Comment on "DNA from Pre-Clovis Human Coprolites in Oregon, North America"

The 2009 coprolite subsample was much smaller than the first, and it appeared as a layered crust with mineral inclusions; it also contained plant and feather fragments (figs. S1 and S2). The micromorphological analysis is again dominated by organic material (fig. S1). Very long stained plant fibers occur as an open layered structure, with occasional intercalated mineral grains (e.g., quartz). The organic matter groundmass is impregnated with micritic calcite. Overall, the micromorphological findings are compatible with those of the subsample analyzed in 2007. FTIR analyses of the bulk powdered portion and the area examined in thin section again revealed no phosphate minerals but confirmed the presence of gypsum, organic matter, quartz, clay minerals (kaolinite), and calcite (fig. S2). FTIR analysis of the feather (fig. S2) showed that the keratin is very well preserved, indicating that it is likely to be an external inclusion and did not pass through the digestive tract of a carnivore.

Interestingly, no absorption of carbonate hydroxyl apatite was present in either sample (although calcite minerals had formed in the second sample), nor was any typically yellowish amorphous cementing material observed in either thin section that could suggest a human or carnivore origin (fig. S4) [figure 3 in (10), figure IVa in (3)]. All carnivores and many omnivores, such as humans, produce calcium phosphate–rich coprolites (e.g., 18 to 34% Ca and 8 to 14% P) [appendix 1 in (9)], which in thin sections occur as yellowish isotropic domains that typically autofluoresce under blue light excitation (11). Although it is true that poor human diets can include large amounts of fiber (12), and large amounts of plant material such as seed remains have been found in the mummified intestines of mummies, this plant material may often still contain cellulose, which is birefringent under crossed polarized light. Humans are poorly equipped to break down cellulose, unlike herbivores; the organic material in the Paisley coprolite is mainly humified and nonbirefringent.

In sum, the subsamples of coprolite specimen 1374-5/5D-31-2 that we examined do not resemble previously described human or carnivore coprolites. The overwhelming abundance of vegetal remains (generally elongated), associated phytoliths, and lack of phosphate points to the specimen being from an herbivore (fig. S4) [figures 2 to 4 in (4); (5)]. The 2007 subsample resembles fragments of dung pellets, whereas the 2009 subsample has the layered character of trampled dung found where herbivores gather or are in relatively confined spaces (5, 13). Both sets of micromorphological and FTIR findings are incompatible with the coprolite specimen 1374-5/5D-31-2 being of human origin, and thus are inconsistent with the DNA results presented in (1).

Supporting Online Material

www.sciencemag.org/cgi/content/full/325/5937/148-c/DC1

Materials and Methods

Figs. S1 to S4

References