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Friday, 18 August 2017

The convention of shrink-wrapping: thoughts for artists

Europasaurus holgeri - twice. These portraits are of the same animal using the same specimen and the same view, but one is restored with extreme shrink-wrapping (above) and the other has a more generous amount of facial tissue (below). But which one is more plausible, and can we even tell from fossil bones alone?
You can't move around palaeoart circles on the internet nowadays without someone being criticised for 'shrink-wrapping' their reconstruction. This refers to the convention of restoring extinct animals with minimised soft-tissues, allowing details of muscle layouts and major skeletal contours to be seen in allegedly healthy living animals. At its most extreme, this includes clearly visible ribs and vertebrae, tissues sunk into skull openings, ultra-prominent limb girdles and skinny, sinewy legs. We owe the term 'shrink-wrapping to sauropod expert and SV:POW author Mathew Wedel who, in a 2010 article, compared the contour-hugging soft-tissues of these restorations to items wrapped in tight plastic for transport.

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.
We might assign three reasons for the popularity of shrink-wrapping. The first is that its development coincided with a reinvention of dinosaurs as bird-like, active and powerful animals rather than oversized, under-muscled cold-blooded creatures. The athletic appearance of shrink-wrapped dinosaurs chimed with this renaissance and contrasted newer art from the plodding, perhaps over-voluminous animals of previous generations. Shrink-wrapping is not a dinosaur-exclusive tradition of course, but the popularity of these reptiles means that palaeoart conventions applied to dinosaurs are inevitably followed in artworks of other species. Secondly, images of prehistoric animals as heroically-built, powerful beings are preferred by many merchandisers and palaeoart fans, these interpretations most closely matching the erroneous but popular portrayal of prehistory as a savage struggle for survival, where only the most powerful animals survived. Thirdly, shrink-wrapping allows palaeoartists to ‘show our work’, demonstrating that the anatomy underlying the skin of a restored animal matches the osteological information provided by fossils.

How shrink-wrapping became unfashionable

Nowadays, 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.
Nowadays, many view skeletal elements as providing an important palaeoartistic foundation for soft-tissue shape, but concede that overlying tissues must have smoothed-over skeletal contours to produce 'softer' body forms. Indeed, there's something of an collective interest in knowing how deep extra-skeletal tissues can get. The answer, it seems, is 'very'. The necks of many birds and mammals are often flexed at much higher angles than we would assume based on their external appearance because their overlying tissues are so thick that the entire neck skeleton posture is hidden (Taylor et al. 2009). The muscles and bones of major anatomical elements – such as necks and proximal limb segments – can also be obscured under skin, fat and integument. Contour-altering structures like horns, spikes, spines, combs, humps, armour, fins, and webbing are often composed of soft-tissue, and the large, savage-looking teeth of mammals and lizards can be completely obscured by facial tissues. We need only look at x-rays of living animal species to see their often-startling lack of correlation between external appearance and internal anatomy.

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. 
It's from this general train of thought that a  push for more bulk, fuzz and fat in palaeoart has been born, and this general philosophy is lining up well with fossil data. We have direct evidence that the bodies of ichthyosaurus (Stenopterygius) and mosasaurs (Prognathodon) bore tall fins and paddle extensions that vastly exceeded the limits of their skeletal margins (McGowan and Motani 2003; Lindgren et al. 2013). Preserved body outlines of ichthyosaurs and plesiosaurs show deep tissues which created smooth, streamlined torsos that are much bulkier than the underlying skeleton (Frey et al. 2017). Fossils of early horned dinosaurs (Psittacosaurus), Tanystropheus and ‘mummified’ hadrosaurs (multiple taxa) show extensive muscle volume that bury their skeletons as well as elaborate structures – soft-tissue filaments, combs and skin membranes – that defy ‘shrink-wrapping’ conventions (e.g. Mayr et al. 2002; Renesto 2005; Bell 2014). The feather outlines on innumerable fossil theropods show that they were just as densely feathered as modern avians, and the fuzzy ‘halos’ of fossil mammals and pterosaurs suggest they too were also adorned with deep layers of filaments. Several pterosaur fossils (PterodactylusPterorhynchus) also preserve unexpectedly broad neck tissue outlines which contrast against their thin, tubular neck vertebrae, as well as elaborations of crest tissues that create body outlines more voluminous than those predicted from musculoskeletal restorations (e.g. Frey and Martill 1998; Czerkas and Ji 2002). The 'shrink-wrapping hypothesis' is being falsified with regularity.
Select fossilised body outlines of exinct taxa: no shrink-wrapping here. A, plesiosaur Mauriciosaurus fernandezi, B, ichythyosaur Stenopterygius quadriscissus; C, dromaeosaur Sinornithosaurus millenii. A, after Frey et al. 2017; B after McGowan and Motani 2003.

Anti-anti-shrink-wrapping

But 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.
In reality, there is a spectrum of tissue depth in living species and some are more 'shrink-wrapped' than others. While no healthy living animal attains the most extreme levels of shrink-wrappery portrayed in palaeoartworks, certain lizards, fish, and crocodylians have anatomies which are more shrink-wrapped than average, possessing large areas of relatively thin, skull-hugging tissues which recall shrink-wrapped art. These thin tissues are highly characteristic of these species and are something something palaeoartists would want to capture if restoring these animals from fossils. We would miss this, however, if we assume that all animals have their tissue volume settings cranked up to maximum.

