Skip to main content
Browse Subject Areas

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

A decorated raven bone from the Zaskalnaya VI (Kolosovskaya) Neanderthal site, Crimea


We analyze a radius bone fragment of a raven (Corvus corax) from Zaskalnaya VI rock shelter, Crimea. The object bears seven notches and comes from an archaeological level attributed to a Micoquian industry dated to between 38 and 43 cal kyr BP. Our study aims to examine the degree of regularity and intentionality of this set of notches through their technological and morphometric analysis, complemented by comparative experimental work. Microscopic analysis of the notches indicate that they were produced by the to-and-fro movement of a lithic cutting edge and that two notches were added to fill in the gap left between previously cut notches, probably to increase the visual consistency of the pattern. Multivariate analysis of morphometric data recorded on the archaeological notches and sets of notches cut by nine modern experimenters on radii of domestic turkeys shows that the variations recorded on the Zaskalnaya set are comparable to experimental sets made with the aim of producing similar, parallel, equidistant notches. Identification of the Weber Fraction, the constant that accounts for error in human perception, for equidistant notches cut on bone rods and its application to the Zaskalnaya set of notches and thirty-six sets of notches incised on seventeen Upper Palaeolithic bone objects from seven sites indicate that the Zaskalnaya set falls within the range of variation of regularly spaced experimental and Upper Palaeolithic sets of notches. This suggests that even if the production of the notches may have had a utilitarian reason the notches were made with the goal of producing a visually consistent pattern. This object represents the first instance of a bird bone from a Neanderthal site bearing modifications that cannot be explained as the result of butchery activities and for which a symbolic argument can be built on direct rather than circumstantial evidence.


Neanderthals’ cognitive abilities are a hotly debated topic. Opinions differ radically between those who think that Neanderthal cognition was comparable in many, if not all respects, to that of contemporaneous and present day Modern Humans [116], and those who believe that differences in cranial morphology [1720], ontogenesis [2124], physiology [2527], and behaviour [2842] support a different cognition. Paleogenetic data demonstrating a significant interbreeding between Neanderthals, Modern Humans, and Denisovans [4347] show that differences in cognition, if any, did not prevent members of these populations from recognizing each other as desirable mates, and securing successful social integration and reproduction of hybrids. Such an outcome would arguably be unlikely in the face of major cognitive differences and if, for example, language was absent [13,48]. A growing body of archaeological discoveries and reappraisal of old finds is also strengthening the position of those who advocate comparable cognition. Complex and changing lithic technologies, hafting techniques, varied hunting strategies enabling Neanderthals to kill dangerous game and exploit a variety of marine [49,50] and plants resources [5155], established ability to ignite and control fire [56], and organisation of living space, are among the innovations that are now recognized as inherent to Neanderthal cultures in various regions of Europe, before any contact with Modern Humans [4,8,9,14,57,58].

In addition, several lines of evidence—burials, collection of rare items, production of engraved and perforated objects, personal ornaments, pigment use, and the extraction of bird feathers and claws—support the notion that Neanderthals engaged in symbolically mediated behavior, independently from the influence of anatomically modern humans. Neanderthal burials of infants, children, and adults have been reported at several sites throughout Europe and the Near East, some of which are associated with grave goods [5962] (but see [63] for a different view). Several Mousterian sites (Canalettes, Combe Grenal, Grotte de l’Hyène at Arcy, Tabatérie, Chez Pourré-Chez-Comte, Cioarei-Borosteni,) yielded evidence for the collection of rare objects in the form of crystal and fossils [64]. Pigment use among Neanderthals dates back as far as 200–250 ka [65], and becomes a more widespread practice after c. 60 ka, as testified not only by the finds of modified ochre, manganese and graphite pieces [14,58,64,66,67] but also processing tools and possible pigment containers [6872]. An ochered fossil marine shell has been discovered in a Mousterian level dated to at least 47.6–45.0 cal kyr BP at Fumane cave in Italy [73], and ochered marine shells come from Cueva de Los Aviones and Cueva Antón archaeological layers dated to c. 50 ka, in the Iberian Peninsula [74].

Bone and stone objects bearing multiple incisions, interpreted as deliberate, possibly symbolic, engravings, are reported from more than forty European sites dated to the Lower and Middle Palaeolithic. A number of these incisions have been reinterpreted as the consequence of natural phenomena [75]. Many others wait for detailed analysis in order to verify the agent responsible for the modifications, and evaluate to what extent, when human made, the incisions may be better explained as the result of butchery or other subsistence activities, or as the expression of symbolically mediated behavior. A case in point is the recently discovered crisscross pattern deeply incised into the bedrock of Gorham`s Cave, Gibraltar, which represents the first reported instance of rock art produced by Neanderthals [76].

Even if it is becoming compelling, however, the evidence is spatially unbalanced with more, or more detailed and recently acquired data, only available for some regions and little or ambiguous information published for others. Another problem that researchers face when assessing instances of Neanderthal complex behavior is linked to the known difficulty of inferring cognition from material culture. Arguments in favor of equal cognition mostly rely on general comparison with the UP or the cultural adaptations of historically known hunter-gatherer populations. Attempts to reconstruct and evaluate past hominin cognition are either based on the analysis of cognitive processes at work among modern experimenters when performing activities similar to those conducted in the past [7781] or from more general frames of inference, such as the chaîne opératoire concept [8286], which try to broadly evaluate the cognitive implication of past behaviour or social transmission strategies [8790] by inferring them from the detailed analysis of archaeological artifacts. In this study, devoted to bird bone decoration by Neanderthal, we will follow a novel research strategy that includes experimental work aimed to compare markings produced by modern humans under specific neuromotor constraints with archaeological notches. Recording the same variables for archaeological and experimental markings allowed to assess the degree of regularity and intentionality reflected by the former.

Weber-Fechner law

Our visual brain demonstrates a universal and reliable range of capacities and limitations with which we can detect and perceive our environment. One such limitation is our capability to distinguish a difference in magnitude of a particular characteristic for two stimuli, such as the difference in length between two distances. The amount of change needed in one stimulus in order for it to be perceived as different from another is considered to be the difference threshold, or just noticeable difference (JND).

The Weber-Fechner law [91,92] states that this error in human perception is constant and proportional to the magnitude of the stimulus in question; this constant is termed the Weber Fraction. A different constant exists for a variety of characteristics, such as length, weight or taste, and provides the minimum difference detectable without an aid. For line length, or the distance between two points, the Weber Fraction has been determined to be 0.029 or 0.030 [9395]. Thus, if one line or distance was larger by 3% or more than another, the difference in magnitude would be perceived, whereas a difference of less than 3% would result in the two distances being viewed as equal.

This approach, when adapted to the production and perception of notches, provides a quantitative measure for evaluating the regularity of spacing in notches, i.e. whether the distance between two notches is perceived to be the same as or different from another distance between two notches. The utility of this principle within an archaeological context has been recognised previously, particularly with reference to material standardisation and the amount of variation in object size [9699]. Above all, the application of universal and reliable neurophysiological and psychophysical principles can serve as a link between our brains and those of our ancestors, and provides a quantitative method of assessing the production, manipulation and perception of archaeological artefacts.

Here we report on a bird bone from the Middle Palaeolithic site of Zaskalnaya VI (Kolosovskaya) Crimea, which bears a set of evenly spaced notches that cannot be explained as resulting from butchery activities. The technological analysis of these notches and their comparison with sets of notches produced by skillful experimenters or present on UP objects identify behavioral consistencies demonstrating the ability and intention of producing a visual conformity comparable to the one that characterizes modern human productions and reflects modern cognition.

Neanderthal bird exploitation

A string of new discoveries, related to bird exploitation, has recently enlarged the panoply of activities conducted by Neanderthals that may reflect their involvement in symbolic activities (Table 1). Sixteen Mousterian and Châtelperronian sites from Italy (Fumane, Rio Secco), Gibraltar (Gorham’s Cave, Vanguard, Ibex), France (Baume de Gigny, La Ferrassie, Combe Grenal, Les Fieux, Mandrin, Grotte de L’Hyene, Grotte du Renne, Grotte du Noisetier, Pech de l’Aze I and IV), and Croatia (Krapina) have yielded terminal phalanges of seven bird species with cut-marks indicating that Neanderthals deliberately removed the claws [100117]. At seven Mousterian sites from Italy (Fumane), France (Grotte du Noisettier, Lazaret, Le Fieux), Germany (Salzgitter-Lebenstedt), and Gibraltar (Vanguard and Gorham’s Cave) cut-marks and scraping marks on upper limb bones indicate that feathers were purposely detached from the wings. Removal of feathers and claws is interpreted as proof that these objects were used as personal ornaments by Neanderthals. Since feathers and claws do not survive archaeologically and no clear modifications for suspending or threading the claws were found so far on bird talons, this hypothesis exclusively lies on circumstantial evidence, i.e. evidence that relies on an inference to connect it to a conclusion. In archaeology, the weakness of hypotheses based on circumstantial evidence is that they do not escape the danger of equifinality, and are difficult to test.

Table 1. Mousterian and Châtelperronian sites with evidence of bird exploitation and modified bird bones.

