Featherz

[MrRabbid]

Why do some people depict every single dinosaur as a fluffball? I know that most, if not all, dinosaur groups had something related to feathers, but then you do have to consider the animal's size and geography of its habitat, so a Torvosaurus or Tarbosaurus drenched in feathers wouldn't be logical- just some feathers on the arms and perhaps a little on the head or back seems right with me.

[Takama]

Welcome to the forum, were feathers are a prominently discussed feature .



The largest Featherd Dinosaur that we found so far was Yutyrannus and it had a complete covering. With this info, we generally assume that Its relatives (the Tyrannosaurs) had a full covering as well.

[MrRabbid]

Welcome to the forum, were feathers are a prominently discussed feature .



The largest Featherd Dinosaur that we found so far was Yutyrannus and it had a complete covering. With this info, we generally assume that Its relatives (the Tyrannosaurs) had a full covering as well.

True, but Yutyrannus lived in a cold environment, while a large number of tyrannosaurs lived in warm climates. If Tyrannosaurus had a full coat of feathers, it would mostly likely overheat, unless this specimen that is being discussed lived to the northernmost stretches of the species's occupation and it shed/gained plumage depending on the season of the year.

[Seijun]

feathers do not = fur emus and ostriches have plenty of feathers and do not overheat.

[tyrantqueen]

feathers do not = fur emus and ostriches have plenty of feathers and do not overheat.

But ostriches and emus are tiny compared to Tyrannosaurus.

It's probably just one of those style things. Some artists draw Tyrannosaurs with a full coat of avian feathers, as seen here in the "Oreo rex"



While others (for example forum member Himmapaan) gives them a bristly coat of protofuzz.



I think I prefer the bottom rex, but both depictions are valid at this point, at least until we find a Tyrannosaurus with fuzz/feathers preserved. I also noticed that Scott Hartman chose not to feather his recent Tyrannosaurus artwork, so I guess unfeathered is a valid choice too..? 

[Dinoguy2]

T. Rex lived from Alaska to Texas. Range spanned both wRm and humid to tropical environments, it was not an exclusively hot climate animal. And the environment if Yutyrannus was not cold year round, but temperate and semi arid. Think modern New England which gets quite hot in the summer.

[Ultimatedinoking]

Or maybe T. Rex was only partaly feathered. Such as having feathers along its back and along its arms, and having bare legs, like an ostrich. Wasn't there a small skin impression of a T. Rex and it showsed a set of small bumps? But then again, Some Moa were feathered all the way done to their ankles. So large size= fewer feathers is not a rule.

[amargasaurus cazaui]

TYrannosaurs Rex scale impressions, "Wyrex"
Not an ambigous fossil, quite clear scales. This for now is all we have for Tyrannosaurus Rex.

[Lythronax]

T. Rex lived from Alaska to Texas. Range spanned both wRm and humid to tropical environments, it was not an exclusively hot climate animal. And the environment if Yutyrannus was not cold year round, but temperate and semi arid. Think modern New England which gets quite hot in the summer.

Hi. I just want to say that, as far as I'm concerned, remains of Tyrannosaurus haven't been found in Alaska, but in Canada. Also it seems that in that time, Texas has an arid or semi-arid climate, which would explain why Alasmosaurus has been found there. And in higher latitudes the climate was more humid, tending to tropical. So probably, T. rex was not exposed to temperatures so cold as Yutyrannus was. This is known because researchers have found crocodiles and other tropical animals in the same locations as T. rex.

With regard to Yutyrannus,  as you said, it  was not experiencing very cold temperatures all year round. But Yutyrannus, unlike insects, had life spans longer than a year. So this species must have had some strategies to survive through the coldest period of all the winters it lived (even it if was only one month every year, for instance). So it seems normal to me that this species had a feather coating, even if it was a seasonal coating. By contrast, T. rex survived the coldest period of the year along with tropical animals (crocodiles, Champsosaurus), which were obviously not prepared to survive the cold that Yutyrannus experienced. Therefore, it's not that obvious that T rex had feathers.

