Only a few days ago a very thorough paper concerning cut-marked bones and primitive stone-tools was published by the open-access journal Frontiers in Ecology and Evolution. The title was most provocative: Human Occupation of the North American Colorado Plateau ∼37,000 Years Ago. The Rowe et al. (2022) paper looks at an open-air site in northern New Mexico about 130km, almost due north of Albuquerque (GPS co-ordinates 36.24555, -106.53289).
Here’s the abstract:
Calibrating human population dispersals across Earth’s surface is fundamental to assessing rates and timing of anthropogenic impacts and distinguishing ecological phenomena influenced by humans from those that were not. Here, we describe the Hartley mammoth locality, which dates to 38,900–36,250 cal BP by AMS 14C analysis of hydroxyproline from bone collagen. We accept the standard view that elaborate stone technology of the Eurasian Upper Paleolithic was introduced into the Americas by arrival of the Native American clade 16,000 cal BP. It follows that if older cultural sites exist in the Americas, they might only be diagnosed using nuanced taphonomic approaches.
We employed computed tomography (CT and μCT) and other state-of-the-art methods that had not previously been applied to investigating ancient American sites. This revealed multiple lines of taphonomic evidence suggesting that two mammoths were butchered using expedient lithic and bone technology, along with evidence diagnostic of controlled (domestic) fire. That this may be an ancient cultural site is corroborated by independent genetic evidence of two founding populations for humans in the Americas, which has already raised the possibility of a dispersal into the Americas by people of East Asian ancestry that preceded the Native American clade by millennia. The Hartley mammoth locality thus provides a new deep point of chronologic reference for occupation of the Americas and the attainment by humans of a near-global distribution.
Rowe et al. (2022), fig. 3 – recovered skeletal elements of the adult mammoth.
The results can be summarised as follows:
1. The AMS C14 date obtained on the individual amino acid, hydroxyproline, gave a date range of 38,900 – 36,250 cal BP, or ca. 37,000BP.
2. In their site description, the authors say: “Although extensively broken, the mammoth bones exhibit little evidence of weathering or hydrologic transport abrasion, and modest root etching. None of the bones exhibits tooth marks or other evidence of carnivore scavenging.. We considered scavenging, trampling, and other non-anthropogenic agents
in our assessment of site formation processes, but the likelihood is exceedingly small that these can account for the thorough, intensive, systematic and highly patterned bone breakage, or the stacking of the bone assemblage..”
3. There were two partial mammoth skeletons at the site, an adult and a calf. The main bone assemblage (95% of which was from the adult), occupied an area of 1.5m x 1.5m with a depth of 1.0m. On top of this ‘pile’ was a 23.7kg boulder, which the authors interpret as a hammerstone and/or anvil. Also within the were numerous, locally sourced, rounded, sandstone, cobbles, weighing up to 3kg. This arrangement of bones is not a position that an animal could have gotten into during a natural death. Given that no indicators of fluvial action was were found on the assemblage, human action is almost certainly the cause of the bone pile.
4. Every bone displayed perimortem damage, save the adult right stylohyoid, which lay near the excavation floor. Two adult vertebral epiphyses remained in articulation with each other but were separated from their parent centra. Presumably, they were held together by an intact joint capsule at time of burial, one of many indications that burial was rapid.
5. The humans who butchered this adult mammoth, seem to have used a set method to dismember it and obtain useful substances, such as meat, brain tissue and oil from the carcass. The authors give several descriptions of bone breakage which can be interpreted as steps in the utilization process: “On every proximal rib fragment (n = 23), the capitulum is damaged, exposing medullary cavities to sediment infilling. Six proximal rib heads (26%) display circular punctures or gouges measuring about 1 cm in diameter. Ten ribs (40%) have small-diameter isolated punctures near their heads and on their shafts. Fifteen ribs (60%) preserve blunt-force impact fractures, and seventeen rib shafts (68%) are spirally fractured, indicating they were fresh when fractured. Short, broad, parallel chopmarks on one rib are consistent with expedient tools. This damage suggests systematic rib detachment from the vertebral column, costal cartilages, sternum, and from each other using cylindrical rods and expedient cutting and chopping tools. Similar highly patterned carcass processing sequences have been described that may vary among taxa, but are largely standardized within a given taxon, and trace into the Old World Lower Palaeolithic.”