Materials and methods

Archaeological context

The Crimean multilayered site of Zaskalnaya VI, also known as Kolosovskaya or the site of Kolosov, after its discoverer Y. G. Kolosov, is located at 45°6' N, 34°36' E, near the village of Vishennoye, Belogorsk District, in the Krasnaya gully, on the right bank of the Biyuk-Karasu river (Fig 1). The shelter has a southern exposure and opens at the foothill zone of the Crimean Mountains, in the eastern part of the peninsula, at an altitude of 205 m above sea level, 60 m above river level, at 35 km distance as the crow flies from the present-day seashore. The height of the rock cliff above the site is 12 m [121,122]. The sedimentary sequence is a collapsed roof above the cultural layer II, which covered a significant part of its ground surface (Fig 2).

Fig 2. Stratigraphy of Zaskalnaya VI, Crimea.

From: [58]–Fig 3.

Zaskalnaya VI was discovered in 1969 and intensively excavated in 1969–1975, 1977–1978, and 1981–1985 [121124]. The excavation covered a surface of 78 m2, and reached a depth of c. 3 m. In 2005, rescue excavations directed by one of us (VS) was conducted at this site.

The stratigraphic sequence (Fig 2) comprises seven Middle Palaeolithic cultural layers, numbered sequentially by Kolosov and colleagues [121,122] from the bottom to the top (VI-I): lowermost layer VI was excavated over a surface of c.10 m2, layer V over an area of 15 m2, layer IV over an area of 34 m2, layer IIIa, layer III over an area of 42 m2, layer II over a surface area of 78 m2, and the uppermost layer I over a surface of c.90 m2 [121,122].

Between 1969 and 1985 only retouched artifacts, cores, and identifiable large bones were spatially plotted. The remainder of the archeological material was attributed to a cultural layer, a square meter, and the upper and lower depth of the cultural layer in that area of the cave. Sieving with a 2 mm mesh was only occasionally performed. In contrast, all archaeological remains larger than 2 cm from the 2005 excavation were spatially plotted and attributed to a cultural layer. Sediment from this excavation was systematically sieved with a 1 mm mesh. All seven layers of Zaskalnaya VI yielded lithic material described as Micoquian of Ak-Kaya tradition [14,121,125]. No UP layers or isolated UP artifacts were found at the site.

Technologically this industry encompasses both non-Levallois centripetal and sub-parallel non-volumetric core reduction as well as bifacial shaping. Flake tools include points, sidescrapers and backed knives. Bifacial shaping, which reaches up to 30% of the tools, was used to produce foliated points, sidescrapers and the typical ruckenmessers or bifacial back knives.

Fireplaces and pits, including one in layer II containing eight bifaces, were excavated in layers II, III, IIIa and IV. They support the stratigraphic integrity of the site.

The exact chronostratigraphic position of the lowermost layers VI-V has not yet been precisely established, but it is reasonable to assume that they should date to the beginning of the last glacial [126]. Radiocarbon dating of bone samples from the uppermost four cultural layers was performed in the Kiev and Oxford laboratories (Table 2). It indicates that the accumulation of these layers covered a time span ranging from approximately 25 ka to 46 ka. The ages obtained for the layers IIIa, III, II, and I are consistent with those obtained for several other Middle Paleolithic sites from Crimea [14,121,127] and support the hypothesis that this region was a Neanderthal refugium [14,58].

Table 2. Radiometric dating of Zaskalnaya VI (Kolosovskaya).

Anthropological remains attributed to Neanderthals have been discovered in layers IIIa, III, and II. They are abundant in layers IIIa and III. Two fragmented mandibles (Zsk VI-72 and Zsk VI-78), fourteen isolated teeth, isolated hand phalanges, a fragmented arm, a forearm bone, and a shin bone were recovered in layer III. Remains of three juvenile Neanderthals, possibly associated with a burial pit, and representing the remnants of a triple burial, come from layer IIIa. A fragmented mandible Zsk VI-72 (left half and a fragment of the right half) with three teeth, along with fourteen isolated teeth, and isolated hand phalanges were recovered in an area of approximately 40 cm of diameter at the limit between squares 32D and 32E. A bifacial tool [58,121] was found in close proximity to the mandible fragment Zsk VI-72. The analysis of the anthropological material showed that the remains belong to two adolescents, a mandible fragment to an individual with the estimated age of 10–12 years, and hand phalanges to an individual aged 14–15 years [58,131134]. A fragmented right half of mandible Zsk VI-78 and four isolated teeth associated with it were recovered in square 35G, along with fragmented radius, left humerus, and right tibia. These remains belong to two adolescents, the mandible fragment to an individual of 14–15 years, the fragmented humerus bone to an individual of 10–12 years [131,132]. Despite the absence of a burial pit, some have suggested that these remains could be interpreted as two reworked child burials [61,122].

The artifact analysed in this paper (Fig 3) was recovered among the remains of avifauna from layer III and described by Tsvelykh and Stepanchuk as an intentionally notched object, possibly used as an eyeless needle in which the notches may have been used to fix a thread and as decoration [120].

Fig 3. A Corvus corax bone fragment with notches from Zaskalnaya VI, layer III.

Scale = 1 cm.

Layer III

Identified all over the site surface and c. 20–30 cm thick, this layer is composed of yellow loamy soil mixed with gravel (Fig 2).

Lithics from layer III are mainly made of fine-grained gray Cretaceous flint, rarely from black and semitransparent brown-colored flint [121]. The majority of artifacts from layer III are not patinated, and contrary to those from layer II, are not covered by concretions [58]. Cores from this layer are flat unifacial (11), bifacial (8) centripetal, and subparallel. Tools include simple (249), double (43), convergent (70) and canted (122) sidescrapers, flake points (36), knives (174), and denticulates (17), other tool types being rare. Bifacial tools are represented by spearheads (4), points (6), scrapers (49), and back knives (111). The scarcity of pre-cores (16) and bifacial forms, the comparatively small size of the cores, and the relatively high frequency of exhausted post-cores and fragmented tools, indicates an intensive use of the lithic raw material [58,121,122].

The fauna from layer III includes mammoth, rhinoceros, horse, saiga, megaloceros, reindeer, red deer, wolf, hare, and small rodents (Table 3). Marine mammals are represented by the remains of the Black sea (short-beaked) common dolphin.

Table 3. Faunal remains from Zaskalnaya VI (Kolosovskaya), layer III.

Faunal remains are heavily fragmented. Although modifications by medium size carnivores are observed, humans are identified as the main agent of bone accumulation and modification [135]. Mammoth bones appear to have been intentionally collected to be used as fuel [135]. Some mammoth bones display long-term weathering and low content of organic matter; others have a relatively fresh appearance, show flake scars, impacts from use as retouchers, or appear to have been shaped into wedge-like artifacts. Horse limb bones were also used as a raw material for artifact production. Most bone retouchers and possible bone polishers from layer III (45) were made of horse limb bones [14,122,136].

The presence of burnt bone-rich hearths, the large number of faunal remains, the intense use of lithic material, and the long-distance transport of exotic resources (e.g. tail vertebrae of a young dolphin) suggest that layer III of Zaskalnaya VI reflects long-term occupations [58,121]. The object analyzed here comes from layer III, squares 29–33 Zh and 29–33 E and Z. It was identified in 2013 during the analysis of the faunal remains from the 1974 excavation.

Bird bone from layer III

The object analyzed in this study is kept at the Institute of Archaeology of NASU, Kiev, Ukraine (specimen designation/number: ZVI/III:011/015.14). As common for bone remains from the layer III, it was covered by a thin layer of concretion that was carefully removed. The skeletal element and species identification is proposed, as for the other bird remains from cultural layer III and adjacent layers II and IV of Zaskalnaya VI, on the basis of the fragment’s diagnostic anatomical features, and comparison with the bird bones from the osteological reference collection of the Paleontological Museum of the Central National Natural History Museum of NASU, Ukraine [137]. Descriptive terms of the anatomical elements follow the currently accepted nomenclature used in the analysis of bird remains [138].

Metric data on the archaeological and experimental objects were acquired with a digital caliper. High quality images of four aspects of the archaeological object, and macrophotographs of areas of interest were taken using a NIKON D5300 and a Canon PowerShot S100 digital cameras. Digital images were edited in the Adobe® Photoshop® CS5.1 Extended software. The object was examined with Leica Z6 APOA motorized microscope equipped with a DFC420 digital camera in order to identify and photographically document natural and anthropogenic modifications. Images were treated with Leica Application Suite (LAS) equipped with the Multifocus module, and Leica Map DCM 3D software. The Multifocus module permits the acquisition of extended depth of field images by relying on the adapted algorithms that combine digital images collected at different heights into a single, sharp, composite image. The obtained microscopic images were digitized and edited in the Adobe® Photoshop® CS5.1 Extended software. The Leica Map DCM 3D allowed production of 3D reconstructions of areas of interest. This equipment was also used to measure distances between adjacent notches. Variables recorded for each notch included maximum length, width, depth, and angle, and top, middle, and bottom distance between adjacent notches. Identification of the origin of the bone modifications is based on the experimental reproduction and microscopic analysis of sequential marks produced on bone and stone objects with different tools and motions [139144].

