Transcript FOSSIL HUMAN REMAINS FROM SITES IN FLORIDA

FOSSIL HUMAN REMAINS FROM SITES IN FLORIDA CONTAINING EXTINCT, LATE PLEISTOCENE MEGAFAUNA:
ASSESSING 14C DATING FEASIBILITY BY USING HIGH RESOLUTION CT SCANNING AND GEOCHEMICAL ANALYSES
Barbara A.
1Department
1
Purdy [email protected],
Thomas W. Stafford,
2
Jr.
2Department
of Anthropology, University of Florida, Gainesville, FL 32611
Abstract
Computerized tomography (CT) and amino acid analyses (AAA) were used to
assess the 14C dating potential of human fossils. The Devil’s Den and Vero Beach
sites in Florida yielded human skeletal remains and several genera of extinct, late
Pleistocene fauna. The rarity and fragmentary nature of the human remains required
non-destructive (CT) and minimally destructive (AAA) testing to assess dating
potential. High-resolution (70 mm) CT was used on Devil Den’s human remains to
identify greatest-density bone (highest dating potential). High-resolution CT
imaging provides: 1) internal morphological data not available by medical CT, 2)
digital images suitable for morphology and osteometrics, and 3) archived data for
eventual stereolithographic reproductions of bones or teeth. AAA on 10 mg of bone
determined the preservation quality and amount of collagen present.
Methods
The rarity of potential Late Pleistocene human remains necessitates using non- to
minimally destructive methods to assess 14C dating potential. Conventional CT scans of
Vero Beach blocks were used to identify human bones within sediment blocks and plan
amino acid analyses and 14C dating. High resolution scans of Devil Den’s human
remains were used to:
1) Locate dense bone where collagen preservation is most likely.
2) Observe tooth morphology beneath enamel.
3) Obtain high resolution digital images of single teeth or entire specimens for
osteometric analysis and the production of stereolithographic plastic models.
Conventional, medical-resolution (~1 mm) CT scans were done at the McKnight
Brain Institute, University of Florida; high resolution (50-100 mm) CT scans were made
at the Center for Quantitative Imaging, Penn State University. Scanning generated
DICOM or TIFF files respectively. These digital data are a permanent archive of both
single-slice data of discrete anatomical elements or virtual reconstruction “models”
based on the total-scan of an entire specimen.
AAA sampling of Devil’s Den remains was conducted on 10 mg of bone powder
removed from 1/16” diameter holes in the densest regions as determined by CT.
Collagen per milligram of bone (nanomoles per milligram) and the spectrum of each of
18 amino acids were measured relative to modern bone. The AAA data established if
the specimen contained collagen for dating, if protein was collagenous or noncollagenous and how many milligrams of bone would be required for 14C dating.
[email protected] & John
Background
Although thousands of diagnostic Clovis artifacts have been discovered in North America,
only extremely fragmentary skeletal remains of two humans (Anzick Montana juvenile;
Arlington Springs, CA female) have been dated to 11,000 RC yr. BP. Consequently, any
possible Clovis-era remains require direct analysis to determine their geologic age. Two
Florida sites with human fossils potentially dating as late Pleistocene are Vero Beach (8IR9),
Indian River County, FL and Devil’s Den, Levy County, FL (8LV84). Both sites yielded fossil
human bones purportedly associated with extinct, late Pleistocene mammal fossils; specimens
are curated at the Florida Museum of Natural History (FLMNH), University of Florida,
Gainesville, Florida.
The Vero Beach fossils at FLMNH comprise two indurated blocks of clastic carbonate and
mollusk fragments, in which are encased cranial bones and teeth of at least two individuals,
respectively. These fossils are attributed to 1915-1916 canal excavations described by E.H.
Sellards in 1916. He published the discovery of a single human’s femora, tibiae, fibulae and
foot bones from brown sands (stratum no. 2) that also yielded Pleistocene fauna. Sellards
observed that “Elephas columbi and Equus leidyi and other extinct species were found at an
equal or higher level in the beds on either side of the human remains.” (Sellards, 1916:132).
of Geology & Geophysics, University of Wisconsin, Madison, WI 53706
Stratigraphically ex situ bones of Megalonyx jeffersoni and Mammut americanum were
attributed to the human fossil horizon.
Later excavations (April 1916) uncovered in situ bird bone and proboscidean ivory with
“… markings which apparently were made by tools.” (Sellards, 1916: 134) and in situ extinct
fauna including Equus spp., Smilodon, and Tapirus. Sellards concluded the human bones were
stratigraphically coeval with the Pleistocene fauna. Other scientists examining the site in 1916
were divided between accepting or rejecting the hypothesized Homo sapiens-extinct fauna
association (McCardy, 1917).
