Feathers of Sinornithosaurus

[Sim]

Sinornithosaurus millenii, the first dromaeosaurid ever to be found with feathers preserved!  Recently, I've been researching Sinornithosaurus to find out more about this interesting animal.  However, there are a few things I'm wondering about.  If anyone can help with any of these things, it would be very much appreciated!

Due to being a microraptorian of similar size to Microraptor, I wonder if Sinornithosaurus could fly.  In some places I've seen it suggested it couldn't due to a lack of large enough wing feathers...  But which specimen of Sinornithosaurus preserves the wing feathers well enough for this to be known?  I haven't been able to find any.  In the paper that names Zhenyuanlong, after describing what's known of Zhenyuanlong's wing feathers, it says

The feathered Liaoning dromaeosaurid Sinornithosaurus, on the other hand, is known from a specimen that apparently had smaller wings comprised of more simple pennaceous feathers and not a more orderly sequence of coverts, primaries, and secondaries23. However, the integument of this specimen is not well preserved and probably does not accurately reflect the wing shape of this species.

To me that looks like confirmation that it's not actually known what the wings of Sinornithosaurus were really like.  And looking at the description of the source that it cites (the 23), the Sinornithosaurus specimen that's being referred to appears to be NGMC 91 aka Dave, which is a juvenile.  This specimen is much smaller than adult Sinornithosaurus, as shown by this comparison: link  The feathering of Dave also seems to much better fit a juvenile dromaeosaurid than an adult.  From the quote above, it also seems that no currently known Sinornithosaurus specimen preserves the wing feathers better than Dave.

One study I read (this study) showed Sinornithosaurus actually shares a lot of adaptations for active flight in its skeleton with Microraptor, which is very interesting.  It concluded it was flightless because it lacked long wing feathers on its forelimbs as shown by the holotype specimen.  But the holotype specimen of Sinornithosaurus, while preserving a remarkable amount of the animal, is incomplete even with regards to bones and is relatively broken up.  And it only preserves patches of feathers.  Another microraptorian, Changyuraptor, also has poorly preserved minimal feathering on its forelimbs similar to the Sinornithosaurus holotype, yet I've only ever seen it restored with full Microraptor-like forelimb wings.

It seems to me in some places Sinornithosaurus is attributed: 1. feathering that would be weirdly undeveloped for a dromaeosaurid and 2. an inability to fly despite its skeleton having a lot of flight adaptations and being closely related to the flight-capable Microraptor, due to basing its feathering on specimens that don't preserve the feathering well - with Dave also being a juvenile (meaning it might not even have feathering like an adult of its species), and the holotype which is an adult with its feathering even less preserved than Dave's.

I've also been wondering what Sinornithosaurus's tail fan might've looked like and if it had leg wings.  The two other microraptorians that preserve feathering, Microraptor and Changyuraptor, both have leg wings.  And their tail fans seem to look similar, with Changyuraptor's tail fan looking like a proportionally bigger version of Microraptor's.

So what I'm wondering now is:
1. Are there any (adult) specimens of Sinornithosaurus that clearly show what its forelimb wings look like?
2. And are there any that show whether it had leg wings?
3. And are there any that show a tail fan?
4. Am I correct in thinking that in The Princeton Field Guide to Dinosaurs, Greg Paul restores Sinornithosaurus millenii with large wings on its forelimbs and hindlimbs similar to Microraptor?

Again, help with any of these things would be much appreciated!


Some other interesting things I found out:

- The juvenile Sinornithosaurus Dave appears to have its fingers completely covered in feathers (except for the claws).

- The study I mentioned earlier that showed Sinornithosaurus has a number of adaptations for flight also said some interesting things about unenlagiines. It found Rahonavis to be one, and suggested it is a two-winged flying dromaeosaurid (in contrast to the four-winged flying dromaeosaurid Microraptor).  It also said Buitreraptor might have been able to fly, and that its aerial ability cannot be fully evaluated until some parts of its skeleton and its forelimb feathers are fully known.

[Sinornis]

I don't know if this will answer any of your questions (I hope it does), but I did find info on Sinornithosaurus in the 2005 book Feathered Dragons, Studies on the Transition from Dinosaurs to Birds.

Sankar Chatterjee discusses the flight capability of Sinornithosaurus in a paper titled Feathered Coelurosaurs from China: New Light on the Arboreal Origin of Avian Flight. He argues that the direct ancestors of birds went through arboreal, climbing, parachuting, and gliding stages before they acquired powered flight. I believe, if my memory serves me right, that he still favors this idea in his re-issued book; Rise of Birds.

