Tyrannosaurid skin impressions

[OpalornisHuali]

It is still possible that they had some feathers.. These skin impressions are so small, one shouldn't jump to conclusions.
I don't think the Saurian model needs to be updated much, just a little.

Personally I prefer a feathered T-rex. However if it ends up that we find one day that T-rex was completely scaly, oh well. Science doesn't care about opinions, after all.
At least we have Yutyrannus!

However those Jurassic park fanboys/fangirls are very annoying about this situation, and if it does end up that Rex was featherless, they'll probably start denying feathers on other dinosaurs like velociraptor, using the excuse:
"well, it's only a theory! Besides, you said T-rex had feathers and look, they didn't in the end! Feathers are stupid!"

[Jose S.M.]

There's enough evidence for feathers on Velociraptor, but yeah I still can see people arguing against it.
Aesthetically I prefer feathered tyrannosaurs as well but yeah science doesn't care about that. It would be nice to find more conclusive evidence to the overall look of this dinosaurs, I personally still don't know what to think exactly.
Even if it's a trivial or silly subject, this makes me think if my tyrannosaurs are inaccurate and how much hehehe.

[ZoPteryx]

http://amateurpalaeontologist.blogspot.com/2017/07/evolution-and-trends-in-tyrannosauroid.html

Here is my post I finished two days ago. Basically summing up my thoughts.

Excellent article!  Really illustrates all the possibilities and considerations we must incorporate when talking about tyrannosaur integument.

[Sim]

Is it some kind of problem if T. rex had zero feathers after all? Being wrong in science is a good thing, because it means we learned something. An attitude I'm seeing a lot on Facebook about this paper is almost like "oh no! We rubbed feathered T. rex in all those awesomebro faces and now we might be wrong and it's going to bite us in the rear!"

To all the feathered dinosaur proponents who went around saying "dinosaurs are cool no matter how they look", time to take their (our) own advice!

This thing about "well maybe the feathers were just in all the little margins we haven't found impressions for yet" is just the God of the Gaps fallacy. I think that Peter Schouten tyrannosaur looks pretty good. You could probably get away with a bit more feathers than that, but not much.

Excellent points, Dinoguy2.  Some things that were said in initial news reporting, such as in the link in the original post of this thread, were absurd.  But as ZoPteryx mentioned, a lot of responses against the study's suggestions about the integument of Tyrannosaurus have been negative knee-jerk reactions.  I think this study on tyrannosaurid integument, and the discussion that has followed, has drawn attention to some very important information, some of it new, and some that the palaeontology community generally was overlooking or misunderstanding.  Personally, I've learnt quite a bit that I didn't previously know, and I feel I'm better informed with regards to dinosaurs and what is plausible for their integument.

However those Jurassic park fanboys/fangirls are very annoying about this situation, and if it does end up that Rex was featherless, they'll probably start denying feathers on other dinosaurs like velociraptor, using the excuse:
"well, it's only a theory! Besides, you said T-rex had feathers and look, they didn't in the end! Feathers are stupid!"

I feel a feathered Tyrannosaurus was argued for too hard.  By feathered I mean "fully"/"properly"/heavily/densely/conspicuously feathered.  Not very fine and sparse filaments as Mark Witton suggested, where the animal would essentially be scaly - I think this form of feathering is plausible for Tyrannosaurus.  I think at some point within the last year or two, it became generally accepted in the palaeontology community that Tyrannosaurus should be feathered, and scaly Tyrannosaurus were generally regarded unfavourably.  However the arguments I saw for this ignored certain things or regarded some things as less important than they actually were.  For example, as Mark Witton explained in his blog post, it's not just skin patches that support a lack of feathers in Tyrannosaurus - Knowledge that in very large terrestrial animals shedding heat is hard, and that feathers are good at trapping heat, has existed for a long time.  It seems to me a lot of the arguing for a feathered Tyrannosaurus didn't deal with this knowledge adequately.  I don't know why this happened.  At most it could be argued that Tyrannosaurus could have been feathered.  But it got taken further than that, with it becoming generally accepted Tyrannosaurus ought to be feathered.

