"How many angels can dance on the head of a pin?"
Can be rephrased as "how many T. rex scales can fit on the head of a pin?" That is the size of a millimeter and that is a little more than the average size of the T. rex "scale" documented in the recent Bell et al. (2017) paper that has got everyone flummoxed from here to kingdom come. Another visual is that more than 20 T. rex scales can be lined up across a penny. Take home point: these "scales" were small.
|From Bell (2017) Note the scale bars in C & E are 5 mm while the scale bars in G & H are 10 mm. |
These scales were minuscule!!
I think such dramatic issues of scale have been a bit washed over in the more hyperbolic proclamations of the scale loyalists: "Yes, we have won!! Good riddance feather nazi elves!!" versus the recalcitrant permutations of the suddenly defensive feather crowd; "This tells us nothing new"; "Taphonomy washed away the feathers"; "Maybe T. rex had a feathered petty-coat?" Now I don't mean to mock such ideas and criticisms on the part of the pro-feather contingent but one can't deny there has been a palpable shift in sentiment from mainly feathered to mainly scaled in tyrant lizards (and by extension other largish theropods). Ironically many of the charges leveled at "awesomebros" or JP stylized scale loyalists are now being charged at the pro-feather faction; clinging to an ideal; putting an aesthetic before data; emotional attachment etc. etc.
Things are definitely a bit more unsettled and chaotic than many are comfortable with. Which is something I have been highlighting for some time in this blog; things are going to be getting more testy; a bit more non-consenus; a bit more uncomfortable for some time before things start to simmer down. Most of all things are going to be getting a bit weirder.
And those Wyrex scales are awfully weird. As I highlighted at the top of the post they are ridiculously small. Mark Witton called it the "Revenge of the Scaly Tyrannosaurus" in his blog post on the topic. If this is revenge via sub-millimetere "scales" it is perhaps the most underwhelming revenge story ever told. Sorry, I've had pimples bigger than those scales. I mean they are freaking small?! What is up with them? To put the size of these scales in perspective they are approximately equal to gila monster scales - komodo dragon scales would dwarf them. For all intents and purposes T. rex adorned in these minuscule scales would look pretty much nekkid. Especially so considering the absolute lack of any larger feature scales, larger keeled scales, osteoderms etc etc. Now, jokes about the puny size of T. rex scales aside, I do agree with Mark Witton on major points - and I'm glad he made this jump - that naked hided tyrannosaurids are not only a defensible option, but a likely one. He also raises the pertinent question - again something that I've been clamoring for here for a while - that many larger traditionally feathered dinosaurs may have lost significant amounts of fluff upon attaining larger size (I do have some reservations on the osteological correlates for large facial scales that Mark seems to abide by but that is for another time). Another pertinent read is Andrea Cau's post on the subject. He makes some very valid and strong arguments, as he has for some time now, that taphonomy is key to a more detailed understanding of the nuances for feather, scale, "integument" preservation. Cau also raises issue with the strange shape and morphology of these scales - an observation I share and if you read the comments on his blog and know my history you can already probably guess where I am going in this piece … C-----A-----R-----U-----N------C…..
I don't know of any concrete studies linking scale size to body size but intuitively such a connection makes sense. I mean larger crocs have larger scales, larger monitor lizards have larger scales, larger boas have larger scales. That is just my off the cuff observations and I'm sure there are exceptions. But, generally speaking, scale size in a related group should get larger as the animals get larger both ontogenetically and in between related species. Did tyrant lizards break this pattern? Should smaller specimens have even smaller scales? Or are they all the same size regardless of size/species? The connection between scale size and body size both ontogenetically and between related species is probably a topic rife for potential studies.
