Evolution and Adaptation

The earliest known relative of the horse in Hyracotherium (or Eohippus). Its full scientific name is Hycotherium leporinum. It lived 55 million years ago and was about the size of a domestic dog. On each front foot, it had four toes; on the back feet, it had only three toes.

On its jaw, it had incisors, cuspids, molars and premolars. This shows it omnivorous. It evolved to adapt to its environment, the easier to eat berries were replaced by the harder to eat plant material. They adapted to have four molars each side instead of three, which allowed them to eat more, this means they survived and passed on their genes, this is called natural selection.

Natural Selection - organisms better adapted survive and produce more offspring

Orohippus (4 molars, 2 premolars) = one more grinding tooth for eating and stronger molar cusps

Epihippus; another premolar becomes a molar (5 grinding molars) --> eat tougher foods, reproduce successfully. Longer legs (speed + height), North American climate drier, took advantage of grassland, grasses evolving, large forest shrinking

Mesohippus: 35 million years ago, less arched back (run faster, run for longer), means 'middle horse', longer legs, necks and faces lengthen (reach food)

Merychippus insignis: 25 million years ago, large and fast, strong sturdy legs, grazed on grass, MILESTONE (walked on a dominant middle toe, started to resemble modern horse)

Pliohippus: 7 million years ago, means 'more horse', lived in grasslands, first to have a single toe (one strong toe to support a heavy body) --> horses without feet properly adapted to running didn't survive and reproduce

Equus: modern horse, 5 million years ago, long necks and faces, 6 to 7 million feet long, living relatives (zebra, sheep, donkey, giraffe, moose, deer) 

Water

• adapt to swim
• adapt to get oxygen
• flippers and tail (no legs)
• dolphins and sea lions

Savanna/Grasslands

• ability to escape
• no thick fur (heat)
• taller (see further)
• giraffe, cheetah
• zebra --> stripes (hard to pick out one individual, heatwaves blend into stripes)

Rainforest

• dark and wet
• competition (adapt to be in the canopy, climb/fly/jump)
• glider, ocelot, tapir, frog

Mountain

• steep terrain
• air pressure
• sturdy on feet
• snow (thick fur)
• blubber/thick skin 
• seasonal coats
• mountain hare, ibex, welsh pony, lynx, snow leopard

• extended phalanges
• light and slender bones
• fused cranial bones
• keel attached to the sternum (large flight muscles)
• webbing between phalanges
• ulna and fibula reduced
• 'chiroptera' - winged hands

Advantages

• the first phalange is small and clawed
• bat bones tend to be light and slender
• elongated bones for a larger surface area
• small hips don't have to work

Disadvantages

• bones break easily
• can't weight bear on hips
• large membrane tears

• shock absorbers
• don't have muscles in the bottom of their legs (ligaments)
• longer legs for longer strides
• long-distance runners
• radius and ulna fused for extra strength
• one toe
• large scapula and pelvis

Advantages

• elongation of limb bones (more ground quicker and less energy)
• large rib cage for increased size of lungs needed for running

Disadvantages

• remnants of lost digits attached to canon bone
• easily break leg bones
• damaged ligaments cause lameness - slow healing time

• long and sleek (less drag, more speed)
• lack of hair
• whale skin excretes droplets of oil that decrease drag
• no ears
• smooth and rubbery skin
• dorsal fin as stabiliser/rudder

Advantages

• elongated skull
• blowhole for breathing at the surface
• compact neck vertebrae
• reduced limbs
• extra phalanges
• extra flexible tail
• floating ribs

Disadvantages

• unable to hold bodyweight out of water
• bones are less rigid (more damage-prone)
• loss of limbs causing the floating pelvis

Advantages

• enlarged and thick hindlimbs for strength and powerful jumping/hopping
• increased size of the femur and tibia/fibula
• hopping movement made by larger hindlimbs and forelimbs

Disadvantages

• lightweight bones can break easily
• curved spine prone to breaking by dropping or hard stamping of hindlimbs