1-evolution Of The Horse

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?   

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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 era  Eocene

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epoch – 60-45 million years

Eohippus  first

known ancestor of the horse  Remains 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 shootsbrowser

Primitive Forest Horse 

Oligocene epoch – 38-17 million years ago  Regression

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 foot  Middle

toe larger  Weight still evenly distributed between toes 

Skull – larger  Wider,

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  

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Focus eye by raising and lowering head Distance vision

Reflexes 

Specialized limb anatomy  

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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

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climate and sparse vegetation

Pliohippus  Migration,

isolation and environmental pressures contributed to many Pliohippus types. Possibly resembled Przewalski, Tarpan or Zebra  Short, muscular neck and protective coloring 

Pliohippus 

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Height of donkey, stiff upright mane Leg anatomy  

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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 Age  Pliohippus

types migrated through North and South America, Africa, Europe and Asia  Sudden extinction in N. & S. America – puzzle  Survived 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    

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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 surefootedness 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

Four basic ancestral horse types 

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

Equus caballus przewalski 

Mongolian wild horse  Thought

to be a direct descendant of this Asiatic wild horse

Four basic ancestral horse types 

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

Potential descendant Akhal-Teke  Central Asia/Southern Russia 

 Turkmenistan

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

Four basic ancestral horse types 

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

Equus ferus 

Tarpan – Eurasian wild horse  Extinct

1875 - Moscow  Konik & Heck horse

Zebra 

One Pliohippus type to Africa - Plesihippus  Three

species of Zebra

Equus grevyi  Equus zebra – mountain zebra  Equus burchelli 

Equus grevyi 

Imperial zebra – largest  Subgenus

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- dolichohippus

More ass-like – 46 chromosomes

Equus zebra 

Mountain zebra – smallest  subgenus

hippotigris

2 subspecies – cape, hartman  32 chromosomes 

Equus burchelli 

Plains zebra  subgenus

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hippotigris

44 chromosomes

Equus Quagga 

Extinct subspecies of plains zebra  Last

wild shot 1870’s  Last 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 kiang  Kiang

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– Tibetan wild ass

India, Kashmir

Other distant relatives to Pliohippus –Neohipparion descendants 

Equus asinus africanus  African

wild ass

Other distant relatives to Pliohippus –Neohipparion descendants 

Equus asinus  ass

– donkey – burro  Domesticated ass – many varieties