Re: [dinosaur] 2016 in paleontology + Dippy's last days in London + burrows around Omeisaurus + more

[Tim Williams <tijawi@gmail.com>]

David Černý <david.cerny1@gmail.com> wrote:

> While you may find them interesting or even important, it's hard to fault a
> brief overview of last year's paleo highlights for not including them. For
> starters, Domyan et al. (2016) is not even a paleontological paper, and it
> has very little to say about the origin of flight – it deals with the topic
> in a single paragraph, which seems to be more of an afterthought in an
> otherwise solid piece of evo-devo research.


Fair cop.  But I wouldn't dismiss the implications of this evo-devo
research for paravian evolution as an afterthought.  The authors also
mention the hindlimb plumage of paravians in the very first paragraph
of the Intro.  Although not a paleo paper (I can't disagree with you
here), it certainly has paleoecological implications regarding
'four-winged'/"tetrapteryx" paravians.


> The Dececchi et al. paper is obviously more relevant in this respect, but I
> still think you are overhyping it by suggesting that it had "a major impact
> on how we view the origin(s) of flight in theropod dinosaurs". It might well
> prove to have such an impact in the future, but right now, less than six
> months after it was published, it's just too early to say. For what it's
> worth, a recent review of avian evolution (Mayr 2016) accepts and reiterates
> Senter's (2006) conclusion that flapping flight was biomechanically
> impossible for early birds, mentions "[t]he physical and biological
> implausibility of a strict 'ground-up' origin of flight" (p. 39), and
> presents a stationary leaping take-off as a highly derived locomotory mode
> associated with a complex of pectoral girdle and wing adaptations that is
> unique to a couple of deeply nested neornithine lineages. Based on that
> alone, I don't think the debate is going away anytime soon.


Mayr (2016) is highly skeptical of any scenario for the origin of
flight that that doesn't involve a "gravity-assisted" gliding stage.
Mayr concurs with Feduccia in this regard (the sentence from which you
derive your quote goes on to cite the "detailed discussion" by
Feduccia in support).  In Mayr's view, powered flapping flight did not
evolve until the base of Ornithothoraces - so in his estimation
_Archaeopteryx_, _Jeholornis_ and even _Confuciusornis_ were "not
capable of sustained flapping flight" (p.48).  Mayr places a lot of
stock in the interpretation of a more ventrally oriented glenoid in
all non-ornithothoracine theropods (including basal birds); this goes
against the grain of most interpretations of a laterally facing
glenoid in paravians (e.g., Parsons and Parsons, 2009).

Thus, Mayr also casts doubt on WAIR as a pre-flight behavior, because
it "requires the anatomical capabilities of wing flapping".  However,
objections to WAIR are that it requires an 'advanced' flight apparatus
(with neornithine-like flapping frequencies and flap angles) - more so
than just flapping per se.  Juvenile gallinaceous birds are poor
models for incipient theropod flight: "Although extant birds hatch
with somewhat reduced forelimb muscle masses and feathering, the
musculoskeletal morphology is still generally comparable with adult
extant fliers." (Dececchi et al., 2016; p.27).

Mayr also seems to equate a "ground-up" origin of flight with
cursoriality.  However, a terrestrial origin of flight does *not*
necessarily require a running take-off.  This has been addressed not
just by Dececchi et al. (2016), but also by Earls (2000) and Caple et
al. (1983).  A leaping take-off, initiated by the hindlimbs, is
typical of extant birds.  There's no reason why this wouldn't also be
true of their theropod ancestors.  In general, I think too much is
made of the demands of the modern avian flight stroke in attempting to
refute 'flapping-start' models of avian flight evolution.  A more
rudimentary, low-amplitude flight stroke in non-ornithothoracine
avians (and some winged non-avian paravians) could have been adequate
for some form of powered flight involving lift- and thrust-generation
(probably short bursts only, in time as well as distance).

Further, according to Earls, "[a]ny downward movement of a feathered
forelimb after the initiation of a leap could potentially add height
or distance to the ballistic path." (Earls, 2000; p.737).  This
decouples the evolution of the take-off from the evolution of powered
flight, and provides a potential path for the evolution of large
aerodynamic wings before the advent of powered flight. The main reason
why I think Dececchi &c's work is so pivotal is that it rejects the
hypothesis that a stationary leaping take-off is a highly derived
locomotory behavior (contra Feduccia, Mayr, &c).  Most of the
prerequisites for a flight stroke (both integument and
musculoskeletal, assuming a laterally facing glenoid) were already
present in Paraves; and the velocity of take-off is predominantly
provided by the hindlimbs (as in extant birds; see above).

I agree that the debate will continue for a very long time to come.
No publication is the last word on this contentious subject.  But I
think it's great that the debate has moved on from
"ground-up"-versus-"trees-down".  IMHO, it is not difficult to
envision an evolutionary scenario by which modern avian flight evolved
in successive stages: wing-assisted leaping; brief fluttering flight;
and finally sustained level flight.  So paravians (including avians)
remained bipeds all the way through the nascent stages of flight, but
didn't necessarily remain terrestrial bipeds. This removes any need
for a 'passive' arboreal gliding stage in the theropod origin of
flight. I've been unimpressed by the slew of papers that have restored
_Archaeopteryx_, _Microraptor_,  _Confuciusornis_ and even
_Anchiornis_ as specialist arboreal quadrupeds and/or
"tetrapteryx"-style gliders.  I think the much-vaunted "arboreal"
abilities of these critters are way 'overhyped', and in some cases
completely fanciful.


References

Caple G, Balda RP, Willis WR. (1983). The physics of leaping animals
and the evolution of preflight. American Naturalist 121: 455-476.

Earls KD. (2000). Kinematics and mechanics of ground take-off in the
starling _Sturnis vulgaris_ and the quail _Coturnix coturnix_. Journal
of Experimental Biology 203: 725-739.

Parsons WL, Parsons KM. (2009) Further descriptions of the osteology
of _Deinonychus antirrhopus_ (Saurischia, Theropoda). Bulletin of the
Buffalo Society of Natural Sciences 38: 43-54.