Shrink-wrapping is a well known convention among those interested in palaeoart but is a relatively modern invention. Palaeoartists restored ancient animals with relatively bulky soft-tissues until the end of the 20th century to an extent where visible deep-tissue anatomy is genuinely exceptional in pre-modern palaeoart (a well known exception are ichthyosaur sclerotic rings, reflecting erroneous interpretation of these structures among early palaeontologists - see Buckland 1836). Shrink-wrapping became popular as conservative reconstruction approaches became dominant in the 1970s and went on to become a standard palaeoart convention soon after. Many, perhaps most, of the restorations produced by late 20th century artists employed shrink-wrapping and it remains conspicuous in artwork produced today. It has even spawned related traditions, such as tightly cropping fur and feathers to ensure animal shapes remain obvious, and has influenced approaches to restoring colour and skin texture, these elements being used to outline the topography of underlying bones. Famous shrink-wrappers include artists like Gregory S. Paul and Mark Hallett, who tend to be on the less dramatic side of the tradition, showing slight contours of the skull features alongside lean, though well-muscled, bodies and limbs. More extreme shrink-wrappers, like Ely Kish and William Stout, have works where shrink-wrapping is taken to a wholly unrealistic level. Gaping vacuities exist between neck vertebrae; rib cages and limb girdles bulge from the torsos; limbs are extremely thin and faces are lipless and gaunt. It’s difficult not to look at some of these works and not think of starving animals or even decaying remains: they do not look like healthy, virile beings.
|William Stout's Quetzalcoatlus, posted at Love in the Time of Chasmosaurs, has to be the most shrink-wrapped being ever rendered in paleoart. If it had any less tissue we'd be looking at moulds of the internal organs.|
How shrink-wrapping became unfashionableNowadays, shrink-wrapping is losing popularity among some parties as scientists and artists note a simple, but obvious problem: modern animals are generally not shrink-wrapped in the way we draw their extinct relatives. The most famous counter-shrink-wrapping arguments are in All Yesterdays (Conway et al. 2012) but something of an anti-shrink-wrapping movement was underway from the mid-2000s onward. Some now argue that, while champions of the rigorous reconstruction movement were right to draw attention to the true shapes of fossil animals and to emphasise their form in art, they might have gone too far in thinning out skin, muscle, fats and other tissues. Few animals have deeply sunken tissues over skull fenestra or distinctions in skin colour and texture correlating with skeletal anatomy, and no animals witnessed outside of veterinary clinics have detailed limb bone outlines projecting through their skin. Even reptiles - meant to be the living poster boys of shrink-wrapping - have a suite of elaborate, contour-altering soft-tissues. They include voluminous fat deposits; large amounts of wrinkly, saggy skin; eyes which bulge prominently from their sockets; deep lip tissues which fully sheath their teeth; jaw muscles which completely fill and swell from their skull housing; thick or pointed scales and, in some species, even expansive, mostly cartilaginous noses.
|Matt Wedel's touching plea to end shrink-wrapping, from 2011. The struggle is still real: if you have spare paint, pixels clay or graphite, please donate generously.|
|Even seals get in on this action, as evidenced from this Irish Seal Sancutary x-ray. Their site appears to be down at time of writing, but SV:POW! has this image hosted there for the time being.|
Anti-anti-shrink-wrappingBut while cries of 'bulkier, deeper, fuzzier!' are generally well-placed in palaeoart discussions, we should be careful not to overshoot the mark. Amid the cry for deeper tissues, we might be overlooking the fact that some living creatures are somewhat shrink-wrapped - at least in some regions. In fact, virtually animals have areas where their extra-skeletal tissues are shallow and skeletal contours are visible. Common areas of thin tissue include the ends of limbs and tails; the midline of the sternal region; and some areas of the face, such as the frontal and nasal regions; the ‘cheek region’ (over the jugal in birds and reptiles, and the zygomatic arch in mammals), and the lower margins of the bottom jaw. Our own anatomy is no exception to these trends, as is borne out by the extremely well-studied tissue depths of human faces (e.g. Stephan and Simpson 2008) or the simple act of looking in a mirror. The osteoderms of sauropsids are another example of close interaction between skin and bone: as with modern armoured reptiles, extinct scaly sauropsids with extensive osteoderm arrangements probably looked pretty darn like their fossil remains - in other words, kinda shrink-wrapped.
|There is no tissue, only Zuul.|
These observations mean we have to be careful with applying a general philosophy to shrink-wrapping rather than scientific investigation. Tissue depth is evidently not a matter of palaeoartistic style or fashion, but a biological variable we should be aiming to predict and infer. If we're aiming to approach this topic like scientists, we should look to see what fossils and comparative anatomy can tell us about tissue depth to make informed, specific predictions about extinct animal appearance and avoiding a one-size-fits-all 'anti-shrink-wrap' philosophy. So, is there anything in the fossil record that elucidates how deeply buried animal skeletons were under muscle, skin and so on?