Experimental notching

The experiment was conducted at the PACEA laboratory, Bordeaux University, and involved nine adult subjects, eight right handed and one left handed, seven females and two males (Table 4). The participants provided their informed consent to participate in this experiment. It included four phases. In the first phase, the subjects were asked to use unretouched flint laminar flakes to produce notches by a to-and-fro motion on humeri of domestic turkey (Meleagris ocellata). Each subject was given a bone and a tool. The tool was replaced if considered inadequate for the task by the subject. This phase of the experiment lasted for 15 minutes. In this phase, which had an objective to prepare and introduce subjects to the task, they were not given any further instructions aside of making the notches with the tool provided on a given media. In the second, third, and fourth phase of the experiment the subjects were given precise instructions regarding the task in order to achieve consistency of the results allowing comparison with the archaeological specimen. In the second phase of the experiment, the subjects were asked to produce 14 similar, parallel, and equidistant notches on domestic turkey`s radii bone. This phase lasted for 15 minutes. In the third phase of the experiment, the subjects were instructed to produce seven evenly spaced, parallel, and similar notches on radii of domestic turkey (Fig 4). The radii were selected in order to be of a size similar to that of the archaeological specimen. The precise location within which the notches are present on the archaeological specimen was marked on each experimental radius with two thin lines and the subjects were asked to locate the seven notches in that space, with the first and last notch coinciding with each line. No time restriction was given to accomplish this task. The fourth phase of the experiment was identical to the third. For each of these phases, top, middle, and bottom distances between adjacent notches have been measured as well as the length and width of each notch, and the angle formed by each notch with the horizontal plan.

Fig 4. Radii of domestic turkey (Meleagris ocellata) used for the experimental phases 3 and 4.

Scale = 1 cm.

Table 4. Information on gender, age and laterality of the experiment`s subjects.

Metric data on notches produced during the first and second phase of the experiment were acquired with the ImageJ software on images taken with NIKON D200 camera. Metric data on notches produced during the third and fourth phase were collected with the ImageJ software on microscopic images obtained with the same equipment used to analyze the archaeological specimen. In order to evaluate the regularity of the spacing, the Weber fraction was used, allowing us to see if the actual distances between experimental notches fit the pattern predicted by the Weber law. Coefficients of variations (CV) were also calculated for the other measured variables.

Archaeological comparative sample

Distances between notches were measured on thirty-six linear series of notches cut on seventeen bones [99] from seven Magdalenian sites in Western Europe. The objects selected for this study were thin and cylindrical, semi-cylindrical or tube-like in nature, predominantly represented by bird bones, and yielded one or more series of transverse notches produced along a portion of the bone length. A series was considered the collection of notches in a linear manner along one side of the object, that contained at least three notches such that the distances between them could be compared. General microscopic analysis of the comparative notch morphology suggests that each series was produced in a single session, demonstrating the same overall shape, cutting style, and end-point morphology. In two cases, it was determined that the object was rotated 180° during the production of a series.


Zaskalnaya VI avifaunal remains

The remains of 41 bird species have been identified at Mousterian sites [145149], and 93 species at UP sites [145] throughout Crimea. These species represent one-third of the present day Crimean avifauna [137].

Layer III differs from the other layers of Zaskalnaya VI for the relatively high number of bird remains. Five species were identified in this layer (Table 5), and two species in layers I and II. Zaskalnaya VI is the only Middle Palaeolithic site from Crimea in which three of these species (pheasant, gray heron and garganey) are found. Most of the bird species are represented in the modern-day Crimean fauna [150]. Numerous additional bird remains are present in the form of indefinable fragments.

Almost all bird bones from Zaskalnaya VI display evidence of crushing of the epiphyses. No detailed analysis, as performed recently on a number of European and African assemblages [151153], has been conducted to establish the agent responsible for the damage. A small quantity of bird remains show etched surfaces suggesting that they were originally incorporated in pellets of birds of prey [137]. No clear cutmarks were identified so far on the avifauna.

The Zaskalnaya VI notched bone

The object (18.14 mm long, 7.06 mm wide, and 2.49 mm thick) is the distal fragment of a right radius (Fig 3). The thin and compact wall of the shaft, the smooth texture of the outer surface and the slightly angular shape of the distal end, indicate that it belongs to a bird rather than a mammal of comparable size. The morphology of the epiphysis and the shaft—in particular the marked ligamental prominence—and the greatest breadth of the distal end (Bd) point to the common raven (Corvus corax) as, by far, the more probable species [154].

Its medullary cavity is infilled with hardened sediment (Fig 3 –aspect II). The fragment was partly covered by concretions before cleaning and a microcrack on the distal end of the bone is still covered at places by micro-concretions (Fig 3 –aspect I). Black spots, probably of manganese, are present on the periosteal and medullar surface, and on the breakage. The bone displays the same color, patina and comparable state of preservation all over its surface, including the breakage, suggesting the latter is ancient. A group of subparallel cutmarks, slightly oblique to the bone`s main axis, are present on the anterior edge, 1 cm above the styloid process (Fig 5).

Fig 5. Cutmarks on the anterior edge of the radius bone fragment, Zaskalnaya VI, layer III.

a. Localization of the cut marks. Scale = 1 mm.

Technological analysis

Seven notches, cut on the posterior aspect of the bone between the epiphysis and the breakage, numbered henceforth 1–7 from the one closest to the epiphysis forward, run over a length of 10 mm (Figs 3 and 6). The surface of each notch is smoothed but still displays microscopic features that allow a technological and metrical analysis (Table 6). Only notch 6 is too superficial to reliably measure the angle formed by the notch walls.

Table 6. Morphological and metric data on Zaskalnaya VI notches.

Fig 6. Microscopic images of the notches on the Zaskalnaya VI bird bone fragment from layer III.

Profile (top) and en face (bottom) views. Scale = 1 mm. a. Magnification of the notches 1–3; b. Magnification of the notches 4–5; c. Magnification of the notches 6–7.

Notches 1, 3–5, and 7 differ from notches 2 and 6 (Figs 6, 7 and 8). The former are parallel and perpendicular to the bone main axis. They are deeply cut and bear striations on the notch bottom indicating that they were produced by the to-and-fro movement of a lithic cutting edge. They all display a comparable asymmetrical section, deeper toward the epiphysis of the bone. On notches cut by the to-and-fro motion of a lithic blade or flake the asymmetry of the notch indicates the location of the ventral aspect of the blank during the cutting process [139]. In the case of notches 1, 3–5, and 7, the fact that the notch wall closer to the epiphysis is steeper indicates that the ventral face of the tool was oriented toward the distal epiphysis of the radius. Similarity in section morphology and angle formed by the walls of these notches, ranging between 90° and 102°, suggests that these notches were made by the same tool in a single session. Gradual increase in the notches’ angle from the epiphysis toward the diaphysis suggests that that the craftsman incised notch 1 first and juxtaposed notches 3–5, and 7 toward the middle of the diaphysis. The type of tool used can be inferred from the notch angles and morphology. Retouched cutting edges generally produce asymmetrical notches with a flat steep side, corresponding to the ventral side of the blank, and a more oblique side displaying multiple steps parallel to the notch bottom, due to the action of the retouch. Sections of notches produced by retouched tools form angles ranging between 60° and 95°. Unretouched cutting edges produce more symmetrical notches with flat sides and angles ranging between 35° and 65°. Angles of notches 1, 3–5, and 7 are wide and fall at the very limit of the notches produced by retouched cutting edges. However, they do not bear the multiple steps on the wide side typical of notches made by retouched tools. Notch 1 presents a single step on the steep left side and notch 3 a step on both sides. No steps are recorded on the others. This evidence, together with a relatively high degree of variability in the overall morphology of these notches, is consistent with the use of a very robust unretouched flake.

Fig 7. 3D reconstruction of the Zaskalnaya VI bone notches.

a. Notches 1–3; b. Notches 4–5; c. Notches 5–7; d. Notches 6–7.

Fig 8. Sections of the Zaskalnaya VI notches.

Labels a-g correspond in order to the notches 1–7.

Notches 2 and 6 are parallel and oriented obliquely to the bone's main axis. They are superficial, have wider and more symmetrical sections than the previous notches, and show irregular edges indicating that they were probably produced by a single passage of a cutting edge. Their different orientation, morphology and production technique indicate that they were probably added after the first set, either with the same tool—perhaps with a different area of the same cutting edge—or a different tool. Although wider than angles measured on notches 1, 3–5, and 7, the angle measured on notch 2 is compatible with the use of the same cutting edge considering that the smoothing affecting the notches may have slightly flattened its surface and that the cutting edge would have been already worn by the production of the previous set of notches when this and notch 6 were incised. Superficial incisions are occasionally produced by mistake when incising notches by a to-and-fro movement of a cutting edge. It is, however, unlikely that notches 2 and 6 result from that process. They are deeper than unintentional notches reported in the literature [139] and observed in our experimental collection. Most importantly side notches produced unwillingly generally display the same orientation of the closest main notch, being the result of the same repeated motion, which is not the case with notches 2 and 6.

Experimental results

During the first phase of the experiment nine subjects incised in total 129 notches on nine domestic turkey’s humeri bones. They produced between 6 and 41 notches per bone, with the average of 14.3 notches per bone. Two subjects cut 6 notches, two other 13 notches per bone. Five subjects produced 9, 11, 14, 16 and 41 notches per bone. The lack of constraints in this phase of the experiment is reflected by discrepancy in placing, distance and orientation of the notches. Some subjects produced notches in continuity on one aspect of the bone, others on different aspects. The length, width, orientation, placing, and distance between notches were highly variable. During the second phase of the experiment, a single subject produced 12 instead of 14 notches, while others fulfilled the task in terms of number of notches required, making in total 124 notches (Fig 9). Therefore, aside from a single mentioned exception for which 11 gap measurements were gathered, 13 measurements of distances between top, middle, and bottom of adjacent notches have been obtained for each specimen, constituting a total of 345 individual measurements (experimental set C). During the third and fourth phase of the experiment, all subjects conformed to the given constrains, producing in total 63 notches (Fig 10). As done for the previous phase, distances between top, middle, and bottom of adjacent notches have been measured for each specimen, comprising 54 measurements per each category (top, middle, and bottom distances), and a total of 162 individual measurements taken together—experimental sets A and B.

