Sunday, May 18, 2008

Paper blogging Just finished up reading the following: Jessica C. Thompson, Nawa Sugiyama and Gary S. Morgan, Taphonomic analysis of the mammalian fauna from Sandia Cave, New Mexico, and the "Sandia man" controversy. American Antiquity 73.2 (April 2008): p337(24). Here's the abstract:
Sandia Cave in New Mexico was excavated in the late 1930s by Frank Hibben, who described a unique type of chipped stone artifact--the "Sandia point"--in association with a faunal assemblage that included extinct Pleistocene species. The site was interpreted as a late Pleistocene Paleoindian hunting station, making it the earliest human occupation known in America at the time. Despite the pivotal role the faunal assemblage has played in interpretations of the site, there was never a confirmed behavioral association between the artifacts and the fossils. A subsequent series of controversies about the age of the site and the integrity of the stratigraphy has since pushed Sandia Cave into obscurity. Results from a recent taphonomic study of the large and small mammal assemblages from the original excavations are reported here. These show that the majority of the fauna were accumulated by nonhuman agents (carnivores, raptors, and rodents), but that a small proportion of large mammal fragments retain human modification. The three major points of controversy are discussed in light of these and other findings, and it is shown that Sandia Cave remains an important datapoint in archaeological, paleontological, and paleoecological studies of the region.

Excellent little paper. Very well written as well. The cave has been controversial as a site of pre-Holocene humans almost ever since work on it was first published and has largely languished in recent decades, usually only brought up in lectures regarding the demonstration of pre-Clovis sites and how most of them haven't been accepted. That's all well and good and I'll get to some of the conclusions relating to that, but what really interested me about the paper was its use of previously-excavated materials. I've posted on this before (though I still haven't done a complete post on the Mayo Site like I've been promising) but this paper demonstrates the possibilities, dangers, and detective work that goes into using older curated material.

First, a disturbing statement: Only 44 percent of the bags retained provenience information by stratigraphic layer. That's the bad news. Sadly, this is probably typical even apart from the preservation of the remains and as we all know, context is nearly everything in archaeology. Especially when stratigraphy and the association of remains and artifacts (and dated material) is of primary importance.

Nevertheless Thompson et al. were able to use the material pretty effectively in no small part due to the excavation techniques employed by Hibben and the fact that the material had preserved so well. They hadn't been washed before being stored so much of the original matrix was still clinging to the fossils. In addition, the excavators had saved some bags that hadn't been screened and thus contained all of the included faunal materials. Using these samples and an analysis of the size ranges of the screened material, they determined that 1/4" screen was probably used. This was important in assessing what sorts of systematic bias due to the excavation techniques was present within the samples.

They used a variety of analytical techniques to attack two basic questions: Was the stratigraphy compromised due to mixing, and what were the most likely agents that acted to accumulate and modify bones present in the cave? The former was one of the major controversies about the site and many had commented on the presence of abundant bioturbation in the form of rodent burrowing. They looked at the level of fossilization in aggregate to see if the assemblages from higher and lower levels followed a pattern indicating time: Those lower down should have a greater proportion fossilized than those higher up. What they found was that the upper (Recent) and lower (Sandia) layers were statistically indistinguishable from one another on the degree of fossilization. That suggests that mixing between the two layers had occurred.

The latter question they examined mostly taphonomically in terms of species and element distribution and modifications to individual bones that would indicate human or animal agency. This is what they found:
It is likely that larger carnivores were the main accumulators of the large mammals, although these fragments may have been later modified by small carnivores in the role of scavengers. Large carnivores identified from the Sandia Cave assemblage include the gray wolf (Canis lupus), a bear (Ursus sp.), and the mountain lion (Puma concolor). Small carnivores include the gray fox (Urocyon cinereoargenteus), ringtail (Bassariscus astutus), ermine (Mustela erminea), spotted skunk (Spilogale putorius), and bobcat (Lynx rufus). . .

Only two percent of the [small mammal] assemblage displays possible traces of human modification, and none were determined to be of high confidence. Those that were identified as possible cut or percussion marks could easily be cut mark mimics from trampling or very tiny rodent gnaw marks. In the instance that some marks were the result of human activity, the proportion is small enough to rule out humans asa major accumulator of the small mammals at the site.

Hence, little evidence that humans had modified the material. In general they conclude:

On the whole, most of the fossil fauna, including extinct species, were accumulated by carnivores and deposited in the cave when it was in a nutritive state. In doing so, they left large quantities of tooth marks and gastrically etched fragments, and also consumed most of the spongy bone present in long bone ends and axial elements. Resident rodents then further modified the bones by gnawing. There are some infrequent traces of human involvement with the fauna, including two bone tools. However, no human modification was discovered on any fragments that could be positively identified as an extinct or extralimital species.

Plus some judos kudos for the original excavators:
Although Hibben's recovery techniques were not gentle, they were relatively thorough for his time. Similarly, the majority of the fauna lacked precise provenience information but a thorough taphonomic analysis was still possible and extremely fruitful. Despite any previous controversies, the fossil assemblage from Sandia Cave remains an important paleontological sample with a small archaeological component that has been recovered with sufficient diligence to make it amenable to modern analyses. Apart from the findings of the study that are specific to Sandia Cave, it also demonstrates that there may be many old, forgotten faunal assemblages that could benefit from being revisited with modern techniques.

It seems unlikely that humans played a major role, if any, in the Pleistocene assemblages on Sandia. The iffy stratigraphy, evidence of bioturbation, and lack of any conclusive taphonomic evidence attributable to humans in the lower levels strongly suggests that the controversy surrounding the site was well-founded. Nevertheless, this paper shows what can be done with material collected even decades ago and demonstrates once again the importance of proper attention being paid to long-term preservation of excavated materials, both the objects themselves and the documentation associated with them.

UPDATE: Rather humorous typo above fixed.