This study is about a less recognised and controversial phenomenon in rock art production. In my opinion certain images and/or elements of an image have intentionally been “hidden” by the manufacturer, possibly for several (often differing) reasons. A small selection of examples from all over the world have been included and illustrated. However, I argue that the most “conspicuously” “hidden” elements are not even present; they are invisible (on purpose!).

By Maarten van Hoek

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“Hidden” Images in Rock Art

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Maarten van Hoek

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Introduction

Literally millions of all sorts of rock art images (both petroglyphs and pictographs) have so far been recorded all over the world (except for Antarctica). Although most of them are clearly visible, many are hard to discern on the rock surfaces they were made on. This “invisibility” may have been caused by increasing weathering and erosion. It is unknown how many images have gone lost forever this way. However, often rock art images are also hard to recognise because of being superimposed by layers of other images. Yet, although interesting, instances of superimposition (see Figure 16) are not the subject of this study.

Instead, this study focusses on rock art images that seem to “trick” the observer by “hiding” (a certain aspect of) an image. This report offers a selection of instances where a rock art image in first instance may escape being noticed, because it seems to have intentionally been “hidden” by the prehistoric manufacturer. Yet, the degree of being “hidden” may vary. Some “tricks” will be recognised immediately; others not. I will start with a non-rock art example to illustrate what I mean.

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The Case of Kuntur Wasi

Kuntur Wasi (the House of the Condor), an ancient Formative Period Cupisnique Temple in the mountains of northern Peru, features several statues and friezes, including some most intriguing examples of diprosopus (one head having two faces). It concerns four stone blocks that all have been sculptured with a menacing head. They are incorporated into the walls of a square, sunken courtyard. Those four sculptured blocks are no form of rock art, but a form of architectural art. Each sculpture is set in the middle of each wall and thus they are facing each other two by two. What is exceptional is that each decorated face comprises one fully frontally depicted MSC-Style head that is actually composed of two profile heads that are facing each other as well. Figure 1 shows the diprosopus (triprosopus?) on Monolith 89-2 at Kuntur Wasi. The result is that actually three heads/faces are shown. Such Cupisnique sculptures could easily have been manufactured as rock art images, but as far as I know there is no MSC-Style rock art image (see Van Hoek 2011 for more information) that can be compared with the Kuntur Wasi sculptures.

Figure 1. Monolith 89-2 at Kuntur Wasi, northern Peru, with the two profile faces facing each other and the menacing frontal face facing the observer. Photographs © by Maarten van Hoek.

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The Case of Chichitarra

The faces on Monolith 89-2 at Kuntur Wasi are clearly an instance of a premeditated artistic expression that is deeply rooted in the worldview of the ancient Cupisnique Cultures of coastal northern Peru. There are, however, instances where the “hidden” nature of a rock art element is just a matter of chance; or a purely personal decision. The image is often – as far as we can judge – not intentionally “hidden”. Yet, it sometimes proves that such a “hidden” element remains unnoticed for a long time, despite several scientific investigations.

A fine example is found “hidden” among a group of petroglyphs on Panel CHI-012 at the rock art site of Chichitarra in the Palpa Valley of southern Peru. The great majority of the images in the Palpa Valley are made by pecking lines. However, there are a few panels on which an image was created by removing the stone around the image. The resulting slightly higher part thus forms an embossed image. The “hidden” image on Panel CHI-012 is a quadruped that is intentionally positioned between the legs of a larger quadruped. But the “hidden” animal has not been manufactured by creating just an outline or a fully pecked area depicting the animal. Instead, the “hidden” zoomorph (orange in Figure 2) has been created by partially using the contours of the larger quadruped (black in Figure 2) and for the rest removing the other parts of the stone surface (dark-blue in Figure 2), necessary to shape the animal.

Figure 2. Panel CHI-012 at Chichitarra, Palpa Valley, southern Peru. Photograph and drawing © by Maarten van Hoek.