The body of Sinornithosaurus was covered by downy feathers, but contour feathers in the hand and tail are not preserved in the fossil record. Because Sinornithosaurus is more derived than Caudipteryx and Protarchaeopteryx, it is likely that it had acquired remiges and rectrices to form a gliding surface. Recent discovery of additional material suggests that Sinornithosaurus developed two types of brancing structures: filaments joined in a basal tuft, and a feather with a central rachis and serially fused barbs. Ji and others reported a nearly complete, Sinornithosaurus-like dromaeosaur, most of whose body is densely covered with featherlike structures. The contour feathers in the arms serially attached barbs.

Some osteological evidence suggests that Sinornithosaurus probably expanded its locomotor repertoire from parachuting to gliding. The shoulder girdle is similar to that of Archaeopteryx, where the glenoid faces laterally, allowing dorso-ventral excursion of the wing. Moreover, the development of the swivel wrist joint indicates that Sinornithosarus achieved an automatic wing folding mechanism for changing the shape of the wing to control gliding. It could supinate the distal part of the wing during and upstroke to minimize drag.

In the chapter, Chatterjee includes two conflicting portrayals, one sees Sinornithosurus falling out of a tree with only small feathers attached to its forearms, the other shows it as a glider with fully formed feathers on its forearms and a frond-like tail similar to Archaeopteryx.

The end of the Chatterjee's paper also discusses the phylogeny of feathers. He mentions that in the fifth stage is the symmetrical contour feathers where vanes are fully formed with an interlocking mechanism. The fossils of Protarchaeopteryx and Caudipteryx have symmetrically vaned feathers in remiges and rectrices. Recent discovery of a Sinornithosaurus-like dromaeosaur shows similar contour feathers in remiges and rectrices. The sixth asymmetrical stage is not mentioned for Sinornithosaurus. 

Prior to Chatterjee's article, another paper titled, Dinosaur Brooding Behavior and the Origin of Flight Feathers, authors Hopp and Orsen believe the forelimb feathers of Sinornithosaurus are insufficient for flight, but are large enough and distributed appropriately along the forelimb to have functioned in brooding.

If Sinornithosaurus didn't fly, I would favor (and personally do) this behavior; researchers hypothesize that once dromaeosaurids took down their prey, they stood atop their prey, grasping it with the killing claw and using "stability flapping" to stay on top of the animal while it was still alive.  Once their claws are locked onto the prey, they are no longer useful in terms of stability, so flapping the feathered forelimbs would be essential to keep the dinosaur balanced on top while it devoured its meal.  Imagine standing on top of a round, wobbly rock – you would have to "flap" your arms to stay balanced.  Imagine how much more balance you could achieve if you had feathers to create a bit of lift and draft to keep you stable.

Please keep in mind that this is an older book with older information.

http://avianmusing.blogspot.com/

[Sim]

In case anyone wanted to look at them, I've edited the first post to include links to the paper that names Zhenyuanlong and the 2014 study that describes adaptations for flight in Sinornithosaurus among other things.


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Thanks for your reply, Sinornis!  I learnt some interesting things from it.


It turns out there are specimens of Microraptor and Anchiornis that only have poorly preserved, 'simple' feathering similar to the Sinornithosaurus specimens, e.g. the Microraptor zhaoianus holotype, the 'bird-eating' Microraptor specimen and the Anchiornis holotype.  However it's known Microraptor and Anchiornis have forelimb wings and hindlimb wings made up of long remiges, and that they have tail fans, because there are also specimens of these animals with better preserved feathering that preserve these features.  It appears feathering isn't well-preserved in the known specimens of Sinornithosaurus, so it's not known what the wing feathers and tail feathers of Sinornithosaurus were like.


I've found this study from December 2016, which is the most recent study in this area I know of: link  In this study the authors say that the existence of potential aerodynamic surfaces formed by pennaceous feathers has never been persuasively documented in Sinornithosaurus, so the presence of volancy in this taxon is uncertain.  So it looks like that's it, the quality of the preservation of the feathers of Sinornithosaurus mean it really isn't known what the wing feathers and tail feathers of Sinornithosaurus were like, and consequently whether it was capable of flight.

In the study, the authors also say Changyuraptor was likely volant but this is not as clear as it is for Microraptor, and that Rahonavis and Buitreraptor may both have been volant unenlagiines, although some have found Rahonavis to be a bird and no preserved feathers are known for either of the two animals.


I hope a future fossil discovery will show what the feathering of (adult) Sinornithosaurus was like!  In the absence of further evidence, I favour Sinornithosaurus being able to fly, and having long remiges forming large forelimb wings, leg wings, and a tail fan similar to that of Microraptor and Changyuraptor.