Looking for clues of 'shrink-wrapped' tissuesFrustratingly, one of the first lines of evidence we have to jettison are those body outline fossils. As great as they are, they can be of limited use for determining subtle variation in tissue thickness as their shapes are readily altered by taphonomy, preservation styles and even our own preparation work. Regions of thin tissue depth will be were especially sensitive to destructive processes and are easily obliterated by imperfect preservation or human error, so their chances of preservation are minimal. Phylogenetic bracketing is also of limited utility because the vastly different cranial architecture of extant and extinct animals makes such investigations almost meaningless. Non-avian dinosaurs, for instance, have skulls which are neither truly croc-like or bird-like, and it's probably not sensible to assume their extant relatives provide reliable insights into their facial tissues.
Predicting regions of thin tissue is thus largely left to comparative anatomy - predicting minimised tissue volumes using fossil bones and the living structural analogues. Among extant species, we see shrink-wrapping largely applying to animal faces, so if we investigate the skulls of ‘soft-faced’ animals like mammals, monitor lizards, snakes, and certain birds, and compare them to species with shrink-wrapped faces, like turtles, crocodylians, chameleons and well-ossified fish, we might find characteristics that correlate with facial tissue depth. These will then give us some criteria to assess tissue depth in fossil species. I've had a go at this, and suggest that osteological attributes related to facial tissue depth include:
Rugosity. Soft-faced animals tend to have smooth bone textures with limited or no areas of rugosity, whereas the skulls of shrink-wrapped species have large areas of rugose textures, often corresponding to specific epidermal features (e.g. scales or keratinous sheaths - see below and Hieronymus et al. 2009). This factor largely seems to reflect the proximity of epidermal tissue, which can leave characteristic textures in species with tightly-bound skin. Soft-faced species generally lack this rugosity because muscles, fat and voluminous integuments (fur and feathers) don’t leave broad osteological features (Hieronymus et al. 2009), or simply because their skin is displaced far enough from the bone that it doesn't alter its surface. We might also note that the skull contours of soft-faced species are generally more rounded than those of shrink-wrapped species, which can be crisp and sharp. Rugosity is a particularly useful criterion because it can show the presence of tight skin tissues with some precision. If one part of a skull is rugose, and another isn’t, there’s a good chance that the smoother region had a different tissue configuration which could - among other things - reflect a deeper or 'softer' facial covering.
|Fossil skulls - like those of the centrosaurine Centrosaurus apertus - are covered with features that allow us to predict aspects of their facial skin. Often - as is the case here - they suggest fairly low-volume structures, like scales and horn sheaths, which generally don't deviate too much from the underlying bone (yes, I know there are exceptions, but we're looking for major trends here). Centrosaurus skull redrawn from this Wikipedia photo, data on facial tissue correlates from Hieronymus et al. (2009).|
Correlates for epidermal projections. Elaborate skin projections – such as soft-tissue horns or crests - leave characteristic osteological signatures (Hieronymus et al. 2009). Given that these projections can alter animal faces quite substantially from the underlying skull shape, the presence of these is a clear indication that the species was not shrink-wrapped. We would expect a lack of correlates for epidermal projections in shrink-wrapped species.
As is often the case with zoological topics there are exceptions to these observations that preclude using any one of these criteria in isolation to determine tissue depth (e.g. smooth bone textures can underlie thin naked skin, so are not always a hallmark of deep tissues). However, applied collectively, they might give a general insight into how shrink-wrapped or 'soft-faced' an extinct animal was. I'm encouraged to see that these proposed osteological features of soft- and shrink-wrapped faces covaried in the past as much as they do for modern species. This doesn't mean these criteria are 'correct' as goes their relationship to tissue depth, but at least shows there's variation in their skull architecture that we can recognise as equivalent to that of modern species, and it isn't unreasonable to think the variance might reflect the same anatomical factors.
If we apply these criteria to some fossil taxa, what predictions might we make? The roomy, smooth-boned and foramina-lite skulls of cynodont-grade synapsids and fossil mammals match predictions for ‘softer-faced’ species, and this might be true of some fossil reptiles – like sauropod dinosaurs - too (this is not a new conclusion: both Matt Wedel and Darren Naish have been saying similar things about sauropods for years). If right, the 'soft-faced' sauropod that greeted you at the start of this post might be more likely that the shink-wrapped toilet-headed version we're so familiar with. At the other end of the spectrum, the highly textured, pitted bones and solidly-built skulls of ankylosaurs and anamniotes meet our criteria for shrink-wrapping very well, and they likely had facial anatomy tightly conforming to their skull shapes.
skull textures strongly indicating minimal tissue depth over much of their skull but smooth, foramina-lite jaw margins. In life, these animals have shrink-wrapped dorsal skull regions and snouts, but vast, fleshy lips, which is what we might predict based on their skull anatomy.