Panel CHI-012 was probably first illustrated by explorer Nereida Apaza from Arequipa in 1979, who apparently did not notice the “hidden” zoomorph, as the “hidden” animal was absent in his sketch (Van Hoek 2021: Fig. 8A). The panel was visited and photographed several times after 1979 (also by my wife Elles and me [in 2006]). When rock art researcher Rainer Hostnig from Cusco, Peru, photographed the panel in 2004, the “hidden” animal was clearly visible in his photo. Unfortunately, the panel was then already desecrated by someone-else who wrote “27 – A” right across the “hidden” animal; apparently not noticing the image (this lettering has since then weathered off, or has been carefully removed). The photograph taken by Cristhian Siguas Ferreyra in 2010 does not show the “hidden” image, which proves that it is just a matter of having luck with the lighting when photographing a petroglyph panel.

Surprisingly, also the illustration by Orefici (Van Hoek 2021: Fig. 8B) does not show the “hidden” zoomorphic image. Also, the “hidden” image – which is important because of the carving technique and its premeditated position – is not mentioned in his text. Moreover, in fact all the petroglyphs on Panel CHI-012 (labelled Roca 14 by Orefici) are inaccurately presented in his drawing  (Orefici 2012: 39). Panel CHI-012 is also illustrated by Peter Fux (2011: 191; Fig. 57-2; FUX-20) and although he accurately draws the embossed quadruped and bird, his drawing does not show the embossed character of two of the petroglyphs.

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The Case of the “Threesome”

Located only 275 m NE of Chichitarra is the rock art site of La Cabañita. It was Núñez Jiménez who first described the majority of the petroglyphs at La Cabañita (1986: 283 – 294). He seems to have recorded at least 32 boulders/panels with petroglyphs, among which is also Panel CAB-002 (1986: Fig. 2000).  This panel shows at least three, intimately arranged petroglyphs of quadrupeds, of which #1 has its head partially shaped by the legs of animal #2 (Figure 3) using more or less the same “hiding” technique as was used with the “hidden” animal on Panel CHI-012 at nearby Chichitarra (see Figure 2). Thus this arrangement is highly premeditated as well.

Figure 3. Panel CAB-002 at La Cabañita, Palpa Valley, southern Peru. Photograph © by Maarten van Hoek.

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The Case of Cuchillo Negro Creek

Cuchillo Negro Creek is a rock art site in New Mexico, USA, where a complex petroglyph echoes the same perception as with the Palpa Valley images. But this time the composing elements are somewhat better recognisable; the two “hidden” elements are less “hidden” and more easily identifiable. It concerns two outlined images of laterally depicted quadrupeds (most likely representing a larger male deer [judged by the antlers] and a smaller female [?] deer) that are joined bottom to bottom, thus facing away from each other (Figure 4).

Figure 4. Petroglyphs at Cuchillo Negro Creek, New Mexico, USA. Drawing © by Maarten van Hoek, based on a photograph by Margaret Berrier.

Interestingly, “hidden”  between the legs of each animal is the image of a bird with outspread wings, both having a short neck that possibly ends in a bicephalic head. Importantly, the vertical lines forming the ends of the wings also serve to form the legs of the deer, while the horizontal lines form the belly of the deer. It is unknown to me whether the natural cavity (N) has been incorporated on purpose. Also the meaning of the deer-bird combination is unknown to me. The whole composition might depict or – rather – symbolise an (actually unrealisable?) copulation scene. The scene is mentioned in some publications (for instance Slifer 1998: 175, Fig. 177), but not explained (as far as I could check).

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The Case of Fishman

In and around the city of Sydney, on the east coast of Australia, are numerous rock art sites featuring outlined petroglyphs of (often large) large marine creatures, kangaroos and (usually somewhat smaller) anthropomorphs; many of them described and illustrated by Peter Stanbury and John Clegg (1990). One of those Sacred Sites, shamefully now located in one of the suburbs of the town and almost completely hidden by buildings, is called Fishman. The site is aptly named after one – possibly unique – image depicting an anthropomorphic figure that is combined in an exceptional way with the image of a sea creature (Figure 5). Also in this configuration parts of the inner lines forming the legs of the anthropomorphic figure, simultaneously form parts of the lines shaping the fish. The fish has an open mouth, the lines of which also form the phallus of the obviously male figure.