[Lythronax]

Hello everyone,

I've been longing to write about this topic in depth for a long time.

Personally, I think that we can't currently know for sure wheter a large adult of Tyrannosauridae was fully or partially covered by feathers. I also believe that at present, in the absence of further evidence, we must say that, most likely, adults of large Tyrannosauridae didn't have feathers. I already introduced my point of view in the post where I talk about the perverse use of phylogenetic inference.

http://www.dinotoyblog.com/forum/index.php/topic,1877.0.html

Before going into Tyrannosauridae and Tyrannosauroidea I would like to tackle some very important information that I think has not yet been discussed in depth (correct me if I'm wrong). I'm talking about the integumentary coverings in Arcosauria. Here I have posted a figure taken from a paper that represents all dinosaur groups, indicating in which groups integumentary structures (scales or feathers) have been found. "S" stands for scales and numbers refer to different types of feathers. This figure is outdated because it doesn't indicate the presence of feathers in Ornithomimosauria. Anyway, this is not that important because it assumes that Coelurosauria has feathers as a primitive condition. The figure would also need to incorporate Sciurumimus, previously considered an Megalosauroidea, but now believed to be the most primitive Coelurosauria known. I do not include Concavenator among the feathered dinosaurs because it seems that the marks on its arms are not necessarily an anchor for feathers (in addition, this type of feathers anchored to the bone would originate in Ornithomimosauria, but not before). That said, what is really important is the presence of integument similar to protofeathers in Heterodontosauridae and Ceratopsidae. People might think that these "protofeathers" are a homoplasy of Heterodontosauridae, Ceratopsidae (both Ornithischia) and Coelurosauria (homoplasy means that a trait is found in several terminal groups but evolved independently). This doesn't sound quite right, and if we also consider the presence of "protofeathers" in Pterosauria, it's more probable that protofeathers are a synapomorphy of these groups, because this trait is a basal character of the group Ornithodira and it was "new" in this group. Ornithodira is a group that comprises Pterosauria and Dinosauriomorpha. Because, according to the criterion of parsimony, it is more probable for a character to appear once than to appear 4 times within a group of closely related groups.

[Lythronax]

At this point I'd like to include a new variable in this equation. I'm talking about the ability to create scales after losing the ability to form feathers. So I would like to address three different stages in the evolution of Arcosauriomorpha that are available to us as extant species. Turtles are not primitive Anapsida, instead, they are more closely related to birds and crocodiles than to the other reptiles (turtle chromosomes are similar to those of birds). So the Anapsida status of turtles is derived and not primitive, that is, their temporal fenestrae have been lost along the evolutionary process, and thus returned to a primitive condition. This is also found in the integument (turtle beta-keratins are more similar to those of birds and crocodiles to those of the rest of reptiles). Personally I think turtles should be included in Arcosauriomorpha, but not in Arcosauria. This is because the beta-keratins of crocodiles and birds are more similar to each other than to those of turtles. Moreover, turtles do not have air sacs, while crocodiles have been found to have functional air sacs which function similarly to the air sacs of birds. The crocodile air sacs are within the lungs, that's why they had not been discovered until recently.

Before going on with the topic of feathers, I want to point out one thing. I just wrote of beta-keratin. Keratin is a protein that gives strength and shape to the skin and comprises integumentary structures such as hair, scales and feathers. Reptiles (including birds) have a type of keratin that mammals don't: beta-keratin. This type of protein has been shown to be different between birds and other reptiles like lizards and snakes (Squamata). And the beta-keratins of birds are the proteins that create the feathers. It turns out that the genes that code for this protein are identical in birds and crocodiles (although birds have more gene subtypes, probably because modern feathers are more complex than the original protofeathers).

