Digital imaging of bone and tooth modification

Authors


Abstract

Digital cameras are capable of producing images of cut marks and other three dimensional subjects comparable to those obtained from the scanning electron microscope (SEM). Until now, the SEM has offered unparalleled depth of field and surface rendition. SEM units are, however, expensive to acquire and maintain, and SEM image production is time-intensive. Furthermore, SEM images lack color and are often incapable of imaging bone modifications because of magnification and chamber size limitations. A digital imaging method for producing extremely high depth of field enlargements of three dimensional, sub-millimeter scale objects circumvents these problems. In our presentation we employ four case studies of hard tissue modification related to: (1) the origins of meat-eating in the human lineage; (2) evidence for cannibalistic behavior among Neanderthals; (3) pre-Columbian evidence of North American dentistry; and (4) the earliest evidence of cranial surgery in North America. Procedures for replica production, image-capture, and image enhancement are provided. The digital images produced are compared to those obtained with the SEM. Image processing software, a crucial component of this method, allows complete control of graphic data, making graphic fraud a larger threat than ever before. Issues in ethics stemming from the application of this technology to scientific analysis are considered. Anat Rec (New Anat) 261:237–246, 2000. © 2000 Wiley-Liss, Inc.

Time quickly erases most evidence related to prehistoric humans and our ancestors. Virtually all of the prehistoric biological record of evolution in our species is composed of fossilized bones and teeth. These structures are preserved because they have a significant inorganic mineral component and maintain structural integrity long after soft tissues succumb to the elements. Bone and tooth morphology are maintained by this inorganic matrix as the organic components are replaced by minerals. Evidence relating to the behavioral repertoire of hominids (humans and all of our lineage back to our common ancestor with the African apes) also comes from artifacts that preserve well: stone tools and modified bones. Only in rare exceptions is evidence of past behavior recorded in perishable material such as wood (Thieme, 1997), or in trace fossils, such as the famous Laetoli footprint trail (Leakey and Hay, 1979). This paucity of preserved behavioral data has constrained paleoanthropology—the study of our prehistoric ancestors—from its infancy, forcing physical anthropologists and archaeologists to closely scrutinize every recovered element for traces of activity.

Bone is capable of recording many activities: many processes leave marks on bone and alter bone assemblages.

BONE AS A RECORD OF BEHAVIOR

Bone is capable of recording many activities: many processes leave marks on bone and alter bone assemblages. The study of these constitutes part of taphonomy, a discipline that has advanced rapidly over the last forty years. Technically this term applies only to the study of postmortem processes, but in practice taphonomists study all aspects of bone and tooth modification, from activities that occurred during the life of an organism (like tooth drilling) to events that occur long after burial (like root etching). The techniques used are widely accepted, and methodological refinements now allow investigators to differentiate pre- or peri-mortem vs. postmortem damage to bone: rodent or carnivore gnawing, hyena digestion, animal trampling, acid etching by plant roots, weathering, cuts made with stone or metal tools, percussion scars associated with marrow extraction, or cooking, roasting, and boiling damage are clearly differentiated (reviewed in Lyman, 1987; White, 1992; summarized in Schick and Toth, 1993). This is possible because each of these activities leaves small-scale diagnostic features on bone. Although recent attempts have been made to quantify bone modifications (Steguweit and Mania, 2000), prevailing techniques are qualitative in nature. White (1992) provides a thorough, descriptive taxonomy of bone modifications with excellent imagery. Below we give two examples of such modifications, but a complete review of the many behavioral signatures preserved on bone is beyond the scope of this paper.

Diagnosing the agencies of modification to bone depends on the analysis of micromorphology. For example, when a stone flake or tool is used to butcher an animal the irregularities of the cutting edge make a unique, braided array of internal ledges and channels (“shoulder effects” and micro-striations; Bunn, 1981, 1984; Oliver, 1989; Potts and Shipman, 1981; Shipman and Rose, 1983a,b). Cuts made by metal knives, alternatively, are characterized by deep V-shaped grooves that lack internal shoulder effects and channels. Single cuts meeting these criteria are not necessarily diagnostic. Fortunately, in the course of meat procurement, removal of large muscles frequently results in multiple cuts marking the bone. Thus, the observation of two or more parallel cuts with nearly identical internal striations and shoulder effects provides very strong evidence for intentional de-fleshing rather than damage due to animal trampling or carnivore gnawing.

