http://orcid.org/0000-0003-0579-8288
Figures
Abstract
Taphonomic analyses of bone-surface modifications can provide key insights into past biotic involvement with animal remains, as well as elucidate the context(s) of other biostratinomic (pre-burial) processes, diagenesis, excavation, preparation and storage. Such analyses, however, first require researchers to rigorously disambiguate between continuums of damage morphologies prior to attributing individual marks to specific actors and effectors (e.g., carnivore tooth, stone tool cutting edge, etc.). To date, a number of bone-modifying agents have been identified, and criteria for identifying their traces have been published. Relatively little research, however, has focused on bone-surface modifications imparted during specimen preparation. Herein we report that air scribes, small pneumatic tools commonly used for preparation in museum contexts, can generate unintentional marks that may mimic surficial modification caused by carnivores. To aid investigators in assessing the hypothesis that a mark in question is derived from air-scribe preparation activities, we provide high-resolution, detailed morphological information imaged with scanning electron microscopy (SEM). The main diagnostic characteristic of air-scribe damage is the occurrence of sequential, variously spaced, sub-millimeter scallop-like stepped bone removals. This morphology can resemble damage imparted by carnivore teeth. In contrast to marks produced by trampling, stone tools and carnivores, however, no continuous internal features, such as linear microstriations, were observed within grooves produced by the air scribe. Thus, the presence of such features can be used to disprove an air-scribe origin. A culmination of the morphological criteria presented herein, cross-cutting relationships with other surficial features (e.g., diagenetic discoloration, weathering textures), the position of occurrence, and an overall contextual framework for the assemblage is suggested for accurate identification of such traces. The ability to recognize or disprove air-scribe damage will allow researchers to confidently proceed with interpreting past biological and sedimentological interactions with animal remains.
Citation: Wiest LA, Ferraro JV, Binetti KM, Forman SL, Esker DA, Kibunjia M, et al. (2018) Morphological characteristics of preparator air-scribe marks: Implications for taphonomic research. PLoS ONE 13(12): e0209330. https://doi.org/10.1371/journal.pone.0209330
Editor: Cyril Charles, Ecole Normale Supérieure de Lyon, FRANCE
Received: May 8, 2018; Accepted: December 4, 2018; Published: December 20, 2018
Copyright: © 2018 Wiest et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper.
Funding: Funding for this project was provided by a Baylor University graduate research grant (GRG-typeR-#2) awarded to LAW, and a National Science Foundation grants BCS-1524036 and BCS-1524041 awarded to JVF and KMB. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Taphonomic analyses of bone-surface modifications can provide key insights into past biotic involvement with animal remains [1–12]. Such studies have proven invaluable in elucidating the diets and paleoecologies of insects, dinosaurs, mammalian carnivores, and Paleolithic hominins, among others [13–24]. These analyses, however, first require researchers to rigorously disambiguate between continuums of damage morphologies prior to attributing individual marks to specific agents and effectors (e.g., carnivore tooth, stone tool cutting edge, etc.). The recent discovery that crocodiles can produce linear damage morphologies that may mimic stone-tool marks highlights how descriptions and explanations of previously unexplored bone-surface modifications can dramatically alter interpretations of ancient assemblages [5, 6, 12, 24, 25].
In recent years, an increasing number of bone-modifying agents have been identified, and criteria for identifying their marks have been published ([26] and refs therein; [27]). Most of these studies focus on biostratinomic (pre-burial) agents. However, the taphonomic history of a bone or fossil (hereafter, bone) spans from the death of the animal until the present day [27–29]. Taphonomic analyses typically occur after bones have been excavated, cleaned, and archived. Relatively little research has focused on bone-surface modifications imparted during this latter portion of the taphonomic record (though see [27] and references therein). This is potentially problematic because excavation and preparation activities can create additional marks on bone surfaces [30, 31]. In some instances, identifying this modern damage is relatively straightforward. Such is the case when cross-cutting relationships can be applied in relation to other taphonomic or diagenetic features preserved on the bone (e.g., staining, root etching, weathering texture) to deduce the relative timing of the trace (i.e., bone-surface mark) generation [32–34]. Other occurrences, especially subtle and/or isolated traces, require further analysis prior to inferring agency, effector, and timing [27, 30].
