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

[Tim Williams <tijawi@gmail.com>]

Mike Habib <biologyinmotion@gmail.com> wrote:

> The weird thing here, for me, is that living arboreal flyers still use 
> leaping launch modes to initiate flight - even the unpowered ones.
> There are no living gravity launchers (that we have found so far, anyway). So 
> even if Mayr had good evidence for arboreal behavior
> near the origin of avian flight, I'm not sure how that would yield a "gravity 
> assisted" model. I suppose he's referring to the gliding
> phase itself?


Yes, that's my impression.  Mayr (2016): "An arboreal animal can use
the energy provided by gravity for gliding, in which case an
incremental formation of structures increasing drag or providing lift
is positively selected for." (p.38)  However, Mayr soon after states:
"Analyses of morphological traits associated with a strictly arboreal
way of life do not support such habits of _Archaeopteryx_ and the
paravian ancestors of birds, but indicate that arboreal adaptations
evolved within the avian lineage (Dececchi and Larsson 2011)."  I
agree wholeheartedly with this particular statement by Mayr.

But Mayr is not convinced that we can confidently "make inferences on
the habits of extinct taxa by comparison with extant animals that live
in very different ecosystems" - hence his skepticism of a strictly
"ground-up" origin of flight, despite the clear terrestrial/bipedal
abilities of _Archaeopteryx_ (which Mayr acknowledges).  Mayr seems to
be saying that _Archaeopteryx_ (and its kin) defy ready
ecomorphological interpretation - at least not without detailed
knowledge of the animal's immediate habitat, which were presumably
quite different to modern angiosperm-dominated habitats.  Hence, Mayr
is casting doubt on the approach of Dececchi & Larsson, whose analyses
inferred a terrestrial (ground-based/non-perching) lifestyle for
_Archaeopteryx_ based on comparison with extant vertebrates (including
birds).  Fair enough - up to a point.  But the same analyses (Dececchi
& Larsson) also found that other early Mesozoic birds clustered with
perching birds, and have limb indices and pedal adaptations consistent
with perching.  So there's good reason to believe that arboreal
adaptations in the mid-Mesozoic were the same or similar to those in
the present.

Further, there's every reason to believe that Mesozoic avians, and
their paravian ancestors, used leaping launch modes to become airborne
- including by true powered fliers to initiate flight.  This is the
most parsimonious interpretation.



References

Dececchi TA, Larsson HCE (2011). Assessing arboreal adaptations of
bird antecedents: Testing the ecological setting of the origin of the
avian flight stroke. PLoS ONE 6: e22292.
doi:10.1371/journal.pone.0022292

Mayr G (2016). Avian Evolution: The Fossil Record of Birds and its
Paleobiological Significance. Chichester, UK: John Wiley & Sons