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Sunday, 24 June 2018

Ricardo Delgado's Age of Reptiles at 25: a palaeontological retrospective

With the 25th anniversary of Jurassic Park cascading through dinosaur social media you could be forgiven for overlooking another influential dinosaur franchise celebrating the same vintage this year. Unveiled in 1993, this long-running series stood out for showing dinosaurs as fast, agile and intelligent animals, and immersed us in an then-unparalleled expanded prehistoric narrative, rich in detail and huge in scale. I'm talking, of course, about Ricardo Delgado's Dark Horse comic series Age of Reptiles.

The award-winning Age of Reptiles series comprises multiple, unconnected stories published throughout the last 25 years, with a bit of a hiatus between its earliest and latest incarnations. The series comprises four serials (Tribal Warfare, 1993; The Hunt, 1994; The Journey, 2009; and Ancient Egyptians, 2015) and two shorter pieces (The Body, 2011; Baby Turtles, 2014 - regrettably, I haven't seen these in entirety). It has a number of fans among those of us who research and illustrate fossil reptiles, and judging from the calibre of movie makers who've contributed endorsements to the comics, it is well regarded in the movie industry, especially for its entirely 'silent', visual means of storytelling. Despite some relatively complex narratives, large casts and use of multiple locations, not a word of dialogue or descriptive text is used to explain plots or character motivations. The 2011 documentary Dinosaur Revolution and its 2012 spin-off Dinotasia were inspired by Age of Reptiles, with Delgado having director credits on two episodes of the former. It's fairly well known that, until late in production, Dinosaur Revolution was effectively meant to be Age of Reptiles: the TV show, but studio cold feet revised the programme into a more conventional documentary.

Cover art for various editions of the Ricardo Delgado's Age of Reptiles comic series, borrowed from Dark Horse Comics. Their website which has a full back catalogue of the series for your browsing and purchasing needs. Sorry for the low res images - I'm deliberately using officially released artwork in this post to avoid unintentional piracy of Age of Reptiles content. Entire sequences of the Age of Reptiles comics have been uploaded without authorisation to the web, and that's not cool, folks: it's stealing.
Age of Reptiles was an important influence on my childhood drawing and, with the series hitting the big two-five this year, I thought I'd share some of what I think makes the series special. It helps, I think, to set the stage in which I first met Age of Reptiles as an eight or nine-year old* dinosaur obsessive in the early 1990s. Though not so long ago, this was a different age for palaeontological media because rendering life-like prehistoric animals for TV or film was much harder than it is today. Making a realistic film or documentary chronicling the lives of prehistoric animals would not only have been very difficult, but also very expensive. Jurassic Park may have broken new ground for dinosaur animation in 1993, but it needed sophisticated animatronics, then-radical computer generated imagery and a Hollywood-grade budget to achieve its visuals. It took several years for this technology to become more widely affordable, with the the bridge between Jurassic Park and our living room viewing - Walking with Dinosaurs - not appearing until 1999. Thus, if I wanted to see 'living' dinosaurs, rather than just disconnected pictures in dinosaur books, I had to made do with the short vignettes with wobbly puppets on the A&E Dinosaur! series, or else hope to find a showing of a Harryhausen dinosaur film on TV.

*My birthday would have been around the time I first saw the comic, and I can't remember if I'd graduated to nine years old when I first saw it.

It was into this landscape that Age of Reptiles placed a weighty clawed foot. I first encountered the first story, Tribal Warfare, through the UK's take on the Jurassic Park comics. Coinciding with the movie release, the international branch of Dark Horse comics published a weekly Jurassic Park magazine that contained a comic story of the movie as well as two other series: Xenozoic Tales (a post-apocalyptic sci-fi story with minimal dinosaurs - I never really got on with it) and something called Age of Reptiles. Juxtaposed against the talky, high-tech worlds of Jurassic Park and Xenozoic Tales, Tribal Warfare immediately stood apart with its silent, patient and entirely immersive opening. Without a word of introduction, we see a sleepy Pteranodon wake up, spread its wings, and then launch over a huge, double-page vista of unspoilt trees and bluffs. The pterosaur sails past a foraging sauropod, which we soon learn is being stalked by a group of dromaeosaurs. We watch the sauropod flee and ultimately fall to its attackers, before a huge tyrannosaurid arrives to claim the carcass from the smaller predators. The animals were colourful, dynamic, imposing and vicious, and played out their drama without interruption from a narrator, talking head or visiting caveman. It was unlike anything I'd ever seen.

Sorry, Walter Cronkite: your A&E dinosaur puppets had nothing on this. Page from the opening comic of Age of Reptiles: Tribal Warfare, where a pack of Deinonychus bring down a titanosaur, while Pteranodon soars past. Anachronistic fauna be damned: for an early 1990s dinosaur fan, this was ambrosia from the loftiest peaks of Olympus. Borrowed from Dark Horse Comics.
Reading the comic in entirety, it was apparent that this was not a story about prehistoric animals living with humans, or anthropomorphic cuddly dinosaurs learning lessons about friendship. Age of Reptiles was the extended, unadulterated prehistoric drama every '80s kid wanted but film or TV had yet to produce. OK, it was in comic format rather than animated on screen, but Delgado's experience with storyboarding and film illustration gave our brains little work to do as we filled in the action between panels.

Age of Reptiles continued to resonate for years after I first encountered it. Much of the dinosaur art I drew for the next 5, 10... 25 years was influenced to a greater or lesser extent by Delgado's creation, to the extent that I rank him as one of my top artistic influences. It may not be as obvious in my modern work as it was 20 years ago, when I was a teenager liberally borrowing from his style (below), but it's still there. Every now and then a Delgadoesque waterfall or critter still sneaks into one of my paintings and I still have a lesson in composition and visual storytelling whenever I re-read his work. Those of you with eagle eyes may have noticed praise for Age of Reptiles in my 2017 book, Recreating an Age of Reptiles, the title of which was chosen as much for its relevance to the comic as it's palaeontological and paleoartistic connotations. Though I don't think Age of Reptiles can qualify as pure palaeoart on grounds of taking a few too many artistic liberties with palaeontological data, it contains many lessons about effective depiction of fossil animals and, 25 years on, I still regard it as some of the best 'palaeontologically-inspired art' (as opposed to entirely science-led palaeoart) out there.

Revisiting some of my 20 year old drawings (I would have been about 13 when I drew these) shows many Delgadoisms. These would all have been influenced by Tribal Warfare, I didn't have The Hunt. The tree outlines, cliffs, waterfalls with sharply defined mist, the hatched scalation, eye shapes and so on were my best attempts to execute an Age of Reptiles style.

Telling palaeostories

As noted above, some of the heaviest praise for Age of Reptiles stems from its ability to tell complex stories without any text. They are not conventional narratives about dinosaurs either, the Age of Reptiles stories recalling cinematic westerns, Mafia dramas and Mad Max-style journeys through post-apocalyptic wastelands. Essays penned by Delgado for some of the comics discuss these influences, often citing classic films as inspiration. It's quite a feat to make western where cowboy hats are traded for scales and, yes, the characters are somewhat anthropomorphised to achieve this, but it rarely feels overdone. Anthropomorphism also lessens as the series continues, just one of many aspects that seems to change - we might say 'mature' - as the series has continued. The animalistic behaviours of Age of Reptiles' characters are aided by Delgado not being afraid of making them real scumbags, as well as a dark sense of humour and regard for his their wellbeing that even Game of Thrones might consider a bit harsh. These attributes make Age of Reptiles a closer approximation of the natural world than other franchises where we see dinosaurs engaging in day-to-day behaviour, and brings a moral ambiguity to his characters. This makes it difficult to root for any one character entirely, but I think that's the point: these aren't comics with moral lessons about human values, but stories about animals that have to be strong and sometimes violent to survive. Executives wondering what to do with dinosaur narratives for documentaries or films could learn a lot from Delgado's work: dinosaurs can do more than just search for those far-flung lush valleys, folks.

Dark Horse's 2015 motion comic is slightly different from the original opening of Tribal Warfare, but it captures some of the arresting cinematic style and dinosaur behaviour of the very first Age of Reptiles comic. From Dark Horse Comics' official YouTube account.