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' tissues

Frustratingly, 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:

How might we predict shrink-wrapping in fossil animals without good soft-tissue remains? It's challenging, but these attributes might give a general idea. From top to bottom: Burchell's zebra (Equus quagga burchellii); water monitor (Varanus salvator); Alligator mississipiensis and Arrau turtle (Podocnemis expansa).
Openness of skull architecture. The skull openings of softer-faced animals - including the temporal muscle openings, orbits and nares – tend to be large. At their most extreme these openings are not fully bordered by bone (e.g. many mammal orbits and nares, the lower temporal fenestrae of lizards). Larger skull openings necessitate a larger fraction of face structure be composed of soft-tissue, such as muscle, organs, and cartilage, and this overwhelms the contours of the bony skeleton to make a 'soft-faced' species. The nasal cartilages of monitors and mammals, as well as bulging mammalian jaw muscles, are examples of this. Conversely, shrink-wrapped species have smaller cranial openings, which impose physical limitations on how much soft-tissue can form the shape of the face. Muscles and organs might protrude from these somewhat, but their impact on facial structure is less than that of species with large skull openings, and more of the face shape reflects bony contours

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).
Pits, grooves and foramina. Shrink-wrapped species tend to have large numbers of perforations in their skulls, while soft-faced species show the opposite (Morhardt 2009). This is particularly evident around their jaws and presumably reflects the greater capacity for soft-faced animals to carry nutrients and sensory information through their soft-tissues, whereas shrink-wrapped animals are forced to run nervous and vascular networks through their face skeletons.

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.

Applying the criteria outlined above might help us roughly sort predict 'shrinkwrapped', 'soft-faced' or intermediary conditions in extinct taxa. The placements of the animals here are only rough, but give an indication of their relation to the tissue-depth criteria outlined above. Fingers crossed that some of these will be corroborated or refuted with soft-tissue discoveries in future.
Careful examination of fossil skulls allows us to also predict partial or regionalised shrink-wrapping in species where some aspects of their facial anatomy conformed to the underlying bone, and others did not. An example of this configuration is demonstrated in some living lizards, like gila monsters, which have 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. 
Time and testing will tell whether these criteria are a genuinely useful means to predict facial anatomy. I hope - as with other aspects of extinct animal appearance - that genuine research into this issue will be carried out one day. Criteria to predict tissue-depth are a desirable tool for any palaeoartist as it's simply more honest and scientific: if we're serious about this reconstructing extinct animals gig, predictive methods and sound hypotheses are infinitely better than sticking to our personal hunches, guesses or erring on what looks coolest. Regardless of whether we can predict tissue depth or not, the take home here is that we should not approach our artwork having already decided how thin or fat the tissue volumes of our subjects will be. There is probably not a single ‘universal truth’ that can be said about restoring tissue depth for all animals, whether we err toward thicker or thinner: the right tissue depth is the most defensible and best rationalised on for each subject and its constituent body parts.


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References

  • 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.

Friday, 28 July 2017

Palaeoartist interview: Johan Egerkrans

Palaeoart has never been a particularly diverse artform. Since the early 1800s most palaeoartists have pursued art attempting to depict fossil animals in realistic ways, with stylistic variation mostly along the spectrum of how obvious our brush strokes and pencil lines are, and how much detail we add. In recent decades we've seen artists deepening their dedication to realism with hyperrealist palaeoart, artworks which look like they've been snapped by high-speed cameras with crisp focuses and ultra-high levels of detail.

But not all palaeoartists are taking this approach. Some take a step away from not only high levels of detail but also realism, producing palaeoart with a more stylised and even abstract bent. Though few in number, the growing roster of ‘stylised’ palaeoartists represent an exciting new frontier for palaeoart. In varying artworks along spectra other than tidiness and detailing, these artists are producing unconventional works recalling pop art, classic western animations, heraldic crests, perspectiveless Medieval art and more. Among the most fascinating aspects of these works is their capacity to maintain respect for scientific credibility even when producing stylised, non-realist art. The forms may be simple or sharply angular, the colours may be garish, but we can still tell what the subjects are, what they are doing, and get a sense of their anatomy.

...which brings us to Johan Egerkrans's Alla tiders dinosaurier. If you like stylised palaeoart, you should check out this book. 
Swedish artist Johan Egerkrans is part of this emerging group of unconventional palaeoartists. Emerging onto the online palaeoart scene only recently, his work has already generated a fanbase and widespread acclaim. It's easy to see the appeal of his creations. Distinctively angular, full of personality and recalling great works of American animation, his digital artworks emphasise and almost caricature the form of fossil animals without undue distortion of their form or disregarding fossil data. Attention to details, anatomy and colours make his work interesting to look at despite it's simplicity compared to traditional modern palaeoart. We're not just seeing generic cartoons of fossil animals, but highly stylised versions of contemporary, scientifically credible palaeoart, informed by a clear appreciation for modern wildlife and the natural world. Notice the pupil colour change between his adult and juvenile Microraptor (below), variable integuments on Gorgosaurus (above), fine attention to animal poses and behaviour, and so on. His use of traditional compositions and poses prevent his work becoming overbearing: in this regard, his work is less intrusive, and even perhaps less cartoony, than some artists employing ‘realistic’ animals in hyper-dynamic poses and compositions.

Egerkrans' parent and offspring Microraptor. Look past the stylisation and this is a pretty accurate take on Microraptor anatomy, right down to the iridescent black plumage. Note the pin feathers and dark pupil on the juvenile - very sensible speculations for juvenile maniraptorans. © Johan Egerkrans.
Each Egerkrans work radiates personality: his animals have real character, and it’s almost impossible not to imagine them taking part in animated vignettes. Several of his works have a strong sense of mischief and dark humour, another rarity among palaeoartworks. I’m particularly tickled by his scene of a capybara running away from terror bird Titanis (below): the bird has a mania that captures real birds at their most frantic and chaotic, while the drab mammal looks overwrought, panicked, but also like it’s going to write a strongly worded letter to the Daily Mail about all this. Comparisons of Egerkrans’ creations to stylised fossil animals rendered for the big screen are inevitable, and mostly leave us wondering what the heck everyone else is doing wrong. Hollywood, give this man a job!