Something else that has been brought up within the first few comments on Mark Witton's blog post is that some arguments for Tyrannosaurus being feathered seem to be incorrectly extrapolating from arguments against scaly dromaeosaurids.  I think it's important to be aware of the different kinds of feathers and anatomy here.  Modern, pennaceous feathers which are a rather versatile form of integument are only known to be present in pennaraptorans.  Other feathered dinosaurs, including tyrannosauroids, are only known to have filamentous feathers which wouldn't function very differently to hair.  It's also interesting that in pennaraptorans, the forelimbs are true wings, from the feathers to the skin to the bone.  So in terms of overall look with regards to feathering, dromaeosaurids, troodontids and oviraptorosaurs would basically look like birds.  Suggesting a dromaeosaurid, troodontid or oviraptorosaur could be featherless is the same as suggesting a bird could be featherless.  I don't think there is any reason to think any of them was featherless.  I think the usefulness of pennaceous feathers in thermoregulation, particularly from the wings, means feathers were locked into these animals, which is consistent with not a single extant bird species being featherless.  As Scott Hartman mentioned here, Utahraptor and Gallimimus aren't anywhere near big enough to qualify for losing their feathers for thermoregulation, while the same isn't true for Tyrannosaurus.  While Gallimimus and Tyrannosaurus aren't pennaraptorans, I think what Scott said is helpful in giving some idea of sizes where feathers wouldn't be lost vs a size where they could be lost.  Utahraptor is at the upper size limit for dromaeosaurids, and it not being large enough to lose feathers is consistent with one of the other largest dromaeosaurids, Dakotaraptor, preserving quill knobs which show it had feathers.

Going back to people denying feathers are present on other dinosaurs, reasons for Tyrannosaurus being featherless don't apply to lots of other coelurosaurs.  Among non-tyrannosauroid coelurosaurs, I think extensive feather loss as has been suggested for Tyrannosaurus could possibly be extended to Therizinosaurus and Deinocheirus.  It's been suggested Deinocheirus had a pygostyle which indicates the presence of feathers, but in the comments of his blog post Mark Witton mentioned he's sceptical of this as fused tail vertebrae don't necessarily equal a pygostyle.  I agree with Mark on this, and my understanding is the feathers that attach to a pygostyle are rectrices, which are only known to exist in pennaraptorans, and ornithomimosaurs are not within this group.  Perhaps supporting this is that, a non-pennaraptoran known to have a "pygostyle" and to preserve tail feathering is known, it's the therizinosaur Beipiaosaurus. And in Beipiaosaurus, even though a "pygostyle" is present, the feathers covering that part of the tail are the same filamentous feathers seen on the rest of its tail, no rectrices are present.

A lack of feathers in Tyrannosaurus is completely irrelevant to feathers in Velociraptor.  Firstly, there is no evidence of feathers from Tyrannosaurus itself.  Velociraptor on the other hand preserves quill knobs which are the attachment point for feathers just like they are in extant birds, so Velociraptor is known to have had feathers.  That's conclusive evidence of Velociraptor having feathers.  Other reasons why arguments for feather loss in Tyrannosaurus don't apply to Velociraptor are:

- Even though Velociraptor and Tyrannosaurus are both in groups with members known to be feathered, Velociraptor is only a fraction of the size of Tyrannosaurus.  Tyrannosaurus is huge.  It's in a size range where feather loss for thermoregulation can occur.  Velociraptor is FAR from that.  With even the largest dromaeosaurids like Utahraptor and Dakotaraptor not being large enough to lose their feathers, there's no way Velociraptor would have lost its feathers.  And funnily enough, even if Tyrannosaurus preserves evidence for a lack of feathers, Dakotaraptor preserves evidence for the presence of feathers, even though these two animals lived in the same time and place.  This is an example that dromaeosaurids would still be feathered even if Tyrannosaurus lacks feathers.

- The pennaceous feathers of Velociraptor and other dromaeosaurids are more versatile than the feathers of tyrannosauroids, both in thermoregulation and in being able to function as more than just a body covering (e.g. flapping in raptor prey restraint).

[stargatedalek]

I would still argue against thermoregulation as a reason for bald Tyrannosaurus because of where it lived, Hell Creek was a lot colder and had a lot more seasonal change than many people assume, and probably even received limited snow in winter. Much of North America was coastal marshes and swamps during the periods where Tyrannosaurs were expanding and growing, and would have been relatively similar in climate.

