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Tuesday, 20 December 2016

The popularity of dinosaurs - for better, for worse

This article is being cross-posted at the website of the London-based 2016 Popularizing Palaeontology workshop as part of a series of blog posts focusing on the discussions and themes of that event. Over the course of this two day workshop curators, artists, historians and palaeontologists presented talks and led round-table discussions about the history and current state of palaeontological outreach. I presented a talk at this workshop - entitled 'The importance and impact of palaeoart in palaeontological outreach', which you can see here. The following is not based on this talk, but rather a theme that seemed - to me - to be consistent across many presentations and discussions, including my own.

Whether it's a giant armoured thyreophoran like Panoplosaurus mirus (thanks to the Empress of Ankylosauria, Victoria Arbour, for advice on this restoration) or a svelte theropod like Chirostenotes pergracilis, everyone likes dinosaurs and we - palaeontologists - like using them in our outreach. But are dinosaurs really universally popular and appropriate for the wide range of outreach we use them in?
The Popularizing Palaeontology workshops held in August 2016 presented fascinating insights into the history and current state of palaeontological outreach. Our many talks and roundtable discussions touched varied topics but several central themes emerged, of which one was the prevalence of dinosaurs in virtually all palaeontological PR exercises. Whatever we discussed - the history of museums, the palaeoart industry, public interest in research or palaeontological influences on cinema - dinosaurs were almost always involved. Even if they weren’t a main focus, their influence there - catalysing certain events, influencing decisions, eclipsing other outreach topics. It would be wrong to say popularising palaeontology is totally synonymous with popularising dinosaurs, but for better and worse, these animals have a major role and influence over public outreach of palaeontological science.

The success of dinosaurs in outreach

Exactly why dinosaurs occupy such an important and influential space in popular culture remains largely mysterious. On paper, dinosaurs are a group of extinct reptiles which are not - superficially at least - so different from other long-dead sauropsids, and yet they have somehow gained global fame and many dedicated followers. My suspicion is that dinosaurs uniquely combine obviously amazing, ‘high impact’ anatomy - large size, fantastic skeletal structures such as horns, huge teeth and so on - with bauplans that are easily understood by the general public, without being so familiar that they’re pedestrian. For instance, everyone can appreciate Allosaurus as an active, large bodied predator even if just looking at its skeleton in a museum, but - as bird-like as it is in detail - the overall form is somewhat alien and intriguing. Other fossil groups, such as ancient carnivorans or whales, are impressive enough but perhaps also too familiar to inspire our imaginations in the same way. At the other end of the spectrum are extinct creatures which are just too unusual for widespread appreciation. Perhaps their anatomy is too strange or their life histories are too obscure and difficult to relate to familiar biology. This applies to many extinct invertebrates, as well as several types of weirder vertebrates. Dinosaur biology is thus near perfect for outreach material: they’re visually impressive, anatomically and biologically accessible, but different enough to warrant interest. Whether this is the actual basis for dinosaurian appeal or not, museum staff, educators and merchandisers have realised for over 150 years that dinosaurs are an excellent way to interest the public and make money, and given them prominent roles in outreach. Aiding any intuitive draw we have to dinosaurs is a lot of social inertia, and part of the enduring appeal of dinosaurs is a long history of ingraining them into popular culture.

The success of dinosaurs in the public eye almost certainly reflects many varied influences, but their unique anatomical qualities may play an important role. Does any other fossil group combine interesting, ‘high impact’ biology, in a format that the public can easily grasp, in the way that dinosaurs do?

For those of us interested in science education, dinosaurs are one of the most important and potent tools at our disposal. We see them as not only fascinating subjects in their own right but as a way to introduce ‘bigger picture’, perhaps fundamentally more important, scientific concepts to lay audiences. Dinosaurs are gateways to discussions of evolution, adaptation, anatomy, biological diversity, extinction, geological time and the changing nature of the planet. They provide, as charismatic and fantastic creatures, perfect characters to maintain interest in discussions of these sometimes complex concepts, and well-known Mesozoic dramas - the breakup of Pangea, formation of the Deccan Trapps, the Chicxulub Impact - offer rich backgrounds to stage our conversations. Dinosaurs are more than just awesome animals: they’re public ambassadors for science, facts and intelligent thinking.

We cannot ignore the economic value of dinosaurs, too - and not just to Hollywood movie makers and toy manufacturers. Dinosaurs provide academia and its satellite industries with vital income because of their easy marketability and merchandising potential. Public interest in dinosaur news, books and artwork keeps authors and palaeoartists in work, while the pull of dinosaur exhibitions in natural history museums not only keeps turnstiles spinning but brings essential revenue - in the form of gift shop purchases, entry fees and cafe visits - to these underfunded venues. I don’t know that anyone has ever attempted to work out the net worth of dinosaurs to education, but, globally, their appeal must bring millions of pounds into venues that perform outreach every year.

Too much of a good thing?

So hurrah for dinosaurs, then, and their role as not only fascinating subjects for research and art, but as bankable, relatable and demanded elements of modern culture. But the popularity of dinosaurs does have an impact on other aspects of palaeontological PR, and in some conversations at our workshop ‘dinosaur’ almost became a bit of dirty word. No-one will deny the positive aspects of dinosaur popularity, but their dominance in popularised palaeontology influences outreach strategies, merchandising and public expectation, and not always in a positive way.

Some of the problems caused by dinosaurs were outlined in detail during talks at our workshop. We heard that a large portion of natural history museum visitors are exclusively concerned with seeing dinosaur exhibits, challenging natural history museums to use the rest of their collections in a meaningful, impactful manner. This is despite many museum goers being unable to distinguish dinosaur remains from those of other animals without the aid of helpful signage. It seems that, for some museum visitors, dinosaurs act like a brand label, or justification for interest, rather than an excuse to visit a museum for a rounded educational experience.

We also heard that bringing attention to non-dinosaur groups can be extremely difficult, and the less dinosaur-like they are, the harder it is. Groups like pre-Cenozoic synapsids, extinct invertebrates, fossil fish and so on struggle for attention and require highly creative outreach tactics to receive any interest. One of the commonest strategies - used frequently for semi-technical books on fossil animals (below) - is to make sure dinosaurs remain prominently mentioned even in those events or products which are focused on completely unrelated groups of animals. We just don’t trust most non-dinosaur clades to draw crowds or revenue on their own and have to spin them as being relevant to dinosaurs in some way. Tellingly, the only groups to escape frequent dinosaur namechecking are those which are already somewhat ‘dinosaur-like’. Giant fossil mammals, pterosaurs and Mesozoic marine reptiles share aspects of size and gross appearance with Mesozoic dinosaurs and might be seen as ‘honorary dinosaurs’ by the public, and perhaps mistakenly interpreted as the genuine article by many. Both dinosaur-targeted museum visits and our resistance to promote palaeontological topics without a dinosaurian safety net questions whether dinosaurs are a genuine ‘gateway’ to wider scientific education, and perhaps suggests a rather narrower interest in prehistoric life among the public.

Just some of the non-dinosaurian textbooks coming your way in 2017. Probably.
Our group also raised the association between dinosaur outreach and very young demographics, and the challenge this presented to educators. The problem isn’t that many children are naturally interested in dinosaurs - if anything, this is something to celebrate and encourage - but the impact this association has on older audiences. Many adults assume that anything to do with dinosaurs, and by extension any prehistoric animal, is automatically related to children, and often very young children. This becomes an issue for to those attempting to perform outreach or market palaeontologically-informed products to older audiences, and particularly outside of online venues. Experience shows that ‘real world’ dinosaur events - regardless of venue, event type or advertising theme - will be primarily stocked by children and parents expecting child-friendly media. I’ve experienced this many times in my outreach career, such as bowing to pressure for colouring-in stations at a palaeoart gallery, being asked whether a public lecture (entitled Palaeoart: the Never Ending Quest for Accuracy) was suitable for toddlers, and being invited to run art stalls and events for older audiences at dinosaur-themed events to find few interested people over 10 years of age.

The general expectation that dinosaur-related events or products skew towards children presents a complex set of challenges. Firstly, it can lead to older audiences deciding a priori that they cannot take anything away from dinosaur outreach because the event - whatever it is - is ‘just for kids’. I’m sure many of us have seen how ‘switched off’ parents of young dinosaur fanatics are when visiting outreach events, even though the people their children are speaking to may be expert scientists, experienced fossil hunters or world-renowned palaeoartists. Secondly, mismatched expectations of outreach events can be frustrating for both outreachers and audiences: attendees may wonder why a dinosaur event is pitched above the level of their children, while outreachers may feel over-prepared or over-invested in their activity programme when confronted with only young audiences. Perhaps the most concerning issue is that many outreachers and merchandisers use young demographics as an excuse for low scientific standards and sensationalism, promoting outdated, erroneous and sometimes idiosyncratic views of palaeontology because their audience is too young and insufficiently educated to know otherwise, or ignoring scientific data where it might curb child appeal. I am sure most readers can think of numerous examples of products - many labelled as ‘educational’ - which show evidence of this, and it’s easy to see how this attitude may play a major role in perpetuating outdated and erroneous ideas about the past.