*Turns out there are some studies linking scale size to body size. I went back and read the chapter of hadrosaur integument, authored by a certain guy named Bell, from the epic Hadrosaurs book from Indiana University Press and came across this gem which I will put here:
from A Review of Hadrosaurid Skin Impressions
"Scale morphology (especially scale counts) in modern squamates and crocodilians is typically conserved intraspecifically and is highly important in species identification (Spearman 1973; Brazitis, 1987; Hall, 1989; Cox et al., 1993; Charette, 1995; Branch, 1998). However, scale size (inferred by the inverse relation to number of scales) has been shown to vary positively with body size in some lizard species (e.g. Scleroporus, Ouferio et al., 2011). Similarly, body size (and hence, scale count) is variable both intra- and interspecifically among some squamates in relationship (both positive and negative) to Bergmann's Rule (i.e. body size decreases at lower latitudes or in warmer climates), which is correlated with minimum annual temperature and aridity (Sears and Angilleta, 2004; Oufiero et al., 2011). Despite these variations, scale morphology is one of the most reliable in the identification of extant squamates and crocodilians, especially in closely related species (Brazaitis, 1987; Charette, 1995). It is notable also that tarsal- and toe-scale patterns have been used successfully to identify individual species of extant avians, particularly raptors (Clark, 1972; Stauber, 1984, 1985; Palma, 1996)."
It is useful to note that the above paragraph is couched in a general discussion asking "can scales be used to identify individual hadrosaur species?". The promise for this sort of inquiry is great for hadrosaurs. For tyrannosaurids - as I will get into below - the promise for this sort of species identification based on scales is not looking as promising. But just for starters, who wants to venture a count on how many sub-millimeter sized scales covered a T. rex? What is the morphology of these scales? Any sort of repeating pattern? Architecture?
Are retro '90s Tyrannosaurs making a comeback? is a recent post by Paleo-King (Nima) on deviantart. While the general thrust of his piece is useful he makes a claim in the comments section that the various tyrannosaurid scale impressions are exactly the same as the well documented hadrosaur scales/mummifications. I do have to take issue with this comparison.
1) Extent of preservation. In hadrosaurids we have full on mummies that give us real life confident appraisals of where and how far scales occurred. So far in tryannosaurids we just have bits and pieces. Together these pieces suggest that "scaly" type integument is our most parsimonious appraisal for most of the body, if not all of it. But keep in mind that we as of yet don't have proof of "scaly" integument on the face and those persistent rumors of non-scaly neck displays in Tarbosaurus. Remember both crocs and birds have dispensed with scales on the face. Why? I'm not sure. It is interesting that both crocs and birds both have highly sensitive, tactile faces as well.
2) Size of scale and variety. While some hadrosaurs show scales on the millimeter range such as the Osborn "Trachodon Mummy" which are 1-5 mm and are described as "pavement scales" these patches of small scale are interspersed with regular patches of "feature scales" which are much larger at 5-10 mm. What we see in terms of scale variety in tyrannosaurids so far is quite limited to very small "basement" type scales of a size smaller than in hadrosaurs. Hadrosaurs both at a distance and up close would have appeared much more textured than tyrannosaurids based on what we know so far. Unless you have some super X-men levels of visual acuity tyrant lizards would have looked basically nekkid.
3) Architecture. Nima points to an obvious architecture in the scales of tyrannosaurids. I have to admit that I can't see it. Carnotaurus shows architecture in the regularity of larger 4-5 cm tubercles arising every 10 cm or so from a more "basement" size scale of 5 mm tubercles. Sauropod and hadrosaur scales show a more obviously repeating scale architecture than tyrannosaurid tubercles. What I see in the tyranosaurid tubercles is something of a much more random, haphazard pattern. Apart from a size threshold of about 1 mm for the tubercles I can't discern any consistency in size; some appear more than twice as big as others and shape - apart from being generally polygonal there is a wide variety of shapes. Some of the tubercles appear rounder; others ovoid; some taper to a point; some wrap around others; and some almost to appear to bud off into other tubercles. This is a far cry from the more standardized scale pattern of hadrosaurs, which are often in repeated hexagonal patterns. Additionally given the 30 square cm patch of ilium scales we can be pretty confident that there was no larger patches of feature scales or repeating rows of larger keeled scales/osteoderms as in Carnotaurus, titanosaurs etc etc.