6. Unusually, the authors used CT scanning to see how the butchering was extended to break down/process individual body elements to extract the maximum amount of resources. For example, the ancient hominins punctured several centra (a centrum is the main, weight-supporting body of a vertebra) and apparently rotated the tool within the body of the bone to release oil.
Also included was an examination of bone flakes. The grain orientation of these elements showed a remarkable consistency, with 78% being struck either parallel to grain of the parent bone or perpendicular to it. This pattern has never been observed in any other bone assemblage. Furthermore, the authors comment: “The phalanges exhibit numerous small-diameter perimortem punctures that subsequently filled with sediment. Whereas carnivore canine penetrations are widest externally, tapering internally to a point, CT scans show these punctures are narrowest externally and broaden into wider chambers, suggesting insertion and rotation of a pointed tool that disrupted trabeculae, facilitating extraction of grease from cancellous bone interiors. The punctures probably occurred in conjunction with efforts to disarticulate grease-rich podial elements and retrieve pedal fat pads.
So called ‘butterfly flakes’, were also studied. These are flakes of bone spalled from diaphysis (the central portion) of a long bone, and result from medium to high velocity impact to a limb diaphysis or rib. They can come from the same, or opposite side of the bone as the impact. They result of tensile loading and consequent failure of the bone. The authors comment: “With rare exceptions, only humans are known to establish conditions in which limbs and ribs can break under tensile failure, producing these highly characteristic fragments.”
In their penultimate, line of evidence, the authors studied arrested fractures within the bones, within the bones using CT/μCT. They carried out comparative experiments using fresh bovid bone: “μCT shows fresh bone placed under static loads (trampling, scavenging, hide penetration) fails in relatively simple fractures.. However, under dynamic percussion-impact point-loading, where both force and loading rates are sufficiently high, CT revealed that a “fracture network” can propagate instantaneously into bone from the impact point, but only one or a few of the fractures rupture and separate flakes from parent bone. If all fractures in a network continued to the point of complete separation, the result would be a larger number of loose fragments, and CT scans of the entire assemblage would show no evidence of the process that generated them. CT reveals that this is not what happens.” In other words their results prove that detailed consideration of how arrested fractures form, rules out their formation due to static loading, and shows that, within the Hartley bone assemblage, they were caused by bone processing by man. In their supplementary materials, they add: “This simple demonstration showed that manually delivered percussion impacts produce sufficient point-forces to generate instantaneous, complex fracture networks, including arrested fractures, as flakes are knapped from dense cortical bone.”
Lastly, the authors considered the ‘bone scraps’ obtained from the excavated matrix, containing the bones, by dry-screening. The authors report: “‘bone scraps’.. were derived from cranial diplöe and postcranial medullary bone. Similar “bone scrap” concentrations are reported in European sites. Hydrologic processes operating at the site fail to account for this extreme degree of fragmentation. However, crushing and boiling medullary bone is a common practice in grease procurement that produces such “bone scraps” as primary debris. While crushing may not increase the grease volume harvested, it increases efficiency because the smaller fragments require less water and fire.”
Rowe et al. (2022). Site, excavated area and geology. Original caption reads: “Figure 1. Hartley mammoth excavation. (A,B) Uppermost part of main bone accumulation. (C) Diagram of bone-bearing sediment wedge (not to scale). (D) Schematic of Toreva block landslides. (E) Cross-section of Rio Puerco canyon. C, sandstone cobbles; R, rib; Tl, left tusk; Tr, right tusk; Fr, frontal; V, thoracic vertebra; white star, 23.7 kg hammerstone/anvil.