Another behavior that leaves telltale signs on bone is marrow extraction. Few animals other than humans and their ancestors can extract this nutritious tissue from its medullary bunker. Hominids, including most modern people, almost always implement the same strategy to extract fatty marrow from a bone shaft with stone tools: they rest the bone on a rock anvil and strike it with another stone to gain access to the marrow cavity. Both the hammerstone and anvil leave characteristic pits and striations associated with impact and slippage on the greasy bone. The blow that finally breaks the diaphysis frequently leaves a conchoidal fracture scar on the bone's cortex. Cracks emanating from the point of impact generally exhibit the spiral pattern associated with broken fresh bone rather than the perpendicular, jagged one associated with brittle, degreased ancient bone.

HISTORY OF BONE MODIFICATION STUDIES

Paleoanthropologists recognized the importance of behavioral signatures left on bone as early as the late 19th century, when workers noted the presence of cuts on animal (faunal) bones from prehistoric localities (Lartet, 1860). Behavioral information in these early studies was used to document the antiquity of humankind by direct association with butchered extinct animals (Lyman, 1987). By the mid-twentieth century humanity's antiquity was well established, and the study that would eventually become taphonomy was undergoing a change of focus. Rather than being satisfied with merely knowing that hominids did interact with the specimens in an assemblage, investigators began to look for more detailed behavioral information, systematically recording the frequency of modifications on bone assemblages and documenting evidence of meat preference and transportation (reviewed in Lyman, 1987). Although discussed as early as 1962 (Guilday et al., 1962), it is only in the last 25 years that researchers have objectively listed diagnostic features and outlined analytical methods for identification of individual bone modifications (Lyman, 1987).

THE SEM

The limitations of light microscopy restricted focus on smaller features of bone modification; whereas two-dimensional objects are readily magnified, three-dimensional objects are not. The depth of focus, referred to technically as “depth of field,” drops geometrically with respect to a specimen's magnification. Consequently, light microscopes have trouble focusing on more than a thin contour across three-dimensional topography. Shipman (1981) was one of the first to address this problem by employing the scanning electron microscope (SEM) in her studies of bone modification. Soon after its development, the electron microscope had been employed in the study of fossil bone histology (Barbour, 1950), and Shipman argued that its superior ability to render surface topography and three-dimensional structures made it very useful (if not indispensable) to bone modification studies as well. Following Shipman's work, SEM micrographs became the de facto standard for publication of bone modification analyses.

Recently, however, attitudes on how truly indispensable the SEM is to bone modification studies have shifted (first noted in Binford, 1985). Most features of bone modification are visible under low-power magnification. Blumenschine et al. (1996) demonstrated that, given three hours of training and a standard hand lens, a student could correctly identify 90% of bone modifications. Why, then, are all publications of important bone modifications still accompanied by SEM images (e.g., Defleur et al., 1999; de Heinzelin et al., 1999; Pickering et al., 2000)? This question is answered simply: micrographs of bone modifications are far more informative than semantic descriptions. A major level of interpretation and subsequent bias is removed by the inclusion of diagnostic imagery.

LIMITATIONS OF SEM

In most studies, the SEM has been used only to document the most informative specimens. The reasons for this restricted application are manifold, falling into two major categories: expense in money and time, and restrictions on specimen size and shape. First, scanning electron microscopes are expensive to purchase and service; maintenance contracts alone represent a significant expense. Further, most SEMs are operated by technicians whose valuable knowledge can be costly. Even with a competent technician, analysis can cost the researcher incredible amounts of time. The first step in the SEM process, the production of a cast, is also the first step in the digital method that follows. For SEM work, however, this step is far more rigorous. Due to the 200°C heat of the microscope's specimen chamber, one must use a beam-stable epoxy and heat cure it for up to 48 h, then coat the specimen with gold palladium (see Robinson and Gray, 1990a). Replica production and imaging of even a small number of specimens can take several days and cost hundreds of dollars.