Figure 5. Petroglyph(s) at Fishman, Australia. Drawings © by Maarten van Hoek, based on an unnumbered drawing published by Peter Stanbury and John Clegg (1990: Page 118).

The meaning of this intentional composition is not explained. Stanbury and Clegg only suggest that the composition is a “pun” of the manufacturer (1990: Page 118). However, it is generally accepted that (all?) rock art images made by the Australian Aboriginals often have a (much) deeper (and often completely different) meaning than is suggested by just the layout of the configuration. Perhaps it depicts a fertilising scene, in which the male anthropomorph is graphically and symbolically linked with its phallus to the female (?) sea creature, possibly in order to generate a prosperous fish-hunt. The site once had an open view towards the ocean (regarded to be female? [as is often the case]), thus linking the site with an important food-source. If my interpretation is correct, I wonder why no other, analogous combinations have been recorded in the area (although many similar anthropomorphs show the same suggestion of a fish-head between the legs, but do not have not the fish-tail). It is therefore likely that creating this specific combination was an individual decision, not replicated by others.

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The Case of the “Hidden” Archer

Overlooking the Colorado River SW the town of Moab, Utah, USA, are the Potash Road rock art sites. One panel features (among many other petroglyphs) an interesting image. At first sight it looks as if a Bighorn Sheep is aiming a bow-and-arrow at another Bighorn (Figure 6). However, in my opinion the petroglyph originally started with creation of a crouched archer that (later?) got a hide of a Bighorn added as disguise, although it is hard to tell whether the hide (brown in Figure 6) was added by the same manufacturer. Attached to the purported hide is the head of a female Bighorn, possibly to lure the male Bighorn. But it is certain that the archer ultimately became a “hidden” part of the configuration, while hiding from the other Bighorns under a hide. This definitely is no instance of random superimposition.

Figure 6. Petroglyphs at Potash Road, Utah, USA (many more details on Bighorn images in Van Hoek 2015). Photograph and drawings © by Maarten van Hoek.

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The Case of the “Trophy-Bird”

Noticed for the first time by us is the “hidden” message of a layered petroglyph depicting a unique “bird” image on north facing Panel A of Boulder AP3-171 at Alto de Pitis; a most important rock art site in the Majes Valley of southern Peru. The panel (Figure 7A) has a most interesting collection of petroglyphs, including some “Trophy” Heads (some unfinished); one of which clearly represents the completely finished image of a “Trophy” Head.

However, of special interest is another petroglyph (Figure 7B; framed in Figure 7A). At first sight it seems to depict a fully frontally depicted bird, as it has two curved wings and two straight legs, both with three digits; all at the anatomical correct positions. Between the two legs, six long, parallel lines depict the tail-feathers of the bird. The square body is filled with small dots, which, however, is not unusual for zoomorphic petroglyphs in the Central Majes Valley. Intriguingly however, it is the only “bird” petroglyph on this panel. But it is more than just a bird. It has a ”hidden” message, which went unnoticed, as the older layer was “hidden”.

In view of the remarkable collection of the (square) “Trophy” Head images on the panel, it was especially the square layout of this “bird” (Figure 7B) that triggered my curiosity, as square-bodied bird petroglyphs are extremely rare in Desert Andes rock art (and also in the Majes Rock Art Region). Could it be that this square-bodied “bird” petroglyph originally started off as a “Trophy” Head? In my opinion that was the case.

Figure 7. A: Panel AP3-171A at Alto de Pitis, Majes, Peru. B: Detail of the “Trophy-Bird” (note the much smaller, circular “Trophy” Head) . Photographs © by Maarten van Hoek.

