Earth Sciences 2266F/G Lecture Notes - Lecture 28: Platybelodon, Pliohippus, Merychippus

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Lec 28
Elephant evolution: very successful group despite their large size
From very beginning, the Moertherium existed
Even earlier than this there is a mole-sized creature that still lives today called Heraxes which is
halfway between this branch and horse branch
From Eocene, the branch that went back to sea started very early
Many branches of elephants evolved, adapting diff ways of grazing (eating grass) and browsing
(eating tree leaves)
Modification of their trunks and jaws differed; e.g. Deinotherium has a characteristic lower jaw
with a hook, probably for digging and for pulling down tree branches
On the right there is Platybelodon which has a lower jaw that can plow through grass (as grass
evolved around this time)
In modern elephants, they are very versatile for eating either grass or tree leaves
They have ridges on their teeth (high crowns, thick enamel; individual cusps) as well for eating
grass (which is tougher to eat/digest b/c of anti-grazing compounds) (grazing specialized teeth
would have long ridges instead of individual cusps)
In the mastodon, they’re browsing  good at grinding softer, tree leaves
During the age of dinosaurs, there was no grass so they didn’t necessarily graze
Explosive evolution and radiation within the carnivore group
Within this group, some adapted to running around on land, and some went back to sea
Most of the carnivores within this group: one group is the dog family (caniformes) and the other
is the feline cats (feliformes)
Feline group is less adapted to living in aquatic environment
Even bears like polar bears spend half its time in water (some people suspect in a million years
they’ll become completely aquatic)
Ungulates (animals with hooves)
Perissodactyls: odd-hoofed animals (1, 3, 5 hooves) (compare to even-hoofed animals
artiodactyls like camels, cows)
Mostly herbivores
Hoofed animals started off with the divergence between herbivores and carnivores but their
carnivore group didn’t do too well – eventually became extinct
Today we still have tapirs, rhinos, horses
Heraxes: People don’t really know if it belongs to ungulates or elephants
Tiny creatures that are prey for African dogs
In their evolution, their bone structure lies halfway between rhino and elephant groups
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