The Age of Reptiles series has paid increasing attention to science since its 1993 debut. Tribal Warfare has anachronistic casting with a mix of dinosaurs and other reptiles from across time and space: Tyrannosaurus rubs shoulders with Deinonychus, Deinosuchus, shastosaurid ichthyosaurs, Saltosaurus, Pternanodon, Parasaurolophus, Carnotaurus and others - it's a grab bag of fan-favourite Mesozoic animals. Their behaviour is also among the most simplistic and anthropomorphised of the series too, with the tyrannosaurids and dromaeosaurids acting like rival gangs from some gritty, gory 70s exploitation film. But in later serials more attention has been paid to real species compositions and animal behaviour is more nuanced. This has been implemented most successfully in Ancient Egyptians, where efforts have been made to feature the correct fauna and palaeoenvironment of mid-Cretaceous Africa, and the depicted behaviours are relatively animalistic. The characterisation of some species also runs against stereotyped portrayals of dinosaurs in popular media, subverting tropes of 'harmless herbivores' and so on. The giant titanosaur Paralititan, for example, is the primary antagonist in the story, being an aggressive, violent species bristling with antagonism in every frame. Annoy these sauropods and you're in trouble, even at risk of being crushed to death under the massive tonnage of their forelimbs. This is a very different role for a sauropod dinosaur in popular media, even contrasting with prior Age of Reptiles stories where they are little more than background animals or prey species. The idea of large herbivores being badass mothertruckers isn't silly either, this being the case for many living herbivores like hippos, certain bovids, and some elephants.

Ancient EgyptiansParalititan in full angry mode. Note the blocky neck profile, distinctive facial tissue, correctly positioned nostrils and distinctive scarring - great stuff. From Dark Horse Comics.
Elsewhere, a male Spinosaurus - the anit-hero for the story - kills the offspring from another male before siring his own (in stark contrast to the nurturing parent-juvenile relationships of earlier Age of Reptiles) and sometimes communicates using rumbling vocalisations emitted from its throat rather than always using open mouth roaring. This is progressive stuff, and - particularly as someone who's experienced pushback against new ideas when working on dinosaur media projects - very refreshing to see in a popular dinosaur product. We can't pretend that Age of Reptiles is a documentary - if it were entirely true to life, 95% of the series would be dinosaurs chewing leaves and pooping - but Delgado deserves full kudos for pushing his creation towards more credible faunal compositions and not holding back when depicting new ideas about dinosaur behaviour. Hollywood, take note: thus far, we've seen no evidence that having half an eye on science has impacted his ability to tell great stories.

Evolving anatomy and Age of Reptiles

Delgado's animal designs have also crept towards realism and scientific credibility since 1993. His reptilian cast is 100% post-Dinosaur Renaissance, and thus has always been appropriately posed, agile, and dynamic, but his creative approach seems to have changed between 1990s and 21st century entries into the Age of Reptiles canon. The taxonomic identities of his animals have always been apparent and his animals look 'realistic', in the sense that they don't look anatomically implausible, but the creatures of Tribal Warfare and The Hunt have a certain 'augmented' quality that is not apparent in later serials. The theropods, for example, are always long-legged beasts with boxy, robust skulls and large, prominent teeth, as well as heavy scalation and exaggerated ornaments. They're recognisable as their real-life counterparts, but look like superpowered versions of the real species. Though not all the animals in the first Age of Reptiles serials received this treatment (most of the herbivorous species are pretty darned good approximations for our 1990s views of these animals, with minimal embellishment) the overwhelming impression is still one of prehistory on steroids. I'm reminded somewhat of William Stout's 1990s palaeoart: Stout's work is probably on the more credible side of the scientific fence, but shares an emphasis on gnarly, enhanced features with Delgado's creations. I wonder if Stout's work was referenced in those early comics.

The Journey and subsequent stories feature more scientifically credible restorations which seem more carefully modelled on their real-life counterparts. The tyrannosaurs in The Journey, for instance, have longer bodies and skulls, and stouter legs, than the 1993 versions and thus look much more like the real deal. The abelisaurs in Ancient Egyptians show the peculiar short arms and blunt heads particular to this group, unlike the fairly 'generic' Carnotaurus we met in 1993. I especially like the titanosaurs of both The Journey and Ancient Egyptians, their designs having robust, wide necks, rotund bodies and stout limbs, as they should. Smaller details are well captured too, with eyes, ears and nostrils being in the right places - not something to be sniffed at in any public-facing dinosaur art.

Cover of the first issue of Age of Reptiles: The Journey. Note the improved tyrannosaurid anatomy compared to that of Tribal Warfare, which you can see in the video above. Also, so many footprints! - another hallmark of later Age of Reptiles art. From Dark Horse Comics.
Additional positive trends include less shrink-wrapping on many species (the pterosaurs, in particular, have a lot more meat on their bones in later stories), closer attention to the anatomy of non-dinosaurian species, and more natural-looking colour schemes. I am curious to know if this reflects influence from broader palaeoart trends, or if Delgado has independently moved away from some of the retrospectively questionable reconstruction choices of early 90s palaeoart. Whatever the influence, though some liberties are taken to create recognisable individual characters or convey thoughts and actions, the tighter, more believable take on these animals is welcome. Within the constraints of creating a comic about prehistoric animals, I think Delgado is doing an increasingly good job of balancing the demands of narrative with science.

If I have one complaint about the accuracy of the animals, it's that several species have remained scaly even when their fossils now unequivocally show feathers or filaments. I hope this changes in future. To the series credit, feathers have crept in here and there (indeed, they've been in the series since 1993) but voluminous, bird-like feather shells have yet (to my knowledge) to feature in animals we know had them, such as maniraptorans and ornithomimosaurs. Still, I admit that I find this less irritating than I do the lack of feathers in that other major dinosaur franchise launched in 1993, mainly because Age of Reptiles doesn't employ consultants to give the prestige of scientific credibility, nor does it make lame excuses about why it's animals look like they do. It is what it is, and never made any claim for being 100% scientifically credible. Moreover, Age of Reptiles has spent the last 25 years trending in the right anatomical direction, whereas the modern Billy and the Cloneosaurus movies are stuck in the past, sometimes taking deliberate steps away from palaeontological science.

Page from Age of Reptiles: The Journey, featuring the unluckiest sauropod hatchling ever committed to print. Age of Reptiles often has a dark sense of humour and the plight of this little guy is both funny and tragic - you'll have to buy the comic to find out what happens. From Dark Horse Comics.

Worlds of space and detail

Moving away from science and into the art itself, there are also lots of subtle details in Delgado's illustrations which enhance the believability of his prehistoric landscapes and bring character to his actors. It's here where Age of Reptiles can teach conventional palaeoartists a few tricks, as reasoned speculation and imaginative concepts are used to bring Delgado's Mesozoic to life. I could list many examples, but one of my favourites is the association of a small preening pterosaur with a specific female tyrannosaurid in Tribal Warfare - a charming addition to a sometimes violent character. Elsewhere, small creatures - bugs, fish, birds, pterosaurs and so on - frequent most frames, sometimes playing out their own minor dramas against the backdrop of the main narrative. Variation in colour, injuries and integument between his animals give each different personalities, as well as unique visual identities. From The Journey onward we see sauropods sleeping in rings with their necks draped over one another, and in one of Age of Reptiles' rare visits to the marine realm, Delgado's giant mosasaurs are covered with parasitic fish. Plus - because why the heck not - the Araripesuchus in Ancient Egyptians are almost always relieving themselves. These small, sometimes inconsequential details really sell the richness of the Age of Reptiles universe and the individuality of each character.

Another page from Ancient Egyptians. The low angle and shading gives the Paralititan a terrific presence in this panel, leaving us in no doubt that a) it's absolutely huge, and b), that Spinosaurus is in trouble. Note the improved pterosaur anatomy vs those in Tribal Warfare (see images, above). Borrowed from Dark Horse Comics.
The composition and framing of Age of Reptiles is also excellent, creating a sense of atmosphere, scale and motion that rivals the greatest palaeoartworks. Delgado's experience in the world of movies and television brings a truly cinematic quality to some parts of Age of Reptiles, and I strongly recommend these comics just to see how varying viewpoints, animal poses and colouration influence the portrayal of ancient species. If Age of Reptiles was a movie, we could imagine it as one with particularly liberated camera motions that swoop, cut and jump between viewpoints and distance. Delgado is not afraid of placing subjects in the middle or even far distance, often at the expense of fine detail but working terrifically for conveying size, motion and character. My favourite images of the series are those with the viewpoint pulled right back to show enormous landscapes, his animals reduced to fractions of the frame (think Douglas Henderson palaeoart, in comic form). His liberal application of footprints - and their role in communicating information about the nature of a scene - becomes apparent in such views. Close-ups are variably used in more intimate, tense of energetic moments, and we see a lot of variation in light and setting to alter atmosphere and and tone. In all, Age of Reptiles is an excellent demonstration of how a strong eye for composition can enhance artwork of prehistoric animals, and how we can tell entire stories in single images.

