The species
M. obliquidens dating from 34.9 to 30.0 Ma found in
Montana,
North Dakota,
South Dakota, and
Nebraska when calculated for estimated body mass were within the margin of 25 to 30 kg (55 to 66 lbs).
Miohippus became much larger than
Mesohippus. They weighed around 40 to 55 kilograms. They were somewhat larger than most earlier
Eocene horse ancestors, but still much smaller than modern horses, which typically weigh about 500 kilograms.
Miohippus was larger than
Mesohippus and had a slightly longer skull. Its facial
fossa was deeper and more expanded, and the
ankle joint was subtly different.
Miohippus also had a variable extra crest on its upper
molars, which gave it a larger surface area for chewing tougher forage. This would become a typical characteristic of the teeth of later equine species.
Miohippus had two forms, one of which adjusted to the life in
forests, while the other remained suited to life on
prairies. The forest form led to the birth of
Kalobatippus (or
Miohippus intermedius), whose second and fourth finger again elongated for travel on the softer primeval forest grounds. The
Kalobatippus managed to relocate to
Asia via the
Bering Strait land bridge, and from there moved into
Europe, where its
fossils were formerly described under the name
Anchitherium.
Kalobatippus is then believed to have evolved into a form known as
Hypohippus, which became extinct near the beginning of the
Pliocene. As many as eight species of
Miohippus were described from the John Day Formation of Oregon, but recent work on the dental variation has determined that only one species of
Miohippus was present within a given member. == See also ==