Titanis and capybara star in Hilarious Scene of Violence. Capybara won an Oscar for its eyebrows. © Johan Egerkrans.
Johan was kind enough to send me a copy of his recent book, Alla tiders dinosaurier, which I thoroughly recommend you check out. There’s no English translation at the moment (one might happen at some point) but the artwork speaks volumes alone and the design and print quality is excellent - it's a nice book to have, even if you're unable to read the text. The follow up, Flygödlor och havsmonster, which focuses on marine reptiles and pterosaurs, is due out later this year. Both are published by B Wahlstroms, and can be purchased from Bokus and other Swedish book retailers (sorry, American readers, there are complications around shipping these books to the USA at the moment). You can check out the art of both books on Facebook, Artstation and Johan's blog. If you're Stockholm-based, you can also check out a dinosaur exhibition featuring the Alla tiders dinosaurier work, which is running until the end of September.

Earlier this month I asked Johan if he’d like to chat to me about his art, books and palaeoart philosophy, and he’s taken time out of his schedule to give the following interview. With thanks to him for taking time to respond to my questions, it’s time for me to stop gushing about his work and hand you over to the man himself…

MW. You’re quite new to the palaeoart scene, but have landed an instant fanbase with your highly distinctive artwork. Can you give us some insight into your artistic background and what brought you into restoring dinosaurs, pterosaurs and so on?

JE. Hi Mark! Thanks for having me on the show!

I started out as a concept artist and, like most people in that field it seems, I´ve nursed  a deeply rooted fascination for paleoart since... Well, forever I guess. At the age of four my dad gave me Burian´s seminal art book “Life Before Man” and that was it; I was hooked and filled countless A4 sheets with scribblings of dinosaurs, therapsids, pterosaurs and other extinct beasties. I´ve still got that same cherished tome in my bookshelf, worn and coming apart at the seams.

Fast forward to the early 2000´s when I got my first fulltime job as an illustrator concepting for a small computer game outfit called Idol here in my hometown Stockholm. There I did designs for monsters, robots, spaceships and stuff like that. A high point was when I got to draw a series of - listen to this - demonically possessed cyborg dinosaurs!  That´s about as awesomebro as things can get. Take that Michael Bay!

I was always had a talent for mimicking different art styles, which came in very handy at that job - one month you did a superhero game in a highly stylised Bruce Timm style, another month it was horror inspired by Clive Barker, Frazettaesque fantasy or something completely different. I really got to flex those versatility muscles in that environment.

Anyway, after a couple of years Idol went belly up, as small computer game outfits are wont to do. I became a freelance illustrator and found myself working more and more with children´s books. In 2013 Nordiska väsen/Vaesen was released - a book about creatures from Scandinavian folklore that I wrote and illustrated. That really was a watershed moment, as the book did rather well (still does - it's sold over 40.000 copies in Sweden alone so far). After that success I had a certain amount of freedom and one of the things I wanted to do was to go back to my paleoart roots in some fashion. The first such project was a children´s picture book called My first book of dinosaurs. It was originally intended to be a rather tongue-in-cheek affair and the initial pictures were intentionally tropey (large theropod roaring on cliff, cassowary Oviraptor). I did take care to stay off the beaten path though so, unusually for a book aimed at young children, there wasn't a T. rex or Triceratops in sight - I went with Giganotosaurus and Styracosaurus instead.

Mention the tropes, and they shall appear. Egerkrans' Smilodon bellowing off a cliff (or maybe suffering a major case of lockjaw). It's difficult not to see this as satirising the most traditional means of restoring sabre-toothed cats: the lower jaw stretched so far as to make its tissues near invisible, and the skull arcing upwards to attain more ferociousness. Image © Johan Egerkrans.
Pretty soon my science geek side kicked in - I did more and more research and realised I wanted the reconstructions to have a certain amount of scientific accuracy, even if the book was aimed at toddlers. The cartoony stylised style I had chosen for the book could be tweaked into some something more “serious” while still retaining the whimsy and charm of those first illustrations. My first book of dinosaurs was followed by a another one about Cenozoic beasts and by this time I had gotten wind of the All Yesterdays movement and had started following a bunch of paleoblogs (this one and Tet Zoo among them). This new wave of paleoart and the philosophy behind it appealed to me. My editor and I decided to do a “real” pop science book about dinosaurs which was released as Alla tiders dinosaurier ("Dinosaurs of All Ages") earlier this year. I´m currently racing towards the finish on the follow up about pterosaurs and Mesozoic marine reptiles.

MW. Strongly stylised palaeoart is rare, perhaps because we focus so rigidly on precision and scientific credibility in our reconstructions. Where do you draw the line between style and adherence to science, and are there cases where you’ve thought ‘screw science, this looks cooler!’

JE. My aim, in a way, is to do what Disney animators did in films like The Jungle Book or The Lion King. Now, Shere Khaan might not be realistic per se, but the design is informed by a deep understanding of tiger anatomy, and what tigers are like - their “essence” if you will, with the risk of sounding a tad pretentious. Thus Shere Khaan becomes the tigeriest tiger around as far as I´m concerned. My paleoart sort of tries to do something similar - only with extinct animals (though I´m nowhere near as talented as those old school Disney animators). To capture that “essence” you sometimes got to break the rules a bit. It´s a “know the rules to break the rules” kinda deal.

It´s a bit like caricatures come to think of it. People often find it easier to recognise a celebrity from a (well made) caricature than from a photo because the drawing exaggerates that person's distinguishing features. In a similar way stylisation allows me to focus on what’s distinctive about a certain species/genus and bring that up to front.

Parvicursor, from Alla tiders Dinosaurier, is a great example of Egerkrans' capacity to find the essential elements of form in an extinct animal and project them through a strong visual style. © Johan Egerkrans.
Another advantage is that it allows me to remain vague when we’re uncertain about some feature of an animal's anatomy. Take for instance the recent dispute whether tyrannosaurs had lips or croclike exposed teeth. The simplified style allows me to draw something in-between, should I so wish, and leave it open to interpretation. That doesn’t mean I do this all the time and never takes a stand, but it remains an option.

A lot of paleoart seems rather overworked. I´m hardly the first to voice this opinion but meticulously rendering thousands of  tiny scales in a dinosaur picture doesn't necessarily make said picture more accurate. Sometimes it´s the complete opposite where hyperrealism only serves to create the illusion of scientific accuracy. I tend to prefer sketchier, looser paleoart - by artists like John Conway, Simon Stålenhag and of course Zdeněk Burian - where the emphasis lies on movement, mood and communicating that aforementioned essence of an animal - what it felt like.

My most common “screw-you-science” is probably the eyes. The peepers of my stem-birds are more mobile than they probably were in real life; they move around and look at things in a human, or at least mammalian way. Avian eyes are usually fixed in a perpetual stare which makes them come off as either vexed or insane (or both). That might be precisely what you’re after, but often you’re looking for something different. I almost always give the animals discernible pupils as we humans are geared to interpret that as more affective than-all black eyes. Windows to the soul and all that.

MW. Your reconstructions are full of personality and humour. I find it very easy to project emotion onto your subjects. Is this something you deliberately seek with your work? Do you render each image with an idea about what each animal is thinking?

JE. I´ve always had a flair for characterisation. It just sort of happens no matter what I draw, be it a robot, a dragon or a lone animal hanging about doing nothing. They always end up seeming to be up to something (my subjects often look rather smug for some reason, apparently it´s my go-to emotion). There´s a hint of anthropomorphism but I try not to overdo it. It´s just little things like an eye ridge tweaked to look as if the animal is raising it´s eyebrows or the hint of a smirk at the corner of the mouth. It should only be just enough to help the viewer empathise with the subject.

MW. The colour choices of your artwork are interesting, blending ‘realistic’ animal colour schemes with background hues rarely seen in palaeoart. It works very effectively, creating a strong sense of atmosphere. Can you take us through your approach to choosing animal colouration and blending these with often contrasting backgrounds?

JE. I always start with the animal itself and let their colouration dictate the tones of the background. The aim is to give them striking, simple colour schemes that still comes off as believable. Once the animal is painted I start with the surrounding environment, which on the whole is a rather intuitive and organic process. I play around in Photoshop until I land in something that works.

The colour choices and compositions are highly influenced by animation backgrounds, especially in the way the scenes are framed. There´s a lot of colour theory at work as well - complementary colors (often good old orange and teal) or split complementary colours (like red and blue) in different overlay layers make the animals “pop” from the background. A cool coloured animal will be framed by a warmer environment and vice versa.

Dimorphodon meets a neighbour (notice the keratin crest on the lower jaw of Dimorphodon - most artists miss that). In addition to showing the personality common to Egerkrans' work, this piece also shows the mix of realistic animal colouration with striking, pseudorealistic background colours. In fully realistic art, this might not work, but here, it does. © Johan Egerkrans.
MW. To me, your palaeoartworks recall some of William Stout’s illustrations. Both have a distinctive, non-realist style, interesting colour schemes and emphasis on the animal subjects. Is Stout an influence on your work?

JE. Very much so. I've always loved his work and his approach to paleoart. His creatures have tons of character and the draughtsmanship is sublime. They’re admittedly a bit skeletal at times but they make that up with personality. That I’m partial to Stout is hardly a surprise, as we're both inspired by the same old masters. Even if it's not obvious in my paleoart, a lot of my work takes cues from turn of the century illustrators like Arthur Rackham, Dulac and John Bauer, just like Stout's art.

MW. The work you produce is included in educational books. How do you think style impacts the scientific or educational prospects for palaeoart?

JE. The illustrations are not intended to be photoreal and that´s sort of the point. It´s obvious that they're an interpretation which forces the viewers to do part of the reconstruction in their own heads. That hopefully gets their imagination going which is the ultimate goal - to connect and get people interested. To make science fun.

The chosen style also saves me from meticulously rendering those thousands of tiny scales and retain my sanity, so that´s a huge plus.

MW. Do you ever stray from your signature style? Will we ever see a ‘realistic’ Egerkransian dinosaur?

JE. As I´ve mentioned before I always adapt my technique to the project at hand and this is just one of several styles I utilise. It´d be interesting to do a paleoart project in a more realistic vein, though I think there´ll always be a certain amount of stylisation. I´m not a realist painter and never will be - others have got that down already.

Umoonasaurus and chums. The barnacled fallen trees turns this image from just another Mesozoic marine scene into something much more atmospheric. © Johan Egerkrans.



MW. I’ve seen that you get a lot of scientific feedback on Facebook posts, a source that many palaeoartists – professional and amateur – can be wary of because of misinformation and confrontational internet users. How useful do you find social media to shape your art, and have you encountered much hostility?

JE. I was flabbergasted at how overwhelmingly positive the response was when I posted my first drawings on the Facebooks. Especially from the academic community. There´s been very little hostile or dismissive remarks - in general people seem to take the works seriously, as ‘proper’ paleoart.

