WASHINGTON — A trio of dogs buried at two ancient human sites in Illinois lived around 10,000 years ago, making them the oldest known domesticated canines in the Americas.
Radiocarbon dating of the dogs’ bones shows they were 1,500 years older than thought, zooarchaeologist Angela Perri said April 13 at the annual meeting of the Society for American Archaeology. The previous age estimate was based on a radiocarbon analysis of burned wood found in one of the animals’ graves. Until now, nearly 9,300-year-old remains of dogs eaten by humans at a Texas site were the oldest physical evidence of American canines.
Ancient dogs at the Midwestern locations also represent the oldest known burials of individual dogs in the world, said Perri, of Durham University in England. A dog buried at Germany’s Bonn-Oberkassel site around 14,000 years ago was included in a two-person grave. Placement of the Americas dogs in their own graves indicates that these animals were held in high regard by ancient people.
An absence of stone tool incisions on the three ancient dogs’ skeletons indicates that they were not killed by people, but died of natural causes before being buried, Perri said.
Some researchers have proposed that whoever made the first excursions into the Americas arrived on dog-powered sleds. People had reached South America at least 15,000 years ago (SN: 12/26/15, p. 10), well before ancient people buried dogs at Illinois’ Koster and Stilwell II sites. It’s unclear whether humans reached South America via coastal or inland routes. But no dog remains have been found in northwestern North America, where the earliest settlers crossing a land bridge from Asia would have entered the New World. Either those people had no dogs, or they and their furry companions stayed on the land bridge, possibly blocked by two massive ice sheets, until rapidly moving inland around 10,000 years ago (SN: 2/16/08, p. 102), Perri said.
“As much as we want to believe that dogs initially pulled us into the New World, that may not have been the case,” Perri said.
Genetic evidence has suggested a second human migration from Asia to North America occurred around 11,500 years ago, with people trekking south through an ice-free corridor into the northern Great Plains. Those people likely brought dogs to the Americas, Perri proposed.
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She and her colleagues studied two of three dogs excavated at the Koster site in the 1970s and a dog unearthed at Stilwell II in 1960. These sites lie about 30 kilometers apart in west-central Illinois.
Perri’s team found that the lower jaws and teeth of the Stilwell II dog and one Koster dog displayed some similarities to those of modern wolves. Another Koster dog’s jaw shared some traits with present-day coyotes, possibly reflecting some ancient interbreeding.
A new genetic analysis positions the 10,000-year-old Illinois dogs in a single lineage that initially populated North America. Dog origins are controversial, but may date to more than 20,000 years ago (SN Online: 7/18/17). Ancient American dogs, including the Koster and Stilwell II animals, shared a common genetic ancestor, cell biologist Kelsey Witt Dillon of the University of California, Merced reported April 13 at the SAA meeting. That ancestor originated roughly 15,000 years ago after diverging from a closely related Siberian dog population about 1,000 years earlier, she said.
Dillon’s team, which includes Perri, studied 71 complete mitochondrial genomes and seven nuclear genomes of dogs from more than 20 North American sites, ranging in age from 10,000 to 800 years ago. Mitochondrial DNA is typically inherited from the mother, whereas nuclear DNA comes from both parents.
Much of the genetic blueprint of those ancient dogs is absent in present-day canines, Dillon said. Only a small number of U.S. and Asian dogs share maternal ancestry with ancient American dogs, suggesting the arrival of European breeds starting at least several hundred years ago reshaped dog DNA in the Americas, she proposed.