Dominant Fossils Found in This Assemblage (Images 1-4, 12,13 cropped from frame):
5. Stylemys (first dry land tortoise – multiple species)
6. Nimravus brachyops (false saber-toothed cats)
8. Eusmilus cerebralis (Nimravid carnivore, false saber-toothed cat)
9. Mesocyon (dog – multiple species)
10. Agriochoerus (bizarre clawed oreodont)
11. Cormocyon copei (dog)
14. Quercus (oak)
15. Herpetotherium merriami (marsupial)
16. Micropternodus morgana (burrowing, mole-like insectivore)
17. Celtis (hackberries)
7. Miohippus (three-toed horse)
18. Dyticonastis rensbergeri (worm lizard)
Filling the Role...
Eusmilus cerebralis was
a feliform (cat like), very similar in body structure to a leopard with
exception of having incredibly long upper canines akin to saber teeth. Even though Eusmilus was “cat like”, it shares no modern descendant. As Nimravids went extinct, felines evolved to
fill the same ecological niches left by Nimravids. E. cerebralis also had the ability to
open its jaw to an almost 90 degree angle, which would likely be an adaptation
for lunging at the necks of prey like three-toed horses and oreodonts. To protect its saber teeth from any sheer
stresses, Eusmilis had bony flanges
that protruded from its mandible (lower jaw).
was a sheep-sized clawed oreodont
unlike anything alive today. They get
their common name from the fact they have large curved claws on their fingers
and toes, rather than hooves like other artiodactyls (even-toed, hoofed
mammals). Their claws and limb
anatomy suggest agriochoerids were able to climb trees, perhaps living like
tree kangaroos today. These forest
browsers lived all over North America for more than 20 million years, but
vanished at the end of the Oligocene.
Why they became extinct is not known, but the opening of habitats in the
Oligocene and early Miocene may have removed the forests favored by Agriochoerus.
Miohippus was a
small three-toed ancestor of modern horses that had longer legs and larger
teeth than earlier horses. Longer legs
allowed it to run quickly and evade predators in open environments. Its larger teeth were adapted to effectively
grind tough vegetation. As climates
continued to change, horses evolved better running and grinding adaptations,
which can be seen in horses today.
Mesocyon is one of
the most common dogs found in the John Day Formation. It was the earliest dog
to reach the size of a coyote. Mesocyon
has a short snout and more blade-like teeth than other earlier dog species,
indicating a more predatory lifestyle.
These features suggest that Mesocyon
was a forest dwelling ambush predator, likely feeding on rabbits, rodents, mouse deer, and possibly small oreodonts and horses that thrived alongside Mesocyon in the forests of the Turtle
is a tiny relative of shrews and moles.
Like moles today, M. morgani
likely had a strong sense of smell and was a good burrower, feeding on worms
and insects living in the soil. Small
mammals like Micropternodus help
create intricate stories of the fossil records paleoecological niches.