Date post: | 16-Nov-2014 |
Category: |
Documents |
Upload: | potionyesterday |
View: | 360 times |
Download: | 6 times |
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