Fig 9. Fourteen notches produced by the modern subjects on turkey`s radii bone during the second phase of the experiment.

Scale = 1 cm.

Fig 10. Seven notches produced on radii of domestic turkey during the third (a-i) and fourth (j-r) phase of the experiment.

Aligned are the sets made by the same subjects.

A Weber-Fechner law for notches on bone rods.

The constant represented by the Weber Fraction (0.029–0.030, or a JND of 3%) was originally established on planar surfaces [92, for a detailed discussion see 99], yet it must be acknowledged that the lengths in question here are of a three-dimensional nature on variably curved surfaces. More recent psychophysical experiments have demonstrated that humans find it more difficult to evaluate distance on curved surfaces and in three dimensions; the ability to estimate the length of lines on curved surfaces in 3D settings yields an error that varies dramatically from individual to individual and is dependent upon factors such as viewing distance, orientation of the surface and/or line and type of surface [155157]. Such results are not directly applicable to the results of our experiments and the analysis of archaeological series as we wish to evaluate the difference threshold between distances rather than the perception of absolute length. Nevertheless, it is plausible to consider that the ability to discriminate distances between notches will be influenced by their existence upon a curved surface and, thus provide a wide-ranging and non-constant error. Furthermore, the notches under examination are not only produced on surfaces of varying curvature, but a production error will be incurred with respect to the materials and practices being used to produce a notch on a bone surface. Whilst individuals may be able to perceive exactly where they wish to place the notch on the bone, an error may exist due to the nature of the bone surface, flint tool and the individual's ability at producing the notch.

An evaluation of the distance measurements for the experimental series demonstrates that the Weber Fraction of 3% is indeed met very rarely and seems to be rather an exception than a rule. In actuality, the experimental production of equidistant sets of notches, submitted to the above biases, can be used to evaluate the Weber Fraction or difference threshold specific to the production and perception of notches made by adult modern humans on bone rods with a to-and-fro movement of a lithic cutting edge, with the intention of making them similar in length, parallel and equidistant. In addition, two of our experiments incorporated constraints of space that allow us to evaluate to what extent this factor may influence the production of sequential notches and make results particularly valuable to assess the archaeological set of notches under study.

The coefficient of variation for distances has been calculated for the three experiments, summarized in Table 7 and Fig 11, and is compared to the value obtained for Zaskalnaya set. Most CVs calculated on sets produced during the unconstrained experiment are lower than 20% (mean = 16%). Most of those from sets made under space constraints range between 15% and 25%, with means of 22% and 21%.

Fig 11. Boxplots representing the coefficient of variation for distances of the experimental and archaeological sets of notches.

Table 7. Coefficients of variation for distances of the experimental and archaeological sets of notches.

Analysis of UP notched bird bones [99] identified only a single series of notches with a coefficient of variation close to the Weber Fraction for patterns on planar surfaces (0.032 or 3.2%). The overall distribution of the coefficient of variation for the distance between two notches highlighted two populations, the first of which fell predominantly between 10% and 25%, and peaked between 15% and 20%. This population, consisting of 15 series, is interpreted to be composed of cases in which the notches were perceived as regularly spaced.

The second population yielded a coefficient of variation largely between 30% and 55%, with an upper limit case of 0.721 (72.1%). This population was posited to represent cases for which the spatial distribution of notches were perceived to be unequal or random, and was considered to include a further 16 examples [99].

The remaining five series of the archaeological sample from the UP represent examples that cannot be considered as regular or random in their spatial distribution but rather display a particular trend in their layout, and should thus be acknowledged. While they demonstrate wide-ranging values for the CV, that would have indicated them as either regularly or randomly distributed, the distances between notches were shown to either increase or decrease, to some extent, over the course of the series. These examples included the two cases in which the bone was rotated 180° during the production of the series. Furthermore, a third example, with a total of 18 notches, included the first 10 notches being produced at distances which would be interpreted as regularly spaced (with a CV of 0.12 or 12.0%) and the remaining 8 notches being increasingly spread out in a linear manner. This case demonstrates a mixture of regular and increasingly distributed notches. It is important, therefore, in the context of this study, to acknowledge that a random spatial distribution is not the only alternative to regularly spaced notches, but that they can also demonstrate alternative and mixed trends in their spatial distribution that would not be reflected by their coefficient of variation.

The CV of distances between the notches on the ZSK specimen is 20.5%, a value that falls within the range of variation for regularly spaced experimental and UP sets of notches and is almost identical or very close to the mean CV calculated on experimental sets of notches cut on the same space available to the Neanderthal craftsman. However, the CV of the ZSK set of notches would have been 30.7%, if notches 2 and 6 were not added.

Multivariate analysis.

The first two components of a PCA using the CVs of the seven morphometric variables recorded on the ZSK notches and series of notches from experimental phases two, three and four account for 90.6% of the variance (Fig 12). They identify the main factors underpinning the differences between these sets. Component 1, mostly influenced by distances between notches, indicates that series from experiment 2 feature the highest variability but also a consistent number of series showing the more regularly spaced and aligned notches. Comparatively, series of notches belonging to experiment 3 and 4 are less regularly spaced and aligned than those from experiment 2. This is likely due to the space constraints imposed during these experiments. Series from experiment 4 split into two groups, one composed of more and the other less regularly spaced notches than those from experiment 3. The ZSK notches fall in the very middle of the experiment 3 and 4 variability. Component 2, mostly influenced by the notches’ width and, to a lesser extent, length and orientation, reveals that most of the series of notches from experiments 3 and 4 are characterised by a lower or similar variability when compared to those from experiment 2. This can also be attributed to the imposed space constraints: the engraver is obliged to consider also the notch size if he/she needs to fit a given number of notches in a small space. ZSK notches fall within the range of experiments 2 and 4 but are clearly more variable in term of notch size and orientation than the large majority of the series from the three experiments. This is due, as made clear by the technological analysis of the ZSK notches, to the fact that unlike the experimental series, the alignment of notches on the raven bone consists of an accumulation of two sequences of notches with a significant change in notch orientation and size between them. The higher coefficients of variation generated by this action is responsible for the outlying position of the ZSK set of notches.

Fig 12. PCA scatter diagram showing distribution of CV for experimental specimens from the phases 2 (1C-9C), 3 (1A-9A) and 4 (1B-9B), and the archaeological object.

The coefficient of variation was calculated for the following six variables: distances top, distances middle, distances bottom, length, width, and angle.


The technological analysis of the notches on the ZSK raven bone indicates that two of them (2 and 6) were apparently added to fill in the gap left between notches 1–3 and 5–7. The possibility that the space between these notches was left on purpose, in order to add at a later stage notches of different length and orientation, with the goal of creating a special pattern composed of longer perpendicular and short oblique notches, is unlikely. It would have been easy for the craftsman to alternate during the same session deeper notches with more superficial and obliquely oriented ones. It is more probable that the Neanderthal took the decision of adding notches 2 and 6, after completing the first set and realizing that its production left two gaps. Two reasons may account for this action. The craftsman may have considered that, if made for functional reasons, i.e. to facilitate the grip of the object, the notches of the first set were not frequent and numerous enough to fulfill that function. Alternatively, he/she may have considered, irrespective of the possible functional reason behind the production of the notches, that it was important to add two notches in order to create a visually more regular and consistent pattern. The second hypothesis is in our view the more probable because adding of the two very small and superficial notches added virtually nothing to the gripping power of the object`s surface.

This interpretation is strengthened by the difference between the perception of the notches after their first accumulation and completion. The identification, achieved in the present study, of the Weber fraction for sets of notches made on small rods and its application to the ZSK notches prior to adding notches 2 and 6 demonstrates that the sequence would not have been perceived as regularly spaced by the UP and living modern individuals. The sequence of notches would have been perceived as regularly spaced by those same individuals after adding notches 2 and 6. This conclusion is supported by results of our analysis of a large sample of experimental alignments of notches made under technological and neuromotor constraints similar to those at work when the ZSK Neanderthal craftsman incised the raven bone, with the deliberate intention of producing equidistant notches. It is also consistent with results obtained when applying this approach to more recent archaeological examples of aligned notches. Thus, adding of the two additional notches on the ZSK raven bone appears to be consistent with the intention to make the notches of final series regularly spaced. This suggests that Neanderthals were perceiving and discriminating equidistant from unequally spaced sequential marks in a way similar to us and that their neuromotor control allowed them to master the techniques and motions necessary to obtain regularity when required. Such conclusion remains valid independently of the functions that the ZSK object might have had. The Neanderthal intention, highlighted by our study, of producing notches that can be perceived as equidistant makes it less likely that they were incised on the raven bone for purely functional reasons such as securing grip during the use of the object as an awl or to fix a thread to use it as an eyeless needle. These and other, including symbolic, functions are entirely possible considering the fragmentary state of the object. It is clear that in order to effectively fulfill any such function the object ‘had’ to be incised with notches, but not necessarily equidistant notches in case of a solely utilitarian purpose. Still, the results of the study pinpoint that a clear effort has been put to reach the goal of producing not just random but instead equidistant notches, that would have been perceived as regularly spaced. This implies that the resulting pattern could have conveyed an information, not directly linked to the object function, communicating to the user, and likely other members of the Neanderthal group. In this respect the sequential notches on the ZSK raven bone represent the first case of bird bone use by Neanderthal for which a symbolic function can be argued on direct rather than circumstantial evidence.

