Hipparion

A long time ago, a small animal lived. It looked like a small horse. It had three toes on each foot. This animal lived in grassy lands. It liked to eat grass for food.

The world began to change. The air changed and the world grew cold. These changes made it hard to live. Soon, these animals were gone.

We can still find their bones today.

Hipparion was a medium-sized animal that lived long ago. It lived between 10 and 5 million years ago. It looked like a small version of a modern horse. But Hipparion was tridactyl, which means it had three toes.

It had one main hoof. It also had two small toes on each limb. In some species, these toes helped them move. These animals lived in the Old World savannah. This was a land of woods and grass.

Hipparion was a mixed-feeder. This means it ate many things, but mostly grass. Scientists saw tiny scratches on their teeth. These marks show they ate lots of grass. They had high teeth to help them chew. Hipparion grew to about 1.4 meters tall at the shoulder. They likely grew up by age three. Large cats and bear-dogs once hunted them. Later, the world began to change. The air grew cold. Carbon dioxide levels in the air went down. These changes caused the animals to die out.

Hipparion was a medium-sized animal that lived long ago. It belonged to a group of animals called the Hipparionini. These creatures lived between 10 and 5 million years ago. They looked like smaller versions of the horses we see today. However, they had a very different foot structure. They were tridactyl, which means they had three toes.

One main hoof was in the center of each limb. Two smaller toes sat on the sides. In some species, these side toes actually helped them move.

These animals lived in the Old World Savannah Biome. This land was filled with both woodlands and wide grasslands.

Hipparion was a mixed-feeder. This means they ate many different things, but mostly they ate grass. Scientists know this because of tiny marks on their teeth. They used a tool called a scanning electron microscope to see them. These tools showed tiny scratches and pits on the enamel. To handle this diet, they had high-crowned teeth. These teeth were about 60 mm tall. This helped them chew tough plants every day.

Scientists have spent a long time studying these fossils. For over one hundred years, the name Hipparion was used very broadly. It once described over one hundred different species. Now, researchers use the name in a more specific way. They call the Eurasia group Hipparion in sensu stricto. This means "in a strict sense." They use different names like Cormohipparion to sort other species. They look at the shape of the skull to tell them apart.

Many fossils tell us about how they lived. Hipparion was about 1.4 meters tall at the shoulder. Their weight was between 135 and 200 kg.

They likely reached full growth by 3 years old. Some fossils show animals that lived to be 10 years old. In places like Spain, they had many predators. Sabertooth cats named Promegantereon and Machairodus lived there. Even bear-dogs and early giant panda relatives may have hunted them.

Hipparion likely came from a species called Cormohipparion. This happened about 11.4 to 11 million years ago. Their last common ancestor with modern horses was Merychippus. Eventually, the world began to change in a big way. The climate became much cooler. The amount of carbon dioxide in the air also went down. These environmental changes caused the animals to go extinct. They disappeared from the land in a pattern from north to south.

Hipparion was an extinct genus of medium-sized equines. These animals belonged to the tribe Hipparionini. They lived during the Late Miocene era, roughly between 10 and 5 million years ago. While they looked somewhat like modern horses, they possessed unique physical features. Understanding Hipparion helps scientists learn about how ancient environments changed. Their history provides a window into the evolution of grazing animals across the Old World.

The physical structure of Hipparion was quite distinct from today's horses. They were tridactyl, which means they had three toes on each limb. One central hoof was flanked by two vestigial outer toes. In certain species, these outer toes were actually functional for movement.

These animals were typically medium in size. They stood about 1.4 meters tall at the shoulder. Their body mass ranged from 135 kg to 200 kg. Their skulls also featured a facial fossa, which is a deep depression located high on the head in front of the orbit.

To survive on a tough diet, Hipparion developed specialized teeth. They were mixed-feeders that primarily consumed grass. This diet required hypsodont dentition, or high-crowned teeth. Their premolars and molars had crowns about 60 mm tall.

Scientists confirmed their diet by using scanning electron microscopy (SEM). This tool allowed them to see microscopic scratches and pits on the tooth enamel. Another unique dental feature was the isolated protocone. This is a specific cusp on the upper molars that was not connected to a tooth crest called the protoloph.

Taxonomy, or the science of naming and classifying organisms, has changed for this genus. For over a century, scientists used "Hipparion" in a broad sense, known as *sensu lato*. This classification included over one hundred different species from the Pliocene and Miocene eras. Today, researchers use more specific groupings. They separate species into different genera like *Cormohipparion* and *Neohipparion*. These distinctions are usually based on differences in skull morphology, which is the study of the shape and structure of the skull. Now, *Hipparion in sensu stricto*, or "in a strict sense," refers specifically to the genus found in Eurasia.

Fossil evidence helps us map where these animals lived and how they grew. Hipparion inhabited the Old World Savannah Biome (OWSB). This environment consisted of a mix of woodlands and wide grasslands. Based on skeletal remains, Hipparion likely reached skeletal and possibly sexual maturity at about 3 years of age. Some fossils indicate that individuals lived to be 10 years old before death. In the Batallones 3 fossil site in Spain, the environment was quite competitive. Isotopic analysis shows that several predators lived alongside them. These included sabertooth cats like *Promegantereon* and *Machairodus*. They also shared the land with amphicyonids, or bear-dogs, such as *Magericyon* and *Thaumastocyon*. Even large mustelids and early giant panda relatives like *Indarctos* likely preyed upon them.

Tracing the lineage of Hipparion reveals its evolutionary connections. The genus likely evolved from *Cormohipparion occidentale* during the Late Miocene, approximately 11.4 to 11.0 million years ago. This ancestor traveled to Eurasia and Africa from North America. Interestingly, the last common ancestor shared by both Hipparion and the modern horse was a species called *Merychippus*. This lineage shows how different equine groups branched out across different continents over millions of years.

The extinction of Hipparion was driven by significant shifts in the Earth's systems. As the Miocene progressed, the planet experienced global cooling. At the same time, carbon dioxide levels in the atmosphere began to decrease. These environmental changes altered the habitats that Hipparion relied upon. As a result, the genus experienced a population decline. This extinction followed a specific geographic pattern, moving from North to South across the Old World. This decline mirrors the trends seen in many other Miocene vertebrates during this period of climatic change.