Evolution of the Horse

Natural Selection

Natural Selection

Chooses individuals who can escape predators

Adapt to drastic changes in the environment

Many types of prehistoric horse developed only one pathway continued.

How can change occur?

Genes – units of inheritance – building blocks for living tissue.

Chromosomes – long protein strands that carry genes

Mutation – sudden variation in protein formation – section of chromosome information can be lost, turned around or twisted

Through evolution mutations occurred and provided variation that gave some animals better survival characteristics.

Dawn Horse

Cenozoic eraEocene epoch – 60-45 million years

Eohippus first known ancestor of the horseRemains of 13 different types have been

found – North America and England

Eohippus

Prehistoric skeleton 8-14 inches tall Arched back Round body Slender legs Weight bearing foot pads

4 toes on front foot 3 toes on hind foot Small splint bones of nonfuntional toes

Eohippus

Small size = need to avoid predators Speed and agility

Leap through bushes Slender legs, gripping toes = rapid maneuverability

over rough uneven ground

Teeth – soft forest leaves & plant shoots- browser

Primitive Forest Horse

Oligocene epoch – 38-17 million years agoRegression of swamps - expansion of forests

and plains Mesohippus

Approx. 2 feet tall Longer legs = increased speed Didn’t rely on dense vegetation for concealment

and protection Ate soft forest leaves

Mesohippus

Three toes on each footMiddle toe largerWeight still evenly distributed between toes

Skull – largerWider, more lateral placement of the eyes

Increased field of vision – binocular Monocular – separate images from each eye

Primitive Plains Horse

Miocene Epoch – 16-11 million years ago Merychippus

First known grazer – lived in herds Modified teeth that could grasp, crop and grind grasses Sharp incisors and grinding molars – continuous eruption Gap between incisors and molars Early canine teeth and wolf teeth – remnants of primitive

teeth

Change in digestive system Small stomach - Small amounts of food at frequent intervals Cecum and Large intestine becoming more important

Merychippus

Vision Focus eye by raising and lowering head Distance vision

Reflexes Specialized limb anatomy

Prevents overflexion of joints Stay apparatus – to allow animal to sleep standing

Speed Short bursts of speed Increased leg length Increased running on central toe Protective hoof formation – acting as a shock absorber

Early Migration

Pliocene epoch – 10 million years ago Dry climate and sparse vegetation

PliohippusMigration, isolation and environmental

pressures contributed to many Pliohippus types.

Possibly resembled Przewalski, Tarpan or Zebra Short, muscular neck and protective coloring

Pliohippus

Height of donkey, stiff upright mane

Leg anatomy One toe on each foot – remnant

splint bones Highly specialized toenail – hoof

Head size Anatomical proportions similar to

modern horse Eyes set wider apart

Pleistocene Epoch

The Ice AgePliohippus types migrated through North and

South America, Africa, Europe and AsiaSudden extinction in N. & S. America – puzzleSurvived on the Eurasian continent

Dinohippus

Recently discovered fossil remains Its foot structure, skull, and teeth are

extremely similar to those of the modern equine

it could be who Equus descended from it

Ancestral Horse Types

Geographic and climatic conditions Temperature and altitude extremes

Moist, rocky coastland - forest horse/celtic pony Flat, treeless plains – steppes horse Barren flatlands – wild horse of Central Asia Scorching deserts – caspian pony

Encouraged evolution of Pliohippus into the ass, the zebra and four basic horse types.

Four basic ancestral horse types

European Forest Horse Northwest Europe – Paleolithic Period 1,000,000 B.C.

Mountainous coastal region demanded endurance and sure-footedness

Small pony, 12.2h, water resistant coat Early horse gradually evolved into two types (before

domestication) Celtic Pony

Coastal regions, little food – small, short legged animal Primitive Heavy Horse

Thrived in lush forest, grew to massive proportions Short legs relative to size, large barrel and heavy coat Used to develop the European Great Horse of the Middle

Ages

Northern Eurasia – Steppes Horse Level, treeless plains Small, stocky – coarser head than its European

counterpart Retained primitive black dorsal stripe, upright stiff

mane and no forelock Cold resistant coat

Thick, shaggy winter coat to protect him from cold frosts in Mongolian steppes

Four basic ancestral horse types

Equus caballus przewalski

Mongolian wild horseThought to be a direct descendant of this

Asiatic wild horse

Wild horse of Central Asia Barren flattlands 15h, largest of the primitive types Slender and swift – survived in arid conditions

Long neck and head, small forehead and a Roman nose. Large-boned, with long legs and large ears and a long back. Slab-sided, sparse mane and tail and a low tail set

Believed to be predecessor to Barbs and Andalusians

Four basic ancestral horse types

Potential descendant

Akhal-Teke Central Asia/Southern Russia

Turkmenistan – 2400 B.C.Known to be a combination of two breeds

Caspian pony Developed stamina and heat-resistance to survive in

a desert environment. Most populous throughout Mesopotamia 12h, fine bones, light legs, a high-set tail, and a silky

mane and tail. Small, concave head, large nostrils and a relatively

short neck. Most likely a forerunner of today’s Arabian

Tarpan, primitive breed now extinct, believed to be related to this horse

Four basic ancestral horse types

Equus ferus

Tarpan – Eurasian wild horseExtinct 1875 - MoscowKonik & Heck horse

Zebra

One Pliohippus type to Africa - PlesihippusThree species of Zebra

Equus grevyi Equus zebra – mountain zebra Equus burchelli

Equus grevyi

Imperial zebra – largestSubgenus - dolichohippus

More ass-like – 46 chromosomes

Equus zebra

Mountain zebra – smallestsubgenus hippotigris

2 subspecies – cape, hartman 32 chromosomes

Equus burchelli

Plains zebrasubgenus hippotigris

44 chromosomes

Equus Quagga

Extinct subspecies of plains zebraLast wild shot 1870’sLast living died 1883 – Amsterdam zoo

Other distant relatives to Pliohippus –Neohipparion descendants

Equus hemionus – Onager – Asian wild ass

Other distant relatives to Pliohippus –Neohipparion descendants

Equus hemionus – Kulan - Mongolian wild ass

Other distant relatives to Pliohippus –Neohipparion descendants

Equus kiangKiang – Tibetan wild ass

India, Kashmir

Other distant relatives to Pliohippus –Neohipparion descendants

Equus asinus africanusAfrican wild ass

Other distant relatives to Pliohippus –Neohipparion descendants

Equus asinusass – donkey – burroDomesticated ass – many varieties