The second category of restriction involves the interaction of the specimen and microscope. Generally, SEMs have small specimen chambers and are highly sensitive to specimen orientation. Most bone modifications are much larger than standard SEM subjects like aphids, pollen grains, or red blood cells. Fitting casts of specimens with larger marks into an SEM chamber can force an analyst to cut the casts into sections and produce images of each separately. This procedure is readily apparent in many SEM images of large modifications; they are presented as mosaics of individual SEM image captures.

Although chamber size can be difficult to cope with, it is not the most problematic mechanical constraint of the SEM. Scanning electron microscopes have stages that allow rotation in three dimensions. Angular changes with respect to the electron beam can enhance the 3-D effect imparted by highlighting edges (Robinson and Gray, 1990b). Unfortunately, large specimens, such as femoral shaft fragments, are naturally curved and different orientations may be ‘highlighted’ in many unpredictable and unwanted ways. Whereas shots taken at several angles can be made into a mosaic to overcome these spectral problems, angular projection errors in these mosaics distort morphology, and contrast problems from uneven lighting in individual frames are unavoidable. One can readily appreciate the extensive time involved in the SEM process by considering the production of a composite SEM image of 2.5-million-year-old cuts on fossil bones from Ethiopia (de Heinzelin et al., 1999). One single image produced for the analysis required two epoxy casts and 18 separate photographs, costing over 12 h of researcher and SEM technician time!

It is easy to see why most bone modification studies cannot employ the SEM in the general analysis of each and every modified specimen in an assemblage. As noted, it is much more common to only acquire SEM images of one or two representative specimens. The research community at large must therefore rely on a very small sample of the available specimens; imaging and publication of a full series of cuts from a bone assemblage is simply too expensive, both in time and money. This restriction has locked bone modification study into a typological framework. Advances in imaging technology, specifically the development of the charged-coupled device (CCD), are now providing a means to circumvent this problem, producing SEM quality images for a fraction of the cost.

DIGITAL IMAGING

CCDs are the light recording components of digital cameras, capturing images as multiple points of variably luminous light (termed pixels). Invented at Bell Technologies by Boyle and Smith (1970), the CCD was soon introduced to NASA, where the device continued to be developed as they phased out vacuum tube-based video systems. By 1978, 500 × 500 pixel versions had been developed; by 1990 this number had increased to 2,048 × 2,048 pixels (Lee et al., 1990). Digital cameras with the latter resolution have become generally available, whereas for commercial use Roper Scientific® now offers a 4,100 × 4,100 pixel CCD camera, the MegaPlus® 16.8i.

At first, CCD-based cameras were used for applications that did not allow conventional film processing, like one-way space ventures and time-sensitive spy satellite missions. In the late 1980s, desktop publishers and print media organizations began to use digital cameras, forgoing the costly and time consuming process of film development, despite hefty price tags (over $30,000 US) and relatively low resolutions. During the 1990s, digital camera resolution increased as modern CCDs were implemented and prices fell. The past few years have seen affordable CCD-based cameras approach the image quality capacity of traditional cameras.

Our method of sample imaging analysis employs a high resolution, CCD-based digital camera with a SLR lens and image processing software, PhotoShop® 5.5, to produce magnified images of bone modifications with depths of field that were previously very difficult to obtain without the SEM. Making this possible are the high sensitivity of the CCD and the ability to instantaneously review captured images. In this project we employ the Nikon® D1, capable of mimicking film speeds of 1600 ASA, using fully adjustable 35mm lenses, and displaying full-scale images immediately upon capture. Similar models are available from Canon® and Kodak®. The CCD's high sensitivity, combined with the dramatically increased control over lighting afforded by instant viewing of captured images, allows a digital camera's iris to be tightened more than that of an analog camera, boosting dramatically the depth of field. Our method applies this potential to the analysis of bone modification, an area previously dominated by the SEM, producing comparable, and in many instances more informative, images. Note that our comparison of the two methods is qualitative, being based on our ability to discern specific, diagnostic features of bone modification like those mentioned. Whereas information available from the two methods is comparable in terms of the visibility of these diagnostic features, subjective aspects of the images preclude quantitative assessment.

