evolution Flashcards
roles of equids in society
food source, spiritual symbols, warfare, hunting, work, transport, sport, companions
horse taxonomy: class
mammalia
family
equidae
genus
equus
domestic breeds are
Equus caballus
equus asinus
african wild ass
equss burchelli
east african zebra
equus grevyl
grevy’s zebra of east africa
equus zebra
south african zebra
equus kiang
asian ass
equus hemionus
middle eastern/asian ass
equus przewalski
last truly wild horse
-from Mongolia
last common ancestor of domestic and przewalski
- 5 million years ago
- no genomic evidence of prze mixing with domestic, so they retain their genetic diversity
accurate picture of horse evolution
- not a straight line
- different traits evolved at different rates; not always evolving together and occasionally reversed
- development was not always gradual either
- ancestors did co-exist
adaptations: digits
from 4 to 1 central digit, adapted for running on hard ground, receiving impact of their heavier bodies, and for kicking predators
adaptations: long, crowned, hard teeth
-adapted for grazing on fibrous/tougher vegetation found on open, dry plains
adaptations: fossae
a depression or hollow point of skull, allowing for greater jaw muscle strength
adaptations: brain
larger cerebral hemispheres
hyracotherium (“eohippus”)
- 54-34 mya
- north american small forest animal
- looked like “a dog”
- ate fruit and soft foliage
- 4 digints in front, 3 on back (1-2 vestigal digits)
epihippus
- 47 mya
- teeth change to allow for tougher food intake
- some premolars more like molars for grinding
mesohippus and miohippus
- medium sized browsers/grazers
- late eocene, oligocene: climate of NA gets drier, grasses evolving and forests shrinking
- larger, taller, less doglike, longer faces, 3 digits, horse brain develops
- 6 grinding teeth
Plains horses: grinders
-crests on teeth enlarged and connected together in series of ridges for grinding
-hypsodont teeth: teeth keep growing and must be worn down through use
cement layer on teeth made them harder
plains horses: runners
- increase body size, leg length
- 1 digit in some
- muscles and legs specialized for forward and back strides
- standing on tips of digits with springy ligaments on central phalanx
parahippus and merychippus
17 mya
- 3 digits
- radius and ulna FUSED so leg rotation is eliminated
- fibula greatly reduced
- eyes moved further back to accomodate large tooth roots
- larger brain
merychippene radiation
miocene
- 19 new grazing horse species in three major groups:
1. hipparions
2. protohippines
3. merychippines (3 and 1 digits horses)
1 digit horses
-late miocene, pliocene, and pleistocene
pliahippus, hipparion, and dinohippus
pilohippus
similar to modern horse
hipparion:
3 digits, grazers and browsers, spread from new to old world
dinohippus
common in NA, probably gave rise to modern Equus
- 1 digit with side ligament to prevent twisting
- long nose
- high crowns, straight grazing teeth with crests lined with cement
old equus
common ancestor 4.5 mya
- 12 species, coexisting with hipparions, protohippines, and astohippus
- pony sized, 1 digit
Splint bones
- metacarpals 2 and 4 are usually vestigial “splint bones” around large central 3rd digit
- rarely, modern equus can be born with small but fully formed side toes
spread of equus
- major glaciations of late piocene (2.6 mya) allows species to cross to
- africa, creating zebras
- asia, mideast, and N Africa as desert-adapted onagers and asses
- asia, mideast, and europe as the true horse E. Caballus
- south america
- other species died out, with Equus surviving
extinction 10,000 years ago
removed equus from Americas
-no definitive reason, could have been due to changes in environment, disease, or overhunting by humans
other existing relatives:
rhinoceroses and tapirs