One of our final discussion touched on perhaps another issue faced by dinosaur outreach: the schism between public and palaeontological appreciation of what dinosaurs are. For palaeontologists, dinosaurs are a constantly - and sometimes rapidly - evolving set of hypotheses and ideas, and this is what we generally try to present to the world in our outreach. But certain dinosaur concepts outgrew palaeontologist-steered media long ago and now occupy their own place in popular culture, one almost entirely divorced from developments of dinosaur science and instead orbiting their portrayals in film, TV and popular literature. Most of these products - even those produced in the last few years - stick to now long-outdated 20th century interpretations of dinosaur biology and, divorced from guiding hands of scientists, solely emphasise marketable aspects such as their size, perceived ferociousness, and unusual anatomy. The result is a public largely familiar with dinosaurs in a scientifically-distanced, simplified and monstrous form rather than the animals reconstructed through biological and geological sciences, and with little appreciation for their evolutionary context, the scientific techniques used to understand them, or their relationship to wider, ‘core themes’ of scientific outreach. Recent studies partly vindicate this view in showing that the public are generally unaware of even the most basic aspects of dinosaur science, such as the near 50-year old revision from the classic ‘tail-dragging’ posture to an elevated tail and horizontal body attitude (Ross et al. 2013). This is despite museums, artwork, documentaries and some of the most successful blockbuster movies of all time showing the latter since at least the 1990s. This being the case (and with an added caveat that the study in question was relatively small), perhaps our issue with dinosaur education is more severe than we thought: are people really engaging with dinosaur media at all, or are our subjects of research, artwork, and hallowed gateways to other sciences little more than time-fillers and distractions?

Despite the best efforts of many scientists, the public at large seem to associate dinosaurs with considerably outdated interpretations and monstrous creatures. Reviewing recent successful entries into one of the most widely-accessed sources of popular dinosaur culture - Hollywood movies - is this surprising? Perhaps the most visually progressive rendering in this set are the sparsely feathered dromaeosaurs from Pixar’s The Good Dinosaur (bottom right). However, the state of their integument still recalls dinosaur palaeoart from the mid-1990s, and not the extensive feather body covering shown by fossil evidence and now commonly restored over certain dinosaur species. Image sources, from top row down; King Kong (2005); Godzilla (2014); Transformers: Age of Extinction (2014); Toy Story (1996 - onwards); Jurassic World (2015); The Good Dinosaur (2015).

So, are dinosaurs as useful as we think for outreach purposes?

The points raise a simple but significant question: how effective is dinosaur-based outreach, really? As noted above, many decisions about outreach are shaped around dinosaur science and resources are poured into promoting dinosaur science itself. But are we right to regard dinosaur outreach as highly as we do?

Trying to balance the positive and negative points raised above, my take is yes, dinosaurs are an effective means to bringing science to people… but probably only certain people. Specifically, they seem to work very well among those who are already tuned into palaeontology, natural history and general science, an audience composed mostly of adult enthusiasts and children. Beyond this, their effect seems to tail off quickly and they may actually be a barrier to effective outreach. Audiences with preconceived expectations of dinosaur-themed content may ignore anything dinosaur related, which is a concern with us giving dinosaurs such privileged consideration in educational material. Are we limiting our promotion of other topics that could engage these uninterested people? And is one of our challenges of popularising palaeontology making dinosaurs and related topics universally attractive, and not just subjects with appeal to specialist audiences or younger people?

Of course, your opinion on this matter may differ. But even so, I think most of us would agree that our wider education about dinosaurs and related matters could be more effective, or at least more nuanced and reflective of more topics, than it currently is. I am optimistic that a groundswell of suitable movements towards this goal may already be underway. Many modern curators, scientists and artists are attuned to matters of science communication and interested in identifying outreach issues, sharing best practise, evolving public engagement methods and reaching new audiences with new topics. The fact that this article is being written as output from a workshop dedicated to popularised palaeontology is evidence of these practises actually occurring, and it feels like the right questions are being discussed. How can we, and when should we, shift focus from dinosaurs? How do we make other forms of life/parts of museum collections of wider interest? How do we more effectively impart new science to publishers, movie makers and other non-educational bodies making palaeontologically-themed media? It’s also pleasing to see more discussions about the once largely backgrounded industry practises of palaeoartistry in both scientific and popular media. Realising the important role that palaeoart has for communicating science, many involved in its production are vocally distancing themselves from the ‘popularised’ image of dinosaurs to more nuanced, scientifically-validated and interesting portrayals of dinosaurs, as well as other forms of prehistoric life. We are still on the uphill part of this journey to revising our outreach approach, but it’s reassuring to know that a body of professionals are looking critically at dinosaur outreach and its wider impact.

Minor victories in recent palaeontological outreach involve effectively communicating to certain, interested audiences that Deep Time was not a dinosaur theme park, and that fossil creatures did not spend all their time battling and roaring at one another. Evidence that this message has hit home with at least some audiences is reflected in the broadening depth and nuance of palaeoart being posted across the internet. Shown here: my take on Jurassic stem-mammals, a gorgonopsian, gliding drepanosaurs, a goniopholidid crocodyliform, Cretaceous albanerpetontid, erythrosuchids, and... Longisquama, whatever the heck that is. Not shown here: dinosaurs in premier view, or roaring. The challenge is getting scenes like this, and subjects like this, to wider audiences.
Most of the discussions and innovation in dinosaur/palaeontolgical outreach are taking place online, and transferring these to ‘real-world’ outreach, where the necessity of resource investment makes change risky, may be our greatest upcoming challenge. Again, however, there are signs of this sort of thing happening, such as the famous (or infamous?) decision to replace the Natural History Museum’s famous Diplodocus cast with a blue whale skeleton. This logic of moving this famous attraction has been questioned by some, but I admire the museum for putting a very relevant and symbolically significant specimen in their most prominent location. In doing so, they’re making a clear statement about what they consider to be important, and what they want the public to engage with. Whether you agree with the controversial reorganisation of the natural history museum or not, the idea of outreachers taking initiative with their educational agenda is something I feel we should echo when popularising prehistoric animals. If our outreach is primarily reaching pre-interested audiences anyway, then why not have faith in their interest and tell them what we - as researchers, artists and curators - think is fascinating and exciting about our field, whether it’s related to dinosaurs or not? It would seem a diverse array of outreach topics is more likely to spread out from palaeo-primed audiences and into broader public interest than one largely revolving around a single, perhaps somewhat over-familiar topic. Perhaps cutting palaeontological outreach’s umbilical chord with dinosaurs would benefit us outreachers too, allowing us to freshen and rethink our approach to popularising neglected groups and focus on their own selling points, instead of using them to greater contextualise dinosaurs.

The risk of failure is what prevents many of us, and our employers, from straying too far from tried and tested means of outreach. And yes, if we’re talking paleontology with the public, dinosaurs are an obvious safety net. But we should take advantage of the fact that we’re more enabled than any previous generation of educators to cooperate, create and promote the subjects we feel are important with only a little inventive thinking and technological knowhow. Individuals can now develop significant outreach resources without the need for expensive designers and developers; online promotion can be essentially free; and the increasing accessibility of printing - both 2D and 3D materials - is lowering the financial risks tied into ‘real world’ outreach events. Any public enterprise involves a level of investment and risk, but resourceful thinking and shouldering the brunt of development ourselves can minimise these.

In closing, I want to stress that I’m not wailing on dinosaurs. As may be evident from my own output, I think they’re fantastically interesting animals with an important role to play in outreach. But for dinosaur outreach to be successful and support, not restrict, other outreach efforts we have to realise their limitations, as well as their strengths, as public ambassadors.

This piece of outreach was supported by Patreon

The paintings and words featured here are sponsored by folks who are certainly very popular in my house, my Patreon backers. Supporting my blog from $1 a month helps me produce researched and detailed articles with paintings to accompany them, and in return you get access to bonus blog content: additional commentary, in-progress sneak-previews of paintings, high-resolution artwork, and even free prints. For this post we'll be looking at my new angry nodosaur painting, discussing ankylosaurs in palaeoart and why they're so darned challenging to render well. Sign up to Patreon to be part of the discussion!

Reference


  • Ross, R., Duggan-Haas, D. and Allmon, W. (2013). The posture of Tyrannosaurus rex: Why do student views lag behind the science? Journal of Geoscience Education, 61, 145-160


Wednesday, 2 November 2016

The blog post where I ask myself “should we make Plateosaurus fluffy?”

Plateosaurus engelhardti restored as a) speculatively filamented and b) speculatively smelly (note the cloud of insects buzzing around its head). Scientists have good reason to think that sauropodomorphs could not be routine shower users, but what about that fuzz?

PS - Blogger has added some weird watermark on this picture that I can't figure out how to remove. If anyone knows, please let me know! 


Palaeoartistry is not a science. Even a conservative reconstruction requires artists to stretch data and evidence further than would be allowed for any scientific study and the whole process relies more on inference and speculation than many of us would like to admit. Yes, palaeoart is data-led and evidence-based, but only in rare circumstances do we have enough data to bring us to a single, reliable interpretation of a fossil species. Most of us would agree that there are some aspects of reconstructions that we can and should be getting 'right' for many species - basic proportions and musculature being top of the list - but beyond these science can often only narrow our choices, not present definitive answers. In lieu of clear scientific guidance, what guides these decisions may be our personal preferences, logical thinking, the demands of a project, or the penchants of our consultants. This means that, odd as it may seem, vastly contrasting reconstructions can be construed equally credible. A weird, alternative take on a fossil species might be just as ‘accurate’ to our knowledge as another preferred or familiar one. When evidence is equivocal for two or more states, we have to concede that one interpretation can be just as 'correct' as another.

With this in mind, I thought it might be pertinent to talk about the above reworked reconstruction of Plateosaurus engelhardti with a filamentous coat, and why – at time of writing at least - it’s perhaps neither ‘right’ or ‘wrong’ to depict this animal in this way. I could have covered it with scales as an alternative and not necessarily been ‘correct’ or ‘incorrect’, either. The question of whether sauropodomorphs were wholly scaly has not escaped discussion in many quarters - it was even mentioned at this blog briefly back in 2013 - so, for a change, and perhaps to mirror the sometimes antagonistic way that similar matters are discussed on social media, I’m going to present my thoughts here as a conversational debate between… myself. The idea is that it will allow for fuller discussion of opposing points, but I suspect it really just reflects the amount of time I spend alone at home with no-one but some chickens and various squamates for company. Whatever, hopefully the 'conversation' below will be balanced: both ‘pro-filaments’ and ‘pro-scales’ have important points to make, and I’m not strongly advocating one or the other here: the point is that both sides have valid points to make, so warrant an equal platform. Over to, er… me, then.