Age of Reptiles is not, and is not meant to be, a scientifically rigorous take on Mesozoic life, but it skirts the edge of palaeoartistry and palaeontological science close enough that those interested in these topics should check it out. It's among the most creative and consistently interesting palaeontological products I'm aware of and, if you like dinosaur science, or dinosaur art, you're going to find something to like here. An omnibus of the first three serials is available, as is the collected issues of Ancient Egyptians - all are still in print and very affordable. Fans might also want to check out Ricardo Delgado's blog, which has a lot of 'behind the scenes' content from the series. CGI might have made it easier to create dinosaurs for film and TV since 1993, but the still-picture storytelling of Age of Reptiles competes with, and often outdoes, the best prehistoric drama that Hollywood can throw at us.

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Thursday, 31 May 2018

Why we think giant pterosaurs could fly

Giant azhdarchid pterosaur in flight. Images like this virtually always trigger discussions about the validity of giant pterosaur flight hypotheses.
Every so often the idea of flightless giant pterosaurs circulates in the press or on social media. It doesn't take much to ignite these discussions: a new giant pterosaur fossil, a PR event from a museum, or simply artwork emphasising the size of giant flying reptiles will see someone, somewhere, questioning their flightworthiness. These suggestions are often made with strong conviction, to the extent of dismissing or even arguing with scientists who study pterosaur anatomy and biomechanics. After all, how can any sensible individual think that animals with 10 m wingspans and body masses hovering around 250 kg were capable of flight? At most they were gliders, or flighted as juveniles and flightless as adults, right?

Confession time: as someone actively involved in research and outreach on these animals, I often find these discussions frustrating, for two reasons. The first is that, among those who actually study pterosaur functional morphology – that is, those who make detailed observations and measurements of pterosaur fossils, compile biomechanical data and use computer modelling to objectively test their flight capacity – there is no controversy about the volant nature of these animals, even at their maximum size. Peer-reviewed claims that pterosaurs were flightless are genuinely rare (perhaps limited to Sato et al. 2009; Henderson 2010 and Prentice et al. 2011 in the last decade) and have a consistent record of being flawed on some critical anatomical or functional detail (Witton and Habib 2010). There is no debate about giant pterosaur flight among those of us who study their fossils: the press and social media fuss about the topic is a genuine palaeontological nontroversy.

The second source of frustration is that, away from technical literature, discussions of giant pterosaur flight frequently suffer from major cases of Dunning-Kruger effect, especially when parties have knowledge of planes. I've experienced this a lot in my career, and not just in the wilds of social media: many of my TV and film consultancy jobs have required defending basic tenets of pterosaur anatomy - even their basic, there-for-all-to-see proportions preserved in articulated fossils - to folks who just can't or won't believe what the fossils show. Having a casual understanding of engine-driven man-made flying machines does not equate to knowing all there is about everything that has ever flown, but you would not know this from some conversations.

Our controversial giant azhdarchid friends Arambourgiania philadelphiae (middle) and Hatzegopteryx thambema (right), compared to a record-breaking giraffe and the Disacknowledgement.
Whether through naivety of palaeontological theory or unwillingness to accept good data, the lack of accessible overviews of current thinking on giant pterosaur flight probably fuels this ongoing nontroversy. What's needed, it seems, is a synthesis of modern ideas on giant pterosaur flight and justification for why pterosaur experts don't challenge this idea. I've attempted this below, including sufficient methodological detail and references so that anyone wanting to understand these ideas will have a useful jumping-off point, and to establish what needs to be overturned to challenge the null hypothesis of giant pterosaur locomotion. Our focus will be on the largest of all pterosaurs, giant members of the clade Azhdarchidae, as they are the main focus of most flightless claims (above). They are also among the most familiar giant pterosaurs, their number including species such as Quetzalcoatlus and Hatzegopteryx. The general points made below pertain to all large pterosaurs, however.

Evidence from comparative anatomy

Giant azhdarchids are invariably known from scant remains, sometimes a handful of fragments representing bones from across the skeleton or, in the case of Quetzalcoatlus northropi, an incomplete left wing (e.g. Lawson 1975; Frey and Martill 1996; Buffetaut et al. 2002; Vremir 2010; Martill and Moser 2018). Ordinarily, fragmentary remains are a barrier to interpreting the locomotory strategies of extinct organisms but flighted lifestyles adapt animal bodies to such an extreme degree that just a few bones can betray volant habits. It’s evident that even the largest pterosaurs bore wing anatomy comparable to their smaller, incontrovertibly flightworthy relatives. Although no complete giant wings are known, our fragments indicate similar linear forelimb bone proportions to smaller azhdarchids. Their wing joints – including details of their elbows, wrists and wing finger knuckle – are well understood, and indicate typical properties of pterosaur wing motion and function. We can make a number of predictions concerning muscle extent for giant taxa, the most important being related to the presence of a huge deltopectoral crest on their humeri. This broad flange of bone, situated at the proximal end of the humerus, anchored many muscles running from the shoulder to the wing and powered flapping motions in flight (Bennett 2003), so is a clear correlate for powered flight in giant species. The seemingly-small deltopectoral crest on the Hatzegopteryx humerus is sometimes raised as evidence of reduced flight ability: it’s actually just badly preserved with lots of bone missing on all margins (Buffetaut et al. 2002).

A collection of giant azhdarchid bones: A, cervical vertebra of Arambourgiania philadelphiae; B, humerus of Quetzalcoatlus northropi, C-D, the rather broken proximal humerus of Hatzegopteryx thambema. Other than their huge size (scale bars represent 100 mm) and some details of robustness, these bones are identical to those of smaller, incontrovertibly flying pterosaurs.
The only significant difference between the wings of giant and smaller azhdarchids concerns bone robustness, especially that of their joints. We would predict expanded wing bone diameters in large fliers as they enhance resistance to bending, and as giant animals they are going to experience proportionally greater bending stresses. If they flew, giant pterosaurs should have very large wing bones indeed, and - as is evident from the adjacent images - this is exactly what we find. Witton and Habib (2010) noted that the humeral shafts of giant azhdarchids are comparable in diameter to those of giant mammals, like hippos, despite the pterosaurs being a fraction of their weight (Witton 2008; Henderson 2010). Giant azhdarchid wing bones perform exceptionally well in bending strength tests, being able to resist multiple bodyweights before failing (Witton and Habib 2010), and their expanded diameters maintaining relative failure levels comparable to those of small or mid-sized pterosaurs, despite their size (Witton et al., in prep).

Pterosaur humeral scaling: as pterosaurs got bigger, their wing bones and joints expanded disproportionately to accommodate greater stresses incurred in flight and launch. Image from Witton (2013).
But for all their expansion, giant azhdarchid wings retain exceptionally thin bone walls. Even in Hatzegopteryx, the most robust of the group, they’re only 4-7 mm thick. This is a high value for a pterosaur, but still (in relation to bone diameter) at the low end of the cortical thickness spectrum. Other giant species have cortices of just 2 mm or so, values only just slightly larger than those of mid-sized pterosaurs. Expanded but bone-lite wings are another feature of flying creatures, being common to most flying birds and all large pterosaurs, and offering their owners a lightweight but bending-resistant flight skeleton. However, what optimises these skeletons for flight compromises resistance to buckling forces, which is why most non-volant animals tend to have much thicker cortices. The correlation between thin bone walls and flight is not watertight (Hutchinson 2001) but it's a feature we would predict for any seriously large flying animal, and is thus consistent with volant habits in giant pterosaur species.