[Dinoguy2]

I think the basic premise here is a bit off, because adult Sinornithosaurus was almost double the size of the larger Microraptor specimens. If Sinornithosaurus was volant, picture something the size of a large eagle!

But yeah, no Sinornithosaurus adult specimens (all one of them) preserve wing feathers. There is a specimen that has been referred but there is no confirmation of its species and it might be a particularly large be Microraptor.

http://dinogoss.blogspot.com/2009/05/four-wings-good-two-wings-bad.html?m=1

[Derek.McManus]

Fascinating stuff! I certainly learned a thing or two from reading the thread! Thanks for posting!

[Sim]

I think the basic premise here is a bit off, because adult Sinornithosaurus was almost double the size of the larger Microraptor specimens. If Sinornithosaurus was volant, picture something the size of a large eagle!

The maximum length for Sinornithosaurus and Microraptor appears to be basically the same.  The restored Sinornithosaurus millenii holotype in Scott Hartman's skeletal appears to be around 1.1m long, and the Microraptor gui holotype appears to be around 1m long.  It's mentioned on The Theropod Database blog here, that the Microraptor hanqingi holotype is about 11-14% larger than M. gui.  (Personally I agree with the argument that M. hanqingi and M. gui appear to be junior synonyms of Microraptor zhaoianus.)  The skeletal proportions of Sinornithosaurus differ somewhat to those of Microraptor though, which results in Sinornithosaurus being larger than Microraptor even if their length is the same.  I think their sizes are close enough to describe them as similar.  My point is there isn't a big size difference between Sinornithosaurus and Microraptor, especially in contrast to the much larger microraptorian Tianyuraptor which appears to be already around 1.8m long as a subadult!

I like the eagle comparison, it helps to picture it!

But yeah, no Sinornithosaurus adult specimens (all one of them) preserve wing feathers. There is a specimen that has been referred but there is no confirmation of its species and it might be a particularly large be Microraptor.

http://dinogoss.blogspot.com/2009/05/four-wings-good-two-wings-bad.html?m=1

It would be nice to get confirmation of the species of that specimen shown in the Dinogoss blog post.  Thanks for all the info.  It's good to know that there aren't any adult Sinornithosaurus specimens that preserve wing feathers.

[Sim]

Fascinating stuff! I certainly learned a thing or two from reading the thread! Thanks for posting!

I'm glad to hear that!


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I've seen that in the second edition of The Princeton Field Guide to Dinosaurs, Gregory Paul says this about Sinornithosaurus millenii:

Poor preservation of feathers has caused many to problematically presume it was not winged despite flattening of central finger.

I think he's exactly right.  He also considers Sinornithosaurus millenii to be volant and reconstructs it with large wings on its forelimbs and hindlimbs similar to Microraptor, and with rectrices similar to Changyuraptor's.  I like his reconstruction of Sinornithosaurus millenii.

[Dinoguy2]

I think the basic premise here is a bit off, because adult Sinornithosaurus was almost double the size of the larger Microraptor specimens. If Sinornithosaurus was volant, picture something the size of a large eagle!

The maximum length for Sinornithosaurus and Microraptor appears to be basically the same.  The restored Sinornithosaurus millenii holotype in Scott Hartman's skeletal appears to be around 1.1m long, and the Microraptor gui holotype appears to be around 1m long.  It's mentioned on The Theropod Database blog here, that the Microraptor hanqingi holotype is about 11-14% larger than M. gui.  (Personally I agree with the argument that M. hanqingi and M. gui appear to be junior synonyms of Microraptor zhaoianus.)  The skeletal proportions of Sinornithosaurus differ somewhat to those of Microraptor though, which results in Sinornithosaurus being larger than Microraptor even if their length is the same.  I think their sizes are close enough to describe them as similar.  My point is there isn't a big size difference between Sinornithosaurus and Microraptor, especially in contrast to the much larger microraptorian Tianyuraptor which appears to be already around 1.8m long as a subadult!

I like the eagle comparison, it helps to picture it!

But yeah, no Sinornithosaurus adult specimens (all one of them) preserve wing feathers. There is a specimen that has been referred but there is no confirmation of its species and it might be a particularly large be Microraptor.

http://dinogoss.blogspot.com/2009/05/four-wings-good-two-wings-bad.html?m=1

It would be nice to get confirmation of the species of that specimen shown in the Dinogoss blog post.  Thanks for all the info.  It's good to know that there aren't any adult Sinornithosaurus specimens that preserve wing feathers.

