This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Anyone who knows anything about Mesozoic dinosaurs will be – or certainly should be – familiar with the fact that our view of what these animals looked like in life has changed substantially within the last several decades. The ‘dinosaur renaissance’ of the late 1960s and 70s saw the flabby-bodied, tail-dragging behemoths of earlier decades be replaced by sprightly, athletic animals with big, bulging limb muscles, erect tails, and dashing patterns and colour schemes. This ‘new look’ for dinosaurs was initiated by (sometime Tet Zoo reader) Robert Bakker and then taken forwards by Greg Paul and Mark Hallett; several other artist-writers of the 1970s and 80s also helped perpetuate ‘new look’ dinosaurs, including John McLoughlin, Peter Zallinger and Doug Henderson (arguably the greatest palaeoartist of them all).
The influence of Greg Paul in particular has been so significant that the majority of ‘modern’ dinosaur renditions – those of Jurassic Park and numerous artworks, museum installations and so on – are, effectively, ‘Greg Paul dinosaurs’. Many palaeontologists don’t like crediting Greg Paul's influence, in part because they dislike or disagree with the arguments, proposals and contentions he has made in his many technical articles and books. I think that ‘Greg Paul the publishing scientist’ is a different entity from ‘Greg Paul the technical artist’, and that Greg’s influence on how we imagine and reconstruct fossil dinosaurs needs to be fairly credited (see comments in Naish 2008, Conway et al. 2012). So, ‘Revolution # 1’ as goes the portrayal of Mesozoic dinosaurs* was instigated by Bakker, Paul, Hallett and their contemporaries, with Greg Paul being of pre-eminent importance.
* Because birds are dinosaurs, it should be noted that articles like the one you're reading now are specifically about those dinosaurs that lived during the Mesozoic Era. Early birds are included in this general subject area, meaning that 'Mesozoic dinosaurs' and 'non-avialan dinosaurs' (= non-bird dinosaurs) are not synonymous.
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I should say, by the way, that all of what I’ve just said is very familiar stuff to those interested in the world of palaeoart. However, many things that are ‘common knowledge’ for certain sets of people are not necessarily familiar to interested parties at large.
Moving on... So, those of us interested in the life appearance of fossil animals grew up with svelte, muscular, sometimes fuzzy or feathery ‘Paulian’ dinosaurs. Blubbery, fat-limbed dinosaurs that somehow persisted into the artwork of the mid-1980s – produced by artists, and presumably given the ok by palaeontologists, who shall remain nameless (some of you will know who I have in mind) – looked weirdly anachronistic when published, and their existence during the 1980s and persistence beyond them has always been inexplicable. What? You mean you hadn’t seen the Paulian dinosaurs that everyone else was drawing by now? Huh. Anyway...
Revolution # 2
Fast forward to the early decades of the 21st century. As ridiculous as it would have seemed to the palaeontologists and palaeoartists of the 1980s and before, feathered non-bird dinosaurs are now “commonplace” (to quote one study), and integumentary fuzz has been discovered on ornithischians and numerous theropods (including big tyrannosaurs). Assorted studies have shed substantial light on dinosaur facial tissues, forelimb orientation, posture, locomotion, muscle size, and tail shape.
We have learnt enough for ‘Revolution # 2’ to occur – the ‘soft dinosaur revolution’ (hat-tip to Jason Brougham for this term).
With Paulian dinosaurs as the framework or bedrock, we have entered the age whereby people are able to add a more realistic amount of musculature, skin and other integumentary structures... to make the animals less shrink-wrapped. The concept of shrink-wrapped dinosaur syndrome (SWDS) arose sometime round about 2010 and has since been widely used in discussions of dinosaur life appearance. I’m not sure who originated the term, since it was used approximately simultaneously by sauropod expert Matt Wedel and palaeoartist John Conway.