The research strategy followed here should be adapted and extended to other Lower and Middle Palaeolithic incised objects in order to establish when the faculty for precisely discriminating regularly from irregularly spaced marks arose and identify the role it may have played in creating symbolic codes.


The authors thank to the Ukrainian National Academy of Science for approval of the temporary export of the object for research purposes at the UMR 5199 PACEA laboratory of the University of Bordeaux. Thanks are also due to the reviewers for their useful comments and suggestions. This research was conducted with the financial support awarded to the authors through the PICS collaborative research project “The emergence of symbolically mediated behavior in Eastern Europe” by the CNRS and NASU (PICS-NASU 3–15). One of the authors (AM) acknowledges financial support of the Wenner-Gren Foundation. This research was also funded by the LaScArBx, a research programme supported by the ANR (ANR-10-LABX-52). Another author (SE) acknowledges financial support of the AHRC and thanks the British Museum, Musée des Antiquités Nationales and Museo Nacional y Centro de Investigación de Altamira for access to the Upper Palaeolithic collections.

Author Contributions

  1. Conceptualization: AM SE VS FdE.
  2. Data curation: AM SE VS AT FdE.
  3. Formal analysis: AM SE VS FdE.
  4. Funding acquisition: AM VS FdE.
  5. Investigation: AM SE VS AT FdE.
  6. Methodology: AM SE VS FdE.
  7. Project administration: AM VS FdE.
  8. Resources: AM VS FdE.
  9. Supervision: FdE.
  10. Writing – original draft: AM SE VS FdE.
  11. Writing – review & editing: AM SE VS AT FdE.