What follows I read it newspaper articles, not in scientific literature. It seems that crocodiles have the genes that are necessary for protofeathers. It was not clear to me if this newspaper article was talking about the fact that crocodiles have the same beta-keratin-coding genes than birds. In this case, the article is misleading, because in addition to the bricks (the genes of beta-keratins), an organism needs also the maps (the gens that lead the assemblage of these proteins to make the feathers), to draw a analogy. Yet it is plausible to assume that crocodiles had an ancestor with protofeathers, as they have proteins that they don't need to build their scales (as in the case of turtles, they don't have these beta-keratines but build scales). This is also consistent with the selective pressures that crocodiles suffered in the Permian. I can't recall these selective pressures now (as I'm not a specialist on the subject), but I do know that these are the same which fostered the origin of hair in mammal-like reptiles (Synapsida), which lived in the same habitats in that period. Nowadays, a very plausible hypothesis suggests that Arcosauria displaced the Synapsida in the end of the Permian, because oxigen levels decreased and Arcosauria had a better the ability to breathe with low levels of oxygen thanks to their air sacs. They were competing for the same ecological niches and were subject to the same selective pressures. Thus, it is plausible that the two groups ended up having similar, but not equal, integumentary structures to allow thermoregulation.

Having established that it is likely that the protofeathers and air sacs are synapomorphic traits in Ornithodira and Crurotarsi (these are the major lineages in Arcosauria), let's look at how the presence of scales and feathers is regulated. It has recently been discovered that the same genes that regulate the formation of scales are the same in crocodiles and in birds, and that the formation process is also the same for the two groups. This process is diferent in Squamata: lizards and snakes. Moreover, researchers have discovered that the coexistence of feathers and scales is not possible in birds. The cause is that for a skin area to develop scales the inhibition of feather formation is indispensable. So it seems that embryonic tissues "do not know" how to make scales if feathers are already there, it is a regulatory mechanism of tissue organization. Therefore feathers and scales can't coexist in the same skin area, what some years ago was deemed plausible, because current elephants and rhinos, which have hairs in areas where the integument is thickened. This shows that we must constantly adjust our assumptions to the evidence we encounter. What is indeed possible is the existence of areas of skin without scales and with little or no feathers (e.g. the faces of parrots). This is what was found in Ornithosauria, where individuals with smooth scaleless integument and with some protofeaghers have been found. This also implies that if a skin area with scales is found in a dinosaur, this area must have had no feathers (ok, this seems obvious, but it is worth to keep it in mind).

All that said, let's look at the selective pressures that explain the presence or absence of feathers. First of all, the primitive condition in Arcosauria is the presence of protofeathers with a thermoregulatory function (which implies some degree of endothermy). But extant crocodiles do not have protofeathers, nor they are endotherms. But, as happened with turtles, which are secondary Anapsida (their Anapsida status is not primitive, being actually Diapsida), the ancestors of crocodiles had probably some degree of endothermy. This holds for two reasons (regardless of the presence of the "genetic machinery" to create protofeathers). The first reason is the presence of air sacs in the lungs, which improves oxygen uptake (this only makes sense if the animal needs more oxygen because of its greater energy requirements) and. At present, crocodiles use them in their adaptation to the aquatic environment. The second reason is their four-chambered heart, totally divided by the septum. This kind of heart occurs only in mammals and birds (homeotherms) to properly distribute blood to the body and to the lungs. In lizards, snakes and turtles, the septum does not completely divide the heart, so that blood of the body and lungs gets mixed. In the case of crocodiles there is also a partial mixing of the blood, but in this case is due to the Panizza foramen connecting the two aortas. This is not a primitive character, but an autapomorphy that arised as an adaptation to the aquatic environment, and thanks to this connection crocodriles can temporarily shut blood circulation to the lungs —when the individual does not want to use oxygen from the lungs or when these are depleted from oxygen is no longer these— in order to concentrate the flow of oxygen in the areas where it's needed. Similarly, the loss of protofeathers could be an adaptation to the aquatic environment and to an opportunistic lifestyle, by which the individual spends little energy to survive for long periods time without eating, waiting until an occasional or seasonal opportunity comes to take advantage of it.