Indeed, the two thin legs (ignoring the [added] digits) together with the six thin tail-lines prove to represent the hair of the “Trophy” Head  (comparable with other images on this panel), while also the two curved wings could have easily been added. More importantly, when scanning the dots inside the body I noticed that one dot was larger and longer than the others. Moreover, it was placed at the anatomically correct position to represent a mouth. The same was true for two large dots that were situated at the correct position of the eyes. The fully pecked, profile head of the “bird” was rather amorphous and because of weathering and the mottled character of the panel, a true “bird’s” head could not be recognised (hence the ‘?’). The pecked area representing the “bird’s” head could have been superimposed upon a short hanging cord. Based on all those convincing indications, it seems only to be justified to accept that the petroglyph started off as a “Trophy” Head (Figure 8A) that was later transformed into a “bird” (Figure 8B). Importantly, it definitely was not a case of accidental superimposition; the transformation from a “Trophy” Head into a “Trophy-Bird” was highly premeditated. But why?

Figure 8. A: The original “Trophy” Head on  Panel AP3-171A at Alto de Pitis, Majes, Peru. B: The resulting “Trophy-Bird”. Drawings © by Maarten van Hoek.

Important in explaining this unique transformation is the fact that in Andean worldview a “Trophy” Head  is a symbol of both life and death (for more information see Van Hoek 2013: 101). The bird-elements have been added to the “Trophy” Head to add the power of the supernatural flight of the “living dead” (the souls of the deceased people in the area) to the realm of the ancestors and deities, which was located at the summit of Apu Coropuna, a Sacred Mountain and the highest volcano of Peru, which is visible from Alto de Pitis about 80 km to the NNW (for a full explanation of this concept see Van Hoek 2013 and 2018).

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The Case of the Ariquilda Anthropomorph

In some cases it is not certain whether (part of) an image was indeed meant to be a “hidden” element. An example is found at the important rock art site of Ariquilda, northern Chile. On Panel ARQn-111 is a most complex anthropomorphic figure with a possible much smaller and simpler figure on its thorax (Figure 9). However, between the legs sits another figure with a square head from which two arms emerge. Was it meant to go unnoticed? Like several other instances mentioned in this study, it uses some of the lines of the largest figure.

Figure 9. Petroglyphs on Panel ARQn-111 at Ariquilda, northern Chile. Photograph and drawing © by Maarten van Hoek.

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The Case of the “Spaghetti Pattern”

It must be emphasised again that creating a “hidden” image must have been intentional and not an instance of a random action. At the extensive rock art site of Miculla (southern Peru) there is a boulder (MIM-010) with a most complex chaos of lines. For that reason it is labelled the “Spaghetti Pattern Stone” by me. At first sight the complex pattern is randomly and confusingly laid out. But a closer look (while trying to ignore some lines) may reveal at least two petroglyphs of quadrupeds (most likely representing camelids of the Miculla Style) and possibly one anthropomorphic petroglyph; all three highlighted in yellow in Figure 10). It is unknown, however, whether the camelids (and the anthropomorph) where manufactured first, and only later incorporated into a complex, “hiding” pattern (or vice versa). A similar, even more complex pattern is found on a boulder in the Vitor Valley of Arequipa, much further to the NW of Miculla. But the photo that I have, does not reveal any “hidden” images.

Figure 10. Petroglyphs on Boulder MIM-010 at Miculla, southern Peru. Photographs and drawing © by Maarten van Hoek.

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The Case of the Deceptive “Butterfly”

Also at Miculla is Boulder MIN-016. On almost vertical Panel B is a squarish motif with internal dots, as well as a complex petroglyph that – at first sight – looks like a butterfly. However, that impression is deceptive. In my opinion the petroglyph comprises three parts, of which the yellow lines seem to have been added later, obscuring the two simultaneously manufactured parts building the “butterfly”. However, the “butterfly” is actually composed of two “seated” anthropomorphic figures (brown and blue in Figure 11) that are both depicted in profile, observing each other. The (exaggerated) large hands/fingers and the (missing) feet are joined. Of course, this is only my subjective interpretation of those “hidden” figures.

Figure 11. Petroglyphs on Boulder MIN-016 at Miculla, southern Peru. Photograph and drawing © by Maarten van Hoek.