  1. 1. d’Errico F, Henshilwood C, Lawson G, Vanhaeren M, Tillier A-M, Soressi M, et al. Archaeological Evidence for the Emergence of Language, Symbolism, and Music–An Alternative Multidisciplinary Perspective. Journal of World Prehistory. 2003;17: 1–70.
  2. 2. d’Errico F, Stringer CB. Evolution, revolution or saltation scenario for the emergence of modern cultures? Philosophical Transactions of the Royal Society of London B: Biological Sciences. 2011;366: 1060–1069. pmid:21357228
  3. 3. d’Errico F, Banks WE. Identifying Mechanisms behind Middle Paleolithic and Middle Stone Age Cultural Trajectories. Current Anthropology. 2013;54: S371–S387.
  4. 4. Villa P, Roebroeks W. Neandertal Demise: An Archaeological Analysis of the Modern Human Superiority Complex. PLOS ONE. 2014;9: e96424. pmid:24789039
  5. 5. Hovers E, Belfer-Cohen A. “Now You See it, Now You Don’t”—Modern Human Behavior in the Middle Paleolithic. In: Hovers E, Kuhn SL, editors. Transitions Before the Transition. Springer US; 2006. pp. 295–304.
  6. 6. Zilhão J. Anatomically Archaic, Behaviorally Modern: the Last Neanderthals and Their Destiny: 23rd Kroon Lecture. Amsterdam: Nederlands Museum voor Anthropologie en Praehistorie, Universiteit van Amsterdam; 2001.
  7. 7. Zilhão J. Neandertals and moderns mixed, and it matters. Evol Anthropol. 2006;15: 183–195.
  8. 8. Zilhão J. The Emergence of Ornaments and Art: An Archaeological Perspective on the Origins of “Behavioral Modernity.” J Archaeol Res. 2007;15: 1–54.
  9. 9. Zilhão J. Aliens from Outer Time? Why the “Human Revolution” Is Wrong, and Where Do We Go from Here? In: Condemi S, Weniger G-C, editors. Continuity and Discontinuity in the Peopling of Europe. Dordrecht: Springer Netherlands; 2011. pp. 331–366.
  10. 10. Langbroek M. Trees and ladders: A critique of the theory of human cognitive and behavioural evolution in Palaeolithic archaeology. Quaternary International. 2012;270: 4–14.
  11. 11. Nowell A. Defining Behavioral Modernity in the Context of Neandertal and Anatomically Modern Human Populations. Annual Review of Anthropology. 2010;39: 437–452.
  12. 12. Holloway RL, Broadfield DC, Yuan MS. The Human Fossil Record, Brain Endocasts: The Paleoneurological Evidence. Hoboken, New Jersey: Wiley-Liss; 2004.
  13. 13. Johansson S. The thinking Neanderthals: What do we know about Neanderthal cognition? WIREs Cogn Sci. 2014;5: 613–620.
  14. 14. Stepanchuk VN. The Lower and Middle Paleolithic of Ukraine (Nizhnii i srednii paleolit Ukrainy). Chernovtsy: Zelena Bukovina; 2006.; (In Russian).
  15. 15. Sher JA, Vishnyatsky LB, Blednova NS. The origin of symbolic behavior (Proiskhozhdenie znakovogo povedeniya). Moscow: Nauchny mir; 2004.; (In Russian).
  16. 16. Visnyatsky LB. Neanderthals: the history of vanished mankind (Neandertal’tsy: istoriya nesostoyavshegosya chelovechestva). Sankt-Peterburg; 2010.; (In Russian).
  17. 17. Bruner E, Manzi G. Saccopastore 1: the earliest Neanderthal? A new look at an old cranium. In: Hublin J-J, Harvati K, Harrison T, editors. Neanderthals Revisited: New Approaches and Perspectives. Dordrecht: Springer Netherlands; 2006. pp. 23–36.
  18. 18. Bruner E. Morphological Differences in the Parietal Lobes within the Human Genus: A Neurofunctional Perspective. Current Anthropology. 2010;51: S77–S88.
  19. 19. Bruner E. Functional Craniology, Human Evolution, and Anatomical Constraints in the Neanderthal Braincase. In: Akazawa T, Ogihara N, Tanabe HC, Terashima H, editors. Dynamics of Learning in Neanderthals and Modern Humans Volume 2 Cognitive and Physical Perspectives. Springer Japan; 2014. pp. 121–129.
  20. 20. Pearce E, Stringer C, Dunbar RIM. New insights into differences in brain organization between Neanderthals and anatomically modern humans. Proceedings of the Royal Society of London B: Biological Sciences. 2013;280: 20130168.
  21. 21. Gunz P, Neubauer S, Maureille B, Hublin J-J. Brain development after birth differs between Neanderthals and modern humans. Current Biology. 2010;20: R921–R922. pmid:21056830
  22. 22. Gunz P, Neubauer S, Golovanova L, Doronichev V, Maureille B, Hublin J-J. A uniquely modern human pattern of endocranial development. Insights from a new cranial reconstruction of the Neandertal newborn from Mezmaiskaya. Journal of Human Evolution. 2012;62: 300–313. pmid:22221766
  23. 23. Neubauer S, Hublin J-J. The Evolution of Human Brain Development. Evol Biol. 2012;39: 568–586.
  24. 24. Neubauer S. Human Brain Evolution: Ontogeny and Phylogeny. In: Bruner E, editor. Human Paleoneurology. Springer International Publishing; 2015. pp. 95–120.
  25. 25. de Boer B. Loss of air sacs improved hominin speech abilities. Journal of human evolution. 2012;62: 1–6. pmid:22078314
  26. 26. Lieberman P. The evolution of human speech. Current Anthropology. 2007;48: 39–66.
  27. 27. Spoor F, Hublin J-J, Braun M, Zonneveld F. The bony labyrinth of Neanderthals. Journal of Human Evolution. 2003;44: 141–165. pmid:12662940
  28. 28. Benazzi S, Douka K, Fornai C, Bauer CC, Kullmer O, Svoboda J, et al. Early dispersal of modern humans in Europe and implications for Neanderthal behaviour. Nature. 2011;479: 525–528. pmid:22048311
  29. 29. Chase PG, Dibble HL. Middle paleolithic symbolism: A review of current evidence and interpretations. Journal of Anthropological Archaeology. 1987;6: 263–296.
  30. 30. Hublin J-J. The earliest modern human colonization of Europe. PNAS. 2012;109: 13471–13472. pmid:22864912
  31. 31. Junker T. Art as a biological adaptation, or: Why modern humans replaced the Neanderthals. Quartär. 2010;57: 171–178.
  32. 32. Mellars P. The impossible coincidence. A single-species model for the origins of modern human behavior in Europe. Evol Anthropol. 2005;14: 12–27.
  33. 33. Mellars P. Neanderthal symbolism and ornament manufacture: The bursting of a bubble? Proc Natl Acad Sci U S A. 2010;107: 20147–20148. pmid:21078972
  34. 34. Finlayson C. The humans who went extinct: Why Neanderthals died out and we survived. Oxford: Oxford University Press; 2009.
  35. 35. Mithen S. The prehistory of the mind: a search for the origins of art, science and religion. London and New York: Thames and Hudson; 1996.
  36. 36. Klein RG. Archeology and the evolution of human behavior. Evolutionary Anthropology Issues News and Reviews. 2000;9: 17–36.
  37. 37. Klein RG. Whither the Neanderthals? Science. 2003;299: 1525–1527. pmid:12624250
  38. 38. Bar-Yosef O. The Upper Paleolithic Revolution. Annual Review of Anthropology. 2002;31: 363–393.
  39. 39. Conard NJ, Bolus M, Goldberg P, Münzel SC. The last Neanderthals and first modern humans in the Swabian Jura. In: Conard NJ, editor. When Neanderthals and Modern Humans Met. Tübingen: Kerns Verlag; 2006. pp. 305–341.
  40. 40. Conard NJ. The Demise of the Neanderthal Cultural Niche and the Beginning of the Upper Paleolithic in Southwestern Germany. In: Conard NJ, Richter J, editors. Neanderthal Lifeways, Subsistence and Technology. Dordrecht: Springer Netherlands; 2011. pp. 223–240.
  41. 41. Floss H. Did they meet or not? Observations on Châtelperronian and Aurignacian settlement patterns in eastern France. In: Zilhão J, d’Errico F, editors. The Chronology of the Aurignacian and of the Transitional Technocomplexes. Lisboa: Instituto Português de Arqueologia; 2003. pp. 273–287.
  42. 42. Wynn T, Coolidge FL. The expert Neandertal mind. Journal of Human Evolution. 2004;46: 467–487. pmid:15066380
  43. 43. Green RE, Krause J, Briggs AW, Maricic T, Stenzel U, Kircher M, et al. A Draft Sequence of the Neandertal Genome. Science. 2010;328: 710–722. pmid:20448178
  44. 44. Kuhlwilm M, Gronau I, Hubisz MJ, de Filippo C, Prado-Martinez J, Kircher M, et al. Ancient gene flow from early modern humans into Eastern Neanderthals. Nature. 2016;530: 429–433. pmid:26886800
  45. 45. Prüfer K, Racimo F, Patterson N, Jay F, Sankararaman S, Sawyer S, et al. The complete genome sequence of a Neanderthal from the Altai Mountains. Nature. 2014;505: 43–49. pmid:24352235
  46. 46. Fu Q, Li H, Moorjani P, Jay F, Slepchenko SM, Bondarev AA, et al. Genome sequence of a 45,000-year-old modern human from western Siberia. Nature. 2014;514: 445–449. pmid:25341783
  47. 47. Fu Q, Hajdinjak M, Moldovan OT, Constantin S, Mallick S, Skoglund P, et al. An early modern human from Romania with a recent Neanderthal ancestor. Nature. 2015;524: 216–219. pmid:26098372
  48. 48. Johansson S. The Talking Neanderthals: What Do Fossils, Genetics, and Archeology Say? BIOLINGUISTICS. 2013;7: 35–74.
  49. 49. Stringer CB, Finlayson JC, Barton RNE, Fernández-Jalvo Y, Cáceres I, Sabin RC, et al. Neanderthal exploitation of marine mammals in Gibraltar. PNAS. 2008;105: 14319–14324. pmid:18809913
  50. 50. Cortés-Sánchez M, Morales-Muñiz A, Simón-Vallejo MD, Lozano-Francisco MC, Vera-Peláez JL, Finlayson C, et al. Earliest Known Use of Marine Resources by Neanderthals. PLOS ONE. 2011;6: e24026. pmid:21935371
  51. 51. Henry AG, Brooks AS, Piperno DR. Microfossils in calculus demonstrate consumption of plants and cooked foods in Neanderthal diets (Shanidar III, Iraq; Spy I and II, Belgium). Proceedings of the National Academy of Sciences. 2011;108: 486–491.
  52. 52. Hardy BL, Moncel M-H. Neanderthal Use of Fish, Mammals, Birds, Starchy Plants and Wood 125–250,000 Years Ago. PLOS ONE. 2011;6: e23768. pmid:21887315
  53. 53. Hardy K, Buckley S, Collins MJ, Estalrrich A, Brothwell D, Copeland L, et al. Neanderthal medics? Evidence for food, cooking, and medicinal plants entrapped in dental calculus. Naturwissenschaften. 2012;99: 617–626. pmid:22806252
  54. 54. Hardy BL, Moncel M-H, Daujeard C, Fernandes P, Béarez P, Desclaux E, et al. Impossible Neanderthals? Making string, throwing projectiles and catching small game during Marine Isotope Stage 4 (Abri du Maras, France). Quaternary Science Reviews. 2013;82: 23–40.
  55. 55. Salazar-García DC, Power RC, Sanchis Serra A, Villaverde V, Walker MJ, Henry AG. Neanderthal diets in central and southeastern Mediterranean Iberia. Quaternary International. 2013;318: 3–18.
  56. 56. Heyes PJ, Anastasakis K, de Jong W, van Hoesel A, Roebroeks W, Soressi M. Selection and Use of Manganese Dioxide by Neanderthals. Sci Rep. 2016;6: 22159. pmid:26922901