[Lythronax]

In the case of dinosaurs, researchers have found individuals whose skin is covered in scales of different size and shape: Ankylosauridae and other Thyreophora were covered in osteoderms, just as crocodiles; in Sauropodomorpha, scaly skin has been found in both adults and soon-to-be-born embryos (hence, the absence of feathers in this group occurs in all life stages); in Triceratops and other derived Ceratopsidae, scaly skin has been found in different parts of body; in Ornithopoda, large patches of scaly skin has been found in various body parts, which has even enabled researchers to tell apart closely related species due to differences in scale patterns. In addition, there is an example of the coexistence of protofeathers and scales in a given individual (but not in the same area of skin). This is the Psittacosaurus, where relatively large patches of scaly skin and of skin with protofeathers have been found on the back of the tail (I will talk about this species and its relatives in another post). In addition, there are examples of scales in Theropoda: in Tyrannosauridae and Juravenator small patches of scaly skin have been found, especially in the ventral part of the body. But patches of scaly skin on the back and on the neck in several large Ceratosauria also found  (which even prosent some osteoderms, like in crocodiles).

Unlike crocodiles, the loss of protofeathers in dinosaurs, as in Hadrosauridae, did not happened because they became ectotherms. We know this from the growth rates of the individuals, which are just a bit below to those of marsupials, and from the isotope readings of fossil remains of both dinosaurs and extant reptiles, which indicate that the body temperature was higher in dinosaurs than in ectotherm reptiles. Thus, it seems that the degree of endothermy of dinosaurs in between mammals and extant reptiles. And the degree of endothermy is probably differs between group of dinosaurs, but I would generally speak of mesothermy in dinosaurs. The efficiency in oxygen uptake and a mesothermal-like metabolism in good weather conditions (high temperatures) is what has allowed dinosaurs to increase so much their size and to keep their biomass, both at the individual and at the population level. This can be seen in the following figure, which shows that endotherm mammals spend a lot of energy to keep their biomass, while reptiles spend little energy in keeping their metabolism, so they can use it for growth. But if we pay closer attention, reptiles are not giants, it's mammals, which are usually largest. This happens because mammals are more efficient in food search and because its internal temperature is high and constant, enabling a higher rate of food assimilation and growth. But reptiles depend on the weather to have a high internal temperature that allows for a high assimilation rate, that's why the largest reptiles live in the tropics. In the case of dinosaurs, because they lived in a time period that was warmer than at present and because they had some degree of endothermy (mesothermy) they were able to compete with ectotherm reptiles and to outgrow them. They didn't spend that many resources on metabolism, so they could grow more.

[Lythronax]

