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The$Evolution$and$Domestication$of$the$
Equus%Caballus!
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Michaela!Trimble!
Biology!22!
Mr.!Kamansky!
May!11,!2016!
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Michaela!Trimble!
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The!horse!is!the!oldest!domesticated!animal!on!earth!today,!with!a!long!and!
well-documented!history.!Spanning!back!50!million!years!ago!the!horse!was!a!small!
multi-toed!animal,!which!gradually!evolved!into!the!large!single-toed!animal!we!see!
today.!The!evolution!of!the!horse!is!nothing!short!of!spectacular,!adapting!to!new!
habitats,!predators,!climates!and!much!more,!the!horse!has!truly!stood!the!test!of!
time.!Although!man’s!first!interactions!with!horses!were!hunting!them!for!survival!
purposes,!horses!gradually!became!work!aids,!and!ultimately!companion!animals.!
This!makes!the!horse!unique!to!most!livestock!animals,!which!are!still!used!mainly!
for!human!consumption.!!
Far!before!horses!were!domesticated,!they!first!evolved!in!North!America!
over!fifty!million!years!ago.!Horses!spread!vastly!across!the!world,!while!they!
gradually!became!extinct!in!North!America.!This!extinction!is!still!quite!the!mystery!
today.!Fossil!remains!of!Equus!have!been!found!across!the!world!in!Asia,!Europe,!
Africa,!and!the!Americas.!It!is!believed!that!the!last!true!North!American!horse!died!
between!fourteen!thousand!to!twelve!thousand!years!ago,!toward!the!end!of!the!
Pleistocene!period,!although,!horses!had!already!spread!to!Asia,!Europe!and!Africa.!!
Fossils!of!horses!were!found!in!sediment!from!the!beginning!of!the!tertiary!
period!during!the!period!of!time!called!Eocene,!approximately!fifty!million!years!
ago.!It!is!possible!to!trace!the!history!of!the!horse!through!the!theory!of!evolution:!
how!they!gradually!went!from!four!toed!animal!to!a!one!toed!animal!who!virtually!
stand!on!their!knuckles,!or!how!their!dental!structure!significantly!changed!due!to!
their!switch!from!a!diet!of!broad!leaved!plants!and!trees,!to!high!dry!grasses.!During!
the!horses’!fifty!million!year!existence!they!have!flourished!in!different!climates!and!
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ecosystems.!Fossils!of!the!horse!can!be!found!in!everything!from!riverbed!clays!to!
sands!and!sad!stones!of!the!great!American!west.!Due!to!the!vast!amount!of!fossils!
that!have!been!discovered!the!evolution!of!the!horses!we!know!today!is!highly!
studied!and!well!documented.!!
Table!1:!(http://www.oocities.org/hoofprintsforhorselovers/evolution.html)!
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!We!start!tracking!the!evolution!of!the!horse!with!Eohippus,!also!know!has!
“Dawn!Horse”!or!sometimes!Hydracotherium,!fossils!of!this!ancestor!have!been!
found!in!North!America!during!the!Eocene!period!previously!mentioned,!nearly!
fifty-five!million!years!ago.!During!the!Eocene!period!the!Eohippus!was!living!in!a!
dense!tropical!forest,!with!a!humid!climate.!Due!to!the!soft!ground!of!the!forests!the!
Eohippus!was!a!soft-footed!animal!with!four!toes!in!the!front!and!3!in!the!back.!In!
order!to!navigate!through!dense!forest!they!were!also!very!small!relative!to!the!
modern!horse,!standing!roughly!twelve!to!fourteen!inches!tall.!The!Eohippus!had!
three!incisors,!one!canine,!four!molars!and!three!grinding!molars!on!each!side!of!its!
jaw.!With!soft!teeth!it’s!diet!consisted!of!soft!foliage,!berries,!fruit!and!herbs.!The!
Eohippus!evolved!into!the!Orohippus,!which!continued!to!evolve.!!
Moving!to!the!Orohippus,!which!was!very!similar!to!Eohippus!and!was!also!found!in!
North!America.!The!Orohippus!or!“Mountain!Horse”,!roamed!during!the!Mid-Eocene!
period!approximately!fifty!million!years!ago.!Orohippus!stood!around!the!same!
height!as!Eohippus!with!similar!feet.!While!the!Orohippus’!diet!consisted!of!the!
same!as!Eohippus,!there!was!considerable!change!in!the!dental!structure.!Although!
the!number!of!teeth!remained!the!same!the!strength!and!size!of!the!teeth!adapted!to!
allow!more!of!a!grinding!action!in!preparation!for!a!diet!change!in!its!future.!The!
Orohippus!branched!into!the!Haplohippus!and!the!Epihippus.!The!Haplohippus!
became!extinct!while!the!Epihippus!continued!to!evolve.!!
! The!Epihippus!was!also!found!in!North!America!and!roamed!during!the!Mid-
Eocene!period!roughly!forty-seven!million!years!ago.!It!was!similar!to!its!previous!
ancestors,!Eohippus!and!Orohippus!standing!between!ten!to!fourteen!inches!tall,!
with!the!same!foot!structures!and!a!similar!diet.!However,!the!dental!structure!
continued!to!evolve.!The!Epihippus!had!only!two!pre!molars,!adding!one!grinding!