Me¹, meet Me²

Me¹ (filaments, opening statement). Should we restore Plateosaurus and other sauropodomorphs with filaments? Maybe. The evolution of dinosaur integument is an increasingly complicated area of study, and the idea that scales alone were the most likely ancestral condition for the major dinosaur lineages is no longer certain. As is well known to many, in the last decade we’re discovered filaments occurring in not only theropods but also in disparate parts Ornithischia too, and detailed new studies are suggesting that filaments in the likes of Psittacosaurus are structurally similar to those of other ornithischians as well as extant and extinct theropods (Mayr et al. 2016). They may even be similar enough to suggest true homology (Mayr et al. 2016), which strongly implies dinosaur skin may have been at least partly fuzzy in its ancestral form. Indeed, with pterosaurs thrown into the mix as well, an ancestrally-filamentous Ornithodira remains not only a valid hypothesis, but one that has passed several important tests in recent years. This being so, a filamented Triassic sauropodomorph is a sensible extrapolation of modern data.

Me² (scales, opening statement). Should we restore Plateosaurus and other sauropodomorphs with filaments? Maybe not. Firstly, studies have shown that our reconstructions of the ancestral ornithodiran integument type remains highly sensitive to the condition of its basalmost species, and we lack fossil data on these forms (Barrett et al. 2015). The 'ancestrally filamentous hypothesis' is enjoying some invigoration from new discoveries and research, but the game is not over yet. Virtually all of our dinosaur skin samples stem from derived species that had plenty of time to modify their integument from the primitive condition, and we have to concede that - whatever we think about the ancestry of dinosaur skin - they were very plastic in integument types. Thus, an important test of this hypothesis will be the recovery of good fossil skin samples from Triassic dinosauromorphs and pterosaurs, and their close relatives. Until we find these, or a fuzzy sauropod fossil, the recovery of scales from all three major dinosaur clades means the argument for 'ancestrally scaled' remains valid.

What's the likelihood of sauropodomorphs having filamentous structures on their skin? Not much, according to Barrett et al. (2015), even in models where dinosaurs are given their best chance of being scaly. But does the absence of skin impressions from non-sauropod sauropodomorphs come into play here?
Secondly, accepting that the evolution of dinosaur integument is complicated, sauropodomorph skin impressions are exclusively scaled. With our current data we can’t say whether this is a derived, reversed condition from a filamentous ancestor or retention of a ‘primitive’ scaled skin type, but whatever: all evidence we have from the sauropodmorph branch of the dinosaur tree seems to show scales. Granted, these specimens all pertain to true sauropods, not their ancestors, but as the closest relatives of Plateosaurus we should probably be using these as guides for our reconstructions. This is supported by the probability study of Barrett et al. (2015), who calculated that sauropodomorphs only have a slim chance (<10%) of non-scaly skin, even when the likelihood of filaments in Ornithodira was maximised.

Me¹. Three points in response here. Firstly, admittedly playing Devil’s Advocate, a <10% chance of sauropodomorphs being filamented is still a chance, right? A filamentous Plateosaurus may not show what is most probable, but it still shows something that science shows is ‘possible’.

Secondly, and more constructively, the fact that skin impressions are not known outside of true sauropods means we may want to question what that the sauropodomorph stats of the Barrett et al. (2015) study really tell us. Does it reflect the condition for all sauropodomorphs, or just Sauropoda? The same probability assessments gives a 50% chance of filaments being ancestral to Saurischia, so the the first sauropodomorphs must have a somewhat higher chance of being filamentous, or at least being closely related to filamented species. Presumably, that 50% chance of filaments doesn’t just plummet the moment we steer evolution to the sauropod line: it’s a long evolutionary road from a basal saurischian to the sorts of sauropods we have with skin impressions, and we have no idea if or when filaments were abandoned on that road. We have a data vacuum of skin at the base of Saurischia: after sauropods, the next closest saurischian with skin impressions to Plateosaurus is the abelisaurid theropod Carnotaurus - hardly a close relative at all. Our absence of skin impressions around the phylogenetic neighbourhood of Plateosaurus, and our data about the likelihood of filaments in saurischians as a whole favours open-mindedness about the life appearance of these animals.

The third point is that if recent claims about dinosaur filament homology are correct, we have to assume that these structures were present in some form in the stock that gave rise to all major clades. Seeing as theropods retained filaments after the theropod/sauropodomorph split at the base of Saurischia, we should probably assume that sauropodomorphs lost their filaments after that divide. If so, a fuzzy Triassic sauropodomorph is not a far stretch.

Me². But - even assuming homology of filaments - if Carnotaurus is scaly, and so are sauropods, we can contrarily hypothesise that saurischians were secondarily-scaly ancestrally. This might even be the most objective reading of the data we have.

Me¹. Perhaps, but is the data supporting that interpretation really reliable? Carnotaurus is actually a weird outlier among theropods, it being the only theropod known with extensively scaly skin impressions. We have to wonder how significant this is against the wider backdrop of extensively filamented coelurosaurs sitting just a little higher up the theropod tree. As the rootward-bracket of the theropod integument bracket it's almost irritatingly important - it has a lot of sway in our reading of dinosaur integument evolution - but we still have to view it as a single outlier against the wider picture of theropod integument. As with any outlier, we have to be cautious about over-interpretation, or thinking one datum can give us the whole picture. As with so many palaeontological issues, we need more information.

The ornithodiran integument evolution 'choose your own brackets' game. When clades without skin samples are featured alongside those with them the amount of missing data becomes apparent, and trying to find obvious patterns becomes tricky. Osteroderms are considered evidence of scales because of their relationships with scaly coverings in modern animals. Compiled from various sources.
And if we need an example of how sensitive our dataset still is, we need only consider Psittacosaurus, Kulindadromeus. Both are deeply nested within Ornithischia but basal to clades dominated by scaly species, and yet both have filaments. No-one would have predicted their integument type from their relatives. Not only does this show that our data may not be reliable enough yet to make confident predictions about integument types, but it suggests skin types might have been quite a bit more varied among even closely related dinosaurs than we anticipated.

Me². The risk here is that we’re pandering to exceptions, unknown data and slim chances. Arguments about the unknown nature of sauropodomorph or early saurischian skin seem like threading loopholes more than effective rebuttals. They play on what we don’t know rather than what we do, and that’s not how science works. There’s lots to be said for keeping an open mind, but we shouldn’t ignore data. Sure, there’s room for doubt here and we may be proved wrong in the future, but palaeoart should probably err on the side of caution, using the best supported, highest probability models to inform reconstructions. ‘Being wrong for the right reasons’ is perhaps the motto we should take when faced with the data gulfs associated with restoring partly known animals.

Me¹. The flip side of this is that ornithodiran integument has been proved complicated and surprising often enough that assuming variation in the poorly known areas is justified. Who expected Kulindadromeus and Psittacosaurus, or Tianyulong? Who, for that matter, would have predicted the first fluffy pterosaur fossils among - at that point - entirely scaly relatives? The point about exploiting unknown data is an important one, but we have a strong precedent for filaments in poorly sampled areas of ornithodiran evolution now. This is less exploiting a loophole than admitting we don’t have a full picture yet, and simply portraying one of the two more likely options of integument form.

Furthermore, Kulindadromeus and Psittacosaurus are great examples of how dangerous our approach to integument reconstruction is when we only have scraps of soft-tissue. It’s only because of their extensive soft-tissue preservation that we know they mixed scales and filaments in different body regions. And it’s not just these dinosaurs that show us that. Pterosaurs have scaly feet to counter their fluffy bodies (Frey et al. 2003), and the extinct mammal Spinolestes is known to have had scales, bristles, and variably long and short fur (Martin et al. 2015). Andrea Cau has even cast doubt on our presumed reasonable knowledge of Carnotaurus skin, pointing out that its skin impressions all pertain to the underside of the animal and that the dorsal surface could be entirely different. We thus have to ask what we really know about sauropod skin: are the bits we have representative of whole animals, or the group as a whole? The most extensive set we have - those from a diplodocid that might be Kaatedocus, described by Czerkas (1992) - show a lot scaling on the body, which meets the predictions we’ve made from smaller pieces of skin found with other sauropods. But it might be naive to think this offers a significant insight into these species, or rules out the chance of localised filaments on some sauropodomorph species.

Me². But where do we draw the line here? There has to be a point where we can say ‘we haven't seen evidence of filaments yet, and we should factor this into our science’ without someone going ‘you don’t know the whole animal yet!’. Some artists take this to an extreme, restoring animals like Edmontosaurus with large filamented regions despite this species being known from several well-studied and extensively-scaled mummified individuals. These have no evidence of filaments whatsoever, despite preserving scales down to millimetre resolution, and yet some folks are still unconvinced, speculating that filaments were poking through gaps between scales and so on. Palaeoart like this Plateosaurus reconstruction almost holds palaeontology to a standard of knowledge that it’s unlikely to ever attain: no, we don’t have skin impressions from every species, we don’t have good skin impressions from many species at all and fossils are never perfect records of animal appearance. But we have to use what we have: science does not work on a philosophy of 'assume whatever until proven otherwise'.

Excellent fossils show that animals like the Cretaceous mammal Spinolestes xenarthrosus had regionalised integument variation, just like modern species. So how much skin do we need from a fossil animal before we can rule out major variation in integument types? Note that the tail fluff in this picture is speculative - the integument preservation of Spinolestes doesn't extend to the tail region.
Me¹. Of course, if we restore animals however we like in our artwork then we’re not doing real palaeoart, just palaeo-based artwork. Palaeoartists must constantly ask where the boundary between informed, sensible extrapolation of data ends and where unbridled speculation begins. So I suppose the question here is ‘does this reconstruction go too far?’ Is a filamented Plateosaurus just nutball craziness, or a reasonable idea based on what we currently know? The fact this discussion has got this far suggests that there must be some validity to this idea, even if some might think it's ultimately a flawed one. But 'flawed' is not the same as 'nonsense'. Depictions of filamentous or scaly sauropodomorphs simply reflect emphasis on different datasets. A scaly interpretation prioritises skin impressions from close relatives, but downplays emerging 'bigger picture' interpretations of ornithodiran integument, and a filamentous one does the opposite. From a 'big picture' perspective we're entering a time when reconstructing any dinosaur with filaments should not be considered ridiculous or outlandish, save for those with well sampled scaly skin tissues. It's not necessarily the best approach, but it's not an invalid one.

