction in Western Hemisphere
The appearance of man in the Paleolithic period
Return to the continent at the Age of Exploration

27. Why? Where did they all go?
Glacial cold?
Insects?
Disease?
The acts of man?
Starvation?
Other mammals that became extinct or disappeared from the W. Hemisphere in the Pleistocene epoch include rhinoceros, camels, saber-tooth tigers, elephants, and the mastodon

28. Survival of Equus Members of family Equidae that survived:
Equus hemionus
Equus burchelli
Equus grevyi
Equus asinus
Equus caballus
Escaped to Asia by land bridge

29. Equus Caballus - The First 5
5 distinct subspecies of Equus caballus developed west of Siberia and China
Przewalski horse
Tarpan
Proto-Oriental
Proto-Warmblood
Proto-Draft

30. Tarpan
Proto-Draft
Proto-Oriental
Przewalski Horse
Proto-Warmblood

31. Lecture Objectives Define evolution Describe the horse family tree
Describe the horse’s anatomical changes and why they came to be