On Virginia’s Chincoteague Island, wild ponies reign supreme. These compact, colorful horses with shaggy manes live in small herds of a stallion and several mares, combing the beaches and snacking on marsh grasses. Popular tourist draws, these ponies were made famous by Marguerite Henry’s 1947 novel Misty of Chincoteague. Each July, tens of thousands of people visit to watch hundreds of the horses swim across the channel from nearby Assateague Island, after which the equines are sold at auction to keep the population in check.
Despite their celebrity, the ponies’ origin is shrouded in mystery. Local lore claims the ponies are descended from horses that swam ashore following the sinking of a Spanish galleon off the Virginia coast sometime around 1750.
But with no documentation of the lost ship, many historians believe the ponies are instead the progeny of runaway livestock, meaning that their origins are much more recent. (Read: Do we finally know where horses evolved?)
Now, DNA preserved in a fossilized horse tooth found 1,200 miles away in the Caribbean may lend credence to this supposedly mythical shipwreck. In a study published today in the journal PLOS One, researchers posit that the tooth belonged to a cousin of the ponies roving Virginia and Maryland’s barrier islands.
Importantly, both the Caribbean horse and Chincoteague ponies share an evolutionary lineage that originated in Bronze Age Spain, says study co-author Nicolas Delsol, a zooarchaeologist at the University of Florida.
While researching century-old fossils, Del Sol came across a 450-year-old shard of horse tooth molar that archaeologists had collected in the 1980s in northern Haiti, at the site of an early Spanish colony called Puerto Real. The tooth, thought to belong to a cow, had sat forgotten in the university’s museum collections for decades.
“It was a serendipitous find,” he said. “I was studying cows, but stumbled across this incredible piece of horse data.”
From a colonial horse’s mouth
Founded in 1503, just 10 years after Christopher Columbus reached the Caribbean, Puerto Real was a prominent Spanish ranching hub surrounded by fertile pasturelands. Colonists imported Spanish horses from southern Europe to help herd cattle, which were raised both for their hides and as food. For that reason, cattle bones are plentiful in the town’s middens, or trash heaps, which are now a treasure trove of information for archaeologists.
Because horses were prized status symbols at the time, however, they were rarely butchered, making them rare in the fossil record, says Delsol. Of the 127,000 Puerto Real animal specimens housed at the university’s Florida Museum of Natural History, only eight belong to horses.
The lucky horse tooth, he says, was discovered not in a midden, but in the vicinity of where Puerto Real’s church once stood.
After freezing and pulverizing a sample of the tooth, Delsol and his colleagues processed the powder and sent it off to a lab for sequencing. Although they had tempered expectations—ancient DNA often degrades in muggy, tropical conditions— the horse’s tooth yielded a remarkable amount of genetic information.
The team focused on the horse’s mitochondrial DNA, a type of DNA passed down from an animal’s mother, which is plentiful in most cells. It’s also a helpful tool for reconstructing an organism’s maternal lineage, enabling Delsol and his team to sequence a complete mitochondrial genome—the earliest “mitogenome” from a domesticated horse in the Western Hemisphere. (Learn about the world’s oldest genome, sequenced from 700,000-year-old horse DNA.)
Armed with the new genome, the researchers aimed to slot the Puerto Real horse within the larger family tree of modern domestic horses. They compared the Puerto Real horse’s mitogenome with a comprehensive analysis of more than 80 mitochondrial genomes of horse populations around the world. That revealed the Puerto Real horse’s closest relative was the Chincoteague pony.
“I had never heard of Chincoteague,” Delsol says. “And then I read this interesting anecdote about a Spanish shipwreck.”
Reclaiming their homeland
Although native to North America, the wild horse species that gave rise to domestic horses, Equus ferus, was not present on the continent for most of the past 10,000 years, after disappearing at the close of the last ice age.
However, when European explorers began colonizing the Caribbean in the late 15th century, they unwittingly reintroduced domestic horses. Once they reached the mainland, horses quickly spread across the continent where their ancestors had once run wild.
But most horses didn’t end up in a place as inhospitable as Chincoteague and Assateague. With limited food options, the ponies subsist solely on marsh grasses, a salty diet that forces them to guzzle twice as much water as the average horse, giving them a perpetually bloated appearance. The briny diet also keeps them generally small in stature. The annual pony swim auction, hosted by the Chincoteague Volunteer Fire Company, which owns the Chincoteague herd, maintains the number of ponies on the windswept island at around 150, which is about all the island can support.
This hostile environment is also why people are so intrigued how ponies got there. The shipwreck-origin hypothesis, notably put forth in Misty of Chincoteague, may now gain ground as the leading theory, Delsol says.
For one, Chincoteague itself sits at a treacherous stretch of the mid-Atlantic that is crisscrossed by hazardous shoals, he says. Evidence of shipwrecks, including several colonial-age vessels, often wash ashore during winter storms.
Emily Jones, an archaeologist at the University of New Mexico who studies how the arrival of horses impacted western ecosystems, believes the new finding illustrates how zooarchaeological remains can fill in blanks in the historical record.
“The feral population on Chincoteague highlights the idea that the spread of horses is not something where we can rely on European documents to tell us the history,” says Jones, who was not involved in the new study. (Read about wild horses and their shrinking population in the American West.)
Delsol believes this tooth fragment has an even greater story to tell: It hints that Spanish settlers were sailing further north into the mid-Atlantic region when their ship sank.
While historical records of these explorations are scant, the information preserved in the colonial tooth may help connect the dots.
“It’s more than just a horse story,” Delsol says.