Me². It must be said that it would be easy to construct this conversation around a scaled version of this animal, and discuss why it doesn’t have filaments. Our base expectation for dinosaur integument and life appearance is in a state of flux, no matter what we personally prefer or assume.

Me¹. I think a point often lost on viewers of palaeoart is that these artworks are not, and cannot, be definitive, incontrovertible renditions of these animals. There are some animals so well represented in fossils that they lend themselves well to ultra-detailed reconstructions which are hard to quibble over to significant degrees - the awesome Bob Nicholls Psittacosaurus model being a great example (Vinther et al. 2016) - but for lesser known animals like Plateosaurus we are only painting hypotheses, not fact-based reality. This painting is one possible reconstruction of Plateosaurus as known in 2016, a time when interpretations of dinosaur skin evolution remain in flux. Time will tell if it's the product of over-interpretation of fossil data, or a lucky gambit later borne out with fossil evidence. I don’t mind getting stuff like this wrong: I’m more interested in painting and exploring credible possibilities of what we know now, not being ‘right’. We may never know what is ‘right’, so there’s not much point worrying about it. There are a couple of essays on this topic in my new book, Recreating an Age of Reptiles (Witton 2016).

Me². You’ve seen RecARep? I hear it’s awesome and that everyone should buy a copy.

Me¹. Wow, that’s desperate. Any actual final points?

Me². In a previous post on the role of pterosaurs in interpreting dinosaur filaments I concluded that: “Forcibly arguing for either scales or filaments at the base of Dinosauria seems premature at this stage, and, whatever our personal hunches are, it seems sensible to accept some ambiguity in this situation for now.” I think that’s true here too. There are certainly arguments to be had on both sides, some stronger than others, but neither side has knock-out data or evidence on the table yet. It’s the same old frustrating cop-out, but we need more fossils, and fossils of the right sort, to resolve this. Specifically, we need early saurischians or dinosauromorphs with good skin preservation, as well as that Triassic sauropodomorph with excellent skin remains. It must be said that these animals are not generally found in fossil Lagerstätten conducive to good soft-tissue preservation, so I’m not advising anyone to hold their breath for this one. But new techniques for detecting soft-tissues and increasing awareness of soft-tissue preservation in lithologies once thought to only preserve bone are reasons to be optimistic that we'll have insight on these matters one day.

Me¹. And ‘frustrating’ is the right word here, too. It seems like dinosaur science has made sufficient headway on understanding integument evolution and predictive methodologies that a reasonable, if provisional answer to the ancestral integument of the three major clades is close. But the puzzle piece needed to get our first good look at the broad picture is still out of reach.

Awkward facial expression, bad fashion sense and a hygiene problem. No wonder no-one likes to paint early sauropodomorphs.
Me². OK, that seems like a point to end. This discussion with yourself didn't seem to go too bad, actually. Unlike that vulture-like ruff around the base of the neck in the Plateosaurus reconstruction. I mean, if you're going to paint a controversial reconstruction, at least make the animal look good.

Me¹. Pfft... Good… bad… I’m the guy with the graphics tablet.

Me². Movie quotes in scientific blog post don’t make you look clever, you know. You just cheapen the whole act.

Me¹. There is no fate but what we make for ourselves.

Me². What...? that doesn’t even fit our context.

Me¹. It wasn’t the airplanes. It was beauty killed the beast.

Me². Sigh, why do I hang around with you? I think we're done here.

So long everyone - I'm away from my computer for the next few weeks so I'm going to be pretty quiet in blog comments, social media and so on. Things will pick up again come December when we'll be addressing the sauropods in the palaeo-outreach room: has the popularity of dinosaurs above other fossil animals become a problem?

This blog post was inarguably supported by Patreon

The paintings and words featured here are sponsored by an excellent group of animals with regional variation in integument, Patreon backers. Supporting my blog from $1 a month helps me produce researched and detailed articles with paintings to accompany them, and in return you get access to bonus blog content: additional commentary, in-progress sneak-previews of paintings, high-resolution artwork, and even free prints. Later this month (much later - around the 28th/29th) I'll be uploading a video version of the presentation I gave over the Halloween weekend at Dinosaur Days 2016, entitled Palaeoart and the Never-Ending Quest for Accuracy. Here's the title slide to whet your appetite:
"Oh, I see you're putting movie easter eggs in this post now too. This is why no professional blogging platform will pick you up."

Sign up to Patreon to get access to this and the rest of my exclusive content!


References

  • Barrett, P. M., Evans, D. C., & Campione, N. E. (2015). Evolution of dinosaur epidermal structures. Biology letters, 11(6), 20150229.
  • Czerkas, S. A. (1992). Discovery of dermal spines reveals a new look for sauropod dinosaurs. Geology, 20(12), 1068-1070.
  • Frey, E., Tischlinger, H., Buchy, M. C., & Martill, D. M. (2003). New specimens of Pterosauria (Reptilia) with soft parts with implications for pterosaurian anatomy and locomotion. Geological Society, London, Special Publications, 217(1), 233-266.
  • Martin, T., Marugán-Lobón, J., Vullo, R., Martín-Abad, H., Luo, Z. X., & Buscalioni, A. D. (2015). A Cretaceous eutriconodont and integument evolution in early mammals. Nature, 526(7573), 380-384.
  • Mayr, G., Pittman, M., Saitta, E., Kaye, T. G., & Vinther, J. (2016). Structure and homology of Psittacosaurus tail bristles. Palaeontology. doi 10.1111/pala.12257.
  • Vinther, J., Nicholls, R., Lautenschlager, S., Pittman, M., Kaye, T. G., Rayfield, E., Mayr, G. & Cuthill, I. C. (2016). 3D Camouflage in an Ornithischian Dinosaur. Current Biology, 26(18), 2456-2462.
  • Witton, M. P. (2016). Recreating an Age of Reptiles. Red Phare.

Tuesday, 25 October 2016

The markwitton.com H. P. Lovecraft Halloween Special



The best holiday of the year is just around the corner: Halloween! It's the season to celebrate the macabre, the weird, the dark and the terrifying. It's the best excuse to watch all your favourite horror movies. And it's the time to spend hours making costumes that you can't really see out of or eat or drink in, but that's OK because you're doing this for the art, not the practicality. Yes, it's Halloween: king of the holidays.

This year, an impending honeymoon and my attendance at Dinosaur Days 2016 (a palaeontology/palaeoart event being held at the WWT Wetland Centre, London, 28-29th October - it's going to be awesome, and you should come along) means I can't celebrate Halloween as normal. But dammit, I'm going to do something, even if that means just celebrating a little here by sharing some off-topic art.

Sometimes, very rarely, I take a break from painting and writing about palaeontology and turn my attention to vintage science fiction, producing paintings of some of my favourite stories, characters or monsters, and the creatures of H. P. Lovecraft are a frequent subject. With Halloween being just around the corner and Lovecraft's tales of sinister cults, strange creatures and other-worldly horrors being pretty note-perfect fodder for this time of year, I'm going to take the blog off-road with a short gallery of my Lovecraft paintings. Although we're going to be pretty palaeontology-lite for this post (folks here for coverage of extinct creatures may be pleased to know we'll be back to normal very soon) we're not abandoning the concepts of biology and evolution altogether. One of the things I find appealing about Lovecraft's work is the frequent nods to biology, geology and evolution, and creating biologically plausible(ish) versions of his creatures was a primary goal of the work shared here. We're not quite in the territory of full-on speculative evolution with this post, but I've tried to make my discussion at least a little informed. Right, enough preamble, let's get stuck in. (Oh, and a major SPOILER WARNING for those of you who haven't read Lovecraft's most famous stories and books.)

Sunday, 9 October 2016

Exposed teeth in dinosaurs, sabre-tooths and everything else: thoughts for artists

Bear-sized gorgonopsid Inostrancevia latifrons. Sabre-teeth? What sabre teeth?
It is something of a trope that prehistoric animals must bare their teeth in palaeoart, even when their mouths are closed. Historically, the majority of palaeoartists covered the teeth of their subjects with lips, cheeks or other types of tissues and only select species – sabre-toothed carnivorans or mammoths – were depicted with exposed tusks or sabre-canines. This changed when artists working in the 1980s and 1990s - Paul, Hallett, Stout - and a certain 1993 movie started showing predatory dinosaurs with toothy overbites and perpetually exposed teeth. This convention has since expanded to all kinds of prehistoric animals, and some galleries of Deep Time now have more toothy grins than a holiday photo album. Theropod dinosaurs in particular are almost always shown with alligator-like overbites that perpetually expose their upper teeth, the large canines of stem-mammals protrude over their lower jaws, and even herbivorous animals with relatively unimpressive dentition (like sauropods) are shown without lips or other forms of dental covering.

Many words – mostly published at blogs, online mailing lists and social media - have been typed to discuss the credibility of lipless palaeoart, but the subject has traditionally received only cursory attention from academics. Happily for artists, this is starting to change. A small set of literature exists which debates the presence of extra-oral tissues in dinosaurs (e.g. Ford 1997; Knoll 2008; Morhardt 2009; Keilor 2013; Reisz and Larson 2016), and most of this agrees that some sort of soft-tissue - at least 'lips' - covered their teeth. However, a running theme of these works is that reliably inferring soft-tissues of the face is not a simple task, and we really need more data to be sure of anything. Work on more recent fossil mammals shows more reliable inferences (e.g. Wall 1980; Antón et al. 1998), obviously benefiting from soft-tissue data from a range of extant, close relatives. New insights on the evolution of mammal cranial nerves are helping to understand the development of sensitive lips and cheeks in stem-mammals (Benoit et al. 2016). It's still early days for understanding fossil facial tissues, but at least it feels like we're off the line.