Let's now go back to the subject of protofeathers and feathers, and to their involvement in mesothermy. I would like to concentrate on the case of Tyrannosauridae and other megatheropoda. I would also like to mention that it is very possible that in Coelurosauria the degree of endothermy be greater than in other groups of dinosaurs (especially in the smaller species of Coelurosauria) and so there may have been an evolutionary trend towards increasing the insulation capacity of the feathers, which later evolved and had other functions). But let's move on. I think that offspring of megatheropoda had feathers. Why? Because they had the potential to have them and because researchers have been found small theropods with feathers. I don't know the exact selective pressures imposed by thermoregulation that forced small theropods to keep their feathers. But it's clear that there were many small feathered theropods with feathers, it was probably an adaptation to prevent heat loss, especially by night. Until recently, it was hypothesized they lost their feathers as they grew up until ending up with only a few or none at all, since increasing in size keeps an individual warmer without the need of feathers. But then, a 9-meter tall feathered Tyrannosauroidea Yutyrannus was found. Automatically, using phylogenetic inference, people reasoned that all great Tyrannosauridae adults could have been profusely feathered, regardless of the 34-million-year separation between Yutyrannus and Tyrannosauridae (not to mention the 60-million-year separation between this species and Tyrannosaurus). So its as if we compare horses with tigers. Although to be fair, by having the same ecological niches, both were subject to the same selective pressures that "keep the design" of the individual. Although Yutyrannus had feathers, I still think that most adult megatheropoda had no feathers. The reason is that scales have been found in several specimens. First, there are Tyrannosauridae individuals with scales in their ventral area (people say then that Tyrannosauridae could still have feathers on their back). Second, in other large theropods (several Ceratosauria) skin with with scales and osteoderms has been found. So it seems that it is not necessary for a large theropod to have feathers on the back to keep its body temperature. By contrast, the only known feathered megatheropoda is Yutyrannus. This may lead some people to think that this dinosaur lived in a different environment than the majority of large theropods. So let's have a look at this idea: this Tyrannosauroidea lived in a region with a cold climate with frosts (average T=10 ºC), not that it was like in our ice ages, but it was quite cold. Instead, Tyrannosaurus lived in a much warmer area (I can't find the data now, but I think the average T was 36 ºC). So it seems normal to me that these two animals had completely different coatings. There is a well-known example, which is the case of mammoths and elephants. So it's entirely plausible to think of an adult Tyrannosauridae with scales but without feathers. But it could also be possible that the coating of feathers was present, but covering fewer areas of the body (like the back).

Before going into the topic of feathers covering the back of large theropods, I would like to talk about elephants. It has been said that Tyrannosauridae had a mass similar to the current African elephant (a mammal with no fur and, were if not not for its large ears, would have hyperthermia problems). This would help us to explain why larger Tyrannosauridae had no feathers. A counterargument was that, althgough having a similar mass, elephants are more compact with a surface to volume ratio lower than Tyrannosauridae. If we add the lower degree of endothermy of dinosaurs to the equation, we can argue that Tyrannosauridae needed an insulating layer to prevent the loss of the "little" heat they generated. However, this argument lacks a variable: if the weather was warmer than it is today, then the thermal gradient between the corporal temperature in Tyrannosauridae and the air temperature was probably lower than the current gradient in elephants. This would entail a lower heat loss in the Tyrannosauridae, because being mesothermal and having lower a ratio of surface/volume than the African elephant, it would not need to have a heat dissipation structure similar to the ears of elephants. However, Tyrannosauridae also had an adaptation thay cooled the skull down by heat dissipation (probably to prevent brain damage): air sacs within the skull. If this is so, why would Tyrannosauridae have an insulation like Yutyrannus if this could entail hyperthermia (probably when exercising)? But many could say that Gorgosaurus and Albertosaurus lived at high latitudes where it was cold. It could be that northern areas were colder than southern areas, but this doesn't mean that northern areas were very cold: just think that these guys coexisted with one of the largest ectotherm reptiles in history: Deinosuchus. So it must have not not been that very cold, otherwise it would have not been possible for Deinosuchus to live up there. Furthermore, it is unknown wether large herbivorous dinosaurs migrated or not in order to avoid the winter. If these animals migrated, large Tyrannosauridae would have also migrated following their food, so they even may not have had to face the northern winters.

[Lythronax]

Let's go back to the issue of the feather coverage on the back. I said that skin was found on the back of several Ceratosauria. Therefore, if an animal with this shape and size has the potential to have feathers but doesn't have any, we must conclude that it doesn't need them. This could be extrapolated to Tyrannosauridae and other megatheropoda. But some might say Ceratosauria is a evolutionary branch that split long ago and that may have lost the ability to produce feathers. Moreover, they lived in another period. It turns out that two of the Ceratosauria with skin lived in the same period of Tyrannosauridae at similar latitudes, although in South America. Then some could say organisms that didn't live in both the same period and area can not be compared. At this point, we can focus on other featherless dinosaurs contemporary to Tyrannosauridae that were their prey. Integument found in different regions of Triceratops can be seen here:

http://www.omniology.com/dinosaur-skin.htm

(The reconstruction with spikes on the back and ventral scales such as those in the neck is a mere speculation that is not supported by any evidence).

