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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. Half-boxes represent doubtful records of true feathers. Compiled from various sources - thanks to blog commenters for pointing out some omissions in a previous version.
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.

32 comments:

  1. Great post! The ornithodiran integument chart is an excellent reference, though it seems to be missing a few data points, most strikingly the scales of Concavenator (and allegedly Allosaurus). The body feathers of ornithomimids were reported as filamentous in the original description of Zelenitsky et al., and scales appear to be present underneath the tail of Scansoriopteryx and on the foot pads of dromaeosaurids (namely "Dave" the juvenile Sinornithosaurus).

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    1. Alby beat me to this one. I'd also like to add to it that whatever you give Ornithomimosauria, you have to give Tyrannosauroidea. Dilong's feathers are almost identicle to those of Ornithomimus, being "stage III" (Prum) in form.

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    2. Doesn't Ornithomimus have evidence for some form of pennebrachium, for which we currently lack evidence in Tyrannosauroidea?

      Note that the scales of Concavenator are located only on the underside of the tail and on the feet, and the mere preservation of scales on the tail and feet does not rule out filaments elsewhere (e.g. Kulindadromeus, Juravenator, and birds). I wouldn't really consider scales preserved in those regions to inform the debate at hand much.

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    3. @John: I don't expect the omissions to add to the debate, but considering scales were marked for birds on the chart based on their feet, I see no reason the others shouldn't have been included.

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    4. I missed these comments when they were first posted guys - thanks for noting the omissions! I'll update the chart above.

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  2. Wonderful post, and exactly the kind of back-and-forth I had when I used to art things. Ultimately I come down on the side of being overly conservative--I found myself nodding in agreeing with Mark Squared, but I can't deny that Mark Prime has good arguments as well.

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  3. Great stuff!
    The vulture-ish cape/neck doesn't appeal to me on Plateosaurus, but I love self-discussions generally... and this one in particular.

    Note: 'inaruably supported by Patreon'?
    unarguably? in a rugby?

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  4. Nice take, I think we all have these internal dialogues. I agree with a lot said here - my take on this topic is that you have to give people a little permission to make mistakes.

    On a related note I am surprised more people are not discussing that SVP2016 talk on soft tissue is theropods... and no I am not referring to Reisz, but another talk that flew a bit under the radar. But it more profoundly stretches the possibility for what many large theropods looked like: The Soft Tissue of the Dorsotemporal Fenestra and its Significance for Dinosaur Biology. Holliday et al.

    Basically at the end of the talk he admonished us to decorate the head of T. rex (and other large theropods) with snoods, wattles, dewlaps and other skin derived display structures. He left out caruncles - everyone seems to hate caruncles for some reason.

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  5. Great post Mark. I'd like to add a little something to the debate if I may.
    As Andrea Cau has said on his blog a couple times, especially in a large blog post, the "uber scaley" Carnotaurus isn't justified, and a far more "shaggy" Theropod along the lines of larger sized Coelurosaurs is far more likely:
    http://translate.google.com/translate?u=http%3A//theropoda.blogspot.com/2016/03/miti-e-leggende-post-moderne-sui.html&hl=en&langpair=it|en&tbb=1&ie=utf-8
    With this in mind, from what we know, Theropods were very fluffy by default, so basal Sauropodomorphs could easily be as well.

    The next thing is the fact that known skin impressions are mummified and preserved in acidic sediment. Acidic sediment is, put quite bluntly, soil that has high acidic content due to decaying plant matter, dung, and other decaying nasty stuff. Here's the thing; to my knowledge, most if not all traditionally "scaley" Dinosaurs have been preserved in acidic sediment. In actuality, the sheer fact that these remains of scaley Dinosaurs are mummified shows how fiborous integument is near impossible to be found in these specimens. The acidic sediment that destroys fiborous integument, along with the sheer mummification process of which involves the drastic dehydration of the skin, does not allow integument to preserve readily. Hence why not a single piece of physical evidence of feathers in any mummified skin/scale remains have been found. Saying that these ancestrally feathery animals somehow completely lost such a feature is honestly absurd. Look at mammals. Even animals who don't need fur what so ever still possess fur simply because their ancestors had them. Whales, Hippos, naked molerats, etc. No use for them, or at least not any major use for them what so ever. This is because there is no need to completely get rid of such a minor feature of the body if it does not negatively affect said organism. Growing said hair takes up very little bodily energy to grow and maintain, so why get rid of it? That's simply wasted time and energy to get rid of it over generations. If this is true for a highly diverse group of ancestrally fuzzy animals today, then why not the extinct equivalent? Andrea Cau made a post about this as well:
    http://translate.google.com/translate?u=http%3A//theropoda.blogspot.com/search%3Fupdated-min%3D2013-01-01T00%3A00%3A00%252B01%3A00%26updated-max%3D2014-01-01T00%3A00%3A00%252B01%3A00%26max-results%3D50&hl=en&langpair=it|en&tbb=1&ie=utf-8

    That's all I have to say, though I'd love your feedback Mark!