Collectively, there seems to be recognition among the academics interested in this topic that understanding the tooth coverage of fossil animals lies largely in understanding living animals. Attempts to understand tooth exposure from skulls alone - through making inferences about tooth size, jaw closure and speculations on how extensive soft-tissues can be before they become untenable - do not consider all necessary data. For example, Prehistoric Times palaeoart adviser Tracy Ford (1997) looked solely at the skulls of predatory dinosaurs to infer the absence of lips, suggesting their teeth were so long that they would pierce lip sheathing once the jaws were closed. This study assumed that predatory dinosaurs closed their mouths to the extent that the teeth of the lower jaw contacted the roof of the mouth, and that the preserved tooth configuration was the condition in life. These points are common issues raised against lipped dinosaurs, but there are several major problems. Dissections and CT scans of reptile heads show that jaw muscles and other soft-tissues have a major influence on mouth closure, to the extent that reptile jaw skeletons are typically loosely closed under their skin, even when the mouth is fully sealed. Taphonomic studies show that teeth slip readily from their sockets after death and often fossilise in far more vampiric states than they were in life. And undermining this further is that no extant taxa with lipped jaws were used to calibrate a limit for oral soft-tissues. Arguments about tooth coverage based on simply looking at skulls, without detailed consideration of modern animals and their anatomy, border on being arguments from incredulity: "I don't believe the anatomy could do that."

Modern animals and their tooth coverage

For an upcoming project, I've been trying to crystallise my approach to restoring ancient animal facial tissues, and deciding whether to cover their teeth or not is an important part of that discussion. I've been deliberately broad in this assessment to attempt to try to sort the wood from the trees: discussions of oral tissues can sometimes get lost in the minutiae of tissue types, uncertain osteological correlates and so on - and many of these discussions result in the same answer: they can't be resolved with current data. That's not to say they aren't important discussions, but it's helpful to step back to see if we can answer the simpler questions as well: what gauge of teeth can be covered by oral tissues? When are teeth actually exposed? And what questions should we, as palaeoartists, be looking to answer when restoring facial tissues?

Reviewing literature and galleries of modern animals, we can see that overwhelming majority of living tetrapods have covered teeth, including all amphibians, most mammals and most reptiles (excluding birds, naturally. Hey, if they wanted to be involved in this post they shouldn't have lost their teeth). Exposed teeth are actually really rare, and a character completely absent in many major clades. The soft-tissues involved in covering the teeth are variable, but 'lips' – either slightly fleshy margins of skin, or skin overlying muscle - are so universal among tetrapods, as well as living relatives like lungfish, that we might assume lip tissues of some kind were ancestral to the group, and breaching these with large teeth is a derived condition evolved independently in a minority of lineages. Crocodylians are the only living tetrapods with fully exposed teeth, but it's increasingly obvious that they're also pretty specialised/derived/downright weird (Grigg and Kirshner 2015). Far from being 'living fossils' frozen in evolution, they have so many anatomical nuances and specialisations that their use as model organisms for other extinct taxa is increasingly questionable. This applies to aspects of their facial anatomy too - we’ll discuss this in more detail below.
Fossil big-tooths - species almost universally depicted with exposed teeth - versus modern animals with huge, but completely covered teeth teeth. A, Inostrancevia latifrons; B, Tyrannosaurus rex; C, Smilodon fatalis; D, crocodile monitor Varanus salvadorii; E, mandrill Mandrillus sphinx; E, hippopotamus Hippopotamus amphibius. With the exception of Smilodon, the fossil taxa are out-toothed by the extant animals, and yet we know their oral tissues can accommodate their teeth without problem. Blue lines approximate lip margins in living species. A, after Kemp (2005); F, after Goldfinger (2004).
Looking inside animal heads (above) shows that facial soft-tissues can cover very, very large teeth – perhaps much larger than we might intuitively expect. Examples from a range of tetrapods – including rhinoceroses, sloths, tapirs, mandrills, baboons, camels, tuataras, snakes, peccaries, bullfrogs, hippopotamuses, monitor lizards, clouded leopards, numerous rodents and others – show that large fangs, robust tusks and other forms of enormous dentition can be retained within lips or cheeks. These large teeth are truly ‘hidden’ without bulges, changes in lip direction or other features to betray their presence, and are thus undetectable unless their owners open their mouths (and sometimes not even then). Many people are shocked by the size of animal teeth when they see their skulls, and the savagery of mammalian herbivore dentition – horses and camel fangs, rhino tusks, baboon canines - are particularly startling.

We owe many of these surprises to animal lips, which are generally much more extensive than we casually assume. Large teeth can slide into soft-tissue sheaths located between gums and lips, and these are quite visible in the open mouths of some species. Amphibians, lizards and many mammals have upper and lower lips of similar size which meet over the teeth and sheaths can form on either jaw, but some mammals – including most carnivorous forms - have very large, fleshy upper lips over thinner, tightly-bound soft-tissues of the lower jaw (Antón et al. 1998). In these species, the canine teeth overbite the lower lip but the upper ‘over-lip’ is large enough to obscure the fact that the tooth is outside the lower mouth tissues. I am unaware of a reversed situation with the lower lip covering a thin upper lip: this may reflect the fact that overbiting dentition is much more common than underbiting. Regardless of the specific configuration, it is clear that we should not underestimate the capacity for facial tissues to obscure even very large, sharp and ferocious-looking teeth. The assumption that all conspicuous teeth of fossil animals were on display in life is thus problematic and does not agree with what we can observe in modern animals (below).

Applying palaeoart-esque considerations of oral tissue capacity to modern mammals suggest hippos are giant hogbeasts and mandrills evolved in Mordor. Restoring modern animals using palaeoart approaches is a completely original concept which in no way owes anything to some book called All Yesterdays (Conway et al. 2013).
When do teeth breach the confines of soft-tissue? Mostly, it seems teeth used to process food remain covered. Mammal tusks and the exposed canines of certain deer are not directly involved in food processing, although this is not to say they are non-functional overall (e.g. elephants use their tusks to break branches, dig, topple trees; deer fight with their large canines). It seems that teeth of extreme size relative to the rest of the dentition are most likely to escape covering with soft-tissue, and it helps – though is not mandatory – if they grow obliquely or directly away from the jawline (this accounts for the majority of living mammal tusks). Teeth can remain covered even when their tips extend to the dorsal or ventral limits of the jaw skeleton, so long as they are aligned more or less vertically within the jaw (e.g. the mandrill skull illustrated above).

What's up with crocodylians?

The elephants – or rather large semi-aquatic reptiles – in the room here are crocodylians: why do they have exposed teeth when all other tetrapods have largely covered mouths? Their teeth are not overly large, nor acutely angled. Some (Reisz and Larson 2016) have argued crocodylian dentition is only possible because of their semi-aquatic habits. The (unpublished, currently conference abstract only) Reisz and Larson hypothesis is that exposed teeth – specifically their enamel component – are at risk from desiccation and breakage without constant hydration from saliva or environmental water (Reisz et al. 2016). This is an interesting idea which potentially gives artists a useful, practical guide to restoring prehistoric animals: anything living outside water with enamel-covered teeth must have covered them with soft-tissue. Despite its unpublished status, this idea has already chimed with some quarters of the online palaeoart community who're restoring anything with enamel-covered teeth with full sheathing.

We need to talk about enamel and exposed teeth. The exposed canines of male wild boars, Sus, have enamel (white shading) coatings on 3/4 of their surface, despite being exposed (dentine is dark grey, cementum is light grey). What does this mean for the enamel desiccation hypothesis outlined above? Image from Hillson (2005).
However, this proposal may not be as simple to implement as it first appears. For one thing, there is a real lack of consistency in tusk composition in living animals (see Hilson 2005). It is true that, as noted by Reisz et al. (2016), the tusks of elephants have caps of enamel and cementum that wear off rapidly, leaving their tusks composed of dentine alone. This would seem to support the desiccation hypothesis, it implying that enamel is a liability outside of the jaw soft-tissues. However, living elephants may be atypical in lacking enamel on their tusks, there being fossil and living mammals which do have substantial enamel components on their exposed teeth. For example, the tusks of several gomphothere species have broad bands of enamel along their lateral surfaces, even as adults (Padro and Alberdi 2008), while the canines of male musk deer are enamel covered on the external surface. The tusks of male wild boars and warthogs only bear dentine on the posterior surface and wear facet, the rest of these large, exposed teeth being covered in enamel. The enamel components of these tusks are not just small caps that get worn off, but expansive coatings that persist on the tooth indefinitely and influence tooth wear (Koenigswald 2011). To confuse things further, walruses have dentine tusks like elephants, despite their aquatic habits seemingly precluding desiccation as a risk for their teeth, and the spiralling tusks of another marine mammal, the narwharls, are covered in enamel. If there is a relationship between enamel and tooth exposure, it is clearly a complicated one, and the presence of absence of enamel in itself seems to have little bearing on this topic in at least modern mammals. (Readers interested in tooth composition should check out the second edition of Samuel Hillson's Teeth (2005), for its extensive documentation and illustration of mammalian dentition).

