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Re: [dinosaur] Serikornis, new Jurassic theropod from China with transitional feathers



> Serikornis sungei gen. et  sp. nov.
>
>
> Ulysse Lefèvre, Andrea Cau, Aude Cincotta, Dongyu Hu, Anusuya Chinsamy, 
> François Escuillié & Pascal Godefroit (2017)
> A new Jurassic theropod from China documents a transitional step in the 
> macrostructure of feathers.
> The Science of Nature 104:74 (advance online publication)
> DOI: 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1007_s00114-2D017-2D1496-2Dy&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=M1qIKQuG_OuDSTuuzbmyhwQPmDJnuhRpQSQJQ2jynJw&s=DSecuzKTwYaaPSKBRLmux-lC43pqIbVuinQ3WDbNfJA&e=
> https://urldefense.proofpoint.com/v2/url?u=https-3A__link.springer.com_article_10.1007_s00114-2D017-2D1496-2Dy&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=M1qIKQuG_OuDSTuuzbmyhwQPmDJnuhRpQSQJQ2jynJw&s=k1-BGFhb5VINWKsZuNuX3KXo3I6kr4S5hLJaVpN0zuE&e=



I'd like to begin by saying well done to the authors - this is a
fascinating discovery.

I agree completely that the absence of true flying adaptations in
_Serikornis_ is consistent with an aerodynamic function NOT being the
driver behind the development of elaborate wing-like plumage in
theropods.  Some form of socio-sexual selection is a more likely
explanation.  In some non-flighted paravians, the forewings (and
tail?) may have been involved in some form of ground-based aerodynamic
behavior (leaping, maneuverability, etc), but this doesn't seem to
have been the case for _Serikornis_ given the morphology of the
feathers attached to its limbs and tail.  Thus, the 'tetrapterygian'
(four-winged) plumage of _Serikornis_ may have been entirely for
display.

It's suggested that _Serikornis_ was both a terrestrial cursor AND an
arboreal climber:

"Moreover, the relatively high ratio
of tibiotarsus length to femur length can be regarded as a good
evidence of cursoriality (Boles 1997). All these characters
suggest that basal paravians were primarily ground-dwelling
animals with good cursorial abilities (Foth et al. 2014; Hu
et al. 2009). However, the manual digits of _Serikornis_ are long
and slender with strongly curved unguals I and III. This supposed
that they could have been effective for climbing trees as
in _Archaeopteryx_ (Feduccia 1993; Manning et al. 2009;
Wellnhofer 2009). In this way, the hindlimbs can be regarded
as less specialized than the forelimbs for grasping."


I'm really skeptical of any quadrupedal climbing abilities in basal
paravians like _Anchiornis_, _Serikornis_, and _Microraptor_.  In
fact, I doubt any basal avialan was capable of quadrupedal climbing
(including _Archaeopteryx_, _Confuciusornis_, _Sapeornis_ etc).  The
manus was simply not adapted for grasping branches - especially if the
second and third fingers were bound together in skin, as is apparent
in _Anchiornis_ (e.g., Wang et al. 2017 DOI: 10.1038/ncomms14576).
More generally, these paravians lacked the mobile joints for climbing
trees (except possibly the shoulder); the hindlimbs were specialized
for parasagittal locomotion, and the semilunate wrist was a swivel.
So even if the tetrapterygian condition is primitive for Paraves or
Eumaniraptora, I doubt that flapping flight of modern birds was
preceded by a four-winged arboreal gliding stage.  Besides, there's no
need for arboreal gliding.  Incipient flight could evolve on the
ground, among small paravians that used their strong hindlimbs to
launch into the air, and used their weak (but relatively large) wings
for leaping and fluttering.  The idea that small four-winged paravians
were scansorial or arboreal gliders always seems 'forced' to me.  It
goes way beyond the osteological evidence.