METHOD

The digital imaging process presented here has three basic steps. Although each is quite flexible, and may be accomplished using hardware configurations other than those outlined here, each is important and must be completed with exacting standards to achieve the desired results. Deviations from the outlined method must be considered carefully, as most will diminish the quality of the final image. In special cases, however, omission of a step is logistically necessary (i.e., Case 4; see below), and can be accommodated.

The first step is to make a cast of the original specimen. The use of a replica is preferable to an original specimen because bone and fossils reflect light poorly. Bone is a composite material, the combination of an inorganic mineral (hydroxyapatite) and connective tissue (collagen). Light passes readily through collagen, rendering fresh bone translucent. Similarly, fossilization of bone leads to replacement of the organic component of bones, frequently by silica or carbonate, and the surface of almost every fossil is mottled in color. For this reason, detailed topography of a bone or fossil can be best observed if an opaque, evenly pigmented cast of the bone modification is made. Note that replication is also required for SEM analyses as: (1) the necessary reflective metallic coating cannot be removed from original specimens; (2) many specimens would require sectioning to fit in the SEM sample chamber; and (3) original fossils generally cannot be transported to SEM facilities.

To test different casting materials we made and imaged one plaster and several epoxy casts using a single mold of an experimentally produced cut mark. These casts and the original bone were imaged (Figure 1). The smooth texture of epoxy reproduces microscopic details of hard tissue modifications better than plaster, and both materials are vastly superior to bone. Rose (1983), Bromage (1987), and Schmidt (1999) outline methods similar to those we employ for the production of epoxy casts (President Jet® molding compound; Coltene, Switzerland and Four-to-One® epoxy; Tap Plastics, CA). One methodological difference is that our method requires epoxy pigment to render the casts opaque (many brands are available at larger hardware stores). The pigment must be well mixed with the epoxy for an even color. In most situations a light, medium gray color is effective. Pure white tends to be too bright, and black pigment, although it superficially simulates SEM images, produces casts that have problems reflecting multiple shades of gray in shadowed areas.

Figure 1.

Comparison of casting materials. A. Bovid calcaneus (heel bone) cut during replicative butchery using stone tools by Nick Toth and Pia Anderson. Images were produced using the outlined method on: B, the actual bone; C, a plaster cast; D, a gray epoxy cast; E, a white epoxy cast; and F, a black epoxy cast. Note that the internal striations are nearly impossible to see on the bone due to its translucent nature and that plaster records less detail than epoxy. Whereas all epoxy casts record the same amount of morphological detail, variations in pigment color can have marked effects on the images that result. Gray pigment is the most universally applicable.

The second step in the method is image capture. Digital images may be captured with several devices, including digital or video cameras and slide or print scanners. The method presented here, however, requires the use of a digital camera capable of immediate display on a computer monitor and compatible with standard C-mount (regular 35 mm) camera lenses. It should have a resolution of at least one megapixel (1,000 × 1,000 pixels) or preferably higher. Most C-mount lenses have internal irises; those used for this method should be capable of apertures of f/16 or higher. Real time output is also crucial. An immediate visual report of the effects of variations in lighting and camera settings on actual images using a computer monitor is far more effective than a camera viewfinder's proxy, where one only sees the true image upon film development. For the images presented here we used a Nikon D1 professional digital camera with a Micro-Nikkor® 55mm f/2.8 lens, two Nikon PK 13 extension rings, Nikon Capture® image acquisition software, and an Apple® Macintosh® G3 computer with a 20-inch monitor.

Reducing the lens aperture diameter (i.e., increasing the f-stop number) deepens its field of focus. Extreme tightening of the iris can bring most microscopic, three-dimensional surfaces completely into focus. This also reduces the total amount of incident and reflected light available, however, making it exceedingly difficult to use chemical-film cameras under these conditions. As discussed previously, digital cameras employ CCDs to register light as opposed to standard silver-based film emulsion. The former are consequently able to handle low light situations very well. This sensitivity of digital cameras, along with the ability to immediately see results of various lighting setups, allows the lens iris to be tightened much farther than feasible with an analog camera, resulting in images with very high depths of field.