  57. 57. d’Errico F. The invisible frontier. A multiple species model for the origin of behavioral modernity. Evol Anthropol. 2003;12: 188–202.
  58. 58. Stepanchuk VN, Vasilyev SV, Khaldeeva NI, Kharlamova NV, Borutskaya SB. The last Neanderthals of Eastern Europe: Micoquian layers IIIa and III of the site of Zaskalnaya VI (Kolosovskaya), anthropological records and context. Quaternary International. 2015;
  59. 59. Pettitt P. The Palaeolithic Origins of Human Burial. New York: Routledge; 2011.
  60. 60. Smirnov Y. Intentional human burial: Middle Paleolithic (last glaciation) beginnings. J World Prehist. 3: 199–233.
  61. 61. Smirnov YA. Mousterian burials in Eurasia. Moscow: Nauka; 1991.; (In Russian).
  62. 62. Zilhão J. Lower and Middle Palaeolithic Mortuary Behaviours and the Origins of Ritual Burial. In: Renfrew C, Boyd MJ, Morley I, editors. Death Rituals, Social Order and the Archaeology of Immortality in the Ancient World. Cambridge: Cambridge University Press; 2016. pp. 27–44.
  63. 63. Sandgathe DM, Dibble HL, Goldberg P, McPherron SP. The Roc de Marsal Neandertal child: A reassessment of its status as a deliberate burial. Journal of Human Evolution. 2011;61: 243–253. pmid:21664649
  64. 64. Soressi M, d’Errico F. Pigments, gravures, parures : les comportements symboliques controversés des Néandertaliens. In: Vandermeersch B, Maureille B, editors. Les Néandertaliens Biologie et cultures. Paris: Éditions du CTHS; 2007. pp. 297–309.
  65. 65. Roebroeks W, Sier MJ, Nielsen TK, Loecker DD, Parés JM, Arps CES, et al. Use of red ochre by early Neandertals. PNAS. 2012;109: 1889–1894. pmid:22308348
  66. 66. Bodu P, Salomon H, Leroyer M, Naton H-G, Lacarriere J, Dessoles M. An open-air site from the recent Middle Palaeolithic in the Paris Basin (France): Les Bossats at Ormesson (Seine-et-Marne). Quaternary International. 2014;331: 39–59.
  67. 67. Bonjean D, Vanbrabant Y, Abrams G, Pirson S, Burlet C, Di Modica K, et al. A new Cambrian black pigment used during the late Middle Palaeolithic discovered at Scladina Cave (Andenne, Belgium). Journal of Archaeological Science. 2015;55: 253–265.
  68. 68. Cârciumaru M, Moncel M-H, Anghelinu M, Cârciumaru R. The Cioarei-Borosteni Cave (Carpathian Mountains, Romania): Middle Palaeolithic finds and technological analysis of the lithic assemblages. Antiquity. 2002;76: 681–690.
  69. 69. Cârciumaru M, Niţu E-C, Cîrstina O. A geode painted with ochre by the Neanderthal man. Comptes Rendus Palevol. 2015;14: 31–41.
  70. 70. Hoffecker JF. Desolate landscapes: Ice-age settlement in Eastern Europe. Piscataway, NJ: Rutgers University Press; 2002.
  71. 71. Smith RF. An Individual-based Comparative Advantage Model: Did Economic Specialization Mediate the Fluctuating Climate of the Late Pleistocene During the Transition from Neanderthals to Modern Humans? Doctoral dissertation. Rutgers, The State University of New Jersey; 2007.
  72. 72. Šajnerová-Dušková A, Fridrich J, Fridrichová-Sýkorová I. Pitted and grinding stones from Middle Palaeolithic settlements in Bohemia: a functional study. In: Sternke F, Costa LJ, Eigeland L, editors. Non-flint raw material use in prehistory: old prejudices and new directions Proceedings of the XV Congress of the UISPP. Oxford: Archaeopress; 2009. pp. 145–151.
  73. 73. Peresani M, Vanhaeren M, Quaggiotto E, Queffelec A, d’Errico F. An Ochered Fossil Marine Shell From the Mousterian of Fumane Cave, Italy. PLoS ONE. 2013;8: e68572. pmid:23874677
  74. 74. Zilhão J, Angelucci DE, Badal-García E, d’Errico F, Daniel F, Dayet L, et al. Symbolic use of marine shells and mineral pigments by Iberian Neandertals. PNAS. 2010;107: 1023–1028. pmid:20080653
  75. 75. d’Errico F, Villa P. Holes and grooves: the contribution of microscopy and taphonomy to the problem of art origins. Journal of Human Evolution. 1997;33: 1–31. pmid:9236076
  76. 76. Rodríguez-Vidal J, d’Errico F, Pacheco FG, Blasco R, Rosell J, Jennings RP, et al. A rock engraving made by Neanderthals in Gibraltar. PNAS. 2014;111: 13301–13306. pmid:25197076
  77. 77. Stout D, Toth N, Schick K, Chaminade T. Neural correlates of Early Stone Age toolmaking: technology, language and cognition in human evolution. Philosophical Transactions of the Royal Society of London B: Biological Sciences. 2008;363: 1939–1949. pmid:18292067
  78. 78. Stout D, Chaminade T. The evolutionary neuroscience of tool making. Neuropsychologia. 2007;45: 1091–1100. pmid:17070875
  79. 79. Stout D, Chaminade T. Stone tools, language and the brain in human evolution. Phil Trans R Soc B. 2012;367: 75–87. pmid:22106428
  80. 80. Hecht EE, Gutman DA, Khreisheh N, Taylor SV, Kilner J, Faisal AA, et al. Acquisition of Paleolithic toolmaking abilities involves structural remodeling to inferior frontoparietal regions. Brain Struct Funct. 2014;220: 2315–2331. pmid:24859884
  81. 81. Stout D, Passingham R, Frith C, Apel J, Chaminade T. Technology, expertise and social cognition in human evolution. European Journal of Neuroscience. 2011;33: 1328–1338. pmid:21375598
  82. 82. Bar‐Yosef O, Van Peer P. The Chaîne Opératoire Approach in Middle Paleolithic Archaeology. Current Anthropology. 2009;50: 103–131.
  83. 83. Lemonnier P. Bark capes, arrowheads and Concorde: on social representations of technology. In: Hodder I, editor. The meaning of things Material culture and symbolic expression. Hammersmith: HarperCollins Academic; 1989. pp. 156–171.
  84. 84. Lemonnier P. Elements for an Anthropology of Technology. Ann Arbor, Michigan: University of Michigan; 1992.
  85. 85. Soressi M, Geneste J-M. Special Issue: Reduction Sequence, Chaîne Opératoire, and Other Methods: The Epistemologies of Different Approaches to Lithic Analysis. The History and Efficacy of the Chaîne Opératoire Approach to Lithic Analysis: Studying Techniques to Reveal Past Societies in an Evolutionary Perspective. PaleoAnthropology. 2011;2011: 334–350.
  86. 86. Schlanger N. Understanding Levallois: Lithic Technology and Cognitive Archaeology. Cambridge Archaeological Journal. 1996;6: 231–254.
  87. 87. d’Errico F, Banks WE. The Archaeology of Teaching: A Conceptual Framework. Cambridge Archaeological Journal. 2015;25: 859–866.
  88. 88. Stout D. Skill and Cognition in Stone Tool Production: An Ethnographic Case Study from Irian Jaya. Current Anthropology. 2002;43: 693–722.
  89. 89. Foley RA, Lahr MM. The evolution of the diversity of cultures. Philosophical Transactions of the Royal Society of London B: Biological Sciences. 2011;366: 1080–1089. pmid:21357230
  90. 90. Lewis HM, Laland KN. Transmission fidelity is the key to the build-up of cumulative culture. Philosophical Transactions of the Royal Society of London B: Biological Sciences. 2012;367: 2171–2180. pmid:22734060
  91. 91. Weber EH. De Pulen, Resorptione, Auditu et Tactu: Annotationes Anatomicae et Physiologicae. Leipzig: Koehler; 1834.
  92. 92. Fechner GT. Elemente der Psychophysik. Leipzig: Breitkopf und Härtel; 1860.
  93. 93. Teghtsoonian R. On the exponents in Stevens’ law and the constant in Ekman’s law. Psychological Review. 1971;78(1): 71–80. pmid:5545194
  94. 94. Coren S, Ward LM, Enns JT. Sensation and Perception. 6th Edition. New York: John Wiley & Sons; 2004.
  95. 95. Levine MW, Shefner JM. Levine & Shefner’s Fundamentals of Sensation and Perception. Oxford and New York: Oxford University Press; 2000.
  96. 96. Eerkens JW. Practice Makes Within 5% of Perfect: Visual Perception, Motor Skills, and Memory in Artifact Variation. Current Anthropology. 2000;41: 663–668.
  97. 97. Eerkens JW, Bettinger RL. Techniques for assessing standardization in artifact assemblages: Can we scale material variability? American Antiquity. 2001;66: 493–504.
  98. 98. Eerkens JW, Lipo CP. Cultural transmission, copying errors, and the generation of variation in material culture and the archaeological record. Journal of Anthropological Archaeology. 2005;24: 316–334.
  99. 99. Evans SC. Communication and Information Storage in the Upper Palaeolithic: An Analysis of Geometrically Engraved Bone and Antler Objects from South-west Europe. Unpublished PhD Thesis, University of Cambridge; 2015.
  100. 100. Peresani M, Fiore I, Gala M, Romandini M, Tagliacozzo A. Late Neandertals and the intentional removal of feathers as evidenced from bird bone taphonomy at Fumane Cave 44 ky B.P., Italy. PNAS. 2011;108: 3888–3893. pmid:21368129
  101. 101. Romandini M, Fiore I, Gala M, Cestari M, Guida G, Tagliacozzo A, et al. Neanderthal scraping and manual handling of raptors wing bones: Evidence from Fumane Cave. Experimental activities and comparison. Quaternary International. 2016
  102. 102. Romandini M, Peresani M, Laroulandie V, Metz L, Pastoors A, Vaquero M, et al. Convergent Evidence of Eagle Talons Used by Late Neanderthals in Europe: A Further Assessment on Symbolism. PLOS ONE. 2014;9: e101278. pmid:25010346
  103. 103. Finlayson C, Brown K, Blasco R, Rosell J, Negro JJ, Bortolotti GR, et al. Birds of a Feather: Neanderthal Exploitation of Raptors and Corvids. PLOS ONE. 2012;7: e45927. pmid:23029321
  104. 104. Radovčić D, Sršen AO, Radovčić J, Frayer DW. Evidence for Neandertal Jewelry: Modified White-Tailed Eagle Claws at Krapina. PLOS ONE. 2015;10: e0119802. pmid:25760648
  105. 105. Morin E, Laroulandie V. Presumed Symbolic Use of Diurnal Raptors by Neanderthals. PLOS ONE. 2012;7: e32856. pmid:22403717
  106. 106. Mourer-Chauvire C. Faunes d’oiseaux du pléistocène de France: Systématique, évolution et adaptation, interprétation paléoclimatique. Geobios. 1975;8: 333–352, IN1–IN11.
  107. 107. Fiore I, Gala M, Tagliacozzo A. Ecology and subsistence strategies in the eastern Italian Alps during the Middle Palaeolithic. International Journal of Osteoarchaeology. 2004;14: 273–286.
  108. 108. Mourre V, Costamagno S, Thiébaut C, Allard M, Bruxelles L, Colonge D, et al. Le site moustérien de la Grotte du Noisetier à Fréchet-Aure (Hautes-Pyrénées)—premiers résultats des nouvelles fouilles. In: Jaubert J, Bordes JG, Ortega I, editors. Les sociétés du Paléolithique dans un Grand Sud-Ouest de la France : nouveaux gisements, nouveaux résultats, nouvelles méthodes. Société préhistorique française; 2008. pp. 189–202.
