Apparently, dogs may have been man’s best friend in North America for quite some time. A new study suggests that domesticated dogs have been on this side of the Pacific for roughly 10,000 years.

Researchers analyzed the skeletal remains of three medium–sized dogs unearthed in Illinois, which they could tell were pets from the way the dogs were buried.

Found at the archaeological sites Koster (located south of Eldrid, IL.) and Stillwell IL in the 1960s and 70's, the skeletons had been sitting in the state museum, collecting dust for years. That was until recently, when Dr. Angela Perri and her team decided to analyze the canine skeletons using modern techniques.

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“The dogs from the Koster site have been iconic early American dogs in the archaeological record for a long time, but they had never been [direct carbon] dated,” study leader Perri, from the Department of Archaeology at the Durham University in the United Kingdom, told Fox News. “When we came across the dog from Stilwell, which had been in museum collections for decades unanalyzed, we decided to date that dog as well and look at them all together."

Direct carbon dating showed that the dogs were buried sometime between 9,630 and 10,190 years ago. To put this in perspective, the first North Americans are believed to have arrived here about 16,000 years ago.

“We had an idea that the dogs would be old, but we weren’t sure how old,” Perri added. “They turned out to be older than we expected.”

According to the study, the three skeletons are the oldest known individually–buried dogs known in the world’s archaeological record. The remains are also older than the previous oldest dog skeleton found in the Americas, which had been unearthed at a 9,300 year–old site in Texas.

“This research pushes back the date for the earliest dogs in the Americas,” Perri explained. “We think humans came into the Americas around 16,000 years ago, but the evidence for the earliest dogs is only around 10,000 years ago. It is still of question of whether dogs came with the first Native Americans or a later group.”

Researchers believe that domesticated dogs can be identified from the fashion in which they were buried. The Stilwell dog, for instance, was found buried beneath the floor of a human dwelling with its legs tucked beneath it. The Koster dogs were each buried in their own separate, shallow graves. There was also no evidence that the specimens had been carved up or skinned, indicating they weren’t an early Illinoisan’s dinner. The specimens also weren’t wolves, that had once been theorized as where the earliest dogs in America had been domesticated from.

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“The dogs are significantly smaller than what we would expect to see in a wolf and have certain characteristics, like smaller teeth and shorter stature, that is typical of domesticated dogs,” Perri said. “We also analyzed one of the Koster dogs in a paper we published in Science earlier this year (‘The Evolutionary History of Dogs in the Americas’), which showed that it was, in fact, a domesticated dog of Eurasian origin, likely originating from animals in eastern Siberia.”

The research also yielded interesting results about the dogs’ diet– their masters fed them a lot of fish. The dogs were also different depending on their location, with the Stilwell folks preferring larger breeds.

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“While the dogs from the Koster site are smaller with more [slender] features and potentially some coyote interbreeding, the dog from Stilwell is larger and more robust,” Perri said. “It is more variation than we expect to see in early dogs and it is exciting because it shows early dogs may have many more secrets to share than we expect.”

The study can be found in the scientific journal American Antiquity.