Thursday, 26 April 2012

Feathered Tyrannosaurids: In Defence of Scaly Dinosaurs

If Gideon Mantell was alive today and able to visit various museums throughout the world, then he would be amazed at how much the appearance of his beloved dinosaurs has changed over the years.  As he passed the various skeletons and reconstructions, he would wonder how on earth the appearance of creatures such as Iguanodon and Megalosaurus could have changed so much and probably the biggest shock to him would be the reconstructions of dinosaurs with feathers – feathers! 
Think about it. How difficult would that be? To Mantell, dinosaurs were simply overgrown cold blooded lizards and, with the knowledge that was available at the time, this was a pretty reasonable assumption. They were seen as great ponderous reptiles, covered in scales, plodding around in the primordial swamps that routinely fought for their lives with tooth and claw. Feathers would never have crossed his mind.
We now know, of course, that Mantell, and all the other early workers, were a long way from the truth although we must also recognise that Richard Owen pointed out that dinosaurs were remarkably bird-like at a very early point in his initial studies. Even after the discovery of Archaeopteryx, feathered dinosaurs were a long way away even though various palaeontologists over the years highlighted the possible relationships between birds and dinosaurs. Without significant evidence of feathered dinosaurs, the majority of palaeontologists, and certainly the general public, recognised the dinosaurs as giant scaly reptilian superstars of the Mesozoic.
However, our perception of dinosaurs has changed. We used to think of sauropods as huge swamp dwellers, theropods as relatively slow moving cold blooded killers, stegosaurs with the brain the size of a walnut and a multitude of other stereotypical analogies. We were all pretty comfortable with this image throughout the twentieth century and dinosaurs remained this way in our minds for a very long time.
But the Renaissance changed all that.  Sauropods became fully fledged terrestrial animals, theropods became swift and agile hunters while stegosaurs were suddenly able to turn on a sixpence and keep their flailing tail spikes in the face of their aggressors. Suddenly, other dinosaurs too became active energetic animals and the possibility that they were warm blooded really gathered momentum. The bird/dinosaur link was again brought to the fore and Bob Bakker reconstructed Deinonychus with integument suggesting that they had probably already developed feathers and that we should expect to find fossils of dinosaurs with such a covering. How prophetic that was!
During the nineties, the superb fossil localities in China burst onto the scene and we were (and continue to be) thrilled by each and every new specimen that is announced to the world.  These specimens are truly remarkable and confirmed, once and for all, that birds are indeed living dinosaurs and, despite the various protestations of creationists and a few fringe scientists who continue to deny the truth, there can be no doubt as to the bird’s dinosaurian origins.
So far, so good but there has been a casualty in this race to the truth and that is the humble dinosaur with traditional reptilian scales. It appears that nearly every dinosaur is now being looked at for traces of feathers. For example we now have basal ornithischians and basal ceratopsians sporting fuzz, quills and bristles.  Every fossilized skin impression is being screened for any signs of a covering that might be considered of feathered origin. This is not a bad thing, of course, but there is now a trend to cover every dinosaur in feathers even if there is only inferred phylogenetic evidence and no physical trace.
Now I am not a “feather denier” – far from it – but I have to admit to a certain sadness as the scaly dinosaurs that I grew up with have slowly been eroded down to almost being of no consequence and of no interest. Brian Switek, amongst others, suggested (tongue-in-cheek I hasten to add) that people such as myself should quit whining and get on with it but they misjudge us.  
Those of us who like our dinosaurs scaly appear to be frowned upon – as if we don’t know what we are talking about and that we really ought to “get with it” and rejoice that the dinosaurs are covered in fuzz and feathers. Well that isn’t going to happen – certainly not by me and, I am sure, not for many others.
Again I reiterate that I am just as fascinated with feathered dinosaurs as any of you but I do feel a tinge of sadness every time another scaly lineage is consigned to the palaeo- rubbish bin. And now we have the impressive Yutyrannus and this one is just another step closer to assaulting that bastion of awesomeness – Tyrannosauridae.

I’ll be blogging properly about Yutyrannus at some point in the future but for now let us consider the one important factor about this interesting tyrannosauroid – its size. One of the considerations that many of us have been hanging on to with regards to tyrannosaurids not sporting feathers was size. It seemed likely that big tyrannosaurids may sport integument when they were young to add a protective insulation to their smaller bodies. After a while they would gradually lose this covering as they became adult animals to become fully loaded scaly tyrannosaurs. This was a get out clause for us whilst, at the same time, also accepting that feathers may have been involved at some point during ontogeny.