In this paper we investigate bone-surface modifications experimentally imparted by an air scribe, a small pneumatic tool commonly used in museum contexts. These hand-held tools utilize compressed air in conjunction with an internal piston to drive a carbide stylus in a high-frequency, reciprocating movement [35]. This action is then applied by the operator to dislodge adhering matrix during preparation. Despite the widespread use of air scribes and obvious potential for imparting traces on specimens, diagnostic criteria for identifying air-scribe damage is currently absent from the paleontological, ichnological, archaeological, and taphonomic literatures. The aim of the present study is to provide morphological information to aid investigators in assessing the hypothesis that a bone-surface feature in question was derived from air-scribe preparation.
Materials and methods
The experimental air-scribe-induced features were generated by a Chicago Pneumatic Air Scribe (CP9361) with an approximately 0.5 mm wide, pointed carbide tip (see [35]) on 26 non-diagnostic Pleistocene chelonian carapace fragments and mammalian bone remains from the Chalbi Basin, northern Kenya, which were exported for destructive geochemical analyses [36, 37]. All specimens possessed well-preserved cortical-bone surfaces. A variety of reasonable transverse speeds, approach angles, and downward pressures were applied to the air scribe by a single operator with the objective of introducing a morphologically diverse range of markings. Each fragment was modified by the air scribe multiple times (typically n > 10). Specimen hardness is between 4 and 5 on the Mohs hardness scale as determined by scratching the fossils with select minerals of known hardness.
The carnivore-induced modifications analyzed in this study were generated by providing 10 feral pig (Sus scrofa) and domestic bovine (Bos taurus) long bones to domestic canines (Canis lupus familiaris). The resulting bone-surface modifications ranged from a few isolated occurrences to an abundance of overlapping traces. Fresh bone hardness is determined to be between 3 and 4 on Mohs hardness scale.
Experimental lithic-tool-induced marks were generated using basalt flakes, hammerstones, and anvils during ongoing butchery experiments with domestic goats (Capra aegagrus hircus). A total of 21 modified long bone fragments were analyzed in this study. Specimens are between 3 and 4 on Mohs hardness scale.
The museum specimen depicted in Fig 1A–1C contains unintentionally produced air-scribe damage on a bone fragment (ca. 2.4 My; Sample LA91-S43#020) recovered from the Lokalalei 1 archaeological site, West Turkana, Kenya, and is housed in the National Museums of Kenya [38].
Sample was recovered from the Lokalalei 1 archaeological site, West Turkana, Kenya, and contains unintentionally induced markings from air-scribe preparation techniques. A) scale bar = 1.0 cm; B, C) scale bars = 1.0 mm. Notice the similarities between these marks and the carnivore-induced tooth scores in Fig 1D and E. D) Carnivore-induced tooth scores and pits on a bovid long bone (Sample 4–2) under a stereomicroscope; scale bar = 1.0 cm. E) Close-up of area highlighted in D; scale bar = 1.0 mm.
Macroscopic bone surface modifications were examined and imaged under low-angle, polarized-LED illumination with limited background light. Visual inspection was conducted with the extended depth of field (EDOF) setting on a Dino-Lite Edge digital microscope (AM7915 Series) with DinoCapture 2.0 software (v. 1.5.26.C), and a stereo-microscope (SZX16, Olympus Corp., Tokyo, Japan). Scanning Electron Microscopy (SEM) images were taken of uncoated samples at low vacuum conditions either with a FEI Versa 3D scanning electron microscope (FEI, Hillsboro, OR, USA) or a Hitachi TM3030 Plus tabletop scanning electron microscope (Hitachi, Tokyo, Japan). All micrographs were taken with 15kV and at ~10mm working distance at the Center for Microscopy and Imaging at Baylor University (Waco, Texas, U.S.A).
Results
Air-scribe marks
The experimental air-scribe marks are categorized in two classes: grooves (Figs 1A and 2: right column) and pits (Fig 3: right column; see [39] for definitions of general morphological terms). Air-scribe pits vary in diameter and depth (~ mm scale), which is dependent on the pressure and duration of the application of the chisel tip to the material. The pits share a common, ‘rosette’-like morphology despite the amount or duration of applied pressure by the operator. This rosette appearance is caused by the repetitive removal of arcuate flakes that leave behind sub-millimeter scallops (Fig 3B and 3D). The individual scallops often have a flat base that cleaves along cortical lamellae boundaries. Scallops toward the center of the pit penetrate deeper bone layers, generating a crater-like overall morphology with a rosette-like crater wall (Fig 3B and 3D).