The feedback is often extremely helpful - there´s lots of very well informed academics hanging about (you yourself and Darren Naish to mention just a few) and you quickly learn to sift the good advice from the bad or opinionated. I approach the forums as a sort of quick and dirty peer review; I´m not an expert and get things wrong all the time and if there´s something wonky someone is bound to point it out. As the ambition is to be as accurate as possible, within the limitations of the style, I try to surround myself with people who actually truly knows about this stuff. As luck would have it a lot of people I admire have proven to be more than willing to help out with comments, constructive criticism, links to papers and by just being supportive in general.

MW. When are you going to get Hollywood on the phone to make your work into a movie? They already look like they’re stills from some epic animated film about Mesozoic life. And they owe us, frankly, after The Good Dinosaur.

JE. I´m still waiting for them to get the straws out of their noses and give me a call. Bastards.

Guanlong and some sort of impudent Mesozoic mammal. Note how the Guanlong is strikingly and variably coloured, and yet still looks grounded. Bringing bright colours into the Mesozoic doesn't necessarily mean painting entire animals in lurid shades. © Johan Egerkrans.
MW. Finally, where’s the best place to find your art and support your work? And how long do we have to wait until your next book?

JE. You can follow my public facebook account “Johan Egerkrans - Illustrator” where I post about new projects and upcoming events like signings. Then of course there is the Paleoartists Facebook group where I´m pretty active.

I´ve also got a blog at http://johan-egerkrans.blogspot.se/ and an Artstation page https://www.artstation.com/artist/egerkrans.

My books can be bought from www.bokus.com or any other Swedish book retailer. You should be able to order them from there if you live in Europe but it's trickier in the States due to the fickle nature of the U.S. customs. Hopefully Alla tiders Dinosaurier will get an English edition at some point, but nothing's set at the moment.

The next book Flygödlor och havsmonster, about your favourites the pterosaurs (and their marine contemporaries), will be out in Sweden this fall. At some point I´d very much like to do a book about Permian and Mesozoic stem mammals (gorgonopsids are hands down my favourite prehistoric animals), but sadly it is a rather tough sell…  

MW. Johan Egerkrans, thanks very much!


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Friday, 16 June 2017

Revenge of the scaly Tyrannosaurus

Reworked version of my 2012 Tyrannosaurus painting, now in it's third guise. There's something about this painting which recalls reconstructions from 1906 rather than those of 2016.
The skeletal anatomy of Tyrannosaurus rex is probably better known and studied than the skeletons of many living animals, but its soft-tissues - and thus much about its life appearance - are poorly represented by fossil remains. Thus, virtually all of our ideas about muscle bulk, soft-tissue body shape and integument have to be reconstructed by phylogenetic proxy and functional prediction. As with all dinosaurs, we've historically felt pretty confident that Tyrannosaurus was entirely scaly, but relatively recent discoveries of filamented tyrannosauroids in China (Xu et al. 2004, 2012), as well as a growing mountain of fuzzy coelurosaur fossils, point to a different conclusion: that Tyrannosaurus was adorned in simple filaments - hair-like equivalents of feathers. Skin impressions for more derived tyrant species - the tyrannosaurids - have proven rare in fossil record (Hone 2016) and, though rumours have circulated about some, they have largely escaped formal description and publication. In the absence of better evidence, the most parsimonious modern takes on everyone's favourite tyrant have involved a fuzzy covering.

In the recent months two papers have challenged this idea. The first, by Thomas Carr and colleagues (2017), purports to find osteological correlates of scales on the facial anatomy of the tyrannosaurid Daspleteosaurus, which they argue (along with other lines of evidence), to suggest crocodylian-like facial tissues and sensitivity. The second, by Phil Bell et al. (2017), describes scaly skin impressions from multiple postcranial regions of a Tyrannosaurus skeleton, and argues that the distribution of these impressions implies a uniform (or near uniform) covering of scales across the body, without much in the way of fuzz.

Because this is Tyrannosaurus, media sites and bloggers have spilled great amounts of ink over these stories. The scientific press has often been far from objective or unbiased. Popular articles have suggested Jurassic World fans might have 'won' the debate over scientists, that science fans are 'due' a return to scaly tyrants after 'losing' Pluto, and that the findings mean 'all is well in the dinosaur world'. The implication is a ridiculous one, like evidence of scalier tyrants is a moral victory rather than a test of a scientific hypothesis. But while the popular press has been celebrating the new papers, members of the palaeoblogosphere have been less enamoured with the findings. Trey the Explainer suggests that Bell et al.'s work doesn't really change what we already knew about tyrant integument, and thus does not invalidate many existing reconstructions. Andrea Cau posits that interpretations of scaly tyrants reflect our prejudices more than science, and that taphonomic factors may explain the absence of filaments. Brian Switek has concerns that the skin patches are too small and spread too widely to give a complete picture of the integument, and echoes concerns about taphonomic interference. The collective response seems to be a defensive one, protecting concepts of filamented tyrannosaurids from a resurgence of a more traditional, scaly model. Would any other dinosaur get this treatment? Perhaps not: as Brian explains in his recent post, this reaction is the T. rex celebrity effect at full bore.

Supermegafluffy Tyrannosaurus, from 2015. They were simpler times.
I've painted many fluffy Tyrannosaurus in the last few years (above) and quite like the idea of everyone's favourite 6 tonne dinosaur bonecrusher being a giant plush toy. However, we also have to concede that our ideas of Tyrannosaurus skin have been largely informed by prediction, not direct data, and that popular, long-held notions are as ripe for scientific revision as any other (lest we forget other famous examples of this - Brontosaurus and Ornithoscelida). Moreover, although some critics are suggesting the papers don't tell us anything new - rumours of scale impressions have been circulating for years - these recent studies give us the first rigorously documented, peer-reviewed glimpse into Tyrannosaurus skin anatomy. This is new, allowing us to form our own opinions on Tyrannosaurus appearance based on actual data, not hearsay. So, rather than putting our gloves up to defend our prior model, I wonder if we should be exploring how this new data might transform our perception of Tyrannosaurus life appearance. That these new studies present conflicting data to our expectations is not grounds to be upset, annoyed or defensive. To the contrary, they allow us to use real data - not predictions - to refine our ideas of tyrannosaurid appearance and evolution. For those of us interested in dinosaurs as real entities, and not movie monsters, that's a good thing.