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The One Case of the “Two-Face” at Three Rivers

The extensive rock art site of Three Rivers in New Mexico (USA) has – among numerous other images – quite a large collection of petroglyphs of isolated heads, many of them intriguingly manufactured folded across a corner of two panels (the phenomenon of those three-dimensional heads was fully described by me: Van Hoek 2020). Of interest in view of this study is a two-dimensional petroglyph of an isolated head on only one panel. At first sight it is “just” a fully frontally depicted head, filled with complex facial features.

However, a closer look reveals that the head is a unique mixture of the right-hand part of a frontal head and a profile head (Figure 12). There is no question about the intent of the (one and only) manufacturer of this petroglyph. What is obscure however, is exactly what message the creator of this masterpiece intended to share with his or her prehistoric audience. Is the profile head only observing the frontal head (half), or – based on the open, dented mouth of the profile head – is it threatening or attacking the other half? Is it portraying a conflict? We will probably never know. Finally, at Three Rivers there are a few more (less impressive) petroglyphs of isolated head petroglyphs that apparently are composed of two, intimately joined heads.

Figure 12. Petroglyph of a unique heads-combination at Three Rivers, New Mexico, USA. Photographs and (my subjective) drawing © by Maarten van Hoek.

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The Case of the “Wrapped” Camelid

The rock art site of Toro Muerto in the Majes Valley of southern Peru undoubtedly contains the greatest number of decorated panels in the Desert Andes (comprising thousands of petroglyphs), and – although we have inspected the great majority of the petroglyphs at that site – I am certain that we missed quite a few images, thus possibly also instances of “hidden” imagery. We definitely missed one example. It has been created on Boulder TM-NNx-024 at Sector-X; the very northern and highest part of the extensive, five kilometres long boulder field (we did not survey Sector-X; see however Van Hoek 2022).

As far as I know there is only one image on Boulder TM-NNx-024. It features a complex petroglyph of an outlined quadruped (A in Figure 13). However, in my opinion the image actually consists of a simple match-stick image of a camelid (B in Figure 13) that has later (?) been “wrapped” by the lines outlining the match-stick animal (C in Figure 13). The “hidden” match-stick camelid remains hidden until one removes the outline. The reason for “wrapping” the match-stick animal is unknown to me. Perhaps it is just decorative. However, the animal may have been “wrapped” in order to create a very specific type of quadruped that occasionally is found at Toro Muerto, for instance the one on Boulder TM-Aa-015 (Figure 14).

Figure 13. Petroglyph of the “wrapped and hidden” match-stick quadruped on Boulder TM-NNx-024, Sector-X at Toro Muerto, southern Peru. Drawings © by Maarten van Hoek, based on a photograph by Lubetima Te Informa (Facebook).

Figure 14. Petroglyphs on Boulder TM-Aa-015 at Toro Muerto. Note the outlined quadruped. Photograph © by Maarten van Hoek.

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Invisible Objects

A final category of (completely) “hidden” elements involves a group of relatively many images “depicting” Invisible Objects. Convincing instances have – so far – mainly been recognised by me in the rock art and geoglyph art of the Desert Andes. My hypothesis is hard to prove, because informed knowledge is lacking. Only the image(s) and the (cultural) context may offer proof. In my opinion however, intentionally creating a completely Invisible Object occurred in Andean rock art and geoglyph art. It is an extreme form of “hiding” an element and/or image within a specific (rock art) context. However, images “depicting” Invisible Objects all involve instances of suggestion (fully discussed by me: see Van Hoek 2019).

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The Pakra Monkeys

To illustrate what I mean, I will now briefly discuss an – in my opinion – convincing example. The premeditated omission of an object in rock art (in this case a wind-instrument) occurs in a very rare scene on a boulder at Pakra in the valley of the Río Pisco, southern Peru, where three monkeys “in concert” are “playing some sort of wind-instrument”; one shown in Figure 14A.

Figure 15. A and B: Petroglyphs at Pakra, southern Peru. C: The Nasca Monkey geoglyph; the wind-instrument added by the author. Drawings © by Maarten van Hoek.