Whatever, the concept emerged among several interested parties. The ‘All Yesterdays Movement’ – which has rigorous skeletomuscular reconstructive work at its core – has emerged from a desire to portray dinosaurs (and other fossil animals) with the right amount of soft stuff (Conway et al. 2012). It’s really not, as some seem to have assumed, built on the idea that anything goes. Muscles may sometimes be more extensive and more voluminous than illustrated within the ‘Paulian’ paradigm (Hutchinson et al. 2011, Persons & Currie 2011), dinosaurs may sometimes or often have sported wattles, dewlaps, soft frills and other epidermal features, and fuzzy and feathery coatings of various species were frequently thick and extensive, not sparse.
In the rest of this article I want to say a few brief things about the life appearance of Mesozoic dinosaurs. The old, chunky, tail-dragging dinosaurs of the 1950s and before are dead, but the shrink-wrapped, sparse-feathered ones of the 1980s should be, too. Again, this idea is familiar to those who keep up to speed on dinosaur life appearance, but I get the impression that it’s not that appreciated overall.
A very brief guide to dinosaur life appearance
Articulated skeletons, trackways, and the way bones fit together show that dinosaurs generally walked and ran with horizontal bodies and tails that were approximately parallel to the ground. Tail-tips might have drooped or dangled, but tails only really sloped downwards in horned dinosaurs, and to a degree in therizinosaurs and brachiosaur-like sauropods. This doesn’t mean that all dinosaurs were all horizontal all the time. Bipedal species of many sorts likely stood with diagonal or even near-vertical bodies when scanning the landscape, testing for odours, or showing off to other animals. And quadrupedal species like certain sauropods (most notably diplodocids) and stegosaurs were also almost certainly capable of semi-erect poses too. Therizinosaurs must have walked and stood with a perpetual diagonal body posture.
Theropods – the predatory dinosaurs and birds – did not walk around with ‘bunny hands’ as used to be shown (that is, with their palms facing the ground). Rather, the arms and hands were articulated such that the palms faced inwards and the hand could not be pronated – that is, it could not be rotated to face downwards (e.g., Gishlick 2001, Senter & Robins 2005). This raises all manner of issues as goes hand function and predatory behaviour, but that’s an issue I can’t cover here. ‘Palms-inward’ hands were also present in bipedal sauropodomorphs (the plateosaurs and their kin) (Bonnan & Senter 2007).
The idea that bird-like non-avialan coelurosaurs were feathered has been popular in some circles since the late 1980s at least. That’s right, feathered (non-avialan) dinosaurs are not a new thing, but were ‘normal’ and oft-illustrated by a whole generation of people interested in the life appearance of dinosaurs. Bakker, Hallett and Paul were all illustrating feathered theropods throughout the late 1970s and 80s but it was Paul’s 1988 book Predatory Dinosaurs of the World (Paul 1988) that launched the idea into mainstream dinofandom (see also Paul 1987). Paul’s arguments were pretty sensible: they basically hinged on the fact that non-bird maniraptorans like Velociraptor are extremely similar in form and anatomical detail to indisputably feathered Archaeopteryx. While quite a few palaeontologists agreed that the notion of a feathery Velociraptor was at least plausible, what I remember from the 1980s and early 90s is those palaeontologists who declared this idea unlikely and overly speculative. Nope, it’s scales scales scales until proven otherwise, they said. Of course, it turns out that Paul and those other palaeoartists were actually right all along.
Well, actually: now that we have lots of feathered non-bird theropods, it turns out that Paul and his followers were too conservative. These animals didn’t have a thin or sparse veneer of feathers on just part of their bodies. Rather, they were thickly clothed in them just as birds are, with fuzz covering much of the face and snout, long feathers obscuring the arms and hands and much of the legs, and fan-like arrangement of large feathers sprouting from the tail. You can do your bit to help spread the news as goes properly feathered non-avialan theropods by backing Rebecca Groom's Palaeoplushie Velociraptor project or by purchasing my new "Just say NO to unfeathered non-avialan maniraptoran theropod dinosaurs" t-shirt at the Tet Zoo Redbubble shop!