Musk deer, Moschus, canines in lateral and medial view. Note the (white) enamel layer on the lateral surface, but dentine (grey) on the medial. From Hillson (2005 - the scale bar is likely erroneous!).
Our second reason to be sceptical of the enamel desiccation hypothesis concerns crocodylian behaviour. It is not widely appreciated that several crocodylians species ‘hibernate’, or more accurately aestivate, for months at a time in dry underground burrows during the hottest summer months (Grigg and Kirshner 2015). During these intervals they do not access water at all. Other, South American species spend dry spells as fully terrestrial carnivores, abandoning aquatic habits and obtaining water largely from the prey they kill (Grigg and Kirshner 2015). These states have to be explained against the suggested need to frequently moisten crocodylian teeth, because they suggest dental desiccation is not as risky as we're all assuming it is. Alternatively, it suggests that the requirement for hydration is so relaxed – literally months can pass without getting the teeth wet – that it probably has little influence on tooth anatomy.

Furthermore, there are important caveats about crocodylian facial tissues that we have to factor into any discussion of their lipless configuration. Crocodylian faces are far more specialised and unusual than they first appear, and this may factor into their lipless mouths. Their highly keratinous facial skin undergoes a developmental pathway unlike that of any other amniote (their facial skin is essentially one, highly 'cracked' scale) (Milinkovitch et al. 2013) and their heads are riddled with hyper-sensitive Integumentary Sense Organs (ISOs). ISOs are a unique crocodylian feature and are attuned, among other things, to sensing tiny vibrations in water (Soares 2002, see Grigg and Kirshner 2015 for a recent overview). In at least some parts of the crocodylian skull ISOs are situated over tiny foramina, presumably housing nervous tissues, and the overlying epidermis is thinned, with a reduced keratin component, to enhance their sensitivity (Soares 2002). We can thus see that ISOs do have a role to play in configuring crocodylian skin, and they present many questions that palaeoartists should be interested in. Are ISOs an important reason for crocodylian faces having such tight, contour hugging and lipless skin? Do the major functional and developmental distinctions of croc faces explain the lack of crocodylian lips? It might explain why virtually no other aquatic tetrapods have abandoned lips - aside from the the odd (and perhaps only) exception like the South Asian river dolphin*, there are no whales, snakes, seals or otters with crocodylian-like, fully exposed teeth. And given that no other lineages have osteological correlates for ISOs, should we put huge caveats around using crocodylians as models for facial tissues in anything other than their own ancestors? I don't know if anyone has answers to these questions yet, but they're food for thought when using crocodylians as ammunition for lipless reconstructions of fossil animals.

*Thanks to Ádám Lakatos for pointing out the toothiness of some river dolphins!

It's still very early days for the enamel/oral covering hypothesis, but modern animals suggest that interpretations of enamel precluding extraoral teeth are definitely more complicated than they first appear, and may even be flawed. If so, the simple presence of enamel on the teeth of fossil organisms may not be as useful to artists as some are currently suggesting. But this conclusion is preliminary, and we need to wait for this idea to mature before it's shot down entirely. We know, for instance, that there's more than one type of enamel among vertebrates. Reptilian enamel, for instance, is both thinner and of different microstructure to mammalian enamel, and these clades have rather different approaches to tooth longevity. This may mean something for enamel desiccation and long-term tooth exposure, and we may think differently on this matter once this research has been completed.

Predicting tooth exposure in fossil species

Fully 'lipped' gorgonopsids and theropods: maybe not be as exciting as their toothy variants, but are they more credible? Well... if modern animals are anything to go by, probably.
All this said, what can we say about the decisions to show prehistoric animals with exposed teeth? My reading of modern tetrapods is that covered teeth is their ‘default’ configuration, and we should apply the same logic to extinct animals. If so, maybe only the more extreme examples of fossil dentition should qualify for perpetual display. Perhaps instead of asking ‘does this animal have lips?’ we should ask why they should not have them. We have to concede that the dentitions of many fossil animals frequently shown with exposed teeth – particularly theropod dinosaurs, gorgonopsids and other carnivorous stem-mammals – are relatively no larger, and in some cases a great deal smaller, than those enclosed inside the oral tissues of living animals, especially once taphonomic tooth slippage is corrected (above). For these species, it is very difficult to justify why their teeth should not be covered.

If this is so, only especially long teeth which project a considerable distance from the margins of the skull and lower jaw should be considered strong candidates for permanent exposure. Select examples might include the canines of certain mammalian carnivores (e.g. Smilodon and other machairodont felids), the tusks of fossil elephants and their relatives, and the larger tusks of dicynodonts. We should also note those fossil reptiles – such as certain crocodyliformes, pterosaurs and marine reptiles – where entire toothrows are composed of dentition so long that their tips extend well beyond the margins of the jaw skeleton. Such extensive dental apparatus would seem to preclude the development of any sheathing tissues, at least akin to those exhibited by from modern animals, and these animals probably had fully exposed toothrows in life. Of course, this conflicts with the observation that food-processing teeth are almost always covered in the modern day. However, we can defend this approach by arguing that their morphology gives a strong reason for ignoring this guideline: it answers the "why we shouldn't give them lips?" question.

The large, procumbent dentition of plesiosaurs and certain pterosaurs argues against them being sheathed in life, although I do wonder if some plesiosaurs are in a 'grey area' here. Could animals like Leptocleidus (right) have covered its teeth with lip-like tissues? Hmm....
We might also set aside this guideline when extant relatives of modern forms provide us with means to predict unusual lip anatomy. For instance, the aforementioned ‘over-lip’ of modern mammalian carnivores is common enough across this group to assume it was present in their fossil relatives. Because we understand how the lips of these animals work, we can make more specific predictions concerning tooth exposure in species with particularly impressive teeth. Thus, we can look at classic reconstructions of machairodontid cats like Smilodon with perpetually bared fangs as reasonable because, unless their lips were arranged differently to virtually all their living relatives, that’s simply how their lip tissues would respond to a massive set of canines. And yes, I'm aware of Dunae Nash's recent discussions about sheathing Smilodon: given that this rests heavily on enamel being a no-no in exposed teeth, I'm unconvinced for the reasons explored above.

The concluding caveat

Of course, it must be reinforced that these are just guidelines - and guidelines based on my own qualitative studies, nonetheless, your mileage with them may vary - and there are exceptions to the suggestions made above. As is well known, for all the suggestion that restoring sabre-toothed cats with exposed teeth is reasonable, one living cat species – the clouded leopard – does cover a set of long upper canines in a lower lip sheath. We would not predict this based on other cat species and, if known only from fossils, clouded leopards would probably be restored with slightly exposed canines. Likewise, the exposed tusks of some deer are not especially massive, and if we followed the suggestions above we'd probably cover them up in a reconstruction. But palaeoart is ultimately a game of prediction and probability, attempting to restore what is most likely to fill gaps in our data, and any game of odds will have some failures. That’s not to say we shouldn’t ignore these exceptional examples - they show that guidelines can't be trusted all the time - but it makes sense for us to know where the guidelines are in the first place. As with all aspects of palaeorestoration, all of us stand a chance to be proved wrong about our artistic decisions: if and when that happens, the best we can hope for is to have been wrong for the right reasons.

This blog post was covered by Patreon

The paintings and words featured here are sponsored by a group of animals which also have sheathed dentition, Patreon backers. Supporting my blog from $1 a month helps me produce researched and detailed articles with paintings to accompany them, and in return you get access to bonus blog content: additional commentary, in-progress sneak-previews of paintings, high-resolution artwork, and even free prints. Sign up to Patreon to get access to this and the rest of my exclusive content!

References

  • Antón, M., Garcia‐Perea, R, & Turner, A. (1998). Reconstructed facial appearance of the sabretoothed felid Smilodon. Zoological Journal of the Linnean Society, 124(4), 369-386.
  • Benoit, J., Manger, P. R., & Rubidge, B. S. (2016). Palaeoneurological clues to the evolution of defining mammalian soft tissue traits. Scientific reports, 6.
  • Conway, J., Kosemen, C. M., Naish, D., & Hartman, S. (2013). All yesterdays: unique and speculative views of dinosaurs and other prehistoric animals. Irregular Books.
  • Ford, T. L. (1997). How to Draw Dinosaurs. Give Theropods no Lip! Prehistoric Times, 25, 49-50.
  • Hillson, S. (2005). Teeth, Cambridge Manuals in Archaeology Series. Cambridge University Press, Cambridge, 373.
  • Goldfinger, E. (2004). Animal anatomy for artists: The elements of form. OUP USA.
  • Grigg, G., & Kirshner, D. (2015). Biology and evolution of crocodylians. Csiro Publishing.
  • Keillor, T. (2013). June, in the Flesh: The State of Life-Reconstruction in Paleoart. In: Parrish, J. M., Molnar, R. E., Currie, P. J., & Koppelhus, E. B. (eds). Tyrannosaurid Paleobiology, Indiana University Press. 157-176.
  • Kemp, T. S. (2005). The origin and evolution of mammals. Oxford University Press.
  • Koenigswald, W. V. (2011). Diversity of hypsodont teeth in mammalian dentitions—construction and classification. Palaeontogr. Abt. A, 294, 63-94.
  • Knoll, F. (2008). Buccal soft anatomy in Lesothosaurus (Dinosauria: Ornithischia). Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 248(3), 355-364.
  • Morhardt, A. C. (2009). Dinosaur smiles: Do the texture and morphology of the premaxilla, maxilla, and dentary bones of sauropsids provide osteological correlates for inferring extra-oral structures reliably in dinosaurs? (Doctoral dissertation, Western Illinois University).
  • Prado, J. L., & Alberdi, M. T. (2008). A cladistic analysis among trilophodont gomphotheres (Mammalia, Proboscidea) with special attention to the South American genera. Palaeontology, 51(4), 903-915.
  • Reisz, R. R. & Larson, D. (2016) Dental anatomy and skull length to tooth size rations support the hypothesis that theropod dinosaurs had lips. 2016 Canadian Society of Vertebrate Paleontology Conference Abstracts, 64-65.
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  • Wall, W. P. (1980). Cranial evidence for a proboscis in Cadurcodon and a review of snout structure in the family Amynodontidae (Perissodactyla, Rhinocerotoidea). Journal of Paleontology, 54, 968-977.