Of special interest however, is the fourth monkey (Figure 15B), which features exactly the same posture as the other three “instrument playing monkeys” (one shown in Figure 15A), without, however, holding an instrument. This example may be an instance of an unfinished image, but it is more likely that it represents a “pars pro toto” image. This means that it may have been a deliberate decision not to equip that monkey with a “wind-instrument”. Possibly it was understood by the ancient audiences that this “empty-handed monkey” is playing a wind-instrument as well. In that case the fourth monkey may be considered to play an invisible instrument; an interpretation only appropriate because of the graphical context of the rest of images on the panel. If only one monkey had uniquely been manufactured in this position (thus without holding an instrument, and without the three other musical monkeys), it could have been an unfinished image or – perhaps more likely – even a complete image. Importantly, the Pakra monkey “playing an invisible wind-instrument” is not a unique example. There is more evidence. One case will now be discussed (more examples in: Van Hoek 2005 and 2019).

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The Nasca Monkey

Earlier (Van Hoek 2005) I suggested that also a huge geoglyph (not a form of rock art!) depicts a (possible) example of a monkey “playing an invisible wind-instrument”. It is found in the huge archaeological complex near the town of Nazca in southern Peru, which is world-famous for its enigmatic geoglyphs. The Nasca Complex also comprises several enormous biomorphic figures and one of them is the well-known Nasca Monkey. Especially the arms, hands and fingers of the Monkey have an atypical pose, which is – as far as I can tell – not seen anywhere else in the rich rock art or geoglyph art of the Desert Andes. The distinctive pose of the arms, hands and – especially – the fingers of the Nasca Monkey geoglyph seem to mimic something special (Figure 15C-left).

In my opinion especially the splayed, curved arms and the hands with the typically splayed fingers are intentionally placed in the “flute-playing” position (Figure 15C-left; notice that the hands are not placed directly opposite each other; a position which can be expected when playing a flute) and thus it is easy to picture this zoomorph to be “playing an invisible flute” (Figure 15C-right), as was tentatively suggested for the first time by me (Van Hoek 2005). Making my hypothesis more acceptable, is the fact that there are also a few images of zoomorphs “playing a wind-instrument” in Desert Andes rock art, including monkeys, for example at Miculla (for more information about monkeys in rock art see Van Hoek 2025).

The following art object also convincingly confirms the legitimacy of the concept of the “hidden” element. In 1934 Alberto Giacometti, a Swiss artist, created a female figure which he called “The Invisible Object (Hands Holding the Void)”. The epicentre of his work is the void between the figure’s hands, the fingers of which are folded in such a way that one almost sees the (spherical) object, which of course is – because of its absence – invisible. Now it is interesting to compare the Swiss-3D position of the hands-fingers with the 2D position of the hands-fingers of the Nasca Monkey (see Figure 15C). Although the positions are different, the voids express the same concept and thus (in)visibility. The invisible object is completely “absent”, but still very much “present”.

And if a Swiss artist can materialise the concept of an invisible object, why could prehistoric people/artists from the Desert Andes not have used the same concept in their (rock) art? Therefore, western-minded (rock) art researchers should always leave open the possibility that the non-visual (referring to an object; not to the metaphorical content [which is invisible]) is part of the (rock art) image, especially when no informed knowledge is available. Hiding elements or images in rock art is definitely a possible way to “visualise” something tangible. The practice of intentionally “hiding” elements could be explained by the concept of taboo, and especially the wind-instrument may well have been an object of taboo in Andean worldview. It is an object to be used by only male (high-status) individuals. But most likely there may be a different explanation for every individual case of a “hidden” or invisible” object, especially when it concerns examples that are much (culturally and/or geographically) distant.

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Conclusions

This study offers a selection of cases where either an element of a rock art image or a complete rock art image seems to have intentionally been “hidden” by the manufacturer. I speak of “hidden” because the element or image is of course visible (even when it takes some time scanning a rock art panel before it reveals itself). This study also argues that those “hidden” images do not represent cases of haphazard superimposition. A fine example of accidental superimposition is the (inverted) anthropomorphic petroglyph at Yonán (Figure 16A and B), an important rock art site in the Jequetepeque Valley of northern Peru. This anthropomorph was not noticed by Núñez Jiménez (Figure 16C). On the contrary, the practice to “hide” elements or images is intentional, and every example may communicate a (very) special, spiritual message, only known by its creator and the informed observer(s).