As Vero Beach faunal remains became scattered among several museums, physical
anthropological studies assumed the human remains’ contemporaneity with the extinct fauna
(see Stewart, 1946) and geochronological studies were never done. The impetus for reexamining the Vero Beach collection are the capabilities of AMS 14C and an imminent
engineering project that will expose the locality’s stratigraphy near the original discovery site.
Direct AMS 14C dating of human skeletal material and re-exposure of the sediments will
definitively test the fossils’ purported late Pleistocene age.
Devil’s Den is an extant, approximately 10 m diameter sinkhole that is a tourist diving
locale. The site has yielded several extinct or extralocal taxa (including Mammut, Megalonyx,
Canis dirus, Smilodon, Equus, Platygonus compressus and Synaptomys australis (Martin and
Webb, 1974)).
A minimum of six human individuals were collected in the 1950’s and 1960’s from the sink
hole and are curated at FLMNH. Although the human remains were “found associated” with
extinct fauna, the sinkhole’s depositional history precludes using fossil associations for
assigning ages. The incremental accumulation of animals over millennia, absence of physical
stratigraphy, and collection of specimens by non-scientists require direct 14C dating to test the
humans’ “association” with extinct, late Pleistocene species.
Literature Cited
MacCurdy, George (1917) The Problem of Man’s Antiquity at Vero, Florida. American
Anthropologist, 1917: 252-261.
Martin, Robert A. and S. David Webb (1974) Late Pleistocene Mammals from the Devil's
Den Fauna, Levy County. In Pleistocene Mammals of Florida, edited by S. David
Webb, pp. 114-145 University Press of Florida.
Sellards, E. H. (1916) Human remains and associated fossils from the Pleistocene of
Florida. Annual Report of the Florida Geological Survey 8:123–160.
Stewart, T. D. (1946) A reexamination of the fossil human skeletal remains from
Melbourne, Florida, with further data the Vero skull. Smithsonian Misc. Collections
106(10):1-28.
High Resolution (70 µm) Total-Specimen CT Scans (Center Quant. Imaging)
DEVIL’S DEN
Devil’s Den Sinkhole (2005)
1
Krigbaum [email protected]
Partial Maxilla
(Photograph)
VERO BEACH SITE (2005)
Devil’s Den Juvenile Mandible
Conclusions
/
A
A
Amino Acid Analyses of
Devil’s Den Human Bones
B/
A
/
A
B
Transverse
CT Section
1. CT RESOLUTIONS < 100 mm ARE REQUIRED
2. ONE CT SLICE PER TOOTH OR SKELETAL ELEMENT
MAY BE SUFFICIENT TO ASSESS DATING
POTENTIAL
3. CT DATA OF ENTIRE SPECIMENS PROVIDE A
DIGITAL ARCHIVE FOR OSTEOMETRIC ANALYSES
Devil’s Den
Temporal
Bone with
Petrosal
4. SAMPLING LOCATIONS ARE READILY MAPPED
5. CD DATA PERMIT STEREOLITHOGRAPHY
OF BONES
v
AND TEETH USED FOR 14C
6. SEVERE LEACHING AFFECTED ALL BONES AND
TEETH
7. NON-COLLAGENOUS COMPOSITIONS PREVAIL
8. ENAMEL IS THE BEST CHOICE FOR 14C & d13C
CT scans of in situ human
mandible, teeth (arrow), and
skull fragments. Note
associated shell.
v
9. ENAMEL GEOCHEMISTRY STUDIES ARE NEEDED
10. DIRECT 14C DATING OF HUMAN FOSSILS WILL
EVALUATE THEIR PURPORTED ASSOCIATION WITH
EXTINCT FAUNA
Un-erupted
Tooth: CT
X-Section
B
Acknowledgments
cochlea
/
B
• Ms. Donna Ruhl and the Human Osteology Advisory Committee
(FLMNH) facilitated loans of specimens for analysis and provided
curation data on collections.
• Drs. Tim Ryan and Avrami Grader, Center for Quantitative
Imaging, Penn State University performed CT scans and analyses
on the Devil’s Den specimens.
• Dr. Frank Bova, McKnight Institute, University of Florida
provided the CT images for the Vero Beach blocks.
• Funding of this research was from the Florida Wetlands Project,
University of Florida.
© Stafford/Purdy/Krigbaum 2005