Now the Monroe County Medical Examiner's office said the results of radiocarbon dating tests are in and the bones are much older -- about 2,400 years -- placing them in the time period of 200-440 B.C.
"Having yet another date on human remains is spectacular," forensic anthropologist Heather Walsh-Haney of Florida Gulf Coast University, who was called in to help with the investigation, told AOL News in a telephone interview today. "What starts out as a forensic case ends up being something that really adds to the picture of ancient people in Florida."
The bones were found in October, when a 61-year-old woman told a Monroe County sheriff's deputy she'd discovered what looked like a jawbone and a portion of a skull while digging in her yard. Earlier in the week, she said she'd found what looked like the upper part of a femur and put the bones in a plastic bag.
After confirming the bones were human, detectives began digging for more, carefully sifting through the dirt in areas that had been identified with the help of cadaver dogs from the nearby town of Islamorada's fire department. They found more pieces of skull bone and some finger bones, the sheriff's department said at the time.
"There are so few bones, it is reportedly difficult to tell very much about them," said Becky Herrin, public information officer for the Monroe County Sheriff's Office, in a blog post about that search.
"Detective Terry Smith says initial examination by the medical examiner indicates they may be from a small-framed person, either a young adult or a person in their late teens – possibly a female," she wrote. "The bones have been there for an extensive period of time, possibly as long as 75 years judging by the apparent density of the bones that have been recovered so far."
Investigators believe the bones most likely were brought into the Keys years ago in fill dirt from an unknown location elsewhere in Florida, Herrin said.
The searchers did not find any ancient artifacts among the bone pieces, Walsh-Haney said, but instead found "cultural material from modern day." Among the tiny bits of old bones, they also found remains from creatures including a cat, fish and a bear, she told AOL News.
Anthropologists have known that ancient people lived in Florida during this time frame and "these bones underscore that length of time," Walsh-Haney said.
"In general, these were people who were healthy. They had big bones compared to modern folks and were well-muscled," Walsh-Haney explained.
The bones are being turned over to the Florida Bureau of Archaeological Research, where they will be examined for more information and the origin of the fill dirt in which they were found, Walsh-Haney said. The bureau also is responsible for making sure historic and ancient human remains are properly protected under state and federal laws.
"For anthropologists, it's hard to get the kind of money needed to date things," she said. "And going back in time, we're looking at conditions where the sea level was much lower ... and people lived mainly along the coasts, so we don't have a lot of remains from this period of time."
It was an "aha" moment savored by all, including Walsh-Haney. "It's pretty spectacular," she said.