Flight models

It’s often asked how animals as large as the biggest azhdarchids could attain and sustain flight. It’s important to stress that no-one imagines giant azhdarchids as breezy fliers flitting around Cretaceous plains like busy songbirds. As animals operating close to the size limits of flight for the azhdarchoid bauplan (Marden 1994; Habib and Cunningham pers. comm. in Witton 2010; Habib 2013) we should assume a flight frequency comparable to our largest modern fliers – creatures like bustards, geese, swans, albatrosses and so forth. Though different in flight mechanics these birds are united in their relatively low launch frequencies, taking to the air when they must (such as to evade danger) or when they have long distances to travel. Launch is very energy-demanding because of their great body masses, and in some cases specific environmental conditions are needed (such as space for taxiing in albatross), limiting their options for frequent takeoff. We should assume the same was true for large azhdarchids: their functional morphology and trackways show strong terrestrial abilities (Hwang et al. 2002; Witton and Naish 2008, 2013) and they probably spent a lot of time grounded, only flying when harassed, or wanting to move far and fast.

When imagining giant pterosaurs flying, we need to have birds like the kori bustard in mind: large, powerful animals which are strong fliers, but unable to flit about the sky like small songbirds or bats. When these guys take off, they mean it. Photo by Arnstein Rønning, from Wikimedia, CC BY 3.0.
Indeed, in all likelihood giant pterosaurs couldn’t launch every few moments. Flying animals tend to allocate about 20-25% of their body mass to flight musculature, which gives our large azhdarchids 50 kg or so of flight muscle to use in launch and flight (Paul 2002; Marden 1994). Even so, models of muscle energy availability show that giant pterosaurs could not launch aerobically (that is, using muscle contractions supplied with oxygen) and they had to rely on stronger, but less endurable, anaerobic muscle contractions. Anaerobic muscle power is essential to launch in the largest birds and almost certainly played a role in extinct giant insect flight, too (Marden 1994, see graph below), so its inferred use in giant pterosaurs is quite plausible. This reliance on anaerobic muscle power would necessitate resting periods between launches (hence the inability to launch continuously like a small flyer) as well as after vigorous bouts of flapping. Witton and Habib (2010) predicted that the hard flapping window for a giant azhdarchid was about 90 seconds, after which a rest was needed. So, does that limit our giants to turkey-like burst flights?


Launch for giant azhdarchids - like Quetzalcoatlus northropi - would be no more challenging than it is for large birds. The dotted line on this graph represents the minimum muscle energy output needed for flight. Using the same mechanism of anaerobic muscle power as large living fliers, giant azhdarchids are on the right side of that line. From Marden (1994).
Probably not. One of the world's leading experts on animal flight, Mike Habib, found that Colin Pennycuick’s freeware Flight programme – software designed to model bird flight - can be easily modified to predict pterosaur gliding and soaring capabilities, even accounting for the differences between feathered and membranous wings (see Witton and Habib 2010 for this methodology). Using this software, Mike and I predicted that giant azhdarchids were supreme soarers, easily able to sustain long-distance gliding even at body masses of 180-250 kg (Witton and Habib 2010). Predicted giant flight velocities exceeded 90 kph and, in that 90 second flapping burst, giant azhdarchids would cover several kilometres - plenty of distance to seek areas of uplift such as deflected winds or thermals. Having located these, azhdarchids could easily adopt energy-saving soaring to recover their flight muscles, their glide ratios being consistent with those of large soaring birds such as storks, Procellariiformes and raptors. Mike has presented calculations that these giants would have sufficient on-board energy resources to travel the planet, their speed and flight range being sufficient to ignore most geographical barriers. Note that these models assume modern day parameters of atmospheric density and gravity: we do not need to modify these to keep giant azhdarchids airborne. Sure, if you did change these parameters you might make the job easier, but the giants already have very strong flight performance without it. If you don't buy this, remember that you can play around with Flight yourself: download the program, get the method and pterosaur parameters from our open access paper and go at it. None of the science behind these animals is mystical - the methods are entirely conventional and repeatable.

Too heavy to fly?

For all this talk of modelling pterosaur flight at quarter-tonne masses, two sets of authors have proposed that giant pterosaurs were simply too heavy to attain flight. Sato et al. (2009) based this on their understanding of procellariiform takeoff, modelling a maximum possible volant mass of 40 kg for these birds and assuming the same limit must apply to pterosaurs. The next year, Don Henderson (2010) compiled a series of volumetric estimates of pterosaur mass including a 450 kg Quetzalcoatlus. Don – probably correctly – assumed that such an animal would be too heavy to fly.

Mike and I addressed both these proposals in a 2010 publication about giant pterosaur flight. On Sato et al. (2009), we found numerous problems with the overt biomechanical links drawn between bird and pterosaur flight. Avian and pterosaur anatomy is comparable enough to assume some broad analogies in wing shape and flight styles (e.g. Hazlehurst and Rayner 1992), but the detailed kinematics of flight – including launch – are too distinct to assume that the size limits of one group apply to the other. There are reasons to think pterosaurs launched in a very different way to birds (see below) and were subject to a different set of scaling regimes and size limits (Habib 2008, 2013; Witton and Habib 2010). Sato et al. (2009) may have predicted a flight mass limit for long-winged, dynamically soaring birds, but the application of this limit to flying reptiles is not supported by our understanding of pterosaur and avian biomechanics.

Don Henderson's (2010) Quetzalcoatlus model compared to the articulated skeleton of the small, completely known azhdarchid Zhejiangopterus linhaiensis. Note the clear distinction in torso size, and the actual torso length of the fossil pterosaur compared to the humerus. Images from Henderson (2010) and Cai and Wei (1994).
We found a much simpler issue with Don Henderson’s half-tonne Quetzalcoatlus model: its body was simply too large. Don based his work on a silhouette in Wellnhofer’s (1991) pterosaur encyclopaedia, a reasonable decision given the paucity of reconstructions of this animal at the time, but ultimately a problematic one for making accurate mass estimations. Azhdarchoids were relatively poorly known in the early 1990s and Wellnhofer’s silhouette reflects this, being a mostly imaginary pterosaur only accurate in wingspan. Crucially, its body is monstrously oversized at 1.5 m long. Complete azhdarchoids discovered since this time, including that of the azhdarchid Zhejiangopterus, have shoulder-hip lengths only 30-50 % longer than their humeri (above) and - in lieu of giant pterosaur torso fossils - we have to assume this was true for the giants, too. The 544 mm long humerus of Q. northropi translates to a predicted torso length of just c. 750 mm – a fraction of the size used in Don’s estimate. Mike and I adjusted Don's calculations to a more reasonable body proportion and, presto, the predicted mass was in the more familiar quarter-tonne range, a value flight models are happy to see launching and soaring without difficulty (Witton and Habib 2010).

The key to everything: quad launch

A critical hypothesis for giant pterosaur flight concerns recent interpretations of their launch strategy. This idea is that pterosaurs – probably all of them – took off from a quadrupedal start, not a bird-like bipedal one. The quad-launch hypothesis has origins in technical literature dating back to 2008 (Habib 2008, 2013, Witton and Habib 2010) but has a longer history through Mike H’s and Jim Cunningham’s contributions to the Dinosaur Mailing List. In retrospect, quad launch can be seen as a unifying hypothesis in studies of giant pterosaur flight, the piece of the jigsaw that allowed us to see how data from comparative anatomy, body masses and relative bone strength fit together. Before quad-launch, pterosaur flight models struggled to transfer giant azhdarchids from the ground to the air and were forced to cap their body masses at unrealistically low values (e.g. 75 kg in Chatterjee and Templin 2004) in order to launch them like big birds. Other than the fact that masses of 75 kg are untenable for creatures the size of giraffes (they’d need to be something like 70-80% air; Witton 2008), bipedal launch models suffer from several biomechanical issues involving bone strength, limb bone scaling and muscle size, as well as inconsistencies concerning pterosaur gaits. It's these issues which Mike and Jim investigated in their studies, making them the first researchers to approach pterosaur launch with objectivity, rather than a priori assuming an avian launch model, and bending pterosaur palaeobiology until it fit.