Insets are interpretive drawings of highlighted areas. A) Segment of a smooth tooth score with relatively smooth margins and faint, internal grooves exhibiting continuity on a bovid long bone; scale bar = 0.5 mm. B) Segment of a transition within an air-scribe groove from a chatter-like morphology (upper half) into a smooth-based groove on a fossilized bone fragment; scale bar = 1.0 mm; Notice the rougher margins in comparison to A. C) Shallow tooth score with chatter marks, a smooth left margin, and an irregular right margin on a bovid long bone; scale bar = 1.0 mm. D) shallow (lower left) and deep (top to bottom) air-scribe grooves on a fossilized bone fragment; scale bar = 1.0 mm. Notice the similarities between the chatter morphology of the lower-left mark and the scores depicted in C and E. Also note the relatively rougher margins. E) Tooth score with pronounced chatter markings and a long-axis-parallel, smooth left shoulder with through-going continuity on a bovid long bone; scale bar = 1.0 mm. F) sinuous air-scribe groove with faint chatter marks, rough margins, and an absence of through-going continuity on a fragment of a chelonian carapace; scale bar = 1.0 mm.
Notice the rosette-like morphology of the pits depicted on the right. A) Shallow tooth pit with associated microgrooves (faint score) on a bovid long bone; scale bar = 1.0 mm. B) Shallow pit generated by an air-scribe on a fossilized mammalian bone fragment. Notice the sequential, stepwise scalloping that creates flat benches on the various layers of cortical lamellae; scale bar = 1.0 mm. C) tooth pit with raised margins on the left and right sides; scale bar = 1.0 mm. D) Somewhat deeper air-scribe-induced pit (relative to B) on a mammalian fragment; scale bar = 1.0 mm. Inset is interpretive drawing of highlighted area.
Air-scribe grooves, similar to the air-scribe pits, also contain rough outer margins composed of variably-shaped, sub-millimeter, negative flake scars that result from the high-frequency reciprocating impacts of the bit (Fig 2B, 2D and 2F). The gross morphology of the grooves (e.g., depth, sinuosity, etc.) varies dependent on the pressure and direction applied by the operator and is undiagnostic. The basal floor of the grooves varies from smooth (Fig 2B) to scalloped and rough (Fig 2D). ‘Chatter-marked’ refers to the sequential arcuate ridges that are perpendicular to the long axis of the groove. Small-scale features that exhibit linear continuity (e.g., shouldering, microgrooves, etc.) within or associated with the air-scribe grooves were not observed for the samples despite the amount or duration of applied pressure by the operator.
Comparison to linear marks made by carnivore teeth.
Scores made by carnivore teeth (linear grooves) and air-scribe grooves overlap in size (~ 1–2 mm) and depth (typically < 1 mm; Fig 1B). Traces produced by either mechanism can have a smooth internal floor (Fig 2A and 2B), or a rough base with fine ridges perpendicular to the long axis (Fig 2C–2F). Unlike the marks produced by carnivores, grooves produced by an air scribe have a sequential scalloping/cratering effect that generates an irregular outer margin (Fig 2B, 2D and 2F). Air-scribe-induced damage does not exhibit any features that are continuous across the series of scallops, such as microgrooves, microstriations, or raised shoulders (cf. Fig 2A and 2E; [34]).
Comparison to pits made by carnivore teeth.
Pit-like features created by air scribes overlap in gross morphology and size with pits generated by carnivore teeth (Fig 3). Both exhibit a sub-circular shape with rough outer margins (Fig 3, cf. left and right columns; [40, 41]), and both can crosscut multiple layers of cortical lamellae and result in the removal of surficial cortical bone (Fig 3). Pits generated by air scribes have a ‘rosette’-like morphology that is generated as a series of steps that increase in depth toward the center of the trace (Fig 3B and 3D). Pits generated by carnivore teeth, on the other hand, do not exhibit the rosette morphology or sequential scalloping, but instead, are more irregularly shaped and have a crushed and flattened base (Fig 3A and 3C; [26]). Tooth pits in this study also have a relatively less-steep sidewall, and occasionally exhibit a raised margin (Fig 3C), whereas the air-scribe marks are typically steeper-walled and do not possess raised, shoulder-like margins (Fig 3B and 3D).