What, exactly, has been argued about scaly tyrants?

A lot of the popular write ups of these recent papers include errors and misrepresentation, so let's recap what is actually being argued about Tyrannosaurus skin. A common social media reaction to Bell et al.'s work is that they've presented 'a patch' of skin, and are extrapolating from that. We need to debunk that right away: they've not described a single patch, but multiple small patches from the neck (alas, exactly where on the neck isn't reported), the top of the pelvis, and the base of the tail (below). All the samples stem from the 'Wyrex' specimen (HMNS 2006.1743.01). The most extensively represented area is the tail base, which has the largest single piece of fossil skin - 30 cm². The other skin samples are not as large, some being just a few centimetres across. Each patch shows the same skin type: uniform, tiny 'basement scales', each less than 1 mm across (Take note, artists: you would not see Tyrannosaurus scales until you were being eaten by their owner). Similar scale patches, also described by Bell et al. (2017), have been found on the torso and tail regions of other tyrannosaurid species, implying similarly scaled regions in these taxa.

Tyrannosaurus skin patches from the neck, pelvic area and tail of the 'Wyrex' specimen as illustrated by Bell et al. (2017). The scale bars for the scale imagery are 5 mm (b - e) and 10 mm (f-h). These things are tiny, and we can assume the skin of the animal would look smooth or leathery in life.
Some folks are suggesting that the size of these skin patches allows us to dismiss their scaly signal, or that even that they're anomalous, reflecting unusual taphonomic conditions that cloud their significance. I'm unsure about these ideas. Most skin impressions are small patches (even scaly skin gets a rough ride during fossilisation) and the fact they're small doesn't diminish the fact that each records a cluster of scales. We have to assume these are not unusual or 'special' areas on the body but generally indicative of surrounding skin fabrics. The fact that each patch is consistent with regard to scale size and texture hints at them being part of a continuous, unbroken integument, and not isolated scaly pockets in a sea of fluff.

But what about arguments that the scale patches are tissues stripped of filaments before preservation, like so many 'monster' carcasses? Filament/scale combos do have precedent in dinosaurs, being present on the tail of Juravenator and those scales of Kulindadromeus with fibre-like tassels (Chiappe and Göhlich 2010; Godefroit et al. 2014). We know from modern animals that fibrous epidermal structures are especially vulnerable to decay and physical weathering, but is there evidence that this has taken place on the Wyrex Tyannosaurus skin patches? At present, it's hard to say because we have no idea what tyrannosaur skin looks like as it decays. It might be significant, however, that the scale patches look very similar across the Wyrex specimen, and that they resemble other tyrannosaurid skin impressions closely. We might expect some variation if taphonomy was really distorting these specimens in a major way, and we're not seeing that. Moreover, the Wyrex skin impressions, though small, are pretty high-resolution. The scales, and their intervening areas, have sub-millimetre proportions and sharply defined edges. There's no tatty scale margins, no obvious spaces for filament attachment, or linear structures crossing the scales to imply a rogue filament impression. We'll remain uncertain if these are anomalous, taphonomically-altered samples until we find other examples of tyrannosaurid skin, but there's no reason to be unduly suspicious of the the samples we have.

Of course, the adage that 'absence of evidence is not evidence of absence' is always important when dealing with the fossil record, and it applies here as a sensible caveat. However, we shouldn't wield this phrase as a definitive counter-argument to reasonable interpretations of available evidence. Palaeontologists have to work with data, not suspicions or gut feelings, and the data we have does not include, or hint at, the presence of filaments. I'm not arguing that taphonomy isn't worthy of consideration here (indeed, the omission of details about 'Wyrex' taphonomic history is an issue with the Bell et al. 2017 paper) but we must beware the logical fallacies of appealing to probability (i.e. taphonomy could explain the lack of filaments, so it does explain the lack of filaments) or special pleading (excluding Tyrannosaurus from the same logic we would apply to other fossil animals when presented with this data).

Tyrannosaurus skull AMNH 5027 - note the 'hummocky' textures on the side of the snout, above and below the orbit, and atop the rostrum, likely indications of scaly skin. Image in public domain, sourced from Wikipedia.
Carr et al. (2017) present a different form of evidence for scales: osteological correlates. I consider some aspects of their study problematic in that it only looks to crocodylians and birds for comparative tissues, despite the clear value other tetrapods have in deducing facial tissue types (Knoll 2008; Morhardt 2009; Hieronymus et al. 2010); it lacks illustrations of the bone textures correlated to scaly integuments; and the conclusion of tyrants bearing crocodile-like face scales is flawed: crocodylians do not have face scales, but a tight, highly cracked sheet of facial skin - Milinkovitch et al. (2013). Nonetheless, I think Carr et al. (2017) are right in concluding the bony textures of tyrannosaur skulls seem indicative of scaly skin. These findings echo previous interpretations of bosses and rugosities in tyrant skulls (e.g. Brusatte et al. 2012; Sullivan and Xu 2016) and aren't controversial. Scales closely associated with bone either leave a 'hummocky' surface texture, which is seen on tyrant snouts (specifically their maxillae and nasals) or small bosses and hornlets, which are found in all tyrannosaurid skulls above their orbits (lacrimal and postorbital bones) and on their 'cheeks' (jugal bones). Hornlets and bosses represent the locations of specific scales in living reptiles (Hieronymus et al. 2009) and can thus give especially good indications of life appearance (check out chameleon skulls for especially good correlation between skull and scale features). The presence of hummocky bone textures and hornlets is a strong correlate for scales, as they rule out coverings of naked or feathered skin. Such skin types do not alter the underlying bone surface (Hieronymus et al. 2009).