There are plenty of other ways for a large animal to stay cool than becoming bald, ways that wouldn't leave them exposed to high wind chills in winter seasons.

[Sim]

Well, the Hell Creek Formation Wikipedia page says, "The climate was mild, and the presence of crocodilians suggests a sub-tropical climate, with no prolonged annual cold."...

And if I'm understanding it right, in the paper's supplementary material, the average annual temperature for Hell Creek is estimated to be "10°C; up to 23°C in the upper 20 m part of the formation".

So it seems to me Hell Creek wasn't too cold.  Especially not in the upper 20m of the formation where it appears to have been quite hot.  I can't imagine Tyrannosaurus being heavily feathered while living in that environment of the upper 20m.  I think an animal the size and build of Tyrannosaurus would've also been fine without heavy feathering in the lower, cooler part of Hell Creek too, but I'm no expert.

There are plenty of other ways for a large animal to stay cool than becoming bald, ways that wouldn't leave them exposed to high wind chills in winter seasons.

What are ways that could apply to Tyrannosaurus?

[stargatedalek]

I think you're overestimating how warm 10 degrees is, that's the same average temperature as the Yixian and "Yutyrannus lived in a colder climate" is often cited in rebuttal of Tyrannosaurus being feathered.

https://en.wikipedia.org/wiki/Yixian_Formation
"Evidence from the study of oxygen isotopes has shown that the average yearly temperature during this time period was 10 degrees celsius (50 degrees Fahrenheit), significantly colder than once thought. "

10 degrees may be above freezing but it definitely isn't warm, and that's by Canadian standards!

Large animals typically keep cool just by submerging, coating themselves in substrate or resting, but birds can also turn their feathers against the wind (wherein the wind lifts underneath the feathers, hence it should apply to any feathering) or in rare cases some desert birds will partially water-log their feathers to keep cool.

[Sim]

I'm not overestimating how warm 10 degrees is as it's a temperature I'm very familiar with here in the UK.  10 degrees is on the cold side, but would it be too cold for an animal like Tyrannosaurus if it didn't have heavy feathering?  I'm inclined to think the answer is no, with the consideration that scales provide more heat retention than bare skin.  But again, I'm no expert.

It's true that Yutyrannus living in a colder climate has often been used to explain why Tyrannosaurus could be featherless, and this is correct for the upper 20m of Hell Creek where the temperature is much warmer than the Yixian.  However, there is also that Tyrannosaurus grew considerably larger than Yutyrannus.  The paper's suggestion that the densely forested environment Yutyrannus lived in could be a reason why it was feathered, in contrast to large tyrannosaurids, also seems plausible to me.

I don't know how becoming coated in substrate could really help a heavily feathered Tyrannosaurus keep cool.  As for turning feathers against wind, I get the feeling the amount of wind needed for this to work as an effective cooling method for a feathered Tyrannosaurus means it often wouldn't be viable, if ever.  The water-based and resting cooling methods seem plausible to me though, although I honestly don't know how effective they could be for a feathered Tyrannosaurus due to the animal's size.

[Neosodon]

The presence of crocodiles is a pretty clear sighn that the climate was not too cold. 10 degrees Celsius is just the low estimate. It was most likely warmer than that. There were featherless dinosaurs like Edmontosaurus and Pachyrhinosaurus that lived in colder environments than hell creek.

There is no reason Tyrannosaurus needed feathers. The question is really could Tyrannosaurus have feathers. If Tyrannosaurus had them it would be like Balaur said. "In short, the smaller size of Yutyrannus, plus the environment, might explain the need for feathers. However, I have come to conclude that the true reason Yutyrannus was extensively feathered is because it simply could."


The old argument for a feathered T. rex and other feathered dinosaurs was based on genealogy. If one member of a group had feathers or scales all the rest did too. That was the basic assumption at least. But I have never liked that theory. Feathers seem to be more random than that for example the surprising appearance of feathers on non therapods such as Kulindadromeus or Tianyulong. Feather like structures supposedly evolved before the dinosaurs so by using the old theory all dinosaurs would have feathers. And we know that is incorrect.