Sauropods with softer faces
Moving on to sauropods... Sauropods were mostly covered in non-overlapping scales but some had osteoderms and tubercles across the back. Diplodocids – and maybe others – had a row of triangular, laterally compressed spines running along the dorsal midline (Czerkas 1992). The hands of ‘advanced’ sauropods were columnar, semi-circular structures where the thumb claw was the only claw present (and even this was reduced and lost in the largest, most speciose sauropod clade: Titanosauria). Hindfeet were oval, backed by a giant fat-pad, and with three (sometimes two, sometimes four) laterally compressed claws on the innermost toes.
Debate continues over the neck posture of sauropods. I’m one of several researchers who thinks – based in part on data from living animals – that sauropods (and other sauropodomorphs) routinely held their necks in high, raised poses, not horizontal or downward-sloping ones (Taylor et al. 2009). Sauropods have traditionally been illustrated with sunken, skeletal faces and nostrils perched high up in the bony nostril openings. However, work on sauropod facial tissues (Witmer 2001) means that we should imagine them with ‘softer’ faces where tissues obscured much of the underlying bony anatomy, and the fleshy nostrils were located down on the muzzle and not well up and back in the bony nostril opening [adjacent illustration take from this SV-POW! article on the life appearance of sauropods]. The notion that sauropods might have had tapir- or elephant-like trunks has been suggested a few times but is not consistent with any aspect of skull anatomy, nor with the tooth wear seen in the group. It’s also contradicted by data on nerve anatomy (animals need big facial nerves to operate a trunk) (Knoll et al. 2006). I’ve written about this idea before – see the links below.
Ornithischians, fuzzy and otherwise
Finally, what about ornithischians – the third great group of dinosaurs, the one that includes stegosaurs, ankylosaurs, ornithopods, ceratopsians and pachycephalosaurs? Beak tissue definitely sheathed the anterior parts of the jaws in these dinosaurs (this is actually preserved in some hadrosaurs) but several other aspects of their facial anatomy have been controversial. The idea that skin and other soft tissue spanned the side of the mouth cavity – this is typically termed ‘cheek’ tissue even though this is very likely technically incorrect – has been popular but occasionally contested. The distribution of nutrient foramina on the jaw bones of these dinosaurs supports the idea that an extensive amount of tissue did indeed cover the sides of their jaws (Morhardt et al. 2009), and the presence of ossifications that fit in the space between the upper and lower jaws of some ankylosaurs show that a tissue web of some sort really was present.
Preserved skin impressions show that many ornithischians possessed polygonal scales over most or all of their bodies; at least some hadrosaurs also had serrated or ribbon-like frills along the back and tail. The gigantic, complex bony nostrils of hadrosaurs and ceratopsians almost certainly housed erectile or inflatable structures of some sort. Soft crests, dewlaps and other structures are suspected or known to have been present in hadrosaurs and other ornithischians, and the horns of ceratopsians, and plates and spines of stegosaurs and ankylosaurs, were certainly enlarged in size (sometimes substantially) by keratinous coverings.
The big deal about ornithischian life appearance right now concerns the presence of filamentous integumentary structures in several taxa: in the heterodontosaurid Tianyulong, the ceratopsian Psittacosaurus, and in Kulindadromeus, a bipedal ornithischian that would once have been identified as an ornithopod but is actually outside the clade that includes ornithopods and marginocephalians. Kulindadromeus is remarkable in that it is partially covered in simple filaments but also in parallel fibres that emerge from broad, plate-like structures, and in bundles of parallel, ribbon-like filaments (Godefroit et al. 2014). None of these structures are longer than 2 or 3 cm. Scales cover the feet and imbricated, rectangular scales – arranged in several longitudinal rows – are present across the dorsal surface of the tail.
The question now is how widespread such filamentous structures were across Ornithischia, and across Dinosauria in general. Were they restricted to one or two lineages, were they normal across the small-bodied members of all lineages, or were they present across diverse small-bodied and large-bodied lineages? And are the structures in ornithischians homologous with the filaments of theropods and pterosaurs? We simply need more data from more fossils before we can go further with this.
Finding information is hard – so, what to do?