Is this the skeletal you're thinking of?
http://scotthartman.deviantart.com/art/Sinornithosaurus-growth-stages-537464362

If so, keep in mind as restored here, the adult Sinornithosaurus has a tail that is proportionally much, much shorter than Microraptor. Even if their top length is around 1m each, in Microraptor more than 2/3 of that would be tail (I personally think an adult Sinornithosaurus would probably have a longer tail than Dave, which would put it closer to 2m in length).

M. hanquingi is weird - it's enormous and its hind wings are MUCH smaller compared to body size as M. gui / M. zhaoianus. Unless it had truly huge forewings, which aren't preserved, there's no way M. hanquingi could get off the ground. And yet, that's about the same size as Chanyuraptor, which I seriously doubt could fly either, though again the forewings aren't preserved, so who knows. But Microraptor could just barely fly according to the recent Dececchi paper and that was based on the raven-sized M. gui holotype, not these eagle-sized things.

[HD-man]

M. hanquingi is weird - it's enormous and its hind wings are MUCH smaller compared to body size as M. gui / M. zhaoianus. Unless it had truly huge forewings, which aren't preserved, there's no way M. hanquingi could get off the ground. And yet, that's about the same size as Chanyuraptor, which I seriously doubt could fly either, though again the forewings aren't preserved, so who knows. But Microraptor could just barely fly according to the recent Dececchi paper and that was based on the raven-sized M. gui holotype, not these eagle-sized things.

Is there a link to that paper? Many thanks in advance.

[Sim]

Is this the skeletal you're thinking of?
http://scotthartman.deviantart.com/art/Sinornithosaurus-growth-stages-537464362

If so, keep in mind as restored here, the adult Sinornithosaurus has a tail that is proportionally much, much shorter than Microraptor. Even if their top length is around 1m each, in Microraptor more than 2/3 of that would be tail (I personally think an adult Sinornithosaurus would probably have a longer tail than Dave, which would put it closer to 2m in length).

Yes, that's the Sinornithosaurus skeletal I was referring to.  In the Microraptor skeletals by Scott Hartman, Jaime Headden and Greg Paul, the tail is actually less than 2/3rds the total length in Microraptor.  Perhaps you were thinking of the M. gui holotype specimen, which doesn't include some of its snout and pelvis which makes its tail look longer?  There are specimens of Sinornithosaurus that aren't Dave that also have a proportionally shorter tail than Microraptor:
https://en.wikipedia.org/wiki/File:Sinornithosaurus_millenii_2.JPG
https://en.wikipedia.org/wiki/File:Sinornithosaurus_millenii.JPG
I don't know how big they are, but to me their proportions appear to resemble the adult Sinornithosaurus's, and not Dave's proportions.  Additionally, Changyuraptor which appears to be around 1.1m long, also has a tail that is proportionally shorter than Microraptor's which can be seen in the paper that names Changyuraptor.  Describing the tail of Changyuraptor, it says:

The tail of HG B016 is proportionally shorter than in Tianyuraptor ostromi and Microraptor zhaoianus but longer than in Sinornithosaurus millenii

M. hanquingi is weird - it's enormous and its hind wings are MUCH smaller compared to body size as M. gui / M. zhaoianus. Unless it had truly huge forewings, which aren't preserved, there's no way M. hanquingi could get off the ground. And yet, that's about the same size as Chanyuraptor, which I seriously doubt could fly either, though again the forewings aren't preserved, so who knows. But Microraptor could just barely fly according to the recent Dececchi paper and that was based on the raven-sized M. gui holotype, not these eagle-sized things.

M. hanqingi is only 11-14% larger than M. gui.  (Approximate measurements I took gave M. hanqingi a length of around 1.1m long.)  To me it seems its hindlimb wing feathers are too poorly preserved to be able to see their true shape and size.  I imagine that's why the December 2016 study I linked to in Reply #2 of this thread says this:

There are three nominal species of Microraptor:Microraptor
zhaoianus (Xu et al., 2000), Microraptor gui (Xu et al., 2003),
and Microraptor hanqingi (Gong et al., 2012). Both M. gui and
M. hanqingi may be junior synonyms of M. zhaoianus (Pei et al.,
2014). Because none of the postulated differences among the
three species concern the plumage or other parts of the volant
apparatus, the taxonomic question is a moot point for purposes of
the present paper, which refers simply to the genus Microraptor.

Is this paper from July 2016 the one you're referring to?: link  I didn't see it say Microraptor could just barely fly, I saw it say:

This suggests that at reasonable speeds, even with a coefficient of lift below that of extant birds, Microraptor was likely capable of ground based take off. Also during leaping take off, the horizontal velocity of birds increases rapidly after the first few strokes (Berg & Biewener, 2010). Therefore, effective flight strokes coupled with a strong ability to jump would supply ample velocity to help achieve vertical takeoff.

