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
Lecture Objectives
• Define evolution
• Describe the horse family tree
• Describe the horse’s anatomical changes
and why they came to be
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
3 Mechanisms of Evolution
• Genetic Drift
• Mutation
• Natural Selection
Horses are a Classic Example of
Evolution
Scientific Classification of the Horse
•
•
•
•
•
•
•
Kingdom
Phylum
Class
Order
Family
Genus
Species
The earliest ancestors of the
horse appeared over 50 million
years ago.
Time Line
Horse Family Tree
Recent: 10,000 years ago to present
Pleistocene: 2.5-0.01 million years
ago
Pliocene: 5.3-2.5 million years ago
Miocene: 24-5.3 million years ago
Oligocene: 38-24 million years ago
Eocene: 58-38 million years ago
http://hometown.aol.com/darwinpage/horses.htm
http://www.angelfire.com/mi/dinosaurs/horse.html
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
Eohippus
50 million years ago
• Carried its weight on central
pad like a dog
• Well adapted to living in
forested and swampy
environment
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
Miohippus or Mesohippus
• Low crowned teeth without cement
• Teeth suitable for grazing on the prairie
• Greater speed, endurance for finding
forage, water, protection, survival
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
Merychippus
• Over 2 feet tall (35 inches)
• Long crowned teeth with cement
• Eye socket position changes
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
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
Pliohippus
•
•
•
•
One toe on front and hind legs
Splints of 2nd and 4th digits
Long crowned teeth with cement
Grandfather of the modern horse
Equus
6 Million Years Ago
Develops into modern day horse after 15 million
generations
Equus’ Evolutionary
Changes
•
•
•
•
Increase in body size
Reduction in toe number
Increase in size of cheek teeth
Longer face
Evolutionary Changes in Horse
Body Size
http://www.txtwriter.com/Backgrounders/Evolution/EVpage03.html
During the Ice Age,
Equus migrated from
North America
throughout the world
over the Bering Strait
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
Extinction in Western Hemisphere
• The appearance of
man in the Paleolithic
period
• Return to the continent
at the Age of
Exploration
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
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
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
Proto-Draft
Proto-Warmblood
Tarpan
Proto-Oriental
Przewalski Horse
Lecture Objectives
• Define evolution
• Describe the horse family tree
• Describe the horse’s anatomical changes
and why they came to be