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

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

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