Figure 16. Petroglyphs on Boulder YON-026 at Yonán, Jequetepeque Valley, northern Peru. Photograph and drawings (only illustrating a part of Panel B) © by Maarten van Hoek, drawing C based on a part of the illustration by Núñez Jiménez (1986: Fig. 387).

My suggestion may also explain why so often a “hidden” element or image is unique. Fine examples are the “Trophy-Bird” at Alto de Pitis, Peru, created to join and to communicate with the ancestors (see Figure 8); the Fishman at Sydney, Australia, connecting fishermen with the food resources of the sea? (see Figure 5); the archer “hunting in disguise” at Potash Road, USA (see Figure 6) and the enigmatic Two-Head at Three Rivers, USA (see Figure 12). In my opinion the most convincing instances of “hidden” elements, concern the objects that are literally “invisible” because they are absent. Those absent elements have on purpose not been drawn by the prehistoric manufacturer!

References

Fux, P. 2011. The Petroglyphs of Chichictara, Palpa, Peru. Documentation and interpretation using terrestrial laser scanning and image-based 3D modelling. Zeitschrift für Archäologie Auꞵereuropäischer Kulturen. Vol. 4; pp. 127 – 205.

Núñez Jiménez, A. 1986. Petroglifos del Perú. Panorama mundial del arte rupestre. 2ª ed., PNUD-UNESCO. 1986 La Habana.

Orefici, G. 2012. Mensajes de nuestros antepasados. Petroglifos de Nasca y Palpa. Inteligo. Lima. Perú.

Slifer, D. 1998. Signs of Life. Rock art of the Upper Río Grande. Ancient City Press, Santa Fe, NM.

Stanbury, P. and J. Clegg. 1990. A field guide to Aboriginal rock engravings, with special reference to those around Sydney. Oxford University Press, Oxford.

Van Hoek, M. 2005. Biomorphs ‘playing a wind instrument’ in Andean rock art. Rock Art Research. Vol. 22-1; pp. 23 – 34. Melbourne, Australia. PDF available at DropBox (PDF-127).

Van Hoek, M. 2011. The Chavín Controversy. Rock Art from the Andean Formative Period. Oisterwijk, Holland. Book available at DropBox (PDF-100).

Van Hoek, M. 2013. The Carcancha and the Apu. Rock Art in the Death Valley of the Andes. Oisterwijk, The Netherlands. Book available at Academia and DropBox (PDF-002).

Van Hoek, M. 2015. The Potash Sheep Shifters. Bighorn Petroglyphs of the Southwest. In: TRACCE – Online Rock Art Bulletin, Italy.

Van Hoek, M. 2018. The Supernatural Flight of the ‘Trophy-Bird’ of Alto de Pitis, Majes Valley, Peru. In: TRACCE – Online Rock Art Bulletin, Italy.

Van Hoek, M. 2019. The Incomplete Versus The Unfinished: Invisible Objects in Desert Andes Rock Art? In: TRACCE – Online Rock Art Bulletin.

Van Hoek, M. 2020. Rock Art Images Wrapped Around the Corner – The Three Rivers 3D Masks. In: TRACCE – Online Rock Art Bulletin, Italy, and in Patina; Utah Rock Art Research Association (URARA). Salt Lake City.

Van Hoek, M. 2021. Seated Biomorphs in Paracas Rock Art. Oisterwijk, Holland. Book available at Academia and at DropBox (PDF-003).

Van Hoek, M. 2022. The Status of Sector-X within the Rock Art Complex of Toro Muerto, Peru. In: TRACCE – Online Rock Art Bulletin, Italy.

Van Hoek, M. 2025. Monkey Petroglyphs in the Rock Art of Coastal Peru: Distribution and Symbolism. In: TRACCE – Online Rock Art Bulletin, Italy.