My theory on non avialan feather evolution is that they evolved in small dinosaurs that lived in cold environments. The perfect example is the Yixian Formation. All of the early feathered coelosaurs I know of lived there such as Sinosauropteryx, Sinocalliopteryx and Dilong. This makes it pretty clear why Yutyrannus was feathered as it also lived at the same time in the same formation and was also a coelosaur. There was something about the Yixian that pushed feather growth. Most likely the cold climate.

The chances of a large dinosaur living in a hot climate being feathered is almost zero. The chances of a small dinosaur living in a cold climate being feathered is very high. Tyrannosaurus was a very large dinosaur living in a moderate climate so even without the fossil evidence of scales the chances of it being feathered is still very low.

Keep in mind this theory only applies to non avialans and can not be used on dromeosaurs and troodontids. But every feathered non avialan was either small or lived in a cold climate.

[amargasaurus cazaui]

If I understood your comments correctly, you are then asserting the filaments known for Tianyulong were homolgous to feathers? I had understood this was contentious to say the least, and undetermined, similar to suggesting the filaments for psittacosaurus were also feathers. While it is possible, I am unsure it is generally accepted they were necessarily feathers rather than simply evolving separately in other lineages.

[Neosodon]

If I understood your comments correctly, you are then asserting the filaments known for Tianyulong were homolgous to feathers? I had understood this was contentious to say the least, and undetermined, similar to suggesting the filaments for psittacosaurus were also feathers. While it is possible, I am unsure it is generally accepted they were necessarily feathers rather than simply evolving separately in other lineages.

For Tianyulong I'm unsure. Quills are thick and more rigid. Filamentous feathers a skinnier and wavier. For something that is in between it is hard to say. But for kulindadromeus I would say they are most certainly feathers.

[stargatedalek]

If I understood your comments correctly, you are then asserting the filaments known for Tianyulong were homolgous to feathers? I had understood this was contentious to say the least, and undetermined, similar to suggesting the filaments for psittacosaurus were also feathers. While it is possible, I am unsure it is generally accepted they were necessarily feathers rather than simply evolving separately in other lineages.

While I certainly wouldn't call them feathers by any means, the safe assumption is that they share a common ancestor with feathers rather than evolved separately. I would go so far as to say the safe assumption is that archosaurs had a group with soft integument fairly early on, hence why crocodiles have genes specifically used for growing soft integument and why every major group of ornithodirans (sans sauropods) has some degree of soft integument. This could mean either that archosaurs lost soft integument early on and then that pre-existing capacity was later re-utilized by several groups, or that many groups individually lost their soft integument.

I'm not overestimating how warm 10 degrees is as it's a temperature I'm very familiar with here in the UK.  10 degrees is on the cold side, but would it be too cold for an animal like Tyrannosaurus if it didn't have heavy feathering?  I'm inclined to think the answer is no, with the consideration that scales provide more heat retention than bare skin.  But again, I'm no expert.

It's true that Yutyrannus living in a colder climate has often been used to explain why Tyrannosaurus could be featherless, and this is correct for the upper 20m of Hell Creek where the temperature is much warmer than the Yixian.  However, there is also that Tyrannosaurus grew considerably larger than Yutyrannus.  The paper's suggestion that the densely forested environment Yutyrannus lived in could be a reason why it was feathered, in contrast to large tyrannosaurids, also seems plausible to me.

I don't know how becoming coated in substrate could really help a heavily feathered Tyrannosaurus keep cool.  As for turning feathers against wind, I get the feeling the amount of wind needed for this to work as an effective cooling method for a feathered Tyrannosaurus means it often wouldn't be viable, if ever.  The water-based and resting cooling methods seem plausible to me though, although I honestly don't know how effective they could be for a feathered Tyrannosaurus due to the animal's size.

I doubt 10 degrees would be too cold for a large bald animal, but it was definitely not warm enough to mandate loss of insulation. I'm skeptical these impressions are scales, but if they are they may well have provided more than enough insulation.

It's not like Hell Creek was an open plain, it had a lot of marshes but was still very forested. I'm not sure why the conifer forests of the Yixian were any more suited to large feathered animals than the deciduous and palm forests of Hell Creek. Scales would probably be better suited to moving though thick brush than feathers.