  109. 109. Leroi-Gourhan A, Leroi-Gourhan A. Chronologie des grottes d’Arcy-sur-Cure (Yonne). Gallia préhistoire. 1964;7: 1–64.
  110. 110. d’Errico F, Zilhão J, Julien M, Baffier D, Pelegrin J. Neanderthal Acculturation in Western Europe? A Critical Review of the Evidence and Its Interpretation. Current Anthropology. 1998;39: S1–S44.
  111. 111. Laroulandie V. Exploitation des ressources aviaires durant le Paléolithique en France : bilan critique et perspectives. In: Brugal JP, Desse J, editors. Petits Animaux et Sociétés Humaines Du complément alimentaire aux ressources utilitaires Actes des XXIVe rencontres internationales d’archéologie et d’histoire, Antibes, 23–25 octobre 2003. Antibes: Éditions APDCA; 2004. pp. 163–172.
  112. 112. Mourer-Chauviré C. Les oiseaux du grand abri de La Ferrassie, à Savignac-de-Miremont (Dordogne). In: Delporte H, editor. Le grand abri de la Ferrassie, Fouilles 1968–1976. Etudes Quaternaires 7; 1984. pp. 99–103.
  113. 113. Roger T. L’avifaune du Pléistocène moyen et supérireur du bord de la Méditerranée européenne : Orgnac 3, Lazaret (France), Caverna delle Fate, Arma delle Manie (Italie), Kalamakia (Grèce), Karain E (Turquie). Paléontologie, Taphonomie et Paléoécologie. Paris: Museum national d’histoire naturelle—MNHN; 2004.
  114. 114. Gerbe M, Thiébault C, Mourre V, Bruxelles L, Coudenneau A. Influence des facteurs environnementaux, économiques et culturels sur les modalités d’exploitation des ressources organiques et minérales par les Néandertaliens des Fieux (Miers, Lot). Transitions, ruptures et continuités en Préhistoire, Actes du XXVIIème Congrès Préhistorique de France, Bordeaux-les Eyzies. 2012;31: 257–279.
  115. 115. Soressi M, Rendu W, Texier J-P, Claud Loïc Daulny É, d’Errico F, Laroulandie V, et al. Pech-de-l’Azé I (Dordogne, France) : nouveau regard sur un gisement moustérien de tradition acheuléenne connu depuis le XIXe siècle. In: Jaubert J, Bordes JG, Ortega I, editors. Les sociétés Paléolithiques d’un grand Sud-Ouest : nouveaux gisements, nouvelles méthodes, nouveaux résultats—Actes des journées décentralisées de la SPF des 24–25 novembre 2006. Société Préhistorique française; 2008. p. 95–132.
  116. 116. Dibble HL, Berna F, Goldberg P, McPherron SP, Mentzer S, Niven L, et al. A preliminary report on Pech de l’Azé IV, layer 8 (Middle Paleolithic, France). PaleoAnthropology. 2009;2009: 182–219.
  117. 117. Gaudzinski-Windheuser S, Niven L. Hominin Subsistence Patterns During the Middle and Late Paleolithic in Northwestern Europe. In: Hublin J-J, Richards MP, editors. The Evolution of Hominin Diets. Springer Netherlands; 2009. pp. 99–111.
  118. 118. Julien M, Vanhaeren M, d’Errico F. L’industrie osseuse châtelperronienne de la Grotte du Renne, (Arcy-sur-Cure). In: Julien M, editor. Le Châtelperronien de la Grotte du Renne (Arcy-Sur-Cure). Supplément à Paléo.: Forthcoming.
  119. 119. Vanhaeren M, Julien M, d’Errico F, Mourer-Chauviré C, Lozouet P. Les objets de parure. In: Julien M, editor. Le Châtelperronien de la Grotte du Renne (Arcy-Sur-Cure). Supplément à Paléo.: Forthcoming.
  120. 120. Tsvelykh AN, Stepanchuk VN. An artefact made of a bird bone from Zaskalnaya VI (Kolosovskaya) Mousterian site in Crimea. Zamyatninskiy sbornik. 2014;3: 124–127. (In Russian).
  121. 121. Kolosov YG, Stepanchuk VN, Chabai VP. The Early Paleolithic of Crimea. Kiev: Naukova dumka; 1993.; (In Russian).
  122. 122. Kolosov YG. The Ak-Kaya Mousterian Culture. Naukova dumka; 1986. Kiev; (In Russian).
  123. 123. Kolosov YG. Palaeoanthropological finds from the Ak-Kaya rock-shelter. Voprosy antropologii. 1973; 162–166. (In Russian).
  124. 124. Kolosov YG. Ak-Kaya Mousterian sites and some results of their investigation. In: Kolosov YG, editor. Issledovanie paleolita v Krymu (1879–1979). Kiev: Naukova dumka; 1979. p. 33–55. (In Russian).
  125. 125. Kolosov YG, Stepanchuk VN. Crimean assemblages with bifacial tools: brief review. A la recherche de l’homme préhistorique Etudes et Recherches Archeologiques de l`Universite de Liege. 2000; 265–274.
  126. 126. Velichko AA, Dushevskij VP, Podgorodetskij PD. The sites of Zaskalnaya V and Zaskalnaya VI. Archaeology and Paleogeography of the Early Paleolithic of the Crimea and Caucasia. Moscow: Nauka; 1978.; (In Russian).
  127. 127. Chabai VP. The Middle Paleolithic of Crimea (Sredniy paleolit Kryma). Kiev: Shlyakh; 2004.; (In Russian).
  128. 128. Stepanchuk V, Kovalyukh N, Van der Plicht J. Radiocarbon age of the Late Pleistocene Paleolithic sites of Crimea. Kamiana doba Ukraini. 2004;5: 34–61. (In Ukrainian).
  129. 129. Hedges REM, Housley RA, Pettitt PB, Ramsey CB, Klinken GJV. Radiocarbon Dates from the Oxford AMS System: Archaeometry Datelist 21. Archaeometry. 1996;38: 181–207.
  130. 130. Chabai VP, Marks AE, Otte M. Variability of Middle and Early Upper Palaeolithic of the Crimea. Arheologia. 1998;4: 19–47. (In Russian).
  131. 131. Danilova EI. Anthropological description of bone remains of Neanderthal children from the cultural layer III of the Mousterian site of Zaskalnaya VI (Crimea). Voprosy antropologii. 1983; 72–87. (In Russian).
  132. 132. Boroutskaya SB, Vasilyev SV, Stepanchuk VN. On the question of paleoanthropology of Crimean Neanderthals. Renewing of studies. Vestnik antropologii. 2007; 101–104. (In Russian).
  133. 133. Stepanchuk VN, Vasiliev SV, Borutskaya SB. Data on the reconstruction of the stratigraphic context of anthropological finds from layers III and IIIa of Zaskalnaya VI (Kolosovskaya). (Dannye k rekonstrukcii stratigraficheskogo i planigraficheskogo konteksta antropologicheskih nahodok iz sloya III i IIIa Zaskal’noj VI (Kolosovskoj). Stratum plus. 2012;1: 111–127. (In Russian).
  134. 134. Gerasimova M., Astakhov SN, Velichko AA. Paleolithic man, his material culture and natural environment (Paleoliticheskij chelovekb ego material’naya kul’tura i prirodnaya sreda obitaniya). Sankt-Peterburg: Nestor-Istoria; 2007.; (In Russian).
  135. 135. Fedorchenko OS. Taphonomical characteristic of faunal remains from layer III. The Late Neanderthals of the Crimea Zaskalnaya VI (Kolosovskaya), layers IIIa and III. Forthcoming. p. 46–60. (In Russian).
  136. 136. Sapozhnikova GV. Bone Instruments of Crimean Neanderthals (After materials of Zaskalnaya VI (Kolosovskaya), Prolom I and Prolom II). Kamiana Doba Ukrainy. 2008; 52–58. (In Ukrainian).
  137. 137. Tsvelykh AN. Avifauna of archaeological layers II, III and IV. The Late Neanderthals of the Crimea Zaskalnaya VI (Kolosovskaya), layers IIIa and III. Forthcoming. p. 73–76. (In Russian).
  138. 138. Livezey BC, Zusi RL. Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion. Zoological Journal of the Linnean Society. 2007;149: 1–95. pmid:18784798
  139. 139. d’Errico F. Microscopic and statistical criteria for the identification of prehistoric systems of notation. Rock Art Research. 1991;8: 83–89.
  140. 140. d’Errico F. L’art gravé azilien: de la technique à la signification. Paris: CNRS éditions; 1994.
  141. 141. d’Errico F. A New Model and its Implications for the Origin of Writing: The La Marche Antler Revisited. Cambridge Archaeological Journal. 1995;5: 163–206.
  142. 142. d’Errico F. Image analysis and 3-D optical surface profiling of upper Palaeolithic mobiliary art. Microscopy and analysis. 1995;51: 27–29.
  143. 143. d’Errico F. Palaeolithic origins of artificial memory systems: An evolutionary perspective. In: Renfrew C, Scarre C, editors. Cognition and material culture: The archaeology of symbolic storage. Cambridge: McDonald Institute for Archaeological Research; 1998. pp. 19–50.
  144. 144. Fritz C. Towards the Reconstruction of Magdalenian Artistic Techniques: the Contribution of Microscopic Analysis of Mobiliary Art. Cambridge Archaeological Journal. 1999;9: 189–208.
  145. 145. Baryshnikov GF, Potapova OR. The Birds of Crimean Middle Paleolithic. Trudy Zool Institute of the USSR Academy of Sciences. 1988;182: 30–63. (In Russian).
  146. 146. Voinstvenskiy MA. The Fossil avifauna of Ukraine. Prirodnaya obstanovka i fauny proshlogo. 1967;3: 3–76. (In Russian).
  147. 147. Kolosov YG. Mousterian sites of Belogorsk area. Kiev: Naukova dumka; 1983.; (In Russian).
  148. 148. Tugarinov AY. The birds of Crimea during the Wurm glaciation (based on the excavations of the Crimean caves). Trudy Sovetskoy sektsii Mezhdunarodnoy assotsiatsii po izucheniyu chetvertichnogo perioda. 1937; 97–114. (In Russian).
  149. 149. Gavris G, Taykova S. Aves from Karabi-Tamchin cave. In: Chabai VP, Monigal K, Marks AE, editors. The Paleolithic of Crimea III The middle Paleolithic and early upper paleolithic of Eastern Crimea. Liège: Etudes et Recherches Archeologiques de l`Universite de Liege; 2004. pp. 295–298.
  150. 150. Kostin YV. The Birds of Crimea. Moscow: Nauka; 1983.; (In Russian).
  151. 151. Val A, de la Peña P, Wadley L. Direct evidence for human exploitation of birds in the Middle Stone Age of South Africa: The example of Sibudu Cave, KwaZulu-Natal. Journal of Human Evolution. 2016;99: 107–123. pmid:27650583
  152. 152. Funk C, Holt E, Taivalkoski A, Howard J, Poltorak D. Avifauna discard packages and bone damage resulting from human consumption processes. Journal of Archaeological Science: Reports. 2016;5: 383–391.
  153. 153. Romero AJ, Díez JC, Rodríguez L, Arceredillo D. Anthropic fractures and human tooth marks: An experimental approach to non-technological human action on avian long bones. Quaternary International. 2016;421: 219–227.
  154. 154. Tomek T, Bocheński ZM. The comparative osteology of European corvids (Aves: Corvidae), with a key to the identification of their skeletal elements. Kraków: Wydawnictwa—Instytut Systematyki i Ewolucji Zwierząt -Polska Akademia Nauk; 2000.
  155. 155. Norman JF, Todd JT, Perotti VJ, Tittle JS. The visual perception of three-dimensional length. Journal of Experimental Psychology: Human Perception and Performance. 1996;22: 173–186. pmid:8742260
  156. 156. Norman JF, Lappin JS, Norman HF. The perception of length on curved and flat surfaces. Perception & Psychophysics. 2000;62: 1133–1145.
  157. 157. Norman JF, Norman HF, Lee Y-L, Stockton D, Lappin JS. The visual perception of length along intrinsically curved surfaces. Perception & psychophysics. 2004;66: 77–88.