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Hipparion

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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.

Hipparion forcei NT
Hipparion forcei NT

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.

Fossil Hipparion in Haining Museum 02 2014-08
Fossil Hipparion in Haining Museum 02 2014-08

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.

Hipparion gracile skull
Hipparion gracile skull

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.

Hipparion cornelianum
Hipparion cornelianum

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.

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🖼️ Images & Media (4)
File:Hipparion forcei NT.jpg
Hipparion forcei NT.jpg
File:Hipparion_gracile_skull.jpg
Hipparion_gracile_skull.jpg
File:Fossil_Hipparion_in_Haining_Museum_02_2014-08.JPG
Fossil_Hipparion_in_Haining_Museum_02_2014-08.JPG
File:Hipparion cornelianum.jpg
Hipparion cornelianum.jpg
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