The vessels are small and ceramic. Some resemble tiny teapots, others look like small pipes, and a few are sculpted into whimsical animal shapes with a little spout on the backside.

When they were discovered in ancient cemeteries scattered across Europe, some archaeologists wondered whether they were used to feed the sick or the elderly. But because they were often buried in graves alongside infants, most experts agreed that the vessels likely served a different purpose.

Call them prehistoric baby bottles.

Now, a new chemical analysis of three of these ancient containers provides further evidence that the vessels were indeed used to feed milk from cows, sheep or goats to human babies.

“People have known about these containers for a long time and assumed they were baby bottles, but nobody had done a thorough analysis on them,” said Julie Dunne, a chemist at the University of Bristol in England, who led the work. “What I liked about this study is that it gave us a nice, close connection to parents of the past.

Dunne works in the university’s Organic Geochemistry Unit, a research group that has chemically analyzed roughly 10,000 shards of pottery from around the world to help archaeologists better understand what foods and other materials the artifacts once contained.

Their work has revealed that lipids, the building blocks of fats, can survive for thousands of years. “What we know from years of experimental work is that fats absorb into the ceramic matrix of the vessel and are often preserved there,” Dunne said. “Because of that, lipids do survive in about 80% of the assemblages we’ve looked at.”

In the new study, Dunne and her colleagues collected samples from three ceramic baby bottles that had been found next to infants in ancient German burial sites. Two of the bottles came from a cemetery complex that scientists believe was in use between 800 and 450 BC; the other bottle was found in a site dated to 1200 to 800 BC. (The earliest-known ceramic baby bottles have been dated to about 5,000 BC.

Dunne said collecting samples from the bottles was a nerve-racking experience. Usually, her team begins by grinding up pieces of old cooking pots. But since the small bottles were still intact, that was not an option.

“We had to adopt a modified strategy,” she said.

They cleaned the interior surfaces of the vessels, then drilled out just enough ceramic powder to be able to see any lipids that had been absorbed by the pottery. Next, they used a chemical process to free the lipids from the ceramic matrix, allowing them to measure the chemical and isotopic fingerprint of each one.

They found that the vessels contained fatty acids from dairy products — almost certainly milk — that came from domesticated ruminant animals, according to their report in the journal Nature. They were not able to tell whether the milk came from cows, sheep or goats.

The work represents “the earliest known evidence of animal milk in small bottles for infants,” Sin Halcrow, a bioarchaeologist at the University of Otago in New Zealand, wrote in an essay accompanying the paper.

Halcrow, who was not involved in the study, added that the work also “provides crucial insight into the diet of developing infants in prehistoric human populations.”

Dunne and her fellow researchers were curious to see how a modern-day infant would respond to a replica of one of the ancient bottles. The rounded shape of the prehistoric bottle fit perfectly in a young child’s hands. When scientists poured in some milk, the baby quickly started sucking the spout.

The ancient baby bottle technology still worked.