These osteological correlates combine with the skin impressions to collectively show Tyrannosaurus as scaly across much of its face, somewhere on its neck, over the pelvic region and along the tail base (below). So far as we can tell, this picture seems consistent with osteological correlates and skin sampling from wider Tyrannosauridae. That's pretty extensive coverage, ruling out the presence of fibres in places that we know other dinosaurs - including other tyrannosauroids - were fuzzy, and implies that tyrannosaurids were mostly scaly. I'm particularly startled at the scales over the hip region as they curb even the long 'fibre capes' we see in some modern tyrant reconstructions, like the famous Saurian Tyrannosaurus. The fact that the scales occur in places known to be ancestrally filamented for tyrants is also intriguing: Bell et al. (2017) speculate that they may be modified feathers - that is, the same as bird scales - rather than a reversion to lizard or croc scales. Hold that thought, we'll come back to it soon.

Everyone's doing maps of Tyrannosaurus with integument details nowadays, and I want in. Note that this is Tyrannosaurus specific, and does not feature scale data from other tryannosaurids.

What's in the gaps?

The million dollar question is what was present between these scaly regions: more scales, or fibres? This is a major point for many respondents to the Carr et al. and Bell et al. papers, as it decides whether we keep our interpretation of Tyrannosaurus as an - at least partly - fuzzy animal. With our scale distribution map as a starting point, several options are available. The first is that fuzz was present in regions not yet represented by skin remains or osteological correlates. This would mostly imply the top of the torso (Bell et al. 2017), but may also be parts of the back of the head, some aspects of the neck (depending on where the neck skin impression came from) and maybe the end of the tail. Over on Twitter, Patrick Murphy has presented a reconstruction which shows what this might look like. I must admit to finding it quite amusing, sort of like T. rex has put on a shawl to visit the opera.

But how dense could these fuzzy patches have been? Bell et al. (2017) suggest that dense fibrous coverings are doubtful, noting that large living mammals avoid patches of thick insulating fibres to aid heat loss. This has not gone down well with some critics, who cite studies of feathers preventing over-heating instead of facilitating it. An oft-cited study in this regard is Dawson and Maloney (2004), who found emu feathers block virtually all solar radiation from the skin, preventing them from overheating in solar exposure that causes similarly-sized hairy mammals to seek shelter.

Feathers: great at blocking solar radiation, also great at trapping body heat. Note how cooking hot these ostriches are on their necks, heads and legs, while the feathers are mostly ambient temperature. This isn't because the body isn't warm, but because the feathers block the heat signature entirely, trapping all that heat around the body. As surface area:volume ratios drop as animals get larger, it stands to reason that the benefits of blocking solar radiation give way to a need shed heat. Image from Wikipedia user Arno / Coen, CC BY-SA 3.0.
Feathers, however, are not magic structures that defy fundamental physical laws of insulation, nor do they liberate animals from the challenges of heat loss at reducing surface area:volume ratios. Beyond a certain size, shedding excess body heat is difficult for any terrestrial animal, and it gets tougher as they get larger. King and Farner (1961, p. 249) described feathers as having "an extremely high insulating value to the feathered surfaces" and a rich literature of studies on modern birds shows that feathers are as effective at trapping body heat as they are blocking solar rays (e.g. King and Farner 1961; Kahl 1963; Philips and Sandborn 1994; Dove et al. 2007). We can almost see them as a little too effective, leading many birds to develop heat-dumping adaptations to circumvent their own insulation, such as highly vascularised, non-feathery body parts as well as a repertoire of postures and behaviours (maximising exposure of unfeathered body parts; flapping wings; urinating on their legs) that aid cooling (e.g. Kahl 1963; Arad et al. 1989; Philips and Sandborn 1994). So yes, feathers are terrific at protecting birds from environmental heat, but that limits their ability to release metabolic heat from their own bodies.

If living birds find feathers a little warm, despite their relatively high surface area to volume ratios, we have to assume a theropod weighing anywhere between 6-14 tonnes is going to find big areas of dense filaments a challenge to thermoregulation too. It is not unreasonable to assume blankets of fibres could be a problem for big tyrants. The counterargument here is that Yutyrannus huali, a largish tyrannosauroid, does have dense fibres everywhere. But Yutyrannnus seems more lithe than Tyrannosaurus - perhaps just 10-25% of its mass, depending on the estimates (Bell et al. 2017) - and lived in a more vegetated, and thus shadier, habitat (Bell et al. 2017). A neat comparison Bell et al. (2017) make along this line uses living rhinos, where hairier species live in shadier settings than the virtually naked ones. In light of this, the reduction of filamented regions, and perhaps lessening their density, is a reasonable inference for animals of the size and habitat of Tyrannosaurus, and would reflect thermoregulatory responses to scaling and shade availability seen in living animals.