Ratios of limb bone strength in birds and pterosaurs. Positive values trend towards strength in humeri vs. femora, while negative values skew towards stronger femora vs. humeri. I've left the caption on for greater explanation. From Habib (2008).
Let's unpack these points in a little more detail. Firstly, the main launch limbs of flying animals are - above body masses of 500 g - stronger than their non-launching counterparts, and scale with more pronounced positive allometry (Habib 2008). This reflects launch being the most demanding part of flight. Look closely at a launching animal (high speed video helps) and you'll see that flight does not begin with a flap, but a leap: something like 80-90 % of launch effort stems from a powerful jump initiated by the main launch limbs. This explains why birds have proportionally robust and strong hindlimb skeletons but relatively slender wing bones: as they increase in size, their legs must become proportionally stronger to initiate flight at greater masses (Habib 2008). Pterosaurs, in contrast, show the opposite condition: their forelimbs are larger and stronger than their legs, with this relationship increasingly pronounced in larger species. Mike's 2008 study quantified this distinction, showing that the section modulus - a value proportionate to the strength of a given cross section - is consistently larger in pterosaur humeri than femora, and vice versa in birds, and that these ratios are more extreme at larger body sizes (see diagram, above). We presented similar data highlighting distinction in limb bone scaling in our 2010 paper, as well as quantifying the relative weakness of azhdarchid femora - their neck vertebrae are actually stronger than this major limb bone. Their humeri, in contrast, were very strong even in giant taxa modelled at the upper limits of pterosaur mass estimates (below). This is already a strong sign of a forelimb-dominated launch strategy in giants, and there's more to consider yet.

Raw data on azhdarchid limb bone strength from Witton and Habib (2010). Note the 'avian expectation' column - pterosaur bones do not scale in the same manner as bird bones, indicating a different regime of biomechanical selection pressures, and thus different limits on parameters like size.
Secondly, the avian skeleton has two large girdles for limb muscles: an enlarged shoulder and chest region for flight muscles, and an enhanced pelvic region to anchor those powerful hindlimb launch muscles. Pterosaurs, in contrast, have only one large limb girdle - their shoulders, making this the de facto likely candidate for powering their launch cycles. Using volumetric modelling, Paul (2002) predicted that a giant azhdarchid would have space for 50 kg of muscle in their pectoral region, a value appropriate for initiating flight in 200-250 kg animals (Marden 1994). This strategy is a far more economical use of muscle mass because the same muscles that power flight can also initiate launch, thus allowing quad launchers to have smaller torsos - and thus lower masses - than bipedal launchers. For all their power, the moment birds have launched their legs are effectively useless - they're just dead weight to be hauled around until it's time to land.

Reconstructed skeletons of large and giant azhdarchids in quad-launch poses, from Naish and Witton (2017). Note how the nearly completely known Quetzalcoatlus sp.D - E - lacks a large site for hindlimb muscles - that's typical of all pterosaurs, and an important argument in favour of quad launch.
This is an critical point for giant pterosaur flight as it allows us to make hypotheses about body size maximums related to launch strategy. Because quad launch is a mass-efficient route to flight we can hypothesise that quad launchers could attain much larger overall sizes and masses than bipedal launchers (Witton and Habib 2010; Habib 2013). As everyone knows, this is borne out in our fossil record of volant birds, which max out at 5-6 m wingspans and masses of 22-40 kg (Ksepka 2014), while giant azhdarchids attained wingspans of 10 m and 200-250 kg body masses. Mass-efficient launch mechanics is almost certainly a major factor in how azhdarchids became so big, especially combined with the exceptional azhdarchoid ability for skeletal pneumaticity (Claessens et al. 2009).

Fossil birds like Pelagornis sandersi are pretty big (extant bird with the greatest wingspan, the wandering albatross, shown top right), but they wouldn't be able to poke giraffes in the face when standing next to them. 5-6 m wingspans are the known size limit for bird flight, and their inefficient launch mechanism is probably the cause. From Ksepka (2014).
A further line of evidence for quad launch concerns pterosaur trackways. Habib (2008) also notes that launch in living tetrapod fliers correlates to terrestrial gait: the number of limbs used to locomote on the ground is the same as the number used to take-off. Birds walk and launch with two legs, while bats walk and launch using all four. An extensive record of pterosaur trackways shows that pterosaurs were quadrupedal animals like bats, and it stands to reason that they also launched from four limbs: they would contrast with our living fliers if they had to shift gaits to take off. Our pterosaur footprint record includes trackways of quadrupedal giant pterosaurs (Hwang et al. 2002), so we can comfortably extend this observation to them, too. Incidentally, the fact that several bats take off quadrupedally is often overlooked in discussions of pterosaur launch: bird-like bipedal launches dominate our consciousness only because we see them taking off every day, but they do not represent the only way tetrapods can become airborne.

Quad launch cycle in vampire bats Desmodus rotundus, traced from video footage: this is a real, proven launch mechanic folks, not something dreamt up by pterosaur workers desperate to prove giant azhdarchids could fly. Several other bats launch in this way, too. From Schutt et al. (1997).
These points - bone strength, concentrations of muscle bulk, limb bone scaling and trackway data - are the cornerstones of the pterosaur quad launch hypothesis, an idea which explains many independently observed features of pterosaur biomechanics, bone proportions and absolute size. Crucially, all of these points can be investigated for giant azhdarchids, and there are no red flags suggesting quad launch did not apply to these pterosaurs. Ergo, we can assume that giant azhdarchids used the most efficient launch mechanism conceivable for a tetrapod, negating any need for unreasonably low mass estimates or cliff jumping to become airborne. We can understand why pterosaur humeri are so strong and their femora so (relatively) weak, as well as the impact this has on overall size. Through birds, we have as inverse proof of this relationship. Furthermore, quad launch negates the need for special assumptions about giant pterosaur flight, allowing us to cast the biggest azhdarchids as 'extreme' versions of the pterosaur bauplaun, not evolutionary weirdos that take us back to the biomechanical drawing board.

Despite the sound scientific basis to quad-launch it is sometimes dismissed out of hand, I think because many folks just can't imagine it working - this excellent video by Mike and Julia Molnar does a good job of showing the kinematics. My experience is that counter-arguments are made without knowledge of its supporting data as they focus on less knowable components of the launch cycle, such as the speed of wing action or intuitive ideas about how high pterosaurs could leap. These are poor argument because they a) are largely speculative, not based on measurable/observable phenomena like bone strength or trackways; and b) ignore the fact that any launch mechanic requires rapid deployment of wings or an ability to obtain good ground clearance. We have to assume giant pterosaurs could achieve these feats no matter what our preferred launch strategy is. Moreover, somewhat ironically, the elevated flight speeds necessitated by giant pterosaur mass actually minimises some of these concerns. Flapping amplitude scales negatively with animal size and flight speed, making ground clearance less of an issue for large fliers than smaller ones (Habib 2008).

Flying the gauntlet

Let's put all this together - congratulations if you've waded through this long, often technical post. Giant azhdarchids...
  • are poorly known, but have anatomy consistent with volant habits in every known aspect.
  • do not seem to have struggled with take-off energetics more than any other large flyer.
  • are often anatomically mischaracterised, being overly compared to extant birds or modelled in ways which distort their likely flight parameters.
  • evolved from animals with a fundamentally more efficient launch strategy than that of birds, which lifts their body mass ceiling well above that predicted for avians. Every tested aspect of giant azhdarchid anatomy points to retention of this launch strategy even at their huge sizes.
  • have flight parameters which, when modelled using conventional animal flight software in modern-grade atmosphere and gravity, equate to excellent flight performance, analogous to that of large soaring birds.
The take-home message is that interpretations of giant azhdarchids as flying animals are based on numerous corroborating lines of investigation and hypotheses which support and predict one another. Moreover, the methods used in these studies are entirely conventional techniques of palaeontological inquiry, and to disregard or ignore them requires dismissal of entire scientific fields of study. Don't buy the limb bone strength studies? Fine, then you also don't buy beam theory or structural engineering. Don't believe the flight analyses? OK, but you're also challenging software written by noted experts in animal flight, using data measured from real flying animals and a deep understanding of aerodynamics.

This is not to say that we know all there is to know about giant pterosaur flight - far from it. They remain poorly known animals and we can only guess at their variation in flight performance. Who knows, maybe a flightless species will turn up one day - this is not a ridiculous concept, we just don't have any evidence for it yet. But, for now, anyone seriously wanting to challenge this interpretation needs to discredit a robust theoretical foundation of pterosaur flight mechanics and provide a superior interpretation of the many strands of evidence we've discussed. This seems like a tall order to me, but it's the gauntlet that anyone who says giant pterosaurs were 'too big to fly' or 'they needed different gravity' has to run. Such comments reflect an ignorance or unwillingness to engage with a growing body of sound technical research on these animals, and - unlike giant pterosaurs - their arguments just don't fly.