The third step in the process is image enhancement: the use of software, like Adobe Photoshop, to change color and brightness values of pixels. There is a critical difference between the algorithm-based enhancement used for this method and manual pixel manipulation. The latter is what most people think of when they hear the words “image enhancement:” the addition of information that was never part of the photographed scene. Such a conception elicits a fear of forgery and a distrust of imagery that has been altered in any way. Although this concern is understandable, it is not a major issue with the algorithm based image processing used for this method (Hayden, 2000). In contrast to cutting, pasting, airbrushing, or other manual manipulations, the algorithms used below neither add data nor alter the placement of features. Rather, they make subtle but real features readily apparent that might otherwise be invisible.

There are many software platforms that allow image enhancement. Scanner and digital camera software interfaces usually offer some enhancement algorithms. Programs like Adobe Photoshop or Corel Photo-Paint® offer a broad array of options. Many third party companies, like Kai's Power Tools®, produce modules (‘plug ins’) for these applications that perform specific enhancement functions. Still others are stand-alone programs that perform limited arrays of graphics algorithms for specific jobs. For example, NIH Image SXM (v. 1.62; available free from NIH: http://reg.ssci.liv.ac.uk/) is designed to enhance SEM images but can perform many basic enhancements on any digitized image. For this project Adobe PhotoShop was used. We highly recommend this application, but note that many others offer algorithms similar to the ones used here.

Most enhancement algorithms are simple to grasp. “Brightness adjustment,” one enhancement found in many software platforms, increases the luminance value of all pixels equally, producing an overall brighter image. More complex algorithms alter some pixel values based on functions of other pixel values in an image. For example, “sharpening” is accomplished by increasing the difference in tonal value between neighboring pixels that are below a certain threshold of similarity and increasing that between those above this threshold. Only the filters used on this project are described below. There are many more enhancements available than we could possibly list, and many besides those employed here would be useful for our method.

“Curves” adjustment can make subtle color differences more readily apparent by increasing the contrast within a specified range of tonal values. The curves function defines a new pixel output value for each pixel input value based on the function of a curved line, placing the old color values on one axis and new color values on the other. The user draws a line to define the relationship between the two. This line can be reported in text by listing the coordinates of its anchor points. Compare Figure 2A to Figure 2B. The regional placement of graphic data like edges and surface features is unaffected, whereas subtle changes in color and brightness are accentuated, facilitating visual perception of these real features. \

Figure 2.

Enhancement algorithms. Comparison of enhancement algorithms discussed in the text. Enhancement applications as follows were applied: A, unaltered image; B, a “curves” algorithm, to increase color variation; C, sharpened only using the PhotoShop “unsharp mask” filter; D, both “curves” and “unsharp mask”; E, multiple iterations of “curves” and “unsharp mask”; and F, the Kai's Power Tools filter “vortex tiling.” Note that the regional geography of surface features is unchanged for all but the last filter (F). In images (E) and (F) the effect of over-enhancement is readily apparent, as it is in most cases of algorithm-based data manipulation. Cases of non-algorithm-based image manipulation (fraud) are more difficult to detect.

Sharpening enhances edges by intensifying or subduing pixel values on either side of them. The “unsharp mask” filter in Photoshop® allows the user to manually adjust the intensity of sharpening, or how much the pixel values are to change, and the radius of the features to which the filter will be applied. The radius is important because sharpening is usually most effective if it is applied to a specific level of resolution. For example, by setting a low value the user can apply the sharpening to only fine details, not sharpening real tonal grades that should be left unaltered. With sharpening, as with curves, the regional placement of surface topography is unchanged.

To maximize visibility of information in an image we combined these two algorithms in each of our examples. Each step of this process is reported in order, with all of the input values that are necessary to replicate the complete transformation (see Appendix for steps taken in Figures 3–6). So long as it is reported in this way, any combination of filters may be used. Hence, this is the most flexible step in our method.

Figure 3.

Cuts on a 2.5-million-year-old bovid jaw bone from the Hata Member, Bouri, Ethiopia. A. Outline of Bouri fossil specimen superimposed on a modern artiodactyl mandible for reference. B. Bouri specimen with black box around entirety of cuts and white box showing the region portrayed in the SEM image (photo courtesy of Tim White). C. SEM image of cuts. D. Digital image of cuts scaled to image (C). E. Digital image of cuts at lower magnification showing parallel cuts. Note that due to SEM chamber size and lower limits on magnification only a small portion of the mark in (C) could be imaged without building a mosaic. With our digital method there is no upper limit on specimen size. See Appendix for a list of enhancement steps.