As I said before, protofeathers can not appear mixed with scales. What has been found it's the way how the emergence of structures similar to protofeathers can be induced in the scales in the scutate (the scutate scales are derived from skin that originally had the capacity to produce feathers). This indicates that Triceratops could have spikes similar to protofeathers, with a scale on their basis (a hybrid structure). But the coexistence of normal scales with feathers has not been proved (by the way, I will tackle the topic of the integument in Ceratopsidae another day). So Triceratops did not need any insulator to maintain its body temperature above that of ectotherm reptiles. But then somebody could say that Ceratopsidae, being stouter than Tyrannosauridae, can be compared to extant elephants and rhinos, which have almost no hair at all. Well, then I will give another example about a dinosaur similar in shape and size to Tyrannosauridae and contemporary to them, being therefore under the same selective pressures (for instance, heat loss). I'm talking about Hadrosauridae (several species), of which wide areas of skin with small scales have been found, both in the arms, the tail and the back (these scales are very similar to those of crocodiles, which have also lost their feathers). And if we keep in mind that a Hadrosauridae only needed 4 years to grow up to 9 meters, I think that his corporal temperature shoukd be high (regardless of the air temperature) to have such a elevated growth and assimilation rates. So while even though we don't know for sure about the selection pressures that were operating at that time, they must have been the same for both groups (Tyrannosauridae and Hadrosauridae). And it seems that the replacement of feathers by small scales would be advantageous in the circumstances of the period. To me, it would be possible that in such large animals it would be beneficial to have a integument that protected them from abrasions from the environment (e.g. branches), we must remember that large animals could not dodge all the "little" objects that they encountered along the way.

To simplify what I just talked about, mammals currently living in mountains or in the north have mor fur than mammals that live in warmer climates. This happens regardless of whether they are carnivores or herbivores. So in the case of dinosaurs, because herbivores without feathers have been found, it is plausible that same-sized carnivores would not have feathers either.

That's why I think that Tyrannosaurus and its closest relatives had feathers in their juvenile stages (as in other contemporary small dinosaurs), but that the surface covered with feathers would decrease with age, giving way to an integument without scales or feathers that would eventually develop small scales (such as those that have found) to reinforce the integument. This had to happen at very early ages to allow for the development of the scales. This is plausible, because in today's crocodiles, scales are not the same in juveniles and adults. This is also seen in the skin of the embryo in sauropods, because they were born with a less scales than the adults.

If they would not develop scales after losing feathers, the skin would at least remain thickened. That said, it seems that Philip Currie found naked skin belonging the neck of a Gorgosaurus (that is, without feathers or scales). I'm not aware of any thorough study of this individual, so for the moment nothing sound can be said about this skin. Maybe these fossil remains have been misinterpreted, just bear in mind that carcasses undergo some degree of decomposition before fossilizing. If this skin were really naked, this could mean that Gorgosaurus had a seasonal feather cover: feathers in the cold season that were lost with the onset of the warmer season. It could also be possible that a same species of Tyrannosauridae, with a wide distribution area, had populations were adults developed feathers, and other populations were they did not, due to climatic differences between regions in the distribution area. Although, as I said before, I think this to be highly improbable, because other contemporary dinosaurs, under the same selection pressures, did not have feathers but scales. And let's remember that researchers have found Tyranosaurus fossils with scales in areas where Yutyrannus had feathers.


So in my opinion, most Tyrannosauridae and other Megatheropoda reconstructions (such as Concavenator) that are fashionable may be wrong. That these feathered dinosaurs are that more or less cool is an entirely different story. Anyway, I think that we already have self-made dragons to satisfy these longings.