Monday, 12 September 2016

A salute to the Erythrosuchidae

Two Garjainia madiba decide who gets the table scraps. The reconstructions here are modified from the life reconstruction I provided for Gower et al. (2014).
I find erythrosuchids, large, big-headed Triassic archosauriforms, very charismatic fossil animals. If nothing else, it's hard not to admire their no-nonsense approach to carnivory. Take a fairly standard reptilian bauplan, weld an oversize theropod dinosaur face to the front, then point it at the things you want to die: simple. They're the Mesozoic equivalent of mounting a howitzer on a golf cart and calling it a tank. We might question the rudimentary nature of the design, but we can't argue with the results.

Alas, erythrosuchids don't get as much love from palaeoartists or outreach projects as they deserve. Their marriage of a proportionally huge, sharp-toothed skull with a crocodile- or lizard-like body is unlike anything around today and it's difficult not to wonder how they functioned as living animals. Closer inspection of their anatomy reveals more sophistication than we might assume from the few illustrations of these animals available online or in books, and it seems that their role in Mesozoic ecosystems and reptile evolution was an important one. These were a successful, abundant group of predators with an evolutionary run spanning the Early and Middle Triassic (12 million years in total) and a near cosmopolitan distribution. Moreover, they remain important species for understanding the early evolution of archosaur-line reptiles. They really do have a lot going for them, but they just haven't quite caught public imagination.

A few years ago I was commissioned to reconstruct the small(ish), early erythrosuchid Garjania madiba for David Gower and his colleagues for their 2014 descriptive paper (below). The brief was for a straight illustration of the animal rather than a restored scene, and I promised the team I would put this reconstruction in a landscape one day. Two years later, I've finally got around to it: the results are above. Posting this painting seems like as good an excuse as any to lavish some much needed attention on these most encephalised of reptiles, so let's get stuck in.

G. madiba reconstruction from Gower et al. (2014). Note prominent bosses on the face, a characteristic feature of this species.

What, exactly, is a erythrosuchid?

You can find erythrosuchids in Triassic rocks on every continent except North America and Antarctica and, although relatively complete specimens are not common, many species are represented by large inventories of bones. Despite this relative glut of material, the classification of erythrosuchids - from the fine anatomical characteristics of the group, to their position in the reptilian tree and the number of species contained in the clade - has been the subject of long-standing, ongoing discussions among palaeontologists. Older erythrosuchid literature is confused by a multitude of different classifications which entwine erythrosuchids with other large-headed, carnivorous archosauriforms such as raisuchians and proterosuchids. Researchers have long realised the problems with these schemes, but unpicking the relationships of these groups and other early archosaur-line reptiles has been tricky. With the arrival of extremely detailed and well sampled cladistic analyses of archosauromorphs (e.g. Nesbitt 2011; Ezcurra 2016) we might be moving towards greater consensus on the systematics of these animals, however. In modern schemes, erythrosuchids are recovered as non-archosaur archosauriforms close(ish) to the base of Archosauria. More specifically, they are the sister clade to the the Eucrocopoda, the large clade that contains the likes of Euparkeria and proterochampsids, as well as the true archosaurs (Ezcurra 2016).
Erythrosuchus africanus skull, restored by Gower (2003). Note the extremely robust construction of the bones and expanded areas for neck muscle attachment.
Several erythrosuchid species are well known: Erythrosuchus africanus from the Middle Triassic of South Africa, Garjainia prima from the Early Triassic of Russia, and Shansisuchus shansisuchus (that's not a typo) from the Middle Triassic of China. These species are represented by associated remains as well as large numbers of fragmentary referred specimens, and allow for a relatively complete insight into their overall form. The largest taxa, like Erythrosuchus, are big animals with head-tail lengths approaching 5 m - the length of a good-sized car - and even small taxa like Garjainia are over 2 m long. The most arresting aspect of eyrthrosuchid anatomy is, of course, their skulls (above). Superficially theropod-like, these long, deep and robust structures are sub-rectangular in lateral view, but taper markedly towards the snout in dorsal or ventral aspect. These animals are yet another reminder that restoring fossil animals needs more than a lateral view of a skeleton: those massive skulls are considerably narrower than we might expect. Their teeth are thecodont, large, serrated and recurved. A characteristic of the group is the complicated shape of the upper jaw, where the jaw tip is vertically displaced from a ventrally bowing maxillary region (Parrish 1992), creating something of a 'notch' towards the front of the jaw. Beneath this, the mandible has a slightly dorsoventrally expanded tip, as well as a swollen posterior region. At least the skull of Erythrosuchus is essentially akinetic, although minor movements of some bones may have been possible (Gower 2003). Although erythrosuchid skulls are fairly conservative in morphology, some species were not above frivolous accessorising: prominent bosses above and below the eye are known from Garjainia madiba (Gower et al. 2014 - see reconstructions, above), and Pickford (1995) reports a long, low boss on the snout of an undescribed Karoo Basin specimen.

Although erythrosuchid skulls were almost certainly pneumatised in some areas, the largest opening in the skull is not, as we might expect in such large headed animals, anything to do with a pneumatic cavity. Rather, it's the lower temporal fenestra, an opening typically associated with allowing bulges of the jaw adductor muscles. This, as well as the presence of a small sagittal crest between the superior temporal openings (which overly the same muscle block) and the depth of the posterior mandible likely betrays the presence of massive adductor muscles in temporal region of the skull. Eryhtrosuchid skull bones certainly look sufficiently robust to withstand powerful biting, the bones forming the temporal fenestra, jaw and orbital margins being extremely massive and thick and tightly interlocking with complex sutures between each bone. Interestingly, Shansisuchus has the same partly invaded orbit shape that Henderson (2003) linked with reinforcement against heavy bite forces in theropod dinosaurs: perhaps similar buttressing was taking place in these Triassic reptiles

The dorsal extent of the occipital face in Eryhtrosuchus africanus, posterior view. The rounded flanges at the top poke above the rest of the skull, and perhaps indicate expanded neck muscles in this and other species. From Gower (2003).
The posterior surface of the skull is interesting. Rather than the relatively flat surface we see in most animals, the posterior erythrosuchid skull is recessed so that several aspects of the skull - the jaws and lateral extents of the occipital surface - extend further back than the vertebral/skull joint. The area which anchored the neck musculature extended across this recessed surface, even exceeding the dorsal margins somewhat by means of a pair of semiscircular flanges projecting above the rest of the skull (visible in at least Erythrosuchus and Garjainia - see above). Assuming a typically reptilian muscle plan, these indicate that muscles anchoring above the skull-neck articulation were larger than usual, as might be expected for animals with ginormous heads. Similar dorsal expansion of the occipital region is seen in tyrannosaurids, and is also thought to reflect large cervical musculature (Paul 1988). It thus seems the vertebrae and posterior skull of erythrosuchids were deeply buried in neck tissues, befitting animals with a giant head to support and utilise in predatory acts. But I wonder if all this support and strength compromised the mobility of the skull-neck joint somewhat. Moving the neck articulation forward to sit within the boundaries of the skull likely shortened the length of the skull flexor muscles, as well as buried the joint in masses of potentially restrictive muscle and bone. Motion of the head may have been limited at the front of the neck, then, but unfortunately for erythrosuchid prey, the size of the shoulder skeleton and stoutly built humeri suggest this was accounted for with powerful muscles at the base of the neck, as well as forelimbs able to shove the forequarters around at speed. Dashing left or right against a charging erythrosuchid was unlikely to save you from a nasty, gigantic and powerful bite.

Behind the skull we see a fairly typical Triassic archosauriform body (below). The neck is short, and especially so in some of the larger species, and the majority of the vertebrae are adorned with tall neural spines: these almost certainly provided anchorage for axial musculature related to supporting the head and back. The pectoral elements, which are also employed somewhat in neck musculature, are also robust. Their tails are moderately long, with deep chevrons in the anterior region likely related to hindlimb musculature. Behind these, the tail becomes rather slender. Gower (2001) proposed that Erythrosuchus vertebrae possessed pits and depressions possibly related to the development of post-cranial pneumaticity, the first found outside of pterosaurs and dinosaurs. This would be a significant find, telling us something of erythrosuchid lung structure as well as the early evolution of postcranial pneumaticity in archosaur-line reptiles. However, both O'Connor (2006) and Butler et al. (2012) argued against this interpretation, noting that the features in question were not associated with internal cavities, thus failing to meet criteria for structures of pneumatic origin. An important caveat to this, however, was raised by Butler et al. (2012): the phenomenon of pneumatic tissues invading vertebrae and other postcranial bones almost certainly did not evolve in one swoop. Its earliest stages may have simply been pneumatic tissues 'pushing' against external bone walls, forming pits and cavities, rather than invading them entirely. If so, the sort of thing Gower (2001) found in Erythrosuchus might be what we'd expect of early stage, postcranial pneumaticity. So while we have to concede that these structures do not meet our current definition of a postcranial pneumatic structure, perhaps we also need to learn more about the early evolution of postcranial pneumaticity before this hypothesis can be ruled out entirely.

Mounted Garjainia prima skeleton as mounted at the Paleontological Institute, Moscow. Certain aspects of this skeleton are reconstructed or sculpted, so take some details with a pinch of salt. From Ivakhnenko and Kurochkin (2008).
The limbs of erythrosuchids are not, to my knowledge, completely known from any species but their major limb bones are powerfully built and surprisingly lengthy: you could never call them 'long-limbed', but they are not the stumpy-legged animals we often see them reconstructed as. Their hands and feet are poorly known. Rare examples of erythrosuchid ankles are thought to indicate an mesotarsal condition (Gower 1996), and their pelves show signs of advanced features that we see developed further in true archosaurs. These features led to our G. madiba reconstruction having semi-erect hindlimbs, while the forelimbs remained sprawling. The typical pose of erythrosuchids remains to be determined from further study of their limb bones.