I know large mammals coat themselves in substrate to cool off, not sure if feathers would interfere with that or not. Probably just soaking the feathers would accomplish the same thing.

[Sim]

My theory on non avialan feather evolution is that they evolved in small dinosaurs that lived in cold environments. The perfect example is the Yixian Formation. All of the early feathered coelosaurs I know of lived there such as Sinosauropteryx, Sinocalliopteryx and Dilong. This makes it pretty clear why Yutyrannus was feathered as it also lived at the same time in the same formation and was also a coelosaur. There was something about the Yixian that pushed feather growth. Most likely the cold climate.

Some of this is contradicted by known information though.  The Yixian is a Cretaceous environment, and the more basal coelurosaurs from this formation e.g. the tyrannosauroids, compsognathids and therizinosaur all only have more primitive filamentous feathers.  However, they coexisted with dromaeosaurids, avialans and oviraptorosaurs which already had advanced pennaceous feathers which shows feathers had been evolving long before the Yixian.  As proof of this, feathers are known from Jurassic dinosaurs such as scansoriopterygids, Archaeopteryx, Anchiornis and Juravenator, and all but the last one already have pennaceous feathers, so the evolution of feathers would've started long before these as well.

The chances of a large dinosaur living in a hot climate being feathered is almost zero. The chances of a small dinosaur living in a cold climate being feathered is very high. Tyrannosaurus was a very large dinosaur living in a moderate climate so even without the fossil evidence of scales the chances of it being feathered is still very low.

Keep in mind this theory only applies to non avialans and can not be used on dromeosaurs and troodontids. But every feathered non avialan was either small or lived in a cold climate.

Dakotaraptor was a large non-avialan that was definitely feathered as shown by its preserved quill knobs, and it didn't live in a cold environment as it's from within the upper 20m of the Hell Creek Formation, where based on the info from the supplementary material, the annual average temperature was 23 degrees Celsius.

It's not like Hell Creek was an open plain, it had a lot of marshes but was still very forested. I'm not sure why the conifer forests of the Yixian were any more suited to large feathered animals than the deciduous and palm forests of Hell Creek. Scales would probably be better suited to moving though thick brush than feathers.

The impression I got reading the paper was that the Yixian was more densely forested than Hell Creek and the other tyrannosaurid environments it referred to.  My thinking is a denser forest means less sunlight and more shade, and as a result the environment is generally cooler even if the actual temperature isn't different to that of a less forested environment.

[amargasaurus cazaui]

Think the main thing there, Dalek is that with heterodontosaurs and psittacosaurus, we do not KNOW yet for sure...the explanation you offered is indeed quite possible, however it is also feasible they arose separately in some families as evolution often does with other traits. I do know that nothing is firm yet regarding Tianyulong and psittacosaurus regarding the integument found with them.
   

[Newt]

I notice the Montauk Monster came up earlier...I don't remember if I ever showed you guys the Montauk Monster I saw floating in the Ohio:

[img=http://orig09.deviantart.net/fff4/f/2016/155/c/0/montauk_monster_by_nathanlparker-da50ic4.jpg[/img]

Anyhow, I'm a little perplexed by how emotional people get about this topic, and how much argumentation proceeds from so little evidence. I am the sort who stops and looks at roadkill, and I gotta say - integument does weird things once its owner is deceased. The few tiny patches presented aren't much to go on. I'm also not convinced by the phylogenetic logic that a trait (such as feathering) once acquired in a lineage should be assumed to be present in all members after that acquisition. I know that no birds have lost their feathering, but (A) birds, despite their numbers, are only one of several feathered dinosaur lineages and shouldn't be assumed to be representative, and (B) birds went through a tight bottleneck in their past. Even fightless birds are descended from flighted ancestors. They may be constrained from losing feathers, both developmentally and as  a result of their small size, in ways other feathered lineages were not - somewhat in the same way that mammals are constrained in number of cervical vertebrae in ways that other vertebrate lineages are not.

Just my two cents.

