According to a Latin American study, the fossilized jaw bone could prove that Central American domesticated dogs existed as early as 12,000 years ago.
Researchers believe that the dogs and their masters could have lived alongside giant animals.
A 1978 excavation in Nacaome, northeast Costa Rica found bones from the Late Pleistocene.
Excavations began in 1990 and yielded the remains of Equus sp, an enormous horse, a glyptodon, a mastodon (an ancestral of the modern elephant), and a piece from the jaw of what was initially thought to have been a coyote skull.
Guillermo Vargas, a Costa Rican researcher, told AFP that he thought it was strange for a coyote to be found in the Pleistocene 12,000 years ago.
"When we began to look at the bone fragments, it was easy to see some characteristics that could have come from a dog.
"So we kept looking... we scanned it... it showed us that it was a dog who lived with humans 12,000 years back in Costa Rica.
Dogs are a sign that humans also live in the area.
"We thought it strange that a sample of a coyote was classified because they arrived in Costa Rica only in the 20th Century."
It is the first of its kind
Although the coyote looks a lot like the domestic dog, it has a distinct jawline and sharper teeth.
"The dog eats leftovers from human food." Vargas said that the dog's teeth do not play a major role in its survival.
"It hunts large prey together with its human companions. This is a good example of that.
It is believed that humans emigrated to America via the Bering Strait, from Siberia to Alaska, during the last great Ice Age.
Raul Valadez from the National Autonomous University of Mexico, who is a biologist, zooarcheologist, and biologist, said that the first domesticated dogs arrived on the continent around 15,000 years ago.
Valadez stated that dogs have never existed without humans to AFP by phone.
Although evidence of human presence during the Pleistocene was found in Mexico, Chile, and Patagonia, it has not been proven in Central America.
Vargas stated, "This could possibly be the oldest dog of the Americas."
The oldest known dog remains that have been tested for their age were discovered in Alaska, at 10,150 years.
Oxford University offered to run DNA and carbon dating tests on the specimen to uncover more genetic information about this animal and its age.
Costa Rica's National Museum holds the fossil, but it cannot be re-identified without validation from a specialist magazine.
Vargas stated that "this dog discovery would be evidence of humans in Costa Rica during an earlier period" than is currently believed.
"It would prove us that there were societies who could keep dogs, had food surpluses and had dogs out to desire, and that these weren’t war dogs that could cause harm."