[Lythronax]

Let's turn to the topic of the largest Maniraptora. They may have been covered with small feathers. Why do I say this? Due to the appearance of advanced feathers for sexual attraction. As I said before, the coexistence of feathers and scales in the same area of skin seems not to be possible. So to keep the feathers, which helped the animal stabilize during a race and were advantageous from the point of view of sexual selection, these dinosaurs could not develop scales near them. Then, it would be possible that these dinosaurs had a layer of small feathers that offered them physical protection, but that would not be necessarily useful in termorregulation (which is the case in some short-haired tropical mammals). So this condition could be present from Ornithomimosauria (group in which what I just said has indeed been found) to Maniraptora such as the largest Therizinosauridae or large Dromeasauridae (like Utharaptor). In the case of Therizinosauridae, I'm not sure about which cover they could have, because in Beipiaosaurus only primitive feathers (also in the arms) have been found. A possible explanation to this could be that Beipiaosaurus moulted their derived feathers after each breeding period. Another option is that the advanced feathers had been lost in this evolutionary line due to lack of use (expensive structures often disappear due to natural selection). Since both explanations are plausible, it could be that the larger Therizinosauridae retained the feathers or, conversely, that they replaced them with scales. Another possibility is that they lost the advanced feathers and maintained the primitive feathers without developing scales (there are several possible solutions, some may be worse than others, but if they are good enough can be maintained throughout evolution). I say this because in this group patches of scaly skin have not been found.

Carl sagan coined the following phrase, often mentioned in paleontology: "Absence of evidence is not evidence of absence". However, we must bear in mind that the failure to find a structure may well mean that it does not exist. What this means is that everything I've written above does not have to be true. But I'm relying on facts that indicate that it is more likely that Megatheropoda in general had no feathers in their adult stage. Of course we are lacking too many the variables to be able to make definitive statements about anything (which, with a 65-million-year gap, is to be expected). So just as adult Yutyrannus was a feathered dinosaur, other adult Megatherapoda may have had feathers. Which ones? We don't know. But in the case of Tyrannosauridae, it doesn't seem that they had feathers in the adult stage. But it may be that we ignore the existence of a variable that indicates that they were feathered (but in any case, their arms lacked feathers with rachis). At present however, we have to rely on current knowledge.

Here there is a link to a website that also discusses this issue. In addition, it deals with the hairy Megatherium.

http://agathaumas.blogspot.com.es/2011/08/la-pellaccia-del-tirannosauro-la.html

I apologize for this incredibly long post I've written. But I think it is necessary to consider all at once to get an idea of how dinosaurs could look like without having to resort to the most radical genetic inference and actualism. As I am not good with languages, I might have misinterpreted the information in English I have collected. Alternatively, I may be wrong because I'm not knowledgeable enough about the ontogenetic processes that lead to integument formation to predict how a tissue behaves. As I said above, my English is not good enough. So forgive me if I am not able to provide fast answers to your comments. Besides, I've mentioned before that I'm not a paleontologist.


References

Dhouailly, D. 2009. A new scenario for the evolutionary origin of hair, feather, and avian scales. Journal of Anatomy 214: 587–606.

Farmer CG, Sanders K. 2010. Unidirectional airflow in the lungs of alligators. Science 327 (5963): 338–340.

Greenwold, M. J. & R. H. Sawyer. 2013. Molecular Evolution and Expression of Archosaurian b‐Keratins: Diversification and Expansion of Archosaurian b‐Keratins and the Origin of Feather b‐Keratins. Journal of Experimental Zoology (Mol. Dev. Evol.) 320B:393–405.

Schachner ER, Hutchinson JR, Farmer C. (2013) Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional airflow in Archosauria. PeerJ 1:e60 http://dx.doi.org/10.7717/peerj.60

Xing, X. & G. Yu. 2009. The origin and early evolution of feathers: Insigjts from recent paleontological and neontological data. Vertebrata PalAsiatica 47 (4): 311–329.

http://en.wikipedia.org/wiki/Autapomorphy (easy definitions of cladistic terms, such as autoapomorphy)