Figure 4.

Cuts on a 100,000-year-old Neanderthal cranial bone (parietal) from Moula-Guercy, France. Image (B) shows the anatomical placement of the parietal fragment. Image (A) is a traditional photograph of the Moula-Guercy parietal cuts (photo courtesy of Tim White); with inset boxes showing the coverage areas of (C) an SEM image of the marks and (D) a digital image. Note the smaller coverage area and contrast problems in the SEM image (C). See Appendix for a list of enhancement steps.

Figure 5.

Prehistoric dental drilling from Sky Aerie, Colorado. A. Jaw bone showing placement of drilled tooth (photo courtesy of Tim White). B. SEM image of tooth. C. Digital image of tooth. Note in the digital image the base of the drill hole and the entirety of the occlusal (chewing) surface of the tooth are in focus. See Appendix for a list of enhancement steps.

Figure 6.

Prehistoric cranial surgery from the Emeryville Shellmound, California. Images (A) and (B) are traditional photographs of the complete cranium and the surgical modification, respectively. Image (C) is a digital image of the cuts. Molding of surface detail required for SEM analysis was impossible for this fragile specimen. Traditional photographs were unable to capture the modification at the scale of the digital image depicted in (C) due to depth of field limitations. See Appendix for a list of enhancement steps.

Even without a detailed outline of enhancement steps, there is little danger of introducing information by going too far with image processing algorithms because images become obviously distorted quickly as enhancement procedures are compounded. Note in Figure 2E after only a few repeated iterations of the “curves” and “unsharp mask” algorithms the image is rendered useless for scientific purposes. Some algorithms do introduce data, but the patterned effects are generally obvious and unlikely to mimic actual morphology. For example, the Kai Power Tools Photoshop plug-in filter “Vortex tiling” produced the fractal in Figure 2F.

CASE STUDIES

For our first case study we utilize data on the earliest evidence of animal butchery by a human ancestor (Figure 3A–E). This material derives from the 2.5-million-year-old Hata Member deposits in the Bouri Member of the Middle Awash study area, Ethiopia (de Heinzelin et al., 1999; Asfaw et al., 1999). Cut and chop marks found on fossil antelopes and horses indicate that these creatures were butchered and that their long bones were cracked open for marrow extraction. The species Australopithecus garhi is the only hominid identified from Hata Member deposits. Not only is this species the likely perpetrator of the bone modification, it is also thought to be very close to the theoretical ancestor of all members of the genus Homo, occurring just before the major brain expansion characteristic of our genus. The Bouri evidence predates other occurrences of modified bone by over 500,000 years. The extension of meat acquisition to this early date required the inclusion of SEM imagery in the original Science publication (de Heinzelin et al., 1999).

For the second case we utilize evidence from the cave site of Moula-Guercy, Ardèche, France (Figure 4A–D). Analysis of materials from this site demonstrates that the ancient inhabitants processed bones of Neanderthals in the same way that they did those of deer. Long bone shafts were broken in a way consistent with the procedure for extraction of marrow using a stone hammer and anvil. Further, a Neanderthal skull bone (parietal) was found to be scarred in the region of the temporalis muscle origin, with multiple parallel cuts attributable to a single stone tool. As with the Bouri material, analysis and publication of these remains was accompanied by SEM imagery (Defleur et al., 1999).

In our third case, SEM analysis was carried out on a drilled human lower canine tooth from the prehistoric archaeological site of Sky Aerie, Colorado, that is associated with the Fremont Culture (880–1170 AD), predating European contact substantially (Figure 5A–C). This is the earliest evidence for dentistry in the American Southwest (White et al., 1997). A drilling experiment was undertaken on a canine tooth from a modern cadaver with flakes of volcanic glass (obsidian). SEM analysis was applied to this experimental specimen as well as the prehistoric Native American specimen. The experimental replicas delineated the morphological features related to stone-based dental drilling and allowed White et al. (1997) to differentiate between human intervention and the normal degeneration of dental enamel due to disease processes.

