Hipparion Three-Toed Horse: Fossil Teeth Reveal Spain's Old Seasons

Hipparion, the three-toed horse in today's news

The Hipparion three-toed horse was an extinct horse that lived in central Spain about 9 million years ago, and it was a distant cousin of the horses we know today. On October 26, 2026, a team of Spanish scientists announced that its fossil teeth work like a diary, holding clues about what summer and winter were like back then.

The study was led by Universidad Complutense de Madrid (UCM), working with Spain's National Museum of Natural Sciences (MNCN-CSIC), the Institute of Geosciences (IGEO, CSIC-UCM) and the University of the Algarve in Portugal. It was published in the science journal Palaeogeography, Palaeoclimatology, Palaeoecology.

The big idea, in plain words: over about half a million years, the seasons in central Iberia became much more different from each other.

What they found, in four points

• They analyzed 141 enamel samples taken from 11 Hipparion teeth.
• The teeth came from two fossil sites: Los Valles de Fuentidueña (Segovia) and Batallones-10 (Madrid).
• All the teeth show the rhythm of the seasons, but in the older teeth the signal goes up and down less. In the younger teeth, it goes up and down much more: stronger seasons.
• Their food hardly changed: they ate mostly C3 plants, the kind found in open woodlands and meadows.

What was Hipparion? A cousin, not a grandparent

Picture a horse about the size of a big pony. A Hipparion skeleton on display at a regional museum near Madrid stands about 135 cm (roughly 13 hands) at the withers.

The coolest part is its feet. Each leg had three toes: a big middle toe with a hoof that carried most of the weight, plus two shorter side toes. Those side toes were already getting smaller, and the strong middle toe helped it run.

Why isn't it the ancestor of modern horses?

The horse family isn't a ladder. It's more like a bush with lots of branches. Hipparion belonged to a branch that did really well for millions of years and then died out.

Today's horses, along with zebras and donkeys, come from a different branch of the same family, the equids. So Hipparion is like a distant cousin: it looks a lot like a horse, but it isn't your favorite mare's great-great-grandparent.

A very common fossil in Spain

Hipparion is one of the most common fossils from the end of the Miocene and the Pliocene in Spain and Portugal. There are so many that scientists talk about "Hipparion faunas"!

At the Batallones fossil site (Cerro de los Batallones), south of Madrid, diggers have found Hipparion of almost every age, from young foals to adults. There are even remains of foals that hadn't been born yet.

How horse feet and teeth changed over time

Horse evolution for kids is easiest to follow as a timeline. The numbers are rounded, because we're talking about millions of years.

1. About 55 million years ago: the first horse relatives were about the size of a fox. They had four toes on their front feet and three on their back feet, and they nibbled soft leaves in forests.
2. About 18 million years ago: some horses, like Parahippus, were starting to switch from eating leaves in forests to eating grass in open country. Their teeth wore down much faster, which favored horses with taller teeth.
3. About 9 million years ago: Hipparion roamed Spain on three toes, with grinding teeth that worked like millstones on tough, fibrous plants.
4. Today: horses stand on one toe per leg, the one that ends in the hoof. The side toes are almost gone, but two thin leftover bones still sit along the cannon bone. They're called splint bones.

Why just one toe?

One big, strong middle toe, with the side toes almost gone, makes the bottom of the leg lighter. That lets the leg swing faster, so the horse can run better to escape predators. In three-toed horses, the side toes barely touched the ground except when jumping or running very fast.

You can find the splint bones on our horse anatomy page.

Why did teeth get taller?

Grass is gritty and wears teeth down like sandpaper. Horses with taller teeth took longer to wear them out, so they lived longer and had more foals.

Modern horses kept that trick: their teeth keep slowly pushing up for most of their lives. That's why they need regular dental checks, which we explain in health basics.

How a tooth works like a diary of the seasons

Enamel is the hard, shiny outer layer of a tooth. In a young horse, the enamel on a molar forms little by little, from the tip down toward the root, over many months.

Each thin layer keeps a "chemical snapshot" of the water the animal was drinking at that moment. So one tooth can hold several summers and winters in a row, like the pages of a diary.

To read it, the researchers drilled tiny samples in a line along the crown of each tooth (they used 10 molars and 1 premolar). This is called serial sampling.

What's an isotope? A simple explanation

Everything is made of atoms, super-tiny pieces like building blocks. The oxygen in water comes in a few "sizes", and scientists compare two of them: a lighter one and a slightly heavier one. These versions are called isotopes.

Rain and river water change their mix of light and heavy oxygen depending on whether it's hot or cold, or whether there's a lot of water or a little. The horse drinks that water, and its enamel saves the mix.

• Small zigzag in the samples: summer and winter were fairly alike.
• Big zigzag: summer and winter were very different.

The Batallones-10 teeth showed a much bigger zigzag than the Fuentidueña teeth. The authors think bigger swings in temperature or in how much water was available could explain it.

Carbon tells us what they ate

Carbon has isotopes too, and they help show what plants an animal ate. C3 plants are most trees, shrubs and grasses of mild climates. C4 plants are mostly grasses from hot, dry places, like corn and sugarcane.

Both groups of Hipparion ate mostly C3 plants all year. So even though the seasons changed, their menu didn't change much.

The Vallesian Crisis: when Hipparion's neighbors changed

The Vallesian is a slice of the Miocene, from about 11 to 9 million years ago, named after the Vallès area of Catalonia. Around the middle of it, about 9.7 million years ago, Europe's mammals went through a big shake-up called the Vallesian Crisis.

During that crisis, many forest-living mammals declined. Animals suited to more open, drier landscapes took their place.

The new study found that the seasons grew stronger right around that time. But two things happening together doesn't prove one caused the other, and this study is based on two fossil sites. The researchers themselves want to check other sites in Iberia and other groups of mammals to see whether the change happened everywhere.

What to do and what to watch next

Want more prehistoric horses? Here are ideas for home, the classroom or a day out.

Junior paleontologist checklist

• Find the "toe bones": look at a drawing of a horse skeleton and spot the two thin bones next to the cannon bone. They're what's left of the side toes.
• Compare with tree rings: a cut tree trunk also records good and bad years in its rings. A Hipparion tooth does something similar, but with seasons.
• Make your own "enamel diary": draw a long molar and color it in stripes, blue for winter and orange for summer. Make one with soft, similar stripes (Segovia) and one with bold, very different stripes (Madrid).
• Visit a museum: in Spain, the Regional Archaeological and Paleontological Museum of the Community of Madrid (Alcalá de Henares) shows Hipparion fossils from Cerro de los Batallones, and the National Museum of Natural Sciences (Madrid) has fossil halls too. Check their websites for opening hours before you go.
• If you find a fossil: don't dig it out or break it. Take a photo, note where it is and tell an adult, a museum or a park ranger. In many places, including Spain, fossils are protected by law.

What to watch for in future news

• New studies using the same method at other fossil sites in Spain and Portugal.
• Tests on other animals from the same time, to see if they also felt the change in seasons.
• More finds from Cerro de los Batallones, where fossils are exceptionally well preserved.

If you love fun facts, keep going with 30 amazing horse facts for kids or meet the Przewalski's horse foals born in Kazakhstan, wild horses that seem to come straight from the past. There are more games and activities in Kids and Play, and classroom guides in Parents & Teachers.