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Equine biology > evolution > Flashcards

Flashcards in evolution Deck (34):
1

roles of equids in society

food source, spiritual symbols, warfare, hunting, work, transport, sport, companions

2

horse taxonomy: class

mammalia

3

family

equidae

4

genus

equus

5

domestic breeds are

Equus caballus

6

equus asinus

african wild ass

7

equss burchelli

east african zebra

8

equus grevyl

grevy's zebra of east africa

9

equus zebra

south african zebra

10

equus kiang

asian ass

11

equus hemionus

middle eastern/asian ass

12

equus przewalski

last truly wild horse
-from Mongolia

13

last common ancestor of domestic and przewalski

4.5 million years ago
-no genomic evidence of prze mixing with domestic, so they retain their genetic diversity

14

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

15

adaptations: digits

from 4 to 1 central digit, adapted for running on hard ground, receiving impact of their heavier bodies, and for kicking predators

16

adaptations: long, crowned, hard teeth

-adapted for grazing on fibrous/tougher vegetation found on open, dry plains

17

adaptations: fossae

a depression or hollow point of skull, allowing for greater jaw muscle strength

18

adaptations: brain

larger cerebral hemispheres

19

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)

20

epihippus

-47 mya
-teeth change to allow for tougher food intake
-some premolars more like molars for grinding

21

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

22

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

23

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

24

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

25

merychippene radiation

miocene
-19 new grazing horse species in three major groups:
1. hipparions
2. protohippines
3. merychippines (3 and 1 digits horses)

26

1 digit horses

-late miocene, pliocene, and pleistocene
pliahippus, hipparion, and dinohippus

27

pilohippus

similar to modern horse

28

hipparion:

3 digits, grazers and browsers, spread from new to old world

29

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

30

old equus

common ancestor 4.5 mya
-12 species, coexisting with hipparions, protohippines, and astohippus
-pony sized, 1 digit

31

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

32

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

33

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

34

other existing relatives:

rhinoceroses and tapirs