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References

  • Bennett, S. C. (2003). Morphological evolution of the pectoral girdle of pterosaurs: myology and function. Geological Society, London, Special Publications, 217(1), 191-215.
  • Buffetaut, E., Grigorescu, D., & Csiki, Z. (2002). A new giant pterosaur with a robust skull from the latest Cretaceous of Romania. Naturwissenschaften, 89(4), 180-184.
  • Chatterjee, S., & Templin, R. J. (2004). Posture, locomotion, and paleoecology of pterosaurs (Vol. 376). Geological Society of America.
  • Claessens, L. P., O'Connor, P. M., & Unwin, D. M. (2009). Respiratory evolution facilitated the origin of pterosaur flight and aerial gigantism. PloS one, 4(2), e4497.
  • Frey, E., & Martill, D. M. (1996). A reappraisal of Arambourgiania (Pterosauria, Pterodactyloidea): one of the world's largest flying animals. Neues Jahrbuch für Geologie und Paläontologie, 199, 221-247.
  • Habib, M. B. (2008). Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana, 159-166.
  • Habib, M. (2013). Constraining the air giants: limits on size in flying animals as an example of constraint-based biomechanical theories of form. Biological Theory, 8(3), 245-252.
  • Hazlehurst, G. A., & Rayner, J. M. (1992). Flight characteristics of Triassic and Jurassic Pterosauria: an appraisal based on wing shape. Paleobiology, 18(4), 447-463.
  • Henderson, D. M. (2010). Pterosaur body mass estimates from three-dimensional mathematical slicing. Journal of Vertebrate Paleontology, 30(3), 768-785.
  • Hutchinson, J.R., 2001b. The evolution of femoral osteology and soft tissues on the line to extant birds (Neornithes).Zoological Journal of the Linnean Society. 131, 169–197.
  • Ksepka, D. T. (2014). Flight performance of the largest volant bird. Proceedings of the National Academy of Sciences, 111(29), 10624-10629.
  • Hwang, K. G., Huh, M., Lockley, M. G., Unwin, D. M., & Wright, J. L. (2002). New pterosaur tracks (Pteraichnidae) from the Late Cretaceous Uhangri Formation, southwestern Korea. Geological Magazine, 139(4), 421-435.
  • Lawson, D. A. (1975). Pterosaur from the latest Cretaceous of West Texas: discovery of the largest flying creature. Science, 187(4180), 947-948.
  • Naish, D., & Witton, M. P. (2017). Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators. PeerJ, 5, e2908.
  • Marden, J. H. (1994). From damselflies to pterosaurs: how burst and sustainable flight performance scale with size. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 266(4), R1077-R1084.
  • Martill, D. M., & Moser, M. (2018). Topotype specimens probably attributable to the giant azhdarchid pterosaur Arambourgiania philadelphiae (Arambourg 1959). Geological Society, London, Special Publications, 455(1), 159-169.
  • Paul, G. S. (2002). Dinosaurs of the air: the evolution and loss of flight in dinosaurs and birds. JHU Press.
  • Prentice, K. C., Ruta, M., & Benton, M. J. (2011). Evolution of morphological disparity in pterosaurs. Journal of Systematic Palaeontology, 9(3), 337-353.
  • Sato, K., Sakamoto, K. Q., Watanuki, Y., Takahashi, A., Katsumata, N., Bost, C. A., & Weimerskirch, H. (2009). Scaling of soaring seabirds and implications for flight abilities of giant pterosaurs. PLoS One, 4(4), e5400.
  • Vremir, M. (2010). New faunal elements from the Late Cretaceous (Maastrichtian) continental deposits of Sebeş area (Transylvania). Acta Musei Sabesiensis, 2, 635-684.
  • Wellnhofer, P. (1991). The illustrated encyclopedia of pterosaurs. Crescent Books.
  • Witton, M. P. (2010). Pteranodon and beyond: the history of giant pterosaurs from 1870 onwards. Geological Society, London, Special Publications, 343(1), 313-323.
  • Witton, M. P. (2008). A new approach to determining pterosaur body mass and its implications for pterosaur flight. Zitteliana, 143-158.
  • Witton, M. P., & Habib, M. B. (2010). On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness. PloS one, 5(11), e13982.
  • Witton, M. P., & Naish, D. (2008). A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS one, 3(5), e2271.
  • Witton, M. P., & Naish, D. (2013). Azhdarchid pterosaurs: water-trawling pelican mimics or “terrestrial stalkers”?. Acta Palaeontologica Polonica, 60(3), 651-660.

Friday, 27 April 2018

Unicorns, dragons, monsters and giants: palaeoart before palaeontology

Quick painting of Polyphemus, the Homeric cyclops, taking very literal inspiration from elephant face anatomy in reference to the well-known idea that fossil elephant skulls inspired the cyclops myth. So, do ancient illustrations of cyclopes count as early palaeoart?
The genre of natural history art we call 'palaeoart' is not a modern invention: it is actually centuries old, emerging in Europe at the same time as palaeontological science. We often credit Henry De la Beche's 1830 painting Duria Antiquior as the original palaeoartwork, but several attempts to reconstruct fossil animals using modern scientific ideas were made beforehand, dating back to at least 1800 (Taquet and Padian 2004). They include relatively speculative paintings, satirical sketches, and detailed anatomical reconstructions (Rudwick 1992; Martill 2014). Duria Antiquior was a major milestone for palaeoart development, but not the origin of the genre itself.

A case can be made for palaeoart being even older than these oft-overlooked works, however. A small number of artworks created by historic, maybe even ancient peoples attempted to restore the life appearance of fossil animals in much the same way we do today, albeit outside of a true scientific context. Whether or not these artworks qualify as true palaeoart is questionable as adherence to scientific theory is a pretty major component of the genre. Scientific methodology as we understand it today was not developed until the 18th century, and this included many concepts essential to palaeoart, such as fossilisation, extinction and geological time. Can we truly define a work as palaeoart if it was made without knowledge of these cornerstones of palaeontological science? My take on this is that artworks attempting to rationalise fossils against contemporary understanding of natural phenomena (even if that rationale is pre-scientific and mythology-based) have the same intention as palaeoart produced today. We can probably consider these early artworks 'proto-palaeoart', the forerunner of the genuine, science-led article we developed in the 19th century.

I thought it might be of interest to run through some early artworks claimed to be among the oldest palaeoart. I won't pretend that this list is exhaustive, but I hope there may be some examples, or facts behind commonly given examples, that will be unfamiliar to most readers. In researching this article, I was surprised at how little data existed behind some claimed examples of historic palaeoart, including several widely 'known' examples. Other cases are more plausible, if missing smoking gun evidence, and a couple are undoubted facts of history. For those interested in the origins of palaeoart, the question is not 'does proto-palaeoart exist?', but 'how much proto-palaeoart is there?'

Of griffins and cyclopes

Archaeological data shows that humans have been interacting with fossils for thousands of years (McMenamin 2007; Mayor 2011). It is not unreasonable to assume that ancient peoples pondered the nature of fossils and perhaps drew or sculpted the creatures they were interpreted as. Othenio Abel (1914) and Adrienne Mayor (2011) have argued that fossil remains influenced or even wholly inspired famous mythical animals such as griffins and cyclopes. As previously discussed here at some length, some researchers propose that fossils of the Asian horned dinosaur Protceratops were subsumed into the mythology of the griffin (e.g. Mayor and Heany 1993; Mayor 2011), while the bones of elephantids – with their huge, eye-like central nasal openings in their skulls – spawned stories and artwork of the one-eyed cyclops (Abel 1914).