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    2. Yes, but Mark's point about feathers not popping up through or between scales still stands. Any section of skin that features scales probably did not sport feathers. The point about whales, hippos, and mole rats is a good one, though. I would be surprised if hadrosaurs didn't have some isolated "whiskers" SOMEWHERE on their body, but nothing more extensive than what you'd see on the mammals you mentioned.

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    3. Does that give room for woolly variants of usually-scaly dinosaurs, like the fluffy Pachyrhinosaur? Analogous to elephants vs. mammoths. Like the feathers are ancestral, the gene has been suppressed but is still there and may pop up in the fenotype if the environment or some other evolutionary factor calls for it. I've seen reconstructions of fluffy arctic Ugrunaaluk, a close relative of the very definitely scaly-all-over Edmontosaurus.

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    4. Worth pointing out is that whales, mole rats, and hippos are quite heavily specialized. Two are aquatic or semi-aquatic and mole rat live underground and huddle together if exposed to cold. Sauropodomorphs probably didn't live in water, underground, or in eusocial colonies where they could huddle for warmth.

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    5. So a more apt comparison may be something like elephants, rhinos, mammoths, gaur, giraffes, ground sloths, cape buffalo, bison, etc, which really gives a lot of range as to how much integument and of what kind.

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    6. @Andrew Raymond, as Matthew Martyniuk has pointed on his blog, the scales of Dinosaurs are incredibly likely to be avian scales as in modern Birds. With that in mind, feathers growing in between these scales is possible if not likely in many circumstances. Owls and many arctic/cold weather birds are great examples of this. Here's the blog post: http://dinogoss.blogspot.com/2013/09/youre-doing-it-wrong-dino-foot-scales.html
      With that in mind, TECHNIQUALLY speaking, even heavily scaley genera and species could in theory be highly feathered to down right wooly, though I'd expect this to be far more prevalent for arctic and cold weather species.
      @Pds3.14 Good point there. I just wanted to make people realize how even a near useless trait is often still present simply because it's an ancestral trait that's not giving a negative impact. This is only assuming feathers would be useless in these cases. This plays into what you were saying about the other better examples like Bovines, Elephants, Rhinoceros, etc. Feathers are still great at other things besides thermoregulation of course, so their presence for use in display/courtship, camouflage, protection, etc. also come into play. Hence why I think it's likely feathers were in one way or another present on every Dinosaur; from a near useless, basal trait like in whales, grand wooly coats for insulation, manes, quills, tail tufts, and much more.

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  6. Excellent summary of the major points in this debate! I've certainly had similar internal debates myself. I would like to add one more major point in favor of more feathered reconstructions: as the majority of dinosaurs are in clades which have only recently been shown to be potentially feathery, the proportion of paleoart depicting most dinosaurs as feathered is currently much smaller than the probability of those dinosaurs having feathers.
    Thus, depicting feathered prosauropods will make the distribution of different reconstructions more accurately represent the distribution of probable life appearances, whereas depicting more scaly prosauropods would have the opposite effect.

    The Barrett et al. paper has one major weakness as evidence for scaly Triassic dinosaurs, namely that the probability of a feathered dinosaur MRCA is sensitive to the condition in the outgroup. Of the twelve analyses which supported a scaly dinosaur MRCA, nine were based on the assumption that basal pterosauromorphs were scaly.

    I have to say I disagree with Andrea Cau on the distribution of scales in Carnotaurus (I've mentioned this on my blog before). My interpretation of Bonaparte et al.'s description of the scales is that Cau's assertion that the scales were from the underside of the animal were incorrect, and that anything more than a 'mane' of feathers would be going against the available evidence.

    All that said, though, many amateur paleoartists go too far in the direction of filamentous integument (the "feathered Edmontosaurus" case). This is also true of synapsids, for which I have seen amateur paleoartists deride even 'pelycosaur' art as not looking mammal-like enough!

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    1. I'm a little wary of the 'making up for lost time' reason, TBH, for the same reason as your last line. I can almost see a reverse-awesomebro attitude in that situation - art being derided for not being daring or bleeding-edge enough, rather than being derided because it shows murderaptors and 'Trex' in stoopid, floofy, scientifically-informed feathers.