7. Next the authors carried out pyrogenic particle analysis. They state: “Wet-screened (0.5 mm mesh) matrix samples from different vertical levels within the main bone accumulation yielded a diverse assemblage of micro-particles that are not eroded constituents of the escarpment supplying clastic particles to the colluvium. Microscopic examination of particles excavated from Old World hearths, in concert with combustion experiments, identified diagnostic residues of controlled fires fuelled by burning wood, plant material, and bone. These particles include siliceous aggregates, subspherical complex aggregates of recrystallized ash, pulverized bone fragments, angular shattered tooth and bone fragments, vitrified plant fragments, and charcoal fragments.” This shows that ancient humans, while at the site were, also using fire to process the bones. Furthermore, they comment: “At the Hartley site, the concentrated biodiversity and different burning states of pulverized bone, fish scales and teeth, and mammal teeth also argue against natural wildfire. This assemblage is not characteristic of flash heating by lightning, where much higher temperatures ~18000C profoundly alter local mineralogy and offer no mechanism for faunal concentration. In summary, this assemblage most likely formed in a controlled fire associated with the mammoth butchering.”
8. Lithic evidence. The lithic evidence was scarce. Only six micro flakes of Pedernal chert were found between 40 and 65 cm deep. Pedernal chert is primarily sourced from San Pedro Mountain in the San Pedro–Sierra Nacimiento range, about 28km south west, of the site. However, recycled gravels of the same type occur throughout the Albuquerque basin. These are chemically indistinguishable from those of the primary deposit (see Murrell and Murrell, 2015 and Projectilepoints.net, 2022) . Therefore, the source for the micro flakes found at the Hartley site, remains uncertain. These were directly matrix surrounding the main bone assemblage. The authors comment: “μCT revealed diagnostic evidence of percussion flaking including prepared, ground percussion surfaces, bulbs of percussion, eraillure scarring, secondary flake scars with conchoidal separation surfaces, and hinge fractures.. Since surfaces can accumulate objects over time, and burrowing can mix sediment, it is conceivable that excavated chert microflakes are more recent surface contaminants. However, they were not found associated with burrows, and the fact that six were present favors their valid association with the mammoth bones.” While the authors do not state the source of the chert, it certainly it seems to have been transported, to the site, by man as part of his toolkit. I was a little surprised that the authors did not explore this topic more thoroughly and state their opinion as to whether there was chert of this sort on/near the site.
One of the microflakes from the Hartley mammoth site, from Rowe et al. (2022). Original caption reads: Figure 13. Chert microflake in three views. (A) Internal aspect; (B) Striking platform; (C) External aspect. Es, eraillure scar on bulb of percussion; Fs, secondary flake scar showing ripple marks; H, secondary flake scar hinge; Pb, bulb of percussion; Gpp, ground percussion platform.
Conclusion
The authors have done such a fine job on their paper, that I will leave them, the final conclusion, on the Hartley Mammoth site:
“The position of the Hartley site deep in the North American Western Interior suggests that the first human arrival in North America, whether overland or via a coastal route, occurred well before ~37,000 years ago. The Hartley site shares much in common with Old World proboscidean butchering sites; it appears that while hunting technologies evolved steadily, butchering practices preserved more stable procedural efficiencies. The Hartley locality exemplifies new methods and nuanced criteria for diagnosing early human occupation sites in the archaeological record. It raises provocative new questions about when, where, and how the Native American clade, with its unprecedented technology, intersected with earlier human occupants of the Americas. It also provides a new deep point of chronologic reference for occupation of the Americas, for attainment by humans of a global distribution, and a temporal recalibration of human ecological impacts across the Western Hemisphere.
References.
Murrell, M.L. and Murrell, J.B., (2015). Secondary Raw Material Sources of Pedernal Chert in the Albuquerque Basin, New Mexico. Kiva, 80(3-4), pp.221-249.
Projectilepoint.net (2022). Pedernal Chert (agate) AKA: Cerro Pedernal Agate/Chalcedony. At: https://www.projectilepoints.net/Materials/Pedernal%20Chert.html accessed 05/08/2022
Rowe, T.B., Stafford Jr, T.W., Fisher, D.C., Enghild, J.J., Quigg, J.M., Ketcham, R.A., Sagebiel, J.C., Hanna, R. and Colbert, M.W., (2022). Human Occupation of the North American Colorado Plateau∼ 37,000 Years Ago. Frontiers in Ecology and Evolution, p.534.
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