[Dinoguy2]

Is this the skeletal you're thinking of?
http://scotthartman.deviantart.com/art/Sinornithosaurus-growth-stages-537464362

If so, keep in mind as restored here, the adult Sinornithosaurus has a tail that is proportionally much, much shorter than Microraptor. Even if their top length is around 1m each, in Microraptor more than 2/3 of that would be tail (I personally think an adult Sinornithosaurus would probably have a longer tail than Dave, which would put it closer to 2m in length).

Yes, that's the Sinornithosaurus skeletal I was referring to.  In the Microraptor skeletals by Scott Hartman, Jaime Headden and Greg Paul, the tail is actually less than 2/3rds the total length in Microraptor.  Perhaps you were thinking of the M. gui holotype specimen, which doesn't include some of its snout and pelvis which makes its tail look longer?  There are specimens of Sinornithosaurus that aren't Dave that also have a proportionally shorter tail than Microraptor:
https://en.wikipedia.org/wiki/File:Sinornithosaurus_millenii_2.JPG
https://en.wikipedia.org/wiki/File:Sinornithosaurus_millenii.JPG
I don't know how big they are, but to me their proportions appear to resemble the adult Sinornithosaurus's, and not Dave's proportions.  Additionally, Changyuraptor which appears to be around 1.1m long, also has a tail that is proportionally shorter than Microraptor's which can be seen in the paper that names Changyuraptor.  Describing the tail of Changyuraptor, it says:

The tail of HG B016 is proportionally shorter than in Tianyuraptor ostromi and Microraptor zhaoianus but longer than in Sinornithosaurus millenii

M. hanquingi is weird - it's enormous and its hind wings are MUCH smaller compared to body size as M. gui / M. zhaoianus. Unless it had truly huge forewings, which aren't preserved, there's no way M. hanquingi could get off the ground. And yet, that's about the same size as Chanyuraptor, which I seriously doubt could fly either, though again the forewings aren't preserved, so who knows. But Microraptor could just barely fly according to the recent Dececchi paper and that was based on the raven-sized M. gui holotype, not these eagle-sized things.

M. hanqingi is only 11-14% larger than M. gui.  (Approximate measurements I took gave M. hanqingi a length of around 1.1m long.)  To me it seems its hindlimb wing feathers are too poorly preserved to be able to see their true shape and size.  I imagine that's why the December 2016 study I linked to in Reply #2 of this thread says this:

There are three nominal species of Microraptor:Microraptor
zhaoianus (Xu et al., 2000), Microraptor gui (Xu et al., 2003),
and Microraptor hanqingi (Gong et al., 2012). Both M. gui and
M. hanqingi may be junior synonyms of M. zhaoianus (Pei et al.,
2014). Because none of the postulated differences among the
three species concern the plumage or other parts of the volant
apparatus, the taxonomic question is a moot point for purposes of
the present paper, which refers simply to the genus Microraptor.

Is this paper from July 2016 the one you're referring to?: link  I didn't see it say Microraptor could just barely fly, I saw it say:

This suggests that at reasonable speeds, even with a coefficient of lift below that of extant birds, Microraptor was likely capable of ground based take off. Also during leaping take off, the horizontal velocity of birds increases rapidly after the first few strokes (Berg & Biewener, 2010). Therefore, effective flight strokes coupled with a strong ability to jump would supply ample velocity to help achieve vertical takeoff.

Yeah, I might have been mentally picturing the M. gui tail specimen with feathers included when I made that particular mental calculation. Still, a 14% increase in mass is significant when you're talking about something as finicky as flight. The original question was "could Sinornithosaurus fly?". The answer is we don't know because we don't have the forelimb feathers needed to calculate wing loading. But we also can't simply extrapolate from smaller specimens for which those calculations have been done. Maybe somebody could use the methods in the Dececchi paper and plus in a weight estimate for a large microraptorian (as we've established, Changyuraptor, Sinornithosaurus, and M. hanquingi are all about the same length at least) and use the M. gui wing area to see what happens. My hunch is that the result would be negative, just because it would be absolutely incredible to me if we had a whole lineage of eagle-sized animals which independently evolved powered flight while the "main" avian lineage remained pretty small for most of the Mesozoic, and the large microraptorians "look" a lot bigger when scaled compared to the smaller ones despite only a ~10% increase in total length (see size comparisons below). But maybe it's just that nobody has thought of this yet.