Needless to say, there’s a ton more that could be said about dinosaur life appearance. What I’ve done here is merely overview, in very brief fashion, some of the more easily summarised subject areas. What do people do when they need up-to-date information on these sorts of issues? That’s not an easy question to answer. The only competent and comprehensive review of dinosaur life appearance is Paul’s 1987 book chapter (Paul 1987), and it’s now woefully out of date.
Your other recourse is to scour through the vast primary literature, or to team up with a friendly expert (and don’t go assuming that palaeontologists are necessarily useful on this sort of stuff. Those who work on phylogenetics, diversity across time, histology and so on are often not up to speed on soft tissue anatomy. Exhibit A: all those execrable and hopelessly inaccurate dinosaur images published in books that were supposedly authenticated by august working scientists). So, what’s needed? The answer: a grand new illustrated work that provides a comprehensive guide to the life appearance of fossil dinosaurs. The good news: plans to produce just such a project are underway right now. Watch this space...
For previous Tet Zoo articles on palaeoart and the life appearance of Mesozoic dinosaurs, see...
Feathers and filaments of non-avian dinosaurs, part I [warning: now out of date]
Feathers and filaments of dinosaurs, part II [warning: now out of date]
The hands of sauropods: horseshoes, spiky columns, stumps and banana shapes
Sauropod dinosaurs held their necks in high, raised postures
The war on parasites: the pigeon’s eye view, the oviraptorosaur’s eye view
Junk in the trunk: why sauropod dinosaurs did not possess trunks (redux, 2012)
And - entirely coincidentally - today also sees the publication of my colleague Mark Witton's article on palaeoart Patterns in Palaeontology: Palaeoart – fossil fantasies or recreating lost reality?
Refs - -
Bonnan, M. F. & Senter, P. 2007. Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds? Special Papers in Palaeontology 77, 139-155.
Czerkas, S. A. 1992. Discovery of dermal spines reveals a new look for sauropod dinosaurs. Geology 20, 1068-1070.
Gishlick, A. D. 2001. The function of the manus and forelimb of Deinonychus antirrhopus and its importance for the origin of avian flight. In Gauthier, J. & Gall, L. F. (eds) New perspectives on the origin and early evolution of birds: proceedings of the international symposium in honor of John H. Ostrom. Peabody Museum of Natural History, Yale University (New Haven), pp. 301-318.
Godefroit, P., Sinitsa, S. M., Dhouailly, D., Bolotsky, Y. L., Sizov, A. V., McNamara, M. E., Benton, M. J. & Spagna, P. 2014. A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. Science 345, 451-455
Knoll, F., Galton, P. M. & López-Antoñanzas, R. 2006. Paleoneurological evidence against a proboscis in the sauropod dinosaur Diplodocus. Geobios 39, 215-221.
Morhardt, A. C., Bonnan M. F. & Keillor, T. 2009. Dinosaur smiles: correlating premaxilla, maxilla, and dentary foramina counts with extra-oral structures in amniotes and its implications for dinosaurs. Journal of Vertebrate Paleontology 29 (supplement to 3), 152A.
Naish, D. 2008. The Great Dinosaur Discoveries. University of California Press, Berkeley.
Naish, D. 2014. Rediscovering the dinosaurs. Science Uncovered 7 (June 2014), 68-72.
Paul, G. S. 1987. The science and art of restoring the life appearance of dinosaurs and their relatives - a rigorous how-to guide. In Czerkas, S. J. & Olson, E. C. (eds) Dinosaurs Past and Present Vol. II. Natural History Museum of Los Angeles County/University of Washington Press (Seattle and London), pp. 4-49.
- . 1988. Predatory Dinosaurs of the World. Simon & Schuster, New York.
Persons, W. S. & Currie, P. J. 2011. The tail of Tyrannosaurus: reassessing the size and locomotive importance of the M. caudofemoralis in non-avian theropods. The Anatomical Record 294, 119-131.
Senter, P. & Robins, J. H. 2005. Range of motion in the forelimb of the theropod dinosaur Acrocanthosaurus atokensis, and implications for predatory behaviour. Journal of Zoology 266, 307-318.
Witmer, L. M. 2001. Nostril position in dinosaurs and other vertebrates and its significance for nasal function. Science 293, 850-853.