An unpublished study of radiocarbon dates of extinct Pleistocene megafauna excavated from the Devil’s Den site in Florida produced unusually recent dates. Specimens from this site were dated to between 7,000 BP-8,000 BP; about 4,000 years after the time most believe these species became extinct. I often wondered why this data seemed to be ignored in the scientific literature and why no one had attempted a follow up study of the specimens from this site. The specimens were described in 1974, then seemingly forgotten. (See: https://markgelbart.wordpress.com/2012/07/08/the-devils-den-fossil-site-may-have-been-located-in-one-of-the-last-refuges-of-the-megafauna/ )Finally, several scientists began analyzing the Devil’s Den specimens again, and they just recently published their data in brand new journal named PaleoAmerica.
Photo of the Devil’s Den site from inside the sinkhole.
I had wrongly assumed the specimens were radiocarbon dated in 1974, but I learned from reading this study that they were dated in 1961 when radiocarbon dating was primitive and not particularly reliable. Moreover, the authors of this new study determined radiocarbon dating of these specimens could not be accurate because they didn’t have enough bone collagen left. They also suggest radiocarbon dating for most Pleistocene-aged specimens found in Florida is not possible because the regional environmental conditions eat away at bone collagen so rapidly. This poses a problem for scientists who want to know if humans overlapped in time with Pleistocene megafauna in North America. Surprisingly, there is little direct evidence of this, despite the universal assumption that they did. Human remains of confirmed Pleistocene age in North America are extremely rare. However, human bones associated with those of extinct Pleistocene mammals have been found in several sites in Florida including Vero Beach, Warm Mineral Springs, Melbourne, and Devil’s Den. Though this is suggestive, it’s possible humans buried their dead in the Pleistocene-aged strata, mixing the bones from different time periods. Scientists need something more definitive than association. Because radiocarbon dating can’t be used at these sites, the authors of this study decided to try rare earth element analysis on the specimens from Devil’s Den.
Here is an explanation of rare earth element analysis. Rare earth elements (a bit of a misnomer because they’re not particularly rare) include elements on the periodic table numbered 57-71. They occur in groundwater in certain fixed ratios. Animals absorb ground water by ingestion and then for thousands of years after they die their bones continue to become saturated with it. Eventually, the bone reaches a saturation point and won’t take in any more. The ratio of rare earth elements in that particular fossil becomes fixed. However, over thousands of years the ratios of rare earth elements in ground water changes. So an animal that lived 13,000 years ago will have a different ratio of rare earth elements than an animal that lived 200 years ago.
The authors of this study compared the ratios and concentrations of rare earth elements from specimens they categorized into 4 groups. They analyzed 26 specimens from 5 different individual human skeletons found in the Devil’s Den sinkhole and compared them with the associated bones of extinct Pleistocene fauna, extant fauna thought to be of Pleistocene age, and extant fauna from the modern local environment. They used specimens of the Florida spectacled bear (Tremarctos floridanus), flat-headed peccary, Jefferson’s ground sloth, mastodon, and muskrat that were found in the sinkhole. The first 4 of these species are extinct, and this species of muskrat hasn’t occurred in Florida for about 3,000 years. The extant fauna thought to be of Pleistocene age found in the sinkhole included white-tailed deer, woodrat, striped skunk, gray fox, and gopher. Local fauna of modern age used in the study were deer, fox squirrel, gray fox, and gopher. Specimens from 4 of the 5 human skeletons shared similar ratios of rare earth elements with Pleistocene fauna, showing they lived during the same time period. One of the human skeletons is probably of Holocene age, but this study demonstrates without a doubt that humans overlapped in time with Pleistocene megafauna.
The authors of this study assume 4 of the human remains are older than 13,000 years old, but they have no way of knowing for sure. The rare earth element analysis shows these individuals lived at the same time as Pleistocene megafauna, and the bones are of great antiquity, but the date of deposition is not known. As I’ve written previously on this blog, I hypothesize some species of Pleistocene megafauna survived in small relict populations well past their accepted terminal extinction date of ~12,500 BP. The exact extinction dates of Pleistocene megafauna in Florida will remain a mystery, especially if radiocarbon dating can’t be used.
Purdy, Barbara; Kathryn Rohlwing and Bruce Macfadden
“Devil’s Den, Florida Rare Earth Element Analysis Indicates Contemporaneity of Humans and Late Pleistocene Megafauna”
PaleoAmerica 1 (3) 2015