Comparison to lithic cut marks and sedimentary abrasion.
The air-scribe grooves are distinct from cut marks produced by lithic technology [14, 42, 43]. Specifically, microstriations and/or associated scratches were not observed with any of the traces produced by the air scribe [42, 26]. The sequential, arcuate scallops, which are ubiquitous with the air-scribe marks, are not observed in the linear lithic marks. Air-scribe damage also has a relatively rougher outer margin, which lacks any raised shoulders (Fig 2B, 2D and 2F).
Likewise, air-scribe grooves are distinct from sedimentary abrasion. Striations caused by trampling are generally fine and shallow, regardless of the particle size of the substrate, and can create a polish on the bone surface [43]. Whereas air-scribe grooves can also be shallow, they are relatively wide in comparison to sedimentary abrasion (Fig 4B). Furthermore, surficial polish was not observed with the experimental air-scribe damage. Chatter marks, such as those depicted in Fig 1, were not observed in sedimentary abrasion marks produced by experimental trampling [43].
A) Percussion pit; notice the roughness and cracking that is not apparent on the air-scribe damage depicted in Fig 3B and 3D; scale bar = 2 mm. B) Irregularly shaped percussion pit with abundant (vertically oriented) microstriations; scale bar = 2 mm. C) Percussion pit with associated microstriations and fine-scale fractures; scale bar = 1 mm. D) Multiple, cross-cutting cut marks with internal microstriations and smooth margins; scale bar = 2 mm.
Comparison to lithic percussion pits.
The gross size and shape of air-scribe pits can somewhat resemble hammerstone percussion pits (compare Figs 3B and 4C), but the latter differ from air-scribe pits and grooves by having internal and associated microstriae, which are not observed in air-scribe marks (Fig 4; [2]). In addition, sequential, arcuate scallops are unique to the air-scribe marks and are not observed in percussion pits.
Discussion
Morphological descriptions of air-scribe marks provide researchers with a means to potentially identify or falsify post-excavation damage that confounds bone-surface modification studies. This has several important implications, as well as raises several questions.
Explanatory mechanisms
Morphological differences between air-scribe-induced marks and alternative forms of bone modification can be attributed to the different mechanics responsible for the removal of material. Namely, carnivore teeth and non-mechanical tools, with the exception of percussion, introduce a relatively slow, static load to the bone surface. Alternatively, the high-frequency reciprocating impacts of the air-scribe bit cause repetitive dynamic loading. Static vs. dynamic loading dictates the shape of the expelled particles (flakes), and thus influences the morphology of the resulting trace [44].
SEM
The key criteria for differentiating air-scribe marks (e.g., small-scale scallops, rough outer edge, etc.) may be observed with a hand lens (10x) or low-power microscopy (~10-40x), and identification does not necessarily require SEM. However, the SEM yields an effective method for imaging specifically the morphology of these traces [45–47]. Glares, color variations, and limited depths of focus, which can introduce artifacts to the images, are the main limitations when light microscopy is utilized. These complications were eliminated when SEM was used to evaluate the ultrastructure of air-scribe damage on bones. Furthermore, modern SEMs do not require coating of non-conductive samples, such as bones, with a fine layer of conductive metal (e.g. iridium, gold, palladium) or carbon, which can induce artifacts as well [48, 49]. In low vacuum/variable pressure mode, as applied in this study, non-conductive samples, such as bones, can be imaged in the SEM in their native state [50–53]. However, the SEM does have limitations. The vacuum chambers of the SEMs have a finite size and limit the size of the sample that can be observed. Of the two SEMs used, the FEI Versa 3D SEM has the largest vacuum chamber and is capable of imaging bone fragments up to approximately 20 cm in length. The Hitachi TM3030 Plus tabletop SEM is limited to samples < 10 cm in length, in which case microscopy needs to be focused on the center region of the sample. Cutting the sample can circumvent SEM-based sample length limitations for studies if sample modification is acceptable. Often cutting the sample is ill advised or not practical for rare finds, in which case making a mold of the structure in question could allow one to still utilize an SEM approach [54].