Line drawing of perhaps the oldest known image of a griffin, from Susa, 4th millennium BCE. From Frankfort (1937).
Superficially, both these claims seem reasonable. Griffins, if you squint a little, do somewhat resemble a Protoceratops with their four legs, beaks and cranial frills interpreted as wings. The skulls of elephants and their relatives look somewhat like the skulls of monstrous giant humans, too, mostly because of their short faces and partially-defined true eye sockets. But what's lacking from these claims is evidence beyond the circumstantial. The Protoceratops-griffin hypothesis is presented as having support from historic events, geographic details and ancient texts, with traders from far eastern lands bringing tales of their fossils to the Greeks in the first millennium BCE. Long term readers may remember I suggested a number of issues with this scenario in a previous article. I won't rehash the full argument here but, in brief: griffins appeared in Near East societies several millennia before they became popular in Ancient Greece, meaning the Orientalisation of Greece during the 8th-5th centuries BCE - when the Greeks adopted culture from Near Eastern and Eastern Mediterranean cultures - more than accounts for the sudden Grecian interest in griffins. Ancient texts said to refer to Protoceratops fossils seem to pertain to (probably fantastical) living species, not fossils, and provide no details of geography of environment that are specific to genuine Protoceratops localities. The trade routes and gold mines said to bring Asian cultures within viewing distance of Protoceratops remains are, in fact, several hundred miles west of all known Protoceratops sites, and there's nothing about griffin form - in any of its guises (griffins are a complex of creatures, not just one) - that necessitates influence from horned dinosaur anatomy: all griffin features are accounted for by living species. Citations and references for these points can be found in my article, so please check it out if you'd like more details. I've not encountered anything since writing that piece to change my opinion on the Protoceratops-griffin hypothesis, so I can't see any reason to consider griffins proto-palaeoart of horned dinosaurs.

Historic and biogeographic details align better with the idea that elephantid fossils may have begat cyclopes. Fossils of elephantids are found around the eastern Mediterranean and their bones were probably known to the Ancient Greeks (Massetti 2008; Mayor 2011). It's plausible that Greeks living several thousand years BCE would be ignorant of living elephants too, these animals dying out in Europe around 11,000 years ago. The nearest contemporary elephant populations were of the now extinct Syrian elephant, over 1000 km away in eastern Turkey. Elephant skulls are pretty odd, and without knowledge of living elephants it might be easy to misinterpret them. Homeric accounts of cyclopes - from the 7th-8th century BCE, among the earliest on record - cast them as cave dwellers, which matches the recovery of elephantid remains from Sicilian caves (Masseti 2008). The link between these bones and cyclopes has been noted for centuries, dating back to the first 'modern' archaeological exploration of Mediterranean islands in the 17th century (Masseti 2008).

A funerary urn showing the cyclops Polyphemus being blinded by Odysseus and his crew, c. 660 BCE. From Wikimedia user Napoleon Vier, CC BY-SA 3.0
These details put elephantid bones in the right place and time to inspire cyclopes but, as hardened sceptics, we must view this as circumstantial evidence only, and thus insufficient to support the elephantid-cyclopes link on its own. It's here where we hit a problem: beyond these details, there's not much else to support this idea. It's important to ask the right questions in sceptical inquiry and in this case it's not 'did elephants inspire cyclopes?, but 'do we need elephants to explain depictions of one-eyed giant humans?'. The answer is probably 'no'. Accounts of ancient cyclopes I'm aware of - both those in illustration and literature - are just giant men with unusual eye anatomy (example above), and without obvious elephantine facial features (tusks, steep-fronted rostra etc.). Citing elephant skulls as a source might complicate the myth more than explaining it - where's the rest of the elephant anatomy gone? An entirely human source - cyclopia, a fatal genetic condition sees human eye anatomy fail to divide fully - is an alternative origin of the cyclopean myth (Kalantzis et al. 2013) which does not require artists to cherry-pick elephant features. Cyclopia is rare among live human births (Kalantzis et al. 2013) but occurs in one of every 200 lost pregnancies - as sure as ancient Greeks saw fossil elephant bones, they also surely saw patients of cyclopia.

We must also consider that a real-world source was not needed at all. One-eyed men and other monocular creatures are ubiquitous throughout mythology all over the world, and it's unlikely they all developed after finding fossil elephant skulls. Eyes are a well established symbol of wisdom, clairvoyance and authority in many cultures, so the modification of eyes - reduction in number, blinding and so on - has clear symbolic value in many legends. It's entirely plausible that Grecian cyclopes had one eye simply because the ancient poets and storytellers thought it suited their characters. It's difficult to prove that fossil elephant skulls were not the basis for cyclopes but with only circumstantial evidence to support the idea, it's no better supported than any other interpretation outlined here or elsewhere.

The Monster of Troy

An artwork argued by Mayor (2011) as the oldest piece of genuine palaeoart adorns a Corinthian vase painted between 560-540 BCE. This image shows an unusual, skull-like face resting on a cliff acting as the Monster of Troy, the creature which fought Heracles as it terrorised Hesione at the outskirts of Troy. Though skeletal in nature, the interactions of the face with other figures on the vase implicates it as a living creature, not the remains of a dead animal. The skull is argued to match the basic anatomy of Miocene mammals known from the eastern Mediterranean region. The giraffid Samotherium is considered a most likely identity (Mayor 2000, 2011), though the artist may have also incorporated elements of fossil ostriches, lizards, whales or crocodiles (Mayor 2000, 2011). If this hypothesis is correct, it would easily be the oldest known palaeoart, and by a huge margin - about 2000 years. Mayor's interpretation has been discussed favourably by a number of authors (Papadopoulos and Ruscillo 2002; McMenamin 2007), though others consider it a matter of ongoing research (Oakley 2009) or pure conjecture (Kitchell 2014).

The Monster of Troy, as depicted on a Corynthian vase, 560-540 BCE. It definitely has a skull-like vibe, but is it the first piece of palaeoart? From Flickr user Lady Erin, CC BY-NC-ND 2.0.
The individualistic nature of the Monster of Troy complicates analysis of its origin, especially because it seems quite loosely drawn compared to other figures on the vase. How literally should we take its features? If we had other, perhaps more refined art of the same concept we might be able to pin down the accuracy of its rendition but, with only one example, we can't be sure if we're dealing with a crude drawing of a real skull or a more stylised, imaginative chimera.

If we take the face entirely literally, we find that some aspects compare well to mammals like Samotherium, particularly its size, the shape of the lower-jaw, the position of the jaw joint with respect to the orbit, and the low profile of the rostrum. However, it differs from Samotherium in a number of ways: a lack of horns; entirely procumbent dentition; long, sharp-looking teeth; a lack of a diastem; the (seeming) presence of a sclerotic ring; and the occurrence of a facial fossa (present in fossil horses and deer, but not Samotherium). The white colour is also not appropriate for Samotherium, fossils of these animals being of tan or brown hues. Some distinctions are potentially explainable within the Samotherium hypothesis: the shortened upper jaw could reflect a broken premaxilla - a common occurrence on large fossil mammal skulls - and the unusual detailing behind the eye could reflect details of the jaw joint and posterior skull anatomy. Others differences are less easily accounted for, leading to those suggestions that lizards, whales and other species might be referenced in the illustration too. This seems like special pleading to me, and a weakness in the idea that the artist was referencing specific fossil specimens. The only evidence for the Monster of Troy being a fossil is that it allegedly looks like one, and if we find differences between it and the fossils it's most likely to represent, they can't just be glossed over: they're counter-evidence to the hypothesis.

Samotherium boissieri.JPG
Samotherium boissieri skull - is this the 'real' Monster of Troy? By Wikimedia user Ghedoghedo, CC BY-SA 3.0.
Again, I wonder if we need to invoke fossils to explain this illustration. The basic anatomy might reflect some features of ungulate skulls, but it's so generalised that something like a living horse or camel would fit the bill as well as a fossil species. Indeed, some aspects - such as colour - are better matches for modern skulls. The fact it's perched on a cliff is perhaps the best reason to think it's a fossil, though other interpretations of the 'cliff' exist, such as it being the entrance to a cave (see Mayor 2000 for a brief summary of other interpretations).

All this considered, I'm not sure what to make of the Monster of Troy. I'm not convinced it's a compelling match to a specific fossil mammal skull nor that it even needs a fossil origin to explain it. Moreover, if it is a chimera, which even proponents of this idea concede it must be to some extent, then its significance to early palaeontology is diluted further as those other elements may not be of fossiliferous origin. If we had other illustrations of the same skull-like creature we might be able to make a clearer determination, but I don't know that there's enough evidence to determine if the Monster of Troy is anything to do with the history of palaeoart.

