Brontotheres, Mesohippus, and Oreodonts, Oh My!

Inside a white triangle with a black border is a silhouette of the rhinoceros-looking brontothere, the symbol indicates a brontothere crossing.
Keep an eye out for the massive brontothere, which may cross your path!

NPS / Astrid Garcia

Some of the larger mammals that you'll encounter are brontotheres, with mesohippus and oreodonts being significantly smaller than these "thunder beasts". As you're making your observations, remember to keep a safe distance.

As you venture deeper into the forest, these animals will reveal themselves to you. For help navigating the forest, walk along the stream, which is a source of water for the animals. Following the stream will also take us to the lake where we can see different animals. The next time you're in nature just enjoy a silent moment to listen closely in which you might see activity from even small critters.
 
Inside a green circle is a backpack, pair of binoculars, and a notepad along with a pen and pencil.
Write down your wildlife observations!
For this activity:
  1. Look and read closely for any signs of these animals.
  2. Use the sliders below to get a closer view.
  3. Write down your observations of what you see.
  4. Read the drop-down answers to learn about each animal.
  5. After completing this activity, challenge yourself by answering these Fossil Riddles.
 
In the forest, you come across a calm stream. You're surrounded by tall Redwood trees. As you move the slider to your left, you notice a large creature start to peek out from behind a Redwood as it walks towards the stream to drink water.

Take out your binoculars to get a closer view by moving the slider to the right, looking towards the stream.

Now, quickly write down what you saw. To get you started, answer these questions. What does the creature look like? What is it doing? Is it alone?

Read about this animal using the drop-down below.
 

Something Big is Coming your Way

On the left is a picture of the forest showing the trunks of the tall Redwood trees. On the right is a binocular view looking more closely at the massive rhinoceros-looking brontothere at the stream with the text "You've spotted a brontothere!" On the left is a picture of the forest showing the trunks of the tall Redwood trees. On the right is a binocular view looking more closely at the massive rhinoceros-looking brontothere at the stream with the text "You've spotted a brontothere!"

Left image
Credit: NPS Graphic

Right image
Credit: NPS Graphic

 

Brontothere (Megacerops)
These were the largest animals to roam the Florissant area 34 million years ago (Eocene). They were massive creatures standing at a height of over 8 feet (2.4 meters) and weighing over two tons!

At first glance, these animals looks like rhinoceros, which are in the same order. However, they have two horns protruding from above their nose that was used as protection from predators and for settling rivalries.

The brontotheres went extinct after the Eocene because they couldn't survive the colder temperatures. 
 

 
You decide to cross the stream. You hear a funny noise and turn around to see these small hog-like creatures. Three of them appeared beside the stream walking by. Move the slider to the left to take out your binoculars and take a closer look at these animals.

You also begin to hear leaves rustling in the forest. There might be a few more walking nearby, so keep an eye out by moving the slider to the right!

Write down what you saw and describe these animals: what color were they, how many were there, how big do you think they were and what were they doing? Read about these animals using the drop-down below.
 

You might need to ruminate a bit on this one and look closely.

On the left is a forest showing a stream with three oreodonts walking by. On the right four small brown hog-looking hog animals are shown in the forest in front of a Redwood tree. On the left is a forest showing a stream with three oreodonts walking by. On the right four small brown hog-looking hog animals are shown in the forest in front of a Redwood tree.

Left image
Credit: NPS Graphic

Right image
Credit: NPS Graphic

 

Oreodont (Merycoidodontoidea)
The name oreodont means "mountain tooth" because of their distinctive molars. These animals are referred to as ruminating hogs and were early cud chewers, meaning that they would chew and digest their food then throw it up and eat it again. Gross right!

These even-hooved animals or artiodactyls looked like a mixture between a camel, sheep and pig, but are most closely (but very distantly) related to camels. 

 
You cross the stream one last time, and you're on the side of the forest that is nearest to the lake. You begin to hear the sound of hooves nearby. If you look to the left, you'll notice some small horses peeking out from behind a couple of massive Redwood trees. Move the slider to the left to look at them with your binoculars.

As you slowly turn to your right, you notice these animals walking towards the stream. Move the slider to the right to see them move.

Write down what you saw and describe these animals: what color were they, how many were there, how big you think they were and what were they doing? Read about these animals using the drop-down below.
 

See something cool? Yay or Neigh?

On the left shows the forest with tall Redwood trees. Out from two of the Redwoods are two small three-toed horses called mesohippus peeking out. A mesohippus is also in the bottom left corner. On the right are two mesohippus in the forest by the stream. On the left shows the forest with tall Redwood trees. Out from two of the Redwoods are two small three-toed horses called mesohippus peeking out. A mesohippus is also in the bottom left corner. On the right are two mesohippus in the forest by the stream.

Left image
Credit: NPS Graphic

Right image
Credit: NPS Graphic

 

Primitive horses: Mesohippus
Mesohippus means "middle horse," and these animals are considered to be the transition between ancestral horses and the modern horse of today. Mesohippus had longer legs and three toes on each leg.

Standing at only 3 feet tall, these primitive horses were able to evade predators by hiding easily.  

Unlike modern horses today, through observation of the fossilized mesohippus teeth, it's been determined that they fed on twigs and fruits instead of grasses. 


 

 
The stream you were walking along led you to the lake. As you look to the trees... or tree, you notice a small animal clinging to the tree bark. Move the slider to the right to take a closer look.

Are you interested in seeing what this animal looks like as a fossil? Move the slider to the left to see this animal preserved in the paper shale.

Write down what you saw and describe this animal and fossil: what color is it, how big do you think it is and what was it doing? Read about this animal using the drop-down below.
 

Everything is Awesome... Opossum!

On the left is the forest of smaller tree beside the lake's edge. On the right is a binocular-view showing an opossum on the tree with a fossil view of the opossum head. Text reads "You've spotted an opossum". On the left is the forest of smaller tree beside the lake's edge. On the right is a binocular-view showing an opossum on the tree with a fossil view of the opossum head. Text reads "You've spotted an opossum".

Left image
Credit: NPS Photo

Right image
Credit: NPS Graphic

 

Mouse Opossum (Nanodelphys)
The fossilized remains of this small critter was found in the lake shales. This small mammal lived in the trees where it would climb on a branch overhanging above the lake until it fell. Its skull, teeth, ribs, right hand, hind legs, and prehensile tail have been preserved. The fur on its carcass became carbonized, or turned into carbon. 

This opossum was omnivorous, eating small animals, insects and fruits. The ancient opossum of Florissant is related to the modern mouse opossum found throughout Mexico to South America.
 

 
Inside of a rounded black square is a dark blue round graphic showing a big question mark in the center of scattered leaf and insect fossils.

Fossil Riddles

Now that you've read about some of the ancient mammals found here, test your knowledge!
 

Where to next?

  1. Go back to the forest
  2. Revisit the Eocene
  3. Return to the Present

Last updated: April 9, 2022

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