      Almost two hundred years of (largely) scaled depictions vs two decades of (burgeoning) feathered dinosaurs? On the face of it, of course the fuzzy and feathered depictions are going to be outnumbered! I don't know if it's that simple, though. For one thing, I think you have to take into account what any given person is exposed to. For us old fogeys who grew up on 80s and 90s books, most of our conception of dinosaurs is going to be scaly - though perhaps those of us who stuck with our dino obsessions 'til now may be more informed and accepting of feathers. For those cotton-pickin' millenials (when they look up from their consarned smartphones, dagnabbit) I'd guess the weight of scaly 'saurs is still greater, but hardly what it once was.

      And that (somehow) brings me on to the other thing: the internet's doing it's job of connecting people and bouncing information and ideas around. We only had the illustrations in what dinosaur books were available, back then. These days we have excellent, up-to-the-minute palaeoblogs (suck-up quotient: almost completed) and social media - presenting articles like this and explaining projects like All Yesterdays - and even direct access to scientific papers. It all feeds online palaeoart communities, although I'm sure I don't need to tell you that! I don't dig through the likes of deviantart as often as I should, but I can see that enthusiasts are experimenting and exploring possibilities in palaeoart depictions, and it's all readily available to browse and view. Don't worry about it! It's already happening. ;)

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    2. "Reverse awesomebro"

      Reverse awesomebro doesn't exist1!1!!11 *proceeds to draw basal diapsids in full flight feathers.*

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    3. As for fuzzy pelicosaurs, I don't think there's reason to rule it out, but there is reason to use caution when depicting f.e. dimetrodon as being covered in fur. It's definitely quite speculative. While Spinolestes was only only 125 million years ago, extant mammals only share a common ancestor 220 million years ago, which means fur must have been quite developed already by that point.

      So I think furry pelycosaurs is within reason, but of course there's no good evidence of it.

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    4. Heh!

      After all my rambling, I think I've figured out just what worries me. It sounds too much like a previous palaeoart drive: to depict dinosaurs as bright and colourful as possible to make up for past decades of grey and brown plodders. My retinas are still buzzing from some of those results. Is it still seen as a good idea?

      I assume we're over the hump of terrible feathered depictions (famous last words) - that being taken out on poor ol' coelurosaurs - so less chance of more unusual clades buzzing retinas as the proverbial lizard-faced monsters in gorilla suits. So then, as you say, no reason to rule it out; but still, no reason it 'has to' be done, either.

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    5. Did Onychodontidans have feathers? We don't know, but we can't rule it out.

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    6. Warren JB, I agree with you about that concern. However, the overwhelming majority of professional/published paleoart remains on the scaly end of the scale, and it's that art which shapes public perception more than an amateur's deviantART account. So I think that despite amateurish overfeathering, paleoartists whose work reaches a wide audience should err on the side of fuzziness when deciding among multiple plausible reconstructions.

      Essentially, I think that erring on the side of over-feathering will do good by 'balancing out' lay opinions of dinosaur integument. Some people might have a casual interest in dinosaurs, checking out popular books and news articles on new discoveries and the like, but not often reading blogs such as this one, and those people's perceptions would be positively affected by a more feather-leaning generation of paleoart.

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    7. I'd tend to argue that we should teach the (genuine) controversy. I.E. show everything from all yesterdays levels of plausible-but-baseless over-feathering to plausible but conservative variants. Feathered spino? Maybe sometimes, but only what could reasonably be inferred, not evidence-denyingly feathered or evidence-denyingly scaled or featherless.

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    8. We know Permian synapsids had fur. Said fur might come from dicynodonts, so fur definitely appeared early on

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    9. Again, I'm thinking we should just start feathering basal Chordata.

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  7. One point which I didn't see argued and which left Barrett et al.'s study ultimately flawed is the effect an animal's size has on integument. Known scaled ornithischians are big, while known feathered ornithischians are small. Theropods follow the same pattern (except Yutyrannus, and some scales on small compsognath-grade taxa that could have been feathered elsewhere as in Kulindadromeus). There are other factors such as climate and taphonomy of course, but if you pretended only specimens that preserve integument preserved tibiofemoral ratios, you'd get a cladogram of probabilities very similar to Barrett et al.'s for the evolution of leg proportions.

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    1. Psittacosaurus is fairly small (smaller than a few feathered theropods) and Ornithomimus and Dakotaraptor are mid-sized, so offhand I would think the probability distribution would be different. That said, it'd probably be worth testing...

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    2. I don't think feathers can be compared to fur when it comes to square-cube law.

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  8. Considering scales in dinosaurs were more akin to those in birds, couldn't we have feathers growing from between scales?

    Also, Carnotaurus skin impressions are actually not that extensive-only a few patches on the shoulder and flank

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  9. I tend to see feathered prosauropods as looking like giant ratites with arms myself.

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