For our fourth case we present the earliest North American evidence of prehistoric cranial surgery (Figure 6A–C). This specimen derives from a Late Middle Period site (ca. 300–500 AD) in California (Ala-309: Richards, 1995). This specimen is significant not only for its early date but also because it is the only definitive evidence of non-trepanation surgical intervention from prehistoric North America above Mexico. Trepanation is generally associated with major cranial trauma such as depressed fractures of the cranium. Here the surgery was performed on a pathological lesion (sinus pericranii) that would not have been life threatening. It is the only known case of prehistoric elective surgery from this broad geographic region.

This last case differs from those above in that SEM analysis was never carried out on the specimen. Given that no known cases of surgical intervention in North America have withstood subsequent review it seemed critical to apply SEM analysis to the modifications. The prehistoric surgeon, however, exposed the lamellae (layers of bone) that comprise the frontal bone's outer cortical plate. The pursuit of SEM analysis would have required that the bone surface be molded for the production of an epoxy cast and would have resulted in extensive surface bone loss. Because of this potential for specimen damage only two options were available to document these cuts: (1) standard 35 mm photomicrographs; or (2) mechanical analysis by surface scanning with a diamond-tipped stylus, as described by During and Nilsson (1991). At the time of publication, documentation of this critical piece of evidence on surgical practices consisted of standard photographs and descriptions of the cuts. The digital method outlined produces far better and more informative images of this modification than were previously available.

The digital method outlined produces far better and more informative images of bone and tooth modification than were previously available.

ETHICS

As discussed, with the application of algorithm-based graphic enhancements there is not a great danger of data introduction (see also Hayden, 2000). This reassurance does not, however, extend to digital image alteration in general. It is quite easy to add or delete features in photographs at will. Although there is no question that enhancement can improve images, the ease with which alterations can be made has vastly diminished our trust in any photographs over the past decade. Scholarly audiences must come to terms with this new plasticity of images.

Although there is no question that enhancement can improve images, the ease with which alterations can be made has vastly diminished our trust in any photographs over the past decade.

Image alteration has actually been possible, albeit time consuming, from the beginning of photography. We have all seen the postcards with a giant bass in the back of a truck; Ansel Adams labored for extended periods of time in his darkroom to “dodge-out” the letters “LP” (Lone Pine High School) from a scenic Sierra hillside (Brower, 1998). The reason this sort of enhancement potential was never a major issue in the past is that it required a restrictive amount of time and skill to produce images that did not look fake. This is no longer the case. One can now quickly produce a realistic 35 mm quality image of nearly anything with just a scanner and imaging software.

A recent high-profile example of the use of imaging software to perpetrate scientific forgery comes from the quest to establish the range of the mysterious coelacanth, a fish once thought to be extinct but discovered live in the Indian Ocean off the coast of Africa in the 1930s. In the late 1990s, a team from U.C. Berkeley and Indonesia found a specimen in the seas of Southeast Asia, radically extending its known range. They analyzed the specimen, turned it over to Indonesian authorities, and published their find in Nature as a brief letter with a photograph (Erdmann et al., 1998). They then began a detailed genetic analysis of tissue samples they collected.

Sometime thereafter, a French-led team with connections in Indonesia was allowed access to the coelacanth specimen. They conducted their own analyses of the sample. Later, the French team published the finding of what they claimed was a new coelacanth species, Latimeria menadoesis (Pouyaud et al., 1999). In a recent submission to Nature, Bernard Séret, Laurent Pouyaud, and Georges Serre claimed that Serre was the first to catch an Indonesian coelacanth. They attempted to vindicate the naming of this new species by presenting a photograph showing a coelacanth lying next to other fish that they had caught.

A staff member at Nature, however, noticed striking similarities between the coelacanth in the image the French group provided and the one published previously by Erdmann et al. (1998) (see McCabe, 2000; McCabe et al., 2000). The novel image was sent to U.C. Berkeley, where a member of the original team of Erdmann et al. (1998) noticed that not only were the lighting and the pose of the coelacanth very similar in both photos, but the distinctive, speckled scale pigment pattern of the specimen—as unique in coelacanths as fingerprints are in humans—was identical in the two photographs. The conclusion was that the French team had submitted a modified photograph showing not a new find, but the original coelacanth identified by the Berkeley researchers (McCabe, 2000; McCabe et al., 2000).