[Neosodon]

My theory on non avialan feather evolution is that they evolved in small dinosaurs that lived in cold environments. The perfect example is the Yixian Formation. All of the early feathered coelosaurs I know of lived there such as Sinosauropteryx, Sinocalliopteryx and Dilong. This makes it pretty clear why Yutyrannus was feathered as it also lived at the same time in the same formation and was also a coelosaur. There was something about the Yixian that pushed feather growth. Most likely the cold climate.

Some of this is contradicted by known information though.  The Yixian is a Cretaceous environment, and the more basal coelurosaurs from this formation e.g. the tyrannosauroids, compsognathids and therizinosaur all only have primitive filamentous feathers.  However, they coexisted with dromaeosaurids, troodontids, avialans and oviraptorosaurs which already had advanced pennaceous feathers which shows feathers had been evolving long before the Yixian.  As proof of this, feathers are known from Jurassic dinosaurs such as scansoriopterygids, Archaeopteryx, Anchiornis and Juravenator, and all but the last one already have pennaceous feathers, so the evolution of feathers would've started long before these as well.

The chances of a large dinosaur living in a hot climate being feathered is almost zero. The chances of a small dinosaur living in a cold climate being feathered is very high. Tyrannosaurus was a very large dinosaur living in a moderate climate so even without the fossil evidence of scales the chances of it being feathered is still very low.

Keep in mind this theory only applies to non avialans and can not be used on dromeosaurs and troodontids. But every feathered non avialan was either small or lived in a cold climate.

Dakotaraptor was a large non-avialan that was definitely feathered as shown by its preserved quill knobs, and it didn't live in a cold environment as it's from within the upper 20m of the Hell Creek Formation, where based on the info from the supplementary material, the annual average temperature was 23 degrees Celsius.

It's not like Hell Creek was an open plain, it had a lot of marshes but was still very forested. I'm not sure why the conifer forests of the Yixian were any more suited to large feathered animals than the deciduous and palm forests of Hell Creek. Scales would probably be better suited to moving though thick brush than feathers.

The impression I got reading the paper was that the Yixian was more densely forested than Hell Creek and the other tyrannosaurid environments it referred to.  My thinking is a denser forest means less sunlight and more shade, and as a result the environment is generally cooler even if the actual temperature isn't different to that of a less forested environment.

I'm not claiming feathers first evolved in the Yixian. I'm just saying that is where they first have a strong showing in the fossil record in non avialans and were they may have been introduced into The Tyrannosaur family tree.

Scansoriopterygids, Archaeopteryx and Anchiornis were avialans I think. They all used there feathers for locomotion. Juravenator was a small non avialan that lived in northern Europe which may have been cool at the time. Dakotaraptor is also an avialan too. All dromeosaurids are avialans I think.

Basically I think downy/filamentous feathers evolved to help small dinosaurs survive in cool environments. The first feathery dinosaurs like Juravenator may have evolved their feathers in cool mountainous environments like the Yixian. Some small dinosaurs then used there feathers for locomotion bringing about the evoloution of avialans and pennacous feathers. Non avialans kept there downy filamentous feathers for insulation like you see with the Yixian. Unless the environment became warm enough and the animal became large enough the feathers would not be lost like you see with Yutyrannus.

This is just my idea based off a vague understanding of avalian vs non avialan but feathered dinosaurs combined with limited fossil material so feel free to point anything out that may be wrong.

[stargatedalek]

Think the main thing there, Dalek is that with heterodontosaurs and psittacosaurus, we do not KNOW yet for sure...the explanation you offered is indeed quite possible, however it is also feasible they arose separately in some families as evolution often does with other traits. I do know that nothing is firm yet regarding Tianyulong and psittacosaurus regarding the integument found with them.

Oh no I'm definitely with you on that, I highly, highly doubt that Psittacosaurus structures are related to feathers but that's already been discussed at length elsewhere. I was referring mainly to Kulindadromeus, which is a lot closer in structure to early feathers and pycnofibres.

It's not like Hell Creek was an open plain, it had a lot of marshes but was still very forested. I'm not sure why the conifer forests of the Yixian were any more suited to large feathered animals than the deciduous and palm forests of Hell Creek. Scales would probably be better suited to moving though thick brush than feathers.

The impression I got reading the paper was that the Yixian was more densely forested than Hell Creek and the other tyrannosaurid environments it referred to.  My thinking is a denser forest means less sunlight and more shade, and as a result the environment is generally cooler even if the actual temperature isn't different to that of a less forested environment.