Yutyrannus has changed all this, and at nine metres long and approaching 1.5 tonnes in weight , is certainly not small and the fact now is that some big tyrannosauroids did indeed display a feathery /fuzzy covering and that the larger, more derived tyrannosaurids are now coming into range. My heart sinks at the thought.
Of course, Yutyrannus is still a basal tyrannosauroid and still possessed fairly large forelimbs with three large clawed digits as opposed to the more derived and reduced sized two digits of tyrannosaurids. It is also Barremian in age (Early Cretaceous – 125 million years old) and was alive at least 40 million years before the appearance of Tyrannosauridae proper. Despite this, and in a phylogenetic context, there is a real chance that proper tyrannosaurids may have at least been partially covered by integument of some form.
We scaly supporters will hang on the fact that Tyrannosauridae is still free of feathers – as far as we know of course. This may very well be a sampling bias since the Liaoning deposits represent a lacustrine environment with very fine sediments that aided superb preservation whilst the traditional tyrannosaurid beds of North America are not.  Still, Tyrannosauridae remains an untouched bastion of scalyness - but the walls are certainly crumbling.
Perhaps I can best put it this way.  The T.rex in Dinosaur Revolution was awesome. But anybody who saw the dancing Gigantoraptor sequence in Dinosaur Revolution can be left in no doubt – is this the kind of thing you want to see a T. rex perform? Do you really want the ultimate theropods, the megastars of the dinosaurian world - the tyrannosaurs - displaying colourful yet gaudy feathers and dancing like a demented turkey cock?
I think not. Like I said – I know the feathered phylogenetic tooth fairy is rattling the front door of Tyrannosauridae but at least let us enjoy the time that is left for our magnificent fully scaled heroes. And if not, there will always be the ankylosaurs…….

21 comments:

Daniel Permutt said...

What if (big if) Tyrannosaurs DID dance around like demented turkeys? Should we bury our heads in the sand and pretend it didn't happen/hope it goes away? ...Yes.

Anonymous said...

Yutyrannus only vitiated the view that large animals must somehow of necessity evolve to lose their insulating cover. Apart from that, it tell us nothing we didn't already know: of course basal tyranosaurs had feathers.

Bruce Mohn said...

Hi Mark:

I feel your pain and definitely sympathize. Sadly for those of us who like the image of theropods with scales (there are a few undeniable scaley theropod fossils out there), the evidence is leaning heavily towards more and more of them being feathered. And while there is not yet direct evidence for feathers in tyrannosaurs, there is a suggestion. I have seen a patch of skin impression from a Tarbosaurus. It is covered with small bumps, about the size of the bumps on a basketball, but not so well defined that they can be definitively said to be the dinosaurian conical, non-overlapping scales. I have seen something similar in birds. Many owls have feathered feet, but if you blow the hair-like feathers back, there are very tiny scales beneath them. I have wondered if that Tarbosaurus skin is analogous to the skin on owl feet?

Mark Wildman said...

Thanks for the comments everyone. It's just a personal thing really and that's the point I was emphasising - I like 'em scaly!

Bruce - thanks for the information about the Tarbosaurus specimen. I would really like to see that at some point.

protohedgehog said...

Well-balanced post Mark! I agree on many points, but at the same time, we can't let our feelings get in the way of what specimens are [potentially] telling us. However, I do think that we, as scientists, need to be more rigorous in conveying to people what is observed, and what is inferred. When feathers are not preserved, it boils down to a question of form and function, so will always be guess work (inference, sorry) until this is better understood in a form-through-time context.

Were bigger tyrannosaurids feathered? It's difficult to say with confidence at the moment. The future is exciting though!

Andrea Cau said...

I agree with Bruce.
We must recognise that feathers are not a bird-like feature we must force in our vision of tyrannosaurs (or other dinosaurs), but a DINOSAURIAN FEATURE, simply a dinosaurian trait as the erect gait (once believed a "bird-like feature"), the elevate growth rates (once believed a "bird-like feature"). The feathers are a dinosaurian tegument, not a birdy coverage for something we have called "a reptile" and thus "a scaly animal". At the same time, I'm beyond the simplicistic "scaly vs feathered" dichotomy: dinosaurs probably can be placed along a spctrum of "scaly-featherness", with most taxa showing an intermediate mixture of the two teguments, exacly like plesiosaurs are not simply pliosaurs vs pleiosaurs but a continuum of plio-plesiosaurian morphologies. It's plausible that ankylosaurs and paravians were the extreme of the continuum, and everything, including Tyrannosauridae, were somewhere inside the continuum. Thus, scaly must not be abandoned at all.

Gorgosaurus said...

I quote you "Sauropods became FULLY FLEDGED terrestrial animals" - get ready, Mark!
Spike.

Mark Wildman said...

*cough* thanks for that Spike!!!

Jon - thanks for the comments. In this instance getting the balance right is always problematic but always good fun.

Andrea - FANTASTIC comments! Thanks very much indeed.

Niroot said...
This comment has been removed by the author.
Niroot said...

I love Andrea's comment. I don't think it could be put much better than that. :)

But I enjoyed your post, Mark. And to show that I do sympathise, I confess I shall be very sorry to find that sauropods and hadrosaurs turn out to have been fuzzy after all. ;) Happily, we do have fossilised scaly skin of the latter. ;)

(Earlier comment deleted due to typo!)