In this case, it was possible to show that the picture had been a forgery. Nonetheless, this example of the ability of researchers to easily manipulate scientific images is very unsettling. Unfortunately, short of using no visual media at all, nothing can be done to eliminate completely the risk of image forgery. As demonstrated above, even undeveloped analog print film can be undetectably violated with faked digital information simply by using a good-quality slide maker.

Although there is no perfect panacea for fraud (see Paalman, 2000), it is possible—even simple—to document all beneficial image enhancements and make them replicable, thereby reducing concerns of over-enhancement. The near universal use of Photoshop for image enhancement means that any laboratory with access to the first electronic version of an image can reproduce exactly all of the enhancements performed to create a published image, so long as they are clearly outlined in the original publication. In this way, those concerned may judge for themselves if any enhancement introduces data along the way to the published image. All scientific publications that include enhanced images should be accompanied by a step-by-step account of each enhancement that was made, including all values and parameters necessary to replicate the result. A copyright-protected version of the original digital image should be made available by authors on request. With such safeguards, digital imaging and enhancement could revolutionize the way we visualize bone modification and other three-dimensional surfaces without opening up a new frontier for scientific forgery.

CONCLUSION

The digital imaging process outlined here is able to document bone modification comparable to SEM imagery in depth of field and surface rendition for objects that do not need extremely high magnification. CCDs, the digital camera photoreceptor elements, are more light sensitive than conventional film. Useful feedback on lighting effects is immediate because images do not require darkroom processing. The resulting dramatic increase in control over lighting allows rendering of much greater depth of field than is feasible with analog cameras. Second, because part of the magnification can be accomplished digitally rather than via lenses, the lens-based magnification does not need to be as high. Surface texture is rendered well because, as for SEM images, researchers use opaque casts of the objects under study.

Possibly the most important advantage of a digital imaging system is its accessibility. The high-end Nikon professional digital camera and capture software used for this project cost about $5,000 US, whereas electron microscope systems can cost $500,000 US and require expensive maintenance contracts. Almost every institution has a camera stand, but not all have SEMs. Digital cameras are far easier to use than electron microscopes and do not require qualified technicians. SEM images, the current standard in publications of important bone modifications, unnecessarily restrict efficiency and limit the amount of data that can be presented. The digital imaging technique described above lifts these restrictions.

APPENDIX

LIST OF ENHANCEMENT PROCEDURES PERFORMED ON CASE STUDY FIGURES

The following enhancement steps are cited in the order in which they were performed. The software used was Adobe Photoshop version 5.5.

Figure 3: (D) “unsharp mask” (amount = 90, radius = 5, threshold = 0).

Figure 4: (A) two iterations of “sharpen more”; (C) “sharpen more”, “contrast” (+25); (D) “curves” (with anchor points at [input 53, output 72] and [input 22, output 20], ‘unsharp mask’ (amount = 19, radius = 6.4, threshold = 0).

Figure 5: (C) “curves” (with anchor points at [input 102, output 62] and [input 202, output 186], “unsharp mask” (amount = 58, radius = 39, threshold = 0).

Figure 6: (C) “unsharp mask” (amount = 46, radius = 6.4, threshold = 0), “levels” (black = 0, gray = 157, white = 255).

Biographical Information

Mr. Gilbert received his BA from UC Santa Barbara and is currently a Ph.D. candidate in Integrative Biology. He is a graduate student instructor for human anatomy and human osteology at U.C. Berkeley and conducts paleontological fieldwork with the Middle Awash Research Project. His focus of study is human evolution and anatomy, Pleistocene African paleontology, and the study of early human behavior. Mr. Richards received his BA and MA from U.C. Berkeley, where he is currently completing his Ph.D. in physical anthropology. He is an instructor for the Fall Program for Freshmen, UCB Extension, and an Adjunct Instructor in Anatomy, University of the Pacific School of Dentistry, San Francisco, CA. His major focus is the study of human evolution with subspecialties in human and non-human basicranial and craniofacial ontogeny, diseases and congenital malformations in prehistory, and the study of prehistoric bone modification.

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