I wouldn't have expected that to make much of a difference, if anything I'd say that cancels out with the added insulation from wind that thick trees offer.

[Sim]

If I understood your comments correctly, you are then asserting the filaments known for Tianyulong were homolgous to feathers? I had understood this was contentious to say the least, and undetermined, similar to suggesting the filaments for psittacosaurus were also feathers. While it is possible, I am unsure it is generally accepted they were necessarily feathers rather than simply evolving separately in other lineages.

For Tianyulong I'm unsure. Quills are thick and more rigid. Filamentous feathers a skinnier and wavier. For something that is in between it is hard to say. But for kulindadromeus I would say they are most certainly feathers.

Well... Beipiaosaurus is known to have two feather types.  The first are simple filamentous feathers that cover its body.  The second have been called EBFFs, or elongated broad filamentous feathers, and these are very long and stiff, and they rise out of the rest of the body's feather covering.  So, it looks like the EBFFs of Beipiaosaurus can be considered filamentous feathers and quills simultaneously.

I'm not claiming feathers first evolved in the Yixian. I'm just saying that is where they first have a strong showing in the fossil record in non avialans and were they may have been introduced into The Tyrannosaur family tree.

Scansoriopterygids, Archaeopteryx and Anchiornis were avialans I think. They all used there feathers for locomotion. Juravenator was a small non avialan that lived in northern Europe which may have been cool at the time. Dakotaraptor is also an avialan too. All dromeosaurids are avialans I think.

Basically I think downy/filamentous feathers evolved to help small dinosaurs survive in cool environments. The first feathery dinosaurs like Juravenator may have evolved their feathers in cool mountainous environments like the Yixian. Some small dinosaurs then used there feathers for locomotion bringing about the evoloution of avialans and pennacous feathers. Non avialans kept there downy filamentous feathers for insulation like you see with the Yixian. Unless the environment became warm enough and the animal became large enough the feathers would not be lost like you see with Yutyrannus.

This is just my idea based off a vague understanding of avalian vs non avialan but feathered dinosaurs combined with limited fossil material so feel free to point anything out that may be wrong.

Avialans are what people often consider birds.  Archaeopteryx and Anchiornis have been classified within this group.  When you've been saying "avialan", do you perhaps actually mean "paravian"?  Paravians are all the avialans, dromaeosaurids, troodontids and scansoriopterygids: https://en.wikipedia.org/wiki/Paraves

[Neosodon]

Avialans are what people often consider birds.  Archaeopteryx and Anchiornis have been classified within this group.  When you've been saying "avialan", do you perhaps actually mean "paravian"?  Paravians are all the avialans, dromaeosaurids, troodontids and scansoriopterygids: https://en.wikipedia.org/wiki/Paraves

Yeah paravian is the right term. Aparently avialan is a term that only refers to birds and dinobirds that are extremely close to birds like Arpteryoptyx. Thanks for pointing that out.
https://en.wikipedia.org/wiki/Avialae

[stargatedalek]

Avialans are what people often consider birds.  Archaeopteryx and Anchiornis have been classified within this group.  When you've been saying "avialan", do you perhaps actually mean "paravian"?  Paravians are all the avialans, dromaeosaurids, troodontids and scansoriopterygids: https://en.wikipedia.org/wiki/Paraves

Wikipedia says:

https://en.wikipedia.org/wiki/Bird
Aves can mean those advanced archosaurs with feathers (alternately Avifilopluma)
Aves can mean those that fly (alternately Avialae)
Aves can mean all reptiles closer to birds than to crocodiles (alternately Avemetatarsalia)
Aves can mean the last common ancestor of all the currently living birds and all of its descendants (a "crown group", in this sense synonymous with Neornithes)

Avialae isn't always synonymous with "bird/Aves". The clearest one to use is #4, and it's been more or less the gold standard since it was proposed (at least among ornithology).

https://en.wikipedia.org/wiki/Avialae
Avialae can also be used in reference to "the theropod group that includes all taxa closer to Passer than to Dromaeosaurus" which is a lot better than "those that fly" which can include everything from dromaeosaurs to modern birds but not all of each.