Evolution of Horse

 

Evolution of Horse


DEFINITION

Evolution of Horses

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 The phylogenetic sequence in the evolution of horse is dependent on environmental conditions. Hyracotherium or Eohippus lived in marshy forests with abundant soft vegetation and protection. Due to climate changes, there was declination in the number of forests. As a result, Hyracotherium had to shift to lands and hard grass. Hence, the molar teeth of these organisms became longer, stronger and sawlike to chew grass. Neck and snout became longer to keep an eye on the enemies. Legs became modified to assist fast running on open ground.  

DEFINITION

Eohippus

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  • The modern horse started evolving about 5 years ago in the eocene epoch in North America. The first species was a fox sized species named as Eohippus. Fossils helped in deriving these information.
  • Richard Owen, a palaeontologist found the first fossils of Eohippus in the year 1841. He renamed the species as Hyracotherium.
  • They spread throughout Asia and Europe. The primitive horses differ from modern horses in three characters: 
    • Smaller body (only 40 cms high), head and neck.
    • Forelimbs with four and hindlimbs with three nailed digits
    • Incomplete cement and no serrations upon molar teeth. 
  • Eohippus adapted the above mentioned characters as they lived in marshes and had to feed on grassy vegetation.

DEFINITION

Mesohippus

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  • Mesohippus arose from Hyracotherium during Oligocene about 3 crore years ago.
    • The characters of Mesohippus were:
    • It was of the size of modern sheep.
    • All its limbs had three nailed digits. The middle digit was longer than others and it supported most of the body weight.
    • Molar teeth had some serrations.

DEFINITION

Merychippus

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  • Merychippus form evolved from Mesohippus in Miocene about 2 crore years ago. 
  • It had following characters:
    • Merychippus was of the size of a mule.
    • Its limb also had three digits with middle one longer than others, but this digit had a hoof instead of a nail. Only this digit could touch the ground and supported the entire body. Remaining digits were useless and reduced. These did not touch the ground. 
    • Molar teeth were larger with well-developed cement and serrations.

DEFINITION

Pliohippus

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  • This form evolved from Merychippus about 50 lakh years ago. 
  • Pliohippus was somewhat larger than the present day mule. 
  • It has following characters:
    • Its limb had a single (third one) hoofed digit. 
    • The rest were reduced to small splint bones hidden beneath the skin. 
    • Its molars were long with well-developed cement and serrations.

DEFINITION

Equus

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  • The modern horse, Equus evolved from Pliohippus about 9 to 10 years ago during Pleistocene in North America. 
  • It spread throughout the world except Australia.
  • It has following characters:
    • Greater height (about 1.5 meters) 
    • Longer neck, snout, molars and limbs
    • Its limbs have a single hoofed digit. Other digits have disappeared.

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