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Re: [dinosaur] Jianianhualong, new feathered troodontid from Lower Cretaceous Jehol Group of China (free pdf)

I agree that "asymmetrical" versus "symmetrical" should not be
regarded as a binary character, since there are different kinds of
"asymmetry".  And it's still not clear why vane asymmetry (functional
asymmetry) evolved in the first place.  Was it originally associated
with terrestrial 'pre-flight' behaviors (leaping, maneuverability,
etc)?  Or was vane asymmetry originally involved in a non-locomotory
function, such as display?  Vane asymmetry is seen in certain
short-armed paravians that clearly couldn't fly (and almost certainly
didn't glide) - like _Jianianhualong_ and _Zhenyuanlong_ (though
asymmetry is not certain). Thus, the oft-stated link between vane
asymmetry and flight ability is not clear cut.

I think Reviewer #1 is spot on when they say, "The ability to glide is
suggested here but not supported; asymmetrical feathers occur in other
non-avian dinosaurs that did not fly, and appear today in some birds
even though they are not used in flying. So their presence does not
automatically relate to any kind of flight."  (The authors, to their
credit, didn't really push any alleged gliding abilities for
_Jianianhualong_ in the published paper.)

It's tempting to argue that short-armed paravians with asymmetric
vanes (e.g., _Jianianhualong_, _Zhenyuanlong_?) were secondarily
non-volant, i.e., they evolved from volant ancestors that lost the
ability to glide or fly.  This is certainly plausible for
_Zhenyuanlong_, if it's closely related to _Microraptor_.
_Zhenyuanlong_ has quite a complex, layered wing (composed of
primaries, secondaries, coverts), with the primaries and secondaries
apparently asymmetrical (though this is not certain, due to the state
of preservation of the plumage).  Aside from relative size, its wings
are strikingly similar to those of the much smaller, long-armed
_Microraptor_.  But a volant ancestry seems less likely for a derived
troodontid like _Jianianhualong_, so its vane asymmetry might have
nothing to do with flight ability (or loss of this ability from a
flighted ancestor).

If vane asymmetry didn't begin as a flight-related character, this is
consistent with vane asymmetry being very basal in Paraves. Functional
asymmetry then led to aerodynamic asymmetry and the 'modern' avian
flight feather, plus further refinements to the flight apparatus;
based on Feo et al. (2015), this happened at or around the level of
Ornithothoraces.  Although the _Jianianhualong_ paper favors the
hypothesis that feather asymmetry was ancestral to Paraves, I think
it's plausible that vane asymmetry evolved in Paraves multiple times.
In other words, certain deinonychosaurs evolved vane asymmetry
separately, and independently of birds.  There is no evidence that the
evolution of any sort of vane asymmetry was initially tied to gliding
or powered flight.

Finally, a phylogenetic comment on the paper.  I'm a bit confused by
the phylogenetic definitions of the clades used in this paper.
Avialae apparently excludes _Archaeopteryx_.  Figure 6 has
_Archaeopteryx_ within Deinonychosauria, although as far as I can tell
this is not explicitly stated.

On Wed, May 3, 2017 at 6:36 AM, Mike Habib <biologyinmotion@gmail.com> wrote:
> Just finished a quick read through of this paper. It is a neat specimen and a 
> generally well-written paper. The idea that feather vane asymmetry might be 
> quite basal is very interesting (albeit not terribly surprising).
> My one criticism at the moment is that while the authors cite the most 
> important literature regarding the relevant dynamics related to feather 
> asymmetry, they don’t really use that literature effectively. The paper, as 
> written, implies that the dynamics of feather asymmetry aren’t well 
> understood. Contrary to this suggestion, the basics of asymmetrical vane 
> twist and stall reduction are known, and the key paper on the subject (Feo et 
> al., 2015) is even cited in this manuscript - but only as support for the 
> statement that asymmetry is complicated! I feel that this oversight matters, 
> because the difference between functional asymmetry and anatomical asymmetry 
> could play into the phylogenetic patterns that the rest of the paper is 
> primarily concerned with.
> Plotting the appearance of feather vane asymmetry in the tail and forelimbs 
> in a phylogenetic framework was a great idea, but I do wish the authors had 
> plotted both anatomical asymmetry (as they did) and aerodynamic asymmetry 
> (which they did not).
> I’d be curious to hear what others think of the manuscript.
> Cheers,
> —MBH
> Michael Habib, MS, PhD
> Assistant Professor, Integrative Anatomical Sciences
> Keck School of Medicine of USC
> University of Southern California
> Bishop Research Building; Room 403
> 1333 San Pablo Street, Los Angeles 90089-9112
> Research Associate, Dinosaur Institute
> Natural History Museum of Los Angeles County
> 900 Exposition Blvd, Los Angeles, CA 90007
> biologyinmotion@gmail.com
> (443) 280-0181
>> On May 2, 2017, at 9:57 AM, Ben Creisler <bcreisler@gmail.com> wrote:
>> Ben Creisler
>> bcreisler@gmail.com
>> A new paper in open access:
>> Free pdf:
>> Xing Xu, Philip Currie, Michael Pittman, Lida Xing, Qingjin Meng, Junchang 
>> Lü, Dongyu Hu & Congyu Yu (2017)
>> Mosaic evolution in an asymmetrically feathered troodontid dinosaur with 
>> transitional features
>> Nature Communications 8, Article number: 14972 (2017)
>> doi:10.1038/ncomms14972
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.nature.com_articles_ncomms14972&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=VNxchIqWbg5Av5JX9LDpOvu9xBh0fjY3NjNT-nKsktE&s=-_ph7ku7I_2srBqkrisbBR4dgN7hi9G8DxQ53ADxUeI&e=
>> Asymmetrical feathers have been associated with flight capability but are 
>> also found in species that do not fly, and their appearance was a major 
>> event in feather evolution. Among non-avialan theropods, they are only known 
>> in microraptorine dromaeosaurids. Here we report a new troodontid, 
>> Jianianhualong tengi gen. et sp. nov., from the Lower Cretaceous Jehol Group 
>> of China, that has anatomical features that are transitional between 
>> long-armed basal troodontids and derived short-armed ones, shedding new 
>> light on troodontid character evolution. It indicates that troodontid 
>> feathering is similar to Archaeopteryx in having large arm and leg feathers 
>> as well as frond-like tail feathering, confirming that these feathering 
>> characteristics were widely present among basal paravians. Most 
>> significantly, the taxon has the earliest known asymmetrical troodontid 
>> feathers, suggesting that feather asymmetry was ancestral to Paraves. This 
>> taxon also displays a mosaic distribution of characters like Sinusonasus, 
>> another troodontid with transitional anatomical features.
>> ===
>> News:
>> https://urldefense.proofpoint.com/v2/url?u=http-3A__news.nationalgeographic.com_2017_05_fossil-2Ddinosaur-2Dtheropod-2Dfeather-2Devolution-2Ddiscovery-2Dchina_&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=VNxchIqWbg5Av5JX9LDpOvu9xBh0fjY3NjNT-nKsktE&s=29b3ebixy2bLbkI7srKUq2w3HbIDitObSyn3h08IfF8&e=
>> https://urldefense.proofpoint.com/v2/url?u=http-3A__gizmodo.com_this-2Dnew-2Ddinosaur-2Dlooked-2Dan-2Dawful-2Dlot-2Dlike-2Da-2Dchicken-2D1794833786&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=VNxchIqWbg5Av5JX9LDpOvu9xBh0fjY3NjNT-nKsktE&s=uFi0ufebGWRldE4I4l_uQH0QYtmkwG7H5ci7Vay9iCE&e=