Partial facial shrink-wrapping seems apt for many fossil species. Gorgonopsians, for instance, might not have soft faces like living mammals as their snouts and foreheads are quite rugose and their nasal openings are small (e.g. Kammerer 2016). These features might indicate the presence of tighter skin over the snout. However, they have few jaw foramina and relatively open regions for jaw musculature, so they might have been fleshier around their jaw margins and at the back of head (below). Tyrant dinosaurs have skulls with relatively small openings compared to some of their theropod relatives, rugose snout textures, several hornlets (Carr et al. 2017), as well as a slightly elevated foramina count (Morhardt 2009). This cranial anatomy is consistent with tighter tissue depth in several areas, if someway short of a fully lipless, crocodylian-like degree of shrink-wrapping. Many pterosaurs show pitting and vascular canals embedded into their jaw margins, and some species have indications of tight sheathing on their crests and jaws, but the presence of striated bony crests – correlates for epidermal projections – as well as large skull openings and smooth bone textures in other parts of the skull, indicate that their faces might not have been entirely skeletal.
|Was gorgonopsian Inostrancevia shrink-wrapped or soft-faced? According to the criteria of this post, maybe a little from column A, a little from column B.|
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- Bell, P.R. (2014). A review of hadrosaurid skin impressions. In D.A. Eberth and D.C. Evans (eds.) The Hadrosaurs: Proceedings of the International Hadrosaur Symposium. Indiana University Press, Bloomington and Indianapolis, pp. 572–590.
- Buckland, W. (1836). Geology and mineralogy considered with reference to natural theology (Vol. 1). Carey, Lea and Blanchard.
- Carr, T. D., Varricchio, D. J., Sedlmayr, J. C., Roberts, E. M., & Moore, J. R. (2017). A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports, 7.
- Conway, J., Kosemen, C. M., Naish, D., & Hartman, S. (2013). All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals. Irregular books.
- Czerkas, S. A., & Ji, Q. 2002). A new rhamphorhynchoid with a headcrest and complex integumentary structures. Feathered Dinosaurs and the origin of flight, 1, 15-41.
- Frey, E., & Martill, D. M. (1998). Soft tissue preservation in a specimen of Pterodactylus kochi (WAGNER) from the Upper Jurassic of Germany. Neues Jahrbuch fur Geologie und Palaontologie-Abhandlungen, 210(3), 421.
- Frey, E., Mulder, E. W., Stinnesbeck, W., Rivera-Sylva, H. E., Padilla-Gutiérrez, J. M., & González-González, A. H. (2017). A new polycotylid plesiosaur with extensive soft tissue preservation from the early Late Cretaceous of northeast Mexico. Boletín de la Sociedad Geológica Mexicana, 69(1), 87-134.
- Hieronymus, T. L., Witmer, L. M., Tanke, D. H., & Currie, P. J. (2009). The facial integument of centrosaurine ceratopsids: morphological and histological correlates of novel skin structures. The Anatomical Record, 292(9), 1370-1396.
- Kammerer, C. F. (2016). Systematics of the Rubidgeinae (Therapsida: Gorgonopsia). PeerJ, 4, e1608.
- Lindgren, J., Kaddumi, H. F., & Polcyn, M. J. (2013). Soft tissue preservation in a fossil marine lizard with a bilobed tail fin. Nature Communications, 4, 2423.
- Mayr, G., Peters, S. D., Plodowski, G., & Vogel, O. (2002). Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus. Naturwissenschaften, 89(8), 361-365.
- McGowan, C. & Motani, R. (2003). Part 8 Ichthyopterygia. Sues H–D (ed.) Handbook of Paleoherpetology. Munchen: Verlag Dr. Friedrich Pfeil. 175 p.
- Morhardt, A. C. (2009). Dinosaur smiles: Do the texture and morphology of the premaxilla, maxilla, and dentary bones of sauropsids provide osteological correlates for inferring extra-oral structures reliably in dinosaurs?. Western Illinois University.
- Renesto, S. (2005). A new specimen of Tanystropheus (Reptilia Protorosauria) from the Middle Triassic of Switzerland and the ecology of the genus. Rivista Italiana di Paleontologia e Stratigrafia (Research in Paleontology and Stratigraphy), 111(3).
- Stephan, C. N., & Simpson, E. K. (2008). Facial soft tissue depths in craniofacial identification (part I): an analytical review of the published adult data. Journal of Forensic Sciences, 53(6), 1257-1272.
- Taylor, M. P., Wedel, M. J., & Naish, D. (2009). Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica, 54(2), 213-220.