Henrique Niza said...

Even though I don't necessarily share your concerns Mark, I can definitely see where you're going with this. I too grow-up with scaly dinosaurs and when I think in T. rex I picture the Jurassic Park model, but I have always "cheered up" for integument as basal to either dinosaurs or Ornithodira.

Still the largest Yutyrannus specimen is 4 times smaller than the largest Tyrannosaurus rex, maybe more and even though it most certainly was entirely covered in feathers the evidence yet doesn't disprove it might have been partly covered instead.

Gorgosaurus said...

Yes, Andrea nailed it - that is a quote-worthy comment.
Spike.

Dracontes said...

You'll have a long mourning process to go through I'm afraid. I can add that naked skin patches have been found for Gorgosaurus ( http://dml.cmnh.org/2011Sep/msg00123.html ) and possibly scales.
In my case, I guess I'm more interested in making predictions as to what future finds will be without that much regard for the outcome. True, my bet is that feathers are a basal character for Ornithodira but I'm not making it one excluding scales as I do recognize by observation that they indeed aren't mutually exclusive ( http://dracontes.deviantart.com/art/Chicken-s-Ankle-142472886 )

I think the poorest argument you put forth above is using fiction (Dinosaur Revolution) as an example of how an avian behavioural repertoire to go with the feathers is detrimental to our image of the animals.
Honestly, I'm fed up with the cinematographic depiction of dinosaurs so I for one welcome our feathered, silly-walking overlords. I'd go so far as to propose that display behavior that to us looks silly is an evolutionary advantage, if various bony correlates (crests, horns, sails) are anything to go by: it would avoid serious injury, allowing animals to decide things more amiably and thus each having more shots at reproduction.

Andrea Cau said...

Thanks for the comments on my comment, and sorry for the typos or the grammar errors of a non-english commenter that forgot to review his words before publishing them. :-)

Mark Wildman said...

Thanks for all the comments everyone!

@ Dracontes - The Dinosaur Revolution reference was not meant to be taken too seriously. But I maintain that the Gigantoraptor sequence is pretty grim - makes me squirm! But thanks for the link - some very cool images that help blur the point where scales end and feathers begin even further.

Niroot said...

@Mark: anent Gigantoraptor sequence from Dinosaur Revolution, I know you weren't so serious with your comment, but I think the makers were aiming squarely for comic effect with that one. I'm afraid I didn't like it much either. I recommend the Gigantoraptors in Planet Dinosaur for a far superior, dignified, convincing and even beautiful bird-like display sequence.

Hadiaz said...

"We scaly supporters will hang on the fact that Tyrannosauridae is still free of feathers – as far as we know of course."

Cheer up, Mark. There are still the facts that "there are a few skin impressions of Tyrannosaurus and they show that it was scaly" ( http://www.amazon.com/Natural-History-Museum-Book-Dinosaurs/dp/184442183X/ref=sr_1_1?s=books&ie=UTF8&qid=1325974924&sr=1-1 ) & that (unlike T.rex) Yutyrannus lived in a cold climate. Besides that, Henrique Niza already pointed out the large size difference btwn T.rex & Yutyrannus. In other words, an adult T.rex would've only been partly feathered (if at all).

"Do you really want the ultimate theropods, the megastars of the dinosaurian world - the tyrannosaurs - displaying colourful yet gaudy feathers and dancing like a demented turkey cock?"

I would think that only maniraptorans (& flamboyant humans) performed dances like that, given the use of true vaned feathers in said dances.

"I recommend the Gigantoraptors in Planet Dinosaur for a far superior, dignified, convincing and even beautiful bird-like display sequence."

I concur. The Gigantoraptor episodes of PD are my favorites.

BTW, I really like that Skrepnick painting.

-Herman Diaz

Alessio said...

Another great article!

And i also agree with Andrea, feathers were probably widespread among dinosaurs with varying degrees depending from the species, enviroment,etc.

Speakin' about my favorite theropod family, i like to think that maybe the northern tyrannosaurids had a much thicker coat of protofeathers than their southern cousins, which lived in a warmer climate... NOT that the latter had less protofeathers, bear in mind, but shorter or something along these lines (it comes to my mind an' armadillo's armor, with hair inbetween the scales).

What do you think?

Mark Wildman said...

Thanks for the comment Alessio. What you suggest may be entirely possible. Even a short, sparse covering, as you describe, can indeed make for reasonable insulation and also help to retain moisture.

I think what all of this confirms is that fuzz and feathers evolved independently several times over for different reasons within different groups of dinosaur.

The humble reptillian scale was quite an evolutionary achievement when you think about it.

Anonymous said...

nice posting.. thanks for sharing.

Mark Wildman said...

It's a pleasure - thanks!

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