*Update. looks like a spoke too hastily, Nick Fonsesca says that Tarbosaurus has some feature scales form the supplementary info and then there is this from the paper:
Although I could not see the feature scales pictured in the supplementary there is indeed some evidence for a more orderly pattern of tubercles on some tyrannosaurid specimens, although not from the Wyrex material. It is of note that these feature scales are from the abdomen. Can they in fact reflect a more basal state retained? (i.e. never became completely feathered). Things are always aflux!!
So are 90's tyrannosaurs making a comeback? Sort of, I would say, but not exactly. The lack of discernible rows of feature scales or keeled scales is an obvious departure from GSP tyrannosaurids or any sort of organized row of larger scales so prominent in 90's style GSp tyrannosaurids.
And here I have to admit a weakness of not trusting my own gut and capitulating to the whole shaggy T. rex visage that has come into vogue in recent years. I blame Saurian. No, just kidding, I jest just a bit. Some have construed some of my posts as an attack on Saurian game design or that saurian should be changed or whatever. I can't disagree more. In fact I feel a bit sorry for the development team at Saurian, they must get pestered by young dino obsessives all the time. Just leave 'em alone at this point!! If Saurian is wrong fundamentally in some ways I think - at this point - these potential errors should be preserved for posterity. It's always interesting and iluminating to look back on paleoart to see how thought and ideas have changed. Saurian can be a great time capsule for what the general thought was of this period.
I do feel a bit of edification in getting back to my gut feeling for my latest tyrannosaurid art, in which I went with mainly nekkid skinned tyrant lizards with some manes and petty-coats of filaments. Proud to say this was completed before the new data came in. Boo - ya!! No need for revisions here, folks! Who says intuition, gut feelings, and following your muse have no place in science!! First published March 23, 2017 Gaslighting the Dinosaur: Just How Weird Can Dinosaurs Get?
|Revelations by Duane Nash|
Another argument that I would like to weigh in on is why Yutyrannus would go fully feathered while similarly sized northern tyrants like Albertosaurus went nekkid in a climate that was presumably not too different in temperature. Not to discount some of the other suggestions but merely augment, let's keep in mind that Yutyrannus was a normal slab chested theropod. Tyrannosaurids came wit da thikkness, they were barrel chested beefcakes, much more better heat retention in the torso. Big bois. Throw in some nice counter current heat exchange for the extremities, maybe a bit of a fat layer too, and you have a pretty good heat retaining system - much better than slimmer, earlier theropods at least. Perhaps a seasonal coat was a thing in northern variants, perhaps the young sported downy coat.
Back to the topic, again, my argument is not one of denying the overall message - that tyrannosaurids had a mainly "scaly" integument - but that the tyrannosaurid "scale" in both size, shape, architecture and pattern is quite distinct from those qualities of scales discerned in Carnotaurus, sauropods, and hadrosaurids. The differences in tyrannosaurid scales between these, presumably more basal integumentary patterns, very well might indicate secondarily derived "scale" patterns. In short that tyrannosaurids - like modern birds - had to reinvent the scale from a mainly feathered ancestral state.
This of course is not a novel concept, indeed the authors of the paper (Bell et al. 2017) seem to lean this way themselves. What I want to offer is that this T. rex "scale" - as suggested by the patterns discerned already - is best approximated by looking not at the exposed skin states of crocodilians with their regularly repeating, consistent, large, and architecturally sound scale designs. No the exposed skin state of tyrannosaurids is best approximated by comparison with the other archosaurs (i.e. birds) that have had to "reinvent" scales after losing them initially upon evolving a completely feathered countenance. When we look at both the small turberculate "scales" on the legs of birds and… wait for it... the minute "scaly" pattens discerned on some examples of carunculate skin of birds we can imagine a sort of novel tyrannosaurid integument that splits the difference between bird leg scales and carunculate skin. This novel skin morphology would be a lot more thicker and durable than carunculate skin but offer adequate blood flow for thermoregulatory and color flushes. Such a novel skin type combining elements of carunculate skin and bird leg tubercles would be consistent with the preposterously small tubercles of tyrannosaurids, their haphazard shapes, and offer immediate benefits for thermoregulatory and display functions.