Comparison with damage from other tools
Table 1 provides a list of observed characteristics for comparing air-scribe damage with marks produced by various other tools used in excavation and preparation; adapted from [27]. Based on these characteristics, the air-scribe damage is most similar to marks produced by a screwdriver and an awl but exhibits several important differences (Table 1). The screwdriver and awl both produce microstriations during a friction-inducing movement, whereas air-scribe damage does not produce microstriations. Screwdrivers and awls do not produce internal flakes during an impact movement, whereas the air scribe does. The latter is attributed to the high-frequency reciprocating movement that is unique to the air scribe. The air scribe is also distinct from the other tools listed in Table 1 in the sense that both friction and impact motions of the air scribe do not produce different characteristics beyond the gross morphology (e.g., pits versus grooves).
I = Impact; F = Friction; L = Linear; S = Sub-rounded; X = present; - = absent.
Analytical issues
Differences in fossilization and preservation that affect the physical properties of a bone can potentially influence the morphology of the resulting trace. The experimental carnivore-induced and lithic-tool-induced traces were generated on fresh bone containing collagen (Figs 1B and 4, respectively), whereas the unintentional and experimental air-scribe marks (Figs 1A and 2: right columns, and 3: right column) were produced on fully fossilized material. This difference in preservation inherently influences the physical properties of the material (e.g. hardness, texture, density), which may alter bone breakage on the macroscopic and microscopic scales [55]. This issue should not confound the results of this study, however, because damage inflicted to fresh bone will fossilize with those same morphological properties. Furthermore, tooth marks would not be produced on fossils and thus the comparison is not problematic.
Ideally, color observations can be used in bone modification analysis for assessing when the trace in question was generated relative to burial and/or fossilization. In many cases cross-cutting relationships with color heterogeneities provide insight into the relative timing for the origin of the trace, which then can be used to infer if the damage is recent, for instance from preparation or excavation [56, 57]. However, in many assemblages the outer and inner cortical-bone coloration is not different (e.g., bonebeds containing fossilized or unfossilized material that is mostly white). Under such a scenario, cross-cutting relationships with color variations do not occur [58]. Thus, the detailed morphology of the structure remains the most reliable criterion to infer if the trace in question is post-discovery or related to bioerosion.
The experimental air-scribe marks described herein were generated by a single device used by a single operator. Other chisel tips and/or types of scribes may introduce a host of slightly different morphologies. Further research is needed to elucidate the range of possible air scribe damage induced by variously shaped scribe tips and on fossils with various properties.
Conclusions
There are morphological differences between the traces generated by air scribes, other commonly used excavation and preparation tools, and biostratinomic agents of bone-surface modification such as carnivores. Sequential, sub-millimeter scallops/craters are unique to the reciprocating impacts of the air scribe. Conversely, the presence of linearly continuous sub-features (i.e., internal grooves, shoulders, microstriations), which are often observed in marks produced by carnivore modification, trampling, or some tools, can be used to falsify the hypothesis that a trace in question was generated by an air scribe. A combination of the morphological criteria presented herein, cross-cutting relationships with other surficial features (e.g., diagenetic discoloration, weathering textures), the distribution of the modification, and an overall contextual framework for the assemblage is suggested for the interpretation of such traces. The ability to recognize or disprove air-scribe preparation damage will allow researchers to confidently proceed with interpreting past biological and sedimentological interactions with animal remains.
Acknowledgments
We thank Steve Driese, Bill Hockaday, Stacy Atchley, and Dan Peppe for providing comments and feedback on an earlier version of this manuscript. We also thank Steve Jabo and an anonymous reviewer for providing useful suggestions for improvement. This work was supported by the National Science Foundation (BCS-1524036 and BCS-1524041) and the Department of Geosciences at Baylor University. The fossil material presented in this study was obtained under permit NACOSTI/P16/44101/11266.
References
- 1. Bunn H.T., 1981. Archaeological evidence for meat-eating by Plio-Pleistocene hominids from Koobi Fora and Olduvai Gorge. Nature, 291(5816), p.574.
- 2. Blumenschine R.J. and Selvaggio M.M., 1988. Percussion marks on bone surfaces as a new diagnostic of hominid behaviour. Nature, 333(6175), p.763
- 3. Cutler A.H., Behrensmeyer A.K., and Chapman R.E., 1999, Environmental information in a recent bone assemblage: Roles of taphonomic processes and ecological change: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 149, p. 359–372.
- 4.
Hasiotis S.T., Fiorillo A.R., and Hanna R., 1999, Preliminary report on borings in Jurassic dinosaur bones: Evidence for invertebrate-vertebrate interactions. In Gillette D.D. (ed.), Vertebrate Paleontology in Utah: Utah Geological Survey; Miscellaneous Publication 99–1, p. 193–200.
- 5. Njau J.K. and Blumenschine R.J., 2006. A diagnosis of crocodile feeding traces on larger mammal bone, with fossil examples from the Plio-Pleistocene Olduvai Basin, Tanzania. Journal of Human Evolution, 50(2), pp.142–162. pmid:16263152
- 6.
Njau, J.K., 2006. The relevance of crocodiles to Oldowan hominin paleoecology at Olduvai Gorge, Tanzania. PhD dissertation (Rutgers, The State Univ of New Jersey, New Brunswick, NJ), 325 p.
- 7.
West, D.L. and Hasiotis, S.T., 2007. Trace fossils in an archaeological context: examples from bison skeletons, Texas, USA. In Trace Fossils (pp. 545–561).
- 8. Britt B.B., Scheetz R.D., and Dangerfield A., 2008, A suite of dermestid beetle traces on dinosaur bone from the Upper Jurassic Morrison Formation, Wyoming, U.S.A: Ichnos, v. 15, p. 59–71.
- 9. Domínguez-Rodrigo M., Pickering T.R. and Bunn H.T., 2010. Configurational approach to identifying the earliest hominin butchers. Proceedings of the National Academy of Sciences, 107(49), pp.20929–20934.
- 10. Ferraro J.V., Plummer T.W., Pobiner B.L., Oliver J.S., Bishop L.C., Braun D.R., et al., 2013. Earliest archaeological evidence of persistent hominin carnivory. Plos One, 8(4), p.e62174. pmid:23637995
- 11. Wiest L.A., Esker D., and Driese S.G., 2016, The Waco Mammoth National Monument may represent a diminished watering-hole scenario based on preliminary evidence of post-mortem scavenging. Palaios, 31(12), pp.592–606.
- 12. Sahle Y., El Zaatari S. and White T.D., 2017. Hominid butchers and biting crocodiles in the African Plio–Pleistocene. Proceedings of the National Academy of Sciences, 114(50), pp.13164–13169.
- 13. Haynes G., 1980, Evidence of carnivore gnawing on Pleistocene and recent mammalian bones: Paleobiology, v. 6, p. 341–351.
- 14. Potts R. and Shipman P., 1981. Cutmarks made by stone tools on bones from Olduvai Gorge, Tanzania. Nature, 291(5816), p.577.
- 15. Martin L.D., and West L.D., 1995, The recognition and use of dermestid (Insecta, Coleoptera) pupation chambers in paleoecology: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 113, p. 303–310.
- 16. Laudet F., and Antoine P., 2004, Dermestidae (Insecta: Coleoptera) pupal chambers from a Tertiary mammal bone (phosphorites of Quercy): Taphonomic and palaeoenvironmental implications: Geobios, v. 37, p. 376–381.
- 17. Mikuláš R., Kadlecova E., Fejfar O., and Dvořak Z., 2006, Three new ichnogenera of biting and gnawing traces on reptilian and mammalian bones: A case study from the Miocene of the Czech Republic: Ichnos, v. 13, p. 1–15.
- 18. Blumenschine R.J., Prassack K.A., Kreger C.D. and Pante M.C., 2007. Carnivore tooth-marks, microbial bioerosion, and the invalidation of Domínguez-Rodrigo and Barba’s (2006) test of Oldowan hominin scavenging behavior. Journal of Human Evolution, 53(4), pp.420–426. pmid:17727916
- 19. Domínguez-Solera S.D. and Domínguez-Rodrigo M., 2009. A taphonomic study of bone modification and of tooth-mark patterns on long limb bone portions by suids. International Journal of Osteoarchaeology, 19(3), pp.345–363.
- 20. Longrich N.R., and Ryan M.J., 2010, Mammalian tooth marks on the bones of dinosaurs and other Late Cretaceous vertebrates: Paleontology, v. 53, p. 703–709.
- 21. Blackwell L.R., Parkinson A.H., Roberts E.M., D’errico F., and Huchet J., 2012, Criteria for identifying bone modification by termites in the fossil record: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 338, p. 72–87.
- 22. Pante M.C., Blumenschine R.J., Capaldo S.D. and Scott R.S., 2012. Validation of bone surface modification models for inferring fossil hominin and carnivore feeding interactions, with reapplication to FLK 22, Olduvai Gorge, Tanzania. Journal of human evolution, 63(2), pp.395–407. pmid:22192864
- 23. Malassé A.D., Moigne A.M., Singh M., Calligaro T., Karir B., Gaillard C., et al., 2016. Intentional cut marks on bovid from the Quranwala zone, 2.6 Ma, Siwalik Frontal Range, northwestern India. Comptes Rendus Palevol, 15(3–4), pp.317–339.
- 24.
Njau, J. and Gilbert, H., 2016. Standardizing terms for crocodile-induced bite marks on bone surfaces in light of the frequent bone modification equifinality found to result from crocodile feeding behavior, stone tool modification, and trampling. FOROST Occasional Publications, No. 3, p. 1–13.
- 25. Lyman R.L., 2004. The concept of equifinality in taphonomy. J Taphonomy 2:15–26.
- 26.
Fernandez-Jalvo Y. and Andrews P., 2016. Atlas of taphonomic identifications: 1001+ images of fossil and recent mammal bone modification. Springer.
- 27. Marin-Monfort M.D., Suñer M. and Fernández-Jalvo Y., 2018. Characterization of recent marks produced on fossil bone surface during sullegic and trephic processes and their influence on taphonomic studies. Quaternary International, 481, pp.3–13.
- 28.
Clark J. and Kietzke K.K., 1967. Paleoecology of the lower nodular zone, Brule Formation, in the Big Badlands of South Dakota. Fieldiana: Geology Memoirs, 5, pp.111–137.
- 29. Ferraro J.V., Binetti K.M., Wiest L.A., Esker D., Baker L.E. and Forman S.L., 2018. Contesting early archaeology in California. Nature, 554(7691), p.E1. pmid:29420468
- 30. White T.D. and Toth N., 1989. Engis: preparation damage, not ancient cutmarks. American Journal of Physical Anthropology, 78(3), pp.361–367. pmid:2929740
- 31. James E.C. and Thompson J.C., 2015. On bad terms: Problems and solutions within zooarchaeological bone surface modification studies. Environmental Archaeology, 20(1), pp.89–103.
- 32. Behrensmeyer A.K., 1978. Taphonomic and ecologic information from bone weathering. Paleobiology, 4(2), pp.150–162.
- 33. Mikuláš R., 1999. Notes to the concept of plant trace fossils related to plant-generated sedimentary structures. Bulletin of the Czech Geological Survey, 74(1), pp.39–42.
- 34. Montalvo C.L., 2002. Root traces in fossil bones from the Huayquerian (Late Miocene) faunal assemblage of Telén, La Pampa, Argentina. Acta Geológica Hispánica, 37(1), pp.37–42.
- 35. Ratkevich R., 1998. Air Tool Preparation of Fossils. Rocks & Minerals, 73(6), pp.418–422.
- 36.
Ferraro, J., Binetti, K., Richmond, B., Braun, D. and F. Manthi. Early and Middle Pleistocene paleoanthropological discoveries in the Chalbi Basin, northern Kenya. Presented April 17, 2012, at the Annual Meeting of the Paleoanthropology Society, Memphis, Tennessee. Abstract at Paleoanthro.org.
- 37.
Ferraro, J., Binetti, K., Richmond, B. and F. Manthi. The Early Pleistocene mammalian fauna of ‘Marsabit Road’, Chalbi Basin, northern Kenya. Presented October 31, 2013 at the 73rd Annual Meeting of the Society of Vertebrate Paleontology, Los Angeles, California. Abstract published in a supplemental issue of the Journal of Vertebrate Paleontology.
- 38.
Brugal, J-P., Ferraro J., Kibunjia, M. and H. Roche. Paleoenvironment and subsistence at Lokalalei 1 (ca. 2.4 My, West Turkana, Kenya). Presented July 23, 2013, at the 4th Biannual Meeting of the Eastern Africa Quaternary Research Association (EAQUA), Nanyuki, Kenya.
- 39. Pirrone C.A., Buatois L.A., and Bromley R.G., 2014, Ichnotaxobases for bioerosion trace fossils in bones: Journal of Paleontology, v. 88, no. 1, p. 195–203.
- 40. Haynes G., 1983, A guide for differentiating mammalian carnivore taxa responsible for gnaw damage to herbivore limb bones: Paleobiology, v. 9, p. 164–172.
- 41. Haynes G., 1988, Mass deaths and serial predation: Comparative taphonomic studies of modern large-mammal deathsites: Journal of Archaeological Science, v. 15, p. 219–235.
- 42. Behrensmeyer A.K., Gordon K.D. and Yanagi G.T., 1986. Trampling as a cause of bone surface damage and pseudo-cutmarks. Nature, 319(6056), p.768.
- 43. Olsen S.L. and Shipman P., 1988. Surface modification on bone: trampling versus butchery. Journal of archaeological science, 15(5), pp.535–553.
- 44. Capaldo S.D. and Blumenschine R.J., 1994. A quantitative diagnosis of notches made by hammerstone percussion and carnivore gnawing on bovid long bones. American Antiquity, 59(4), pp.724–748.
- 45. Shipman P., 1981. Applications of scanning electron microscopy to taphonomic problems. Annals of the New York Academy of Sciences, 376(1), pp.357–385.
- 46. Bromage T.G., 1984. Interpretation of scanning electron microscopic images of abraded forming bone surfaces. American Journal of Physical Anthropology, 64(2), pp.161–178. pmid:6431824
- 47. Boyde A. and Jones S.J., 1996. Scanning electron microscopy of bone: instrument, specimen, and issues. Microscopy Research and Technique, 33(2), pp.92–120. pmid:8845522
- 48. Stokroos I., Kalicharan D., Van der Want J.J.L. and Jongebloed W.L., 1998. A comparative study of thin coatings of Au/Pd, Pt and Cr produced by magnetron sputtering for FE-SEM. Journal of Microscopy 189:79–89. pmid:21845775
- 49. Golding C.G., Lamboo L.L., Beniac D.R. and Booth T.F., 2016. The scanning electron microscope in microbiology and diagnosis of infectious disease. Scientific Reports 6: 26516. pmid:27212232
- 50. James B., 2009. Advances in “wet” electron microscopy techniques and their application to the study of food structure. Trends in Food Science & Technology 20:114–124.
- 51. Miyazaki H., Uozaki H., Tojo A., Hirashima S., Inaga S., Sakuma K., et al., 2012. Application of low-vacuum scanning electron microscopy for renal biopsy specimens. Pathology–Research and Practice 208:503–509.
- 52. Georgiadis M., Müller R., Schneider P. 2016. Techniques to assess bone ultrastructure organization: orientation and arrangement of mineralized collagen fibrils. Journal of the Royal Society Interface 13: 20160088. http://dx.doi.org/10.1098/rsif.2016.0088
- 53. Zechmann B., 2018. Beam deceleration improves image quality of butterfly wing scales in the scanning electron microscope. Texas Journal of Microscopy 49: 26–27.
- 54. Bader K.S., Hasiotis S.T. and Martin L.D., 2009. Application of forensic science techniques to trace fossils on dinosaur bones from a quarry in the Upper Jurassic Morrison Formation, northeastern Wyoming. Palaios, 24(3), pp.140–158.
- 55. Andrews P. and Fernandez-Jalvo Y., 1997. Surface modifications of the Sima de los Huesos fossil humans. Journal of Human Evolution, 33(2–3), pp.191–217. pmid:9300342
- 56. Wieberg D.A. and Wescott D.J., 2008. Estimating the timing of long bone fractures: correlation between the postmortem interval, bone moisture content, and blunt force trauma fracture characteristics. Journal of Forensic Sciences, 53(5), pp.1028–1034. pmid:18624891
- 57. Huculak M.A. and Rogers T.L., 2009. Reconstructing the sequence of events surrounding body disposition based on color staining of bone. Journal of Forensic Sciences, 54(5), pp.979–984. pmid:19549030
- 58.
O’Harra C.C., 1920. The White River Badlands (Vol. 13). South Dakota.