Large tyrannosauroids, like Yutyrannus huali, show that dinosaurs weighing perhaps 1.5 tonnes could be covered in feathers. But does this reflect the fact that this animal lived in shadier, vegetated habitats than the tyrannosaurids? This idea isn't silly: adaptation to specific circumstances has a major role to play in shaping animal skin anatomy, and could well explain why some tyrants are fuzzy, and others seem less so. (If you want to see the rest of this picture, check out this Patreon post)
Could Tyrannosaurus have had extremely fine, widely-distributed filaments - perhaps similar to something like elephant hair? This isn't entirely falsified by the new data, although the skin impressions we have show no evidence of such a covering despite preserving tiny integument details. Granted, animal filaments can be extremely fine, and they might be beyond the preservation potential and mechanics of even these high-res impressions. However, if we're arguing for filaments of this size and patchiness then - certainly for artistic purposes - we should concede that the animal would be essentially scaly, in the same way that most rhinos, elephants and hippos are essentially naked (below). From a thermoregulatory perspective, short, sparse filaments could make sense as these have the surprising ability to draw heat from the body in modern elephants, helping them stay cool (Myhrvold et al. 2012). Given the potential for overheating under dense filament coats in giant animals (Bell et al. 2017), I see this as more plausible than a 'cloak' of fibres between our scaly waypoints.

Scaly, minimally-filamented Tyrannosaurus. There's some tufts on the neck, but that's it. Is this model more consistent with the thermoregulatory requirements of a 6-14 tonne animal?
A last interpretation of this new data is that Tyrannosaurus was actually just scaly, with no fibres whatsoever. This is the most contested suggestion made by Bell et al. (2017), but it's not unreasonable with our current knowledge. Existing skin data, representing seven parts of the body if you pool all the distinct skull correlates and postcranial points (add several more if you want to extrapolate scale patches from other tyrants), shows enough scales and consistency in the scalation pattern that uniform scale coverage is not a ridiculous or indefensible concept. I appreciate that some folks will point to regional fuzziness of animals like Kulindadromeus in response, and its sharply defined areas of different integument types, and that's valid point. But we can also point to plenty of dinosaurs with extensive or entirely scaly hides and - if there's any value to linking body size and thermoregulatory regimes - they're a better match to Tyrannosaurus body mass than any known fuzzy species. For the time being, wholly scale models fit our existing data just as reasonably as partly fuzzy ones so, archaic and counter-intuitive as it seems - a scaly Tyrannosaurus is not an unreasonable interpretation for the life appearance of this animal, given our current data.

Beyond Tyrannosaurus: 'unlocking' dinosaur skin constraints

My take-home from these new papers is that our models of Tyrannosaurus skin have not crystallised, but we're a little more constrained in how we can imagine this animal, and have to concede a scalier appearance than many of us thought likely. But the implications of the Bell et al. study go beyond Tyrannosaurus in implying new ways to think about dinosaur skin evolution. With incontrovertibly fuzzy animals lining much of the the tyrannosauroid tree and its root, our scalier Tyrannosaurus gives us one of the best examples of a dinosaur replacing fuzz with scales. This is a far-reaching conclusion for those of us interested in dinosaur life appearance, complicating the already confusing evolutionary pattern of scale and fuzz distribution within the group. Ideas that some dinosaurs could be 'secondarily scaled' are supported by this discovery, and we have to wonder if classically fuzzy lineages - including many other theropod lines - are as tightly locked into fuzz, fibres and feathers as we once thought. Could large dromaeosaurs be a little lighter on fuzz than we imagine? Did Therizinosaurus look less like a giant pigeon and more like a walking Christmas dinner? We don't know, but now have reason to wonder.

Fluffy Tyrannosaurus juveniles, one of the possibilities created by the idea that tyrannosaurs might have avian-like 'dynamic' skin. The recovery of scales in non-scaly clades is not as simple as it might first appear!
Furthermore, the notion that Tyrannosaurus scales could be modified feathers (Bell et al. 2017) opens possibilities about mixes of filaments and scales. It's important to realise that not all scales are alike: 'reptile'' scales' are developmentally and genetically distinct from those we see in birds, which are actually secondarily modified feathers (Chang et al. 2000; Dhouailly 2009). Reptilian skin cannot be forced to grow feathers or filaments (Chang et al. 2000) and is developmentally static: once scales are formed, they're with them for life. Bird skin, however, is far more dynamic, and allows for all manner of ontogenetic and even seasonal variation in scale:feather ratios, changes to feather types, and modification of scale size (Lennerstedt 1975; Stettenheim 2000). If, as suspected, our tyrannosaurid skin samples represent fibrous integument masquerading as a scaly one, is this a sign of a bird-like 'unlocked' skin configuration where epidermal dynamism was possible? If so, Tyannosaurus could have changed appearance considerably with age (fluffy when small, scaly when big - above) or season (reflecting changes in climate or behaviour)? It must be stressed that we don't have any direct insight into these sorts of changes at the moment, and the hypothesis of tyrannosaurid scales being modified feathers needs testing. But the irony - we might have data indicating Tyrannosaurus could change its appearance readily, vindicating debaters on both sides of the scaly and fuzzy debate - is not lost on me. Maybe, just this once, everyone wins?

Summing up time

Let's tie this all together. A lot of ambiguity remains about the skin of Tyrannosaurus and its relatives, and it's not wise to hold any opinion about their life appearance too strongly at present. However, unduly downplaying the creep of scaly evidence into the tyrannosaurid fossil record isn't useful or logical. The skull skin correlates and fossil skin patches show that scales were present in numerous, widely-distributed parts of the body, and - until we see evidence to the contrary - this is good reason to assume scalier Tyrannosaurus than we might be used to. And yes, this does mean that some of our favourite, fluffier interpretations are now directly contradicted by fossil data, and consigned to our ever growing book of historic, discredited reconstructions. But this is always a possibility in palaeontology: our views of these animals are only ever hypotheses based on a sparse, biased fossil record, and every new discovery risks overturning someone's favourite concept. The fact we're able to move on from these reconstructions is positive, as it means we're a little less uncertain about the past, and a little closer to the truth.

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