Carunculate skin answers the question of why - when compared to other scaled dinosaurs - T. rex scales are diminuitive, non-architectural, no consistent shape, sort of globular, and devoid of rows, repeating patterns etc etc.
Oh yeah, and before you go "there goes Duane and his caruncles again" know that others have been pointing out this similarity between tyrannosaurid "scales" and carunculate skin as well…
|credit Marco Muscioni|
You can take a wild guess how often the term caruncle comes up in the Bell paper (or the Carr paper for that matter). A big fat nada, zero, zilch, ninguno. I guess we don't have to talk about carunculate skin if we pretend it does not exist. Robert Bakker, I'm disappointed in you, especially since you have worked a lot with Luis Rey who gave us one of our first caruncle ridden theropods. Robert Bakker, you should read more antediluvian salad. Yes, the hate, disdain, disapproval, and ignorance for carunculate skin knows no bounds both from professionals and lay enthusiasts. And so perpetuates the false dichotomy of feather vs. scale, leaving out the retarded stepchild of carunculate skin… always the bridesmaid, never the bride.
Ye shall know it when ye sees it…
What was once scaled becomes feathered then becomes something new…
A quasi scaled, nekkid skinned, caruncled beast. Not completely serpent or fowl.
Ladies and gentlemen this is what modern theropods (i.e. birds) do when they get rid of their feathers. If we assume feathers and scales are more than a little competitive developmentally, when feathers diminish a nekkid skin is left. In order to toughen up this nekkid skin faux scales can be reinvented as they have been on the legs of modern birds. In other areas, especially of the head, nape, and neck a more motley growth pattern of various carunculate skin devices can commence. Carunculate skin can also have a superficially scaly facade. In large and gigantic theropods that mostly or completely lost feathers carunculate skin and tuberculate scales analogous to modern bird leg scales can potentially combine and envelope the torso as well, creating new motley and outlandish textures.
The dark little secret of carunculate skin is that it is found in not just one modern bird family, but many. We are left to consider two possibilities. Carunculate skin is basal to birds and quite possibly goes way back into theropods or: that it evolved independently in many different bird lineages. Both scenarios bode well for such epidermal growth to be quite common and expected in theropods that dispensed with feathers or possibly even some dinosaurs that never evolved feathers?!? (I'm looking at you Edmontosaurus)
|Dang Tao Chicken "Do these caruncles make my feet look fat?"|
And finally, for the haters, social media harassers, stalkers, chastisers, discounters, "don't listen to Duane he is not teh true paleontologist", and all around perpetrators. You inspire me. Keep it coming. I stole the show with Spinosaurus and I'm doing it again right here. This C-walk is for you.
CARUNCLES BIATCH!! Up in Your Grill!!
- Bell, P. R., Campione, N. E., Persons, W. S., Currie, P. J., Larson, P. L., Tanke, D. H., & Bakker, R. T. (2017). Tyrannosauroid integument reveals conflicting patterns of gigantism and feather evolution. Biology Letters, 13(6), 20170092.
- Bell, P.R. A Review of Hadrosaur Skin Impressions. Hadrosaurs. Indiana University Press 2014
- Carr, T. D., Varricchio, D. J., Sedlmayr, J. C., Roberts, E. M., & Moore, J. R. (2017). A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports, 7.
- Cau, Andrea. Those Scales Are Scales? Theropoda. June 7, 2017 webpage
- Nima (Paleo-King) Are retro 90's Tyrannosaurs making a comeback? 2017 webpage
- Witton, Mark. Revenge of the Scaly Tyrannosaurus. Mark-Witton.blogspot June 16, 2017. webpage
"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine