A new study published online May 3 in the Journal of Vertebrate Paleontology settles a century-long debate among scientists regarding the age of human and mammal remains found at Vero Beach, Florida, in the early 1900s. Bruce MacFadden and colleagues determined all the bones are from the same time period, providing evidence that modern humans coexisted with extinct ice-age beasts 13,000 years ago in the Western Hemisphere.
I asked MacFadden, a member of AAAS and the Curator of Vertebrate Paleontology at the Florida Museum of Natural History, about the discovery.
AAAS MC: Tell me about the Vero Beach site and the debate surrounding the remains found there.
Bruce MacFadden, AAAS member and Curator of Vertebrate Paleontology, Florida Musuem of Natural History: The skeletal remains of extinct megafauna and humans were found in Vero, Florida, almost a century ago by geologists from the Florida Geological Survey (under the leadership of E. H. Sellards, State Geologist). The bones and teeth were from the same late Pleistocene stratigraphic levels, suggesting the human and animal remains were the same age. Because of the potential importance of this association, prominent archaeologists (Ales Hrdlicka) and geologists (Rollin T. Chamberlain) weighed in on this discovery. Hrdlicka pronounced the humans to be intrusive burials and therefore not the same age context as the extinct megafauna.
This has been where the debate has been for almost a century - whether the human remains were the same age as the other bones or were deposited at the site at a later time. Over the past half-century, attempts to radiocarbon date key specimens have either been equivocal or not possible (we also tried and there was not enough material to date).
AAAS MC: What method did you use to analyze the remains, and what did the results tell you?
MacFadden: We analyzed the relative uptake of rare-earth elements, or REEs. This is a time-dependent phenomenon: as bones fossilize, they absorb naturally-occurring metals from the surrounding sediment, and we can distinguish fossils of different ages deposited at the same site. If Hrdlicka had been correct, then the humans would have had much lower concentrations than the extinct Pleistocene megafauna. Our study revealed that the late Pleistocene fauna and humans have statistically indistinguishable concentrations of REEs, suggesting they co-existed.
AAAS MC: Can you tell how long ago humans and extinct ice age mammals lived together at this site?
MacFadden: Not directly from this technique. My guess from what is known about the timing of human spread through the Americas, plus when the megafauna became extinct elsewhere in North America, is that their co-existence could only have been a few to several thousand years. Our analysis shows the human and megafauna remains were all from the late Pleistocene epoch about 13,000 years ago.
AAAS MC: How does this discovery affect what we know about the lives of the first humans in North America?
MacFadden: We now know that modern humans reached the Western Hemisphere during the last ice age and rapidly populated many regions of North America, including Florida. When the Vero Beach site was first discovered in the early 20th century, most scientists did not believe that humans were in the Western Hemisphere that early.
AAAS MC: What other animals' remains were found alongside human remains at Vero Beach? Can you speculate at all about how humans may have interacted with these other species?
MacFadden: Florida during the late Pleistocene was rich with animal life, including extinct megafauna (ground sloths, armadillos, capybaras, dire wolves, mastodons, and mammoths) as well as species that still exist today (white-tailed deer, opossum, and many rodents). One would think that humans would have interacted with the native fauna. Scientists think humans followed large animals for a food supply, but little is known about the lives of early humans in the Western Hemisphere.