A point of contention among researchers is whether or not erythrosuchids had osteoderms. Two examples of such structures have been found in association with a specimen of Erythrosuchus, but they show no consistency in their morphology (Gower 2003). Moreover, the extensive inventory of Erythrosuchus and other erythrosuchids have yet to show additional evidence of dermal bones (Ezcurra et al. 2013). The safe bet, for the time being at least, is to assume these reptiles did not have osteoderms, and that those previously referred to the group were a fluke association from another animal.

The life and times of Triassic big-heads

We have much to learn about many aspects of erythrosuchid palaeobiology: details of their dietary preferences, locomotor mechanics and likely habitats remain only provisionally researched. Much of what we've learned about their lifestyles comes from 'bigger picture' assessments of Triassic diversity and faunal turnover, so we can only paint a broad-brush picture of their ecology at this time. That's not to say we have no specific palaeobiological insights into these animals, however. For instance, there is consistent histological evidence that erythrosuchids grew quickly, perhaps at rates comparable to pterosaurs and dinosaurs, until they reached reproductive maturity (de Ricqlès et al. 2008; Botha-Brink and Smith 2011; Ezcurra et al. 2013). Given that this trait is not limited to erythrosuchids among Early and Middle Triassic reptiles, this is one reason it's thought that archosaur-line reptiles may not be ancestrally ectothermic. Whatever the cause, rapid growth may have played some role in the success of erythrosuchids and other reptiles as ecosystems were rebuilt in the early Mesozoic (Sookias et al. 2012).

Erythrosuchid ecology remains only lightly investigated, but they have been considered arch terrestrial predators by some (Sennikov 1996 - see below). Interestingly, their size puts them among the largest terrestrial animals known from their respective faunas (Sookias et al. 2012). This is unusual: in post-Middle Triassic ecosystems we generally find herbivores are the largest animals in terrestrial ecosystems, so what's going on here? It's thought that physiological distinctions between large Early-Middle Triassic reptiles and the synapsid herbivores they coexisted with may explain the size difference (briefly summarised, archosauriform growth rates and respiratory anatomy may have permitted larger overall body size than therapsids - see Sookias et al. 2012), but how did this translate into ecological balance? Energy is lost as it is transferred between species in food webs, so how did populations of relatively 'giant' top-tier erythrosuchids sustain themselves on consistently smaller prey? Perhaps they were simply comparatively rare, or very energy-efficient, or maybe they supplemented their diet with non-terrestrial food items - did they also take food from aquatic realms, perhaps?

An Early Triassic terrestrial food web, reconstructed for the Yarenga Formation by Sennikov (1996). In this scheme, most things ended up in the bellies of erythrosuchids or rausuchians.
Speaking of aquatic habitats, the concept of erythrosuchids as strictly terrestrial predators is not the only interpretation of their habits. Indeed, for much of the 20th century erythrosuchid proportions were considered evidence of aquatic or semi-aquatic habits: their huge heads and robust limbs were thought to permit only cumbersome, laboured movement on land (see Ezcurra et al. 2013 for a brief review). The words offered by Reig (1970) paint an excellent summary of these older interpretations: "We doubt that bulky and clumsy animals like Erythrosuchus and Shansisuchus should be considered very active animals... It is more likely that they were inhabitants of swamp marshes, able to prey upon big, slow herbivorous vertebrates, inhabiting the same environments, which could be caught by a relatively slow and heavily built predator" (p. 261). Potentially further evidence of semi-aquatic lifestyles are the relatively thick limb bone walls common to all erythrosuchids, these being comparable in thickness to those of modern alligators (Botha-Brink and Smith 2011; Gower et al. 2014).

In recent years, however, erythrosuchids seem to have been perceived as more terrestrial animals (Sennikov 1996; Botha-Brink and Smith 2011; Ezcurra et al. 2013). Their thick bone walls are explained as being a consequence of their large size rather than aquatic habits (Botha-Brink and Smith 2011) and the deficit of obvious aquatic adaptations in their skeletons has been noted by several authors (Botha-Brink and Smith 2011; Ezcurra et al. 2013; Gower et al. 2014).

Aquatic, semi-aquatic or fully terrestrial? This guy's meant to have taken a dip in the water, but was it intentional or accident? We may not have the data to say exactly what erythrosuchids did for a living yet.
All this said, I must admit to desiring more work in this area. The habits of strange Triassic animals are difficult to fathom in many instances, and we're yet to see particularly comprehensive assessments of the most basic elements of erythrosuchid functional anatomy, let alone application of modern techniques like isotope analysis, stress modelling of jaws and so on to this problem. My gut feeling - and thus in no means a basis for a hypothesis - is open to both interpretations of erythrosuchid habits, and I wouldn't be surprised if terrestrial and aquatic prey were on their radars. I'm suspicious about the weight of the head being a problem for terrestrial locomotion. A decade of looking at terrestrially-competent, large-headed pterodactyloid pterosaurs and recent monkeying about with mass fractions of giant-necked Tanystropheus suggest our intuitive grasp of front-heaviness might be poorly calibrated. Animal heads and necks are often much lighter than we think in contrast to torso and limb masses, and we should remind ourselves that erythrosuchid skulls are actually quite narrow, presumably well-pneumatised structures. This is the sort of thing that can be relatively easily investigated using digital models, and we might hope this approach is applied to erythrosuchids in future. But if that supports a terrestrial habit, the notched upper jaw and swollen mandibular tip of erythrosuchids argues contrarily: similar jaw tips are seen in fish-eating animals like modern crocodylians and pike conger eels, as well extinct presumed fishers such as spinosaurids and some pterosaurs. Might this not imply that small swimming animals were sometimes eaten by erythrosuchids, too? Lest we forget, animals do not necessarily need to be dedicated swimmers to be able to eat aquatic prey. There's a lot of scope for further work and investigation here, and it would be great to see some dedicated functional assessments and ecological investigations of erythrosuchids in future.

I love it when a bauplan comes together

Perhaps one of the most interesting things mentioned recently about erythrosuchids is how little their postcrania differs from those of other archosauriforms, despite their substantial cranial modifications (Ezcurra 2016). This is something we see again and again in Triassic reptiles: relatively conservative bodies with highly localised outlandish anatomy, and is true even for the weirdest Triassic creatures. For example, Tanystropheus isn't that strange aside from its incredible neck, and (what we know of) the body of Sharovipteryx is not that atypical in spite of its leg-wings. I wonder if Triassic animals get the short shrift in popular circles because they're viewed as boring 'also rans' taxa which evolved strange, untenable anatomies but without moving too far from a typically 'reptilian' visage.

But perhaps what we're seeing with these animals is far more interesting than it first appears: a display of the intrinsic adaptability of the archosauromorph bauplan, and how applicable it was to many lifestyles with only localised modification. We can be particularly impressed with erythrosuchids because of their rapid evolution so early in the Triassic: they very quickly and successfully jumped into the niche of large, hypercarnivorous apex-predator after the end-Permian extinction event, and then held that niche worldwide for 12 million years. The fact they did so without much additional modification to the postcrania is evidence that their success was not a fluke, and that the basal archosaur-line body plan was a strong one. Perhaps instead of looking at erythrosuchids and other Triassic archosauromorphs as those strange, but ultimately dull animals that struck it lucky before the more successful ones took over, we might view them as some of the earliest evidence that the archosaur-line bauplan had real potential, and a sign of what was to come.

Big blog posts about big headed reptiles need big support - thank goodness for Patreon

The paintings and words featured here are sponsored by a group of tetrapods with more modestly proportioned skulls, my Patreon backers. Supporting my blog from $1 a month helps me produce researched and detailed articles with paintings to accompany them, and in return you get access to bonus blog content: additional commentary, in-progress sneak-previews of paintings, high-resolution artwork, and even free prints. For this post, we'll be looking at the history of the painting up top, documenting its long 2-year journey from illustration to, er, a more detailed illustration. I'll also share the bizarre, sausage piglet monster version of Garjainia that you were never meant to see. Sign up to Patreon to get access to this and the rest of my exclusive content!

References

  • Botha-Brink, J., & Smith, R. M. (2011). Osteohistology of the Triassic archosauromorphs Prolacerta, Proterosuchus, Euparkeria, and Erythrosuchus from the Karoo Basin of South Africa. Journal of Vertebrate Paleontology, 31(6), 1238-1254.
  • Butler, R. J., Barrett, P. M., & Gower, D. J. (2012). Reassessment of the evidence for postcranial skeletal pneumaticity in Triassic archosaurs, and the early evolution of the avian respiratory system. PloS one, 7(3), e34094.
  • de Ricqlès, A., Padian, K., Knoll, F., & Horner, J. R. (2008). On the origin of high growth rates in archosaurs and their ancient relatives: Complementary histological studies on Triassic archosauriforms and the problem of a “phylogenetic signal” in bone histology. In Annales de paleontologie (Vol. 2, No. 94, pp. 57-76).
  • Ezcurra, M. D., Butler, R. J., & Gower, D. J. (2013). ‘Proterosuchia’: the origin and early history of Archosauriformes. Geological Society, London, Special Publications, 379(1), 9-33.
  • Ezcurra, M. D. (2016). The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4, e1778.
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  • Gower, D. J. (2001). Possible postcranial pneumaticity in the last common ancestor of birds and crocodilians: evidence from Erythrosuchus and other Mesozoic archosaurs. Naturwissenschaften, 88(3), 119-122.
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  • Henderson, D. M. (2003). The eyes have it: the sizes, shapes, and orientations of theropod orbits as indicators of skull strength and bite force. Journal of Vertebrate Paleontology, 22(4), 766-778.
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  • Paul, G. S. (1988). Predatory dinosaurs of the world: a complete illustrated guide. Simon & Schuster.
  • Pickford, M. (1995). Karoo Supergroup palaeontology of Namibia and brief description of a thecodont from Omingonde. Palaeontologia Africana, 32, 51-66
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