Here be Lindwurms

Moving on two thousand years to the 16th century, our next example is an artwork with a confirmed fossil basis. Our inquiries into artwork from this time onward are aided significantly by surviving texts from this interval. As we've already encountered, interpreting the origin of art is challenging without knowing the context of its creation, so the existence of well-documented artefacts and text allows for much more certainty in our pursuit of pre-science palaeoart. Much of the following stems from Abel's (1939) account of fossils and mythology.

The giant Lindwurm statue of Klagenfurt, Austria, built in 1590. It's said to be partly informed by woolly rhinoceros remains. The chap on the right, representing Hercules, was added in the 17th century. From Wikimedia user Johann Jaritz, CC BY-SA 3.0.
Though 16th century Europe heralded many major facets of our modern age, myth and fable were still major parts of culture, and giant fossils were still regarded as remains of fantastical animals. A vast, 6 tonne statue of a four-limbed, two-winged dragon known as the ‘Lindwurm’ is probably the oldest known incontrovertible piece of proto-palaeoart. Only part of the statue, which was erected in Klagenfurt, Austria in 1590, has a fossil basis however, its head being based on the skull of a woolly rhinoceros (Coelodonta antiquitatis) recovered from a gravel pit or mine near Klagenfurt in 1335. The Lindwurm has a prominent role in Klagenfurt lore as the town was said to be founded only after this creature was dispatched and the area became safe to live in. I'm not sure if the skull or the legend came first - the town was established in the 12th century, two centuries before the skull would be found - but we can be certain that Coelodonta fossils have longstanding historical significance in Klagenfurt, the skull residing in town council chambers for centuries before being put on public display, where it remains today. The statue was constructed by Ulrich Vogelsang, but it's evident that he only considered very basic elements of Coelodonta anatomy during the sculpting. Indeed, other than size, the Lindwurm head does not resemble Coelodonta at all, so it seems likely that the skull was more inspirational than referential. Still, at least we know the two objects were meant to represent the same entity, which is no mean feat in the pursuit of proto-palaeoart.

The giants and plesio-dragons of Mundus Subterraneus

Athanasius Kircher's 1678 German textbook Mundus Subterraneus - an early thesis on geography, biology, mineralogy and geology - contains several illustrations of animals which may have been informed by fossils. They include many types of giant human, which were said to be social, cave-dwelling species based on the bones of large animals found in caves - almost certainly remnants of Pleistocene mammals. Kircher also wrote about several types of dragon, many of which were of period-typical, worm-like form, but Abel (1939) noted one unusual dragon illustration that may have been influenced by a real giant reptile: a plesiosaur.

Is St. George fighting a plesiosaur-inspired dragon in this 1678 illustration from Mundus Subterraneus? Abel (1939, also the source of this image) thought so, noting the shift towards plesiosaur-like proportions and anatomy compared to more conventional European dragon depictions of the time.
The illustration is plesiosaur-like in many respects, with a barrel-like body, small head, long and slender neck, a true tail, and curiously small ‘paddle-like’ wings instead of broad, membranous wings typical of dragon depictions. It's not a perfect plesiosaur depiction by any means - it also has ears, a beak, and four legs - but Abel (1939) considered this reinvention of dragon form so dramatic that it could represent the arrival of a new source of inspiration for dragon anatomy, of which plesiosaurs are a possible contender. Marine reptiles, including plesiosaurs, were almost certainly uncovered during quarrying work in the historic Swabia region (now southern Germany) as rocks we now call the Posidonia Shale were exploited to build growing settlements. The Posidonia Shale is a site of exceptional preservation with abundant invertebrate fossils and rarer, but often complete and articulated, marine reptile skeletons. Posidonia quarrying dates back to at least the 16th century and, given that the quarrying was executed by hand, 17th century quarrymen would have seen fossils of many kinds, almost certainly including some well preserved plesiosaur remains. Had these discoveries caused a stir among local learned individuals, as well a giant reptile entombed in stone might have, it's not inconceivable to think they could have been identified as dragons, and ultimately influenced Mundus Subterraneus.

As with our discussion of cyclops art, these details are only circumstantial evidence and they do not prove beyond doubt that plesiosaurs were referenced in Kircher's dragon art. But I find this case a little more compelling because our records of the early modern period are better, so the correlation between historic events is tighter and the contrast to other dragon illustrations more obvious. Moreover, whereas ancient cyclops art doesn't really look like the fossils said to inspire it, I can see some obvious plesiosaur-like details in Kircher's illustration. It's difficult to be certain about the relevance of plesiosaurs fossils to the image but, for me, this is a possible, if unconfirmed, piece of proto-palaeoart.

The most awesome unicorn, ever

Our final example is surely one of the nuttiest attempts to restore ancient animal anatomy in all of history. Pleistocene mammoth and rhinoceros bones found in a cave near Quedlinberg, Germany, in 1663 were reassembled by an unknown artist into a skeletal reconstruction of a bipedal unicorn, christened unicornum verum ('true unicorn') or, sometimes, the Quedlinberg Monster. Doubtless this image is familiar to many readers already, but it's worth looking at again. Just how is that thing meant to work?


Reconstruction of the “unicornum verum” by Otto von Guericke (1678), and later used by German philosopher Gottfried Wilhelm Leibniz in his “Protogaea” (1749) (image in public domain).
History of Geology
Page from the 1749 book Prototagea showing unicornum verum, a truly bizarre composite of fossil rhinoceros and mammoth bones. The illustration above is clearly a mammoth molar, hinting at the true identity of the 'unicorn' bones.
The artistic history behind unicornum verum is somewhat mysterious (Ariew 1998). The illustration became widely known through Gottfried Wilhelm Leibniz's posthumously published 1749 book Protogaea, a scholarly account of geology and natural history. Leibniz's book printed a copy of one example of the illustration, but did not state where the images originated. The most famous example - above - is often credited to German naturalist Otto von Geuricke, the scholar who described the remains, or Leibniz himself. However, Geuricke was probably not the artist, and Leibniz definitely wasn’t (he explicitly states this in his written work). Another version of the skeleton, published in 1704, is said to be based on a third depiction by Johann Mäyern, a Quedlinberg counsellor. Whoever rendered the images, they represent the oldest known illustrations of restored fossil skeletons (we might quibble if skeletal reconstructions are true palaeoart or not - whatever your view, they're close enough for our purposes here, I think). Though some bones are fairly 'generic' and difficult to identify, mammoth teeth and scapulae, as well as rhino vertebrae with long neural spines (reversed to be ribs) are discernible. I am not sure what the ring-shaped structure at the end of the spine is - I assume it's a vestigial pelvis. Apparently the bones informing the skeletal were broken as they were excavated (Ariew 1998), which might account for some peculiarities of their appearance.

Unicornum verum in the flesh. It's a little undersized: Leibniz gave the length of the horn at five ells (an ell being the length of a man's forearm (typically about 450 mm, or 18"), which is over 2 m.
Leibniz indicates that narwharls were a major influence on unicorn mythology of this time, which might explain why unicornum verum resembles a swimming animal to some degree. The reconstruction is so unusual that some scholars have wondered if it was a joke or hoax. Ariew (1998) suggests Leibniz - a polymath of notable contribution to mathematics, physics, philosophy and other fields - was an unlikely hoaxer based on his other work. Indeed, Protogaea is by all accounts a straight, scholarly thesis on natural history which demythologises fossils and calls out fantastic interpretations - trickery and pranks would contrast markedly with the tone of the book. Leibniz also says he visited the caves housing the bones in question, providing details of how one enters them, and vouched for the size, manner of collection and anatomical details of the bones found therein. If he was hoaxing, he played a very straight game, and it's perhaps more probable that he considered unicornum verum a genuine animal, and the illustrations a reasonable take on its anatomy.

By the end of the 18th century the seeds of true palaeontological science and palaeoart were being sowed, ready to develop fully in the 19th century. Leibniz's apparent conviction for unicornun verom and its illustration might seem charmingly naive given what would emerge just decades after Protogaea was published, one of the last examples of mythology inspiring scientific thought and early palaeoart before hard science took over. But his illustration of a restored skeleton, rather than a fanciful creature, as well as his associated documentation of the discovery and locality of the 'unicorn' bones, shows how approaches to fossils and their illustration was maturing. This bizarre restoration is a link between two different eras in our artistic interpretations of fossils, taking a near-scientific approach to a mythological concept.

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References

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