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Re: Dromaeosaurid tails like rhamphorhynchid tails from flight use

I would rather think character optimization should indicate whether or
not the features of Mahakala are primitive or derived for
dromaeosaurs, not time after divergence, at least if we follow


2013/1/17 Matthew Martyniuk <martyniuk@gmail.com>:
> I'd be careful assigning such significance to Mahakala. It is at least
> 75 Ma removed from the common ancestor of all dromaeosaurs. So while
> Mahakala may be among the most basal dromaeosaurs, that doesn't
> necessarily mean it's the most primitive. Monotremes are the most
> basal living mammals, but that doesn't mean the ancestral mammal was
> platypus-like. It's always possible that such odd (for a dromaeosaur)
> features as very small forelimbs and un-stiffened tails in Mahakala
> were due to some novel ecological niche (burrowing?).
> Matt
> On Thu, Jan 17, 2013 at 1:12 AM, Tim Williams <tijawi@gmail.com> wrote:
>> Ben Creisler <bcreisler@gmail.com> wrote:
>>> W. Scott Persons IV & Philip J. Currie (2012)
>>> Dragon Tails: Convergent Caudal Morphology in Winged Archosaurs
>>> Acta Geologica Sinica - English Edition 86 (6): 1402–1412
>>> DOI: 10.1111/1755-6724.12009
>>> http://onlinelibrary.wiley.com/doi/10.1111/1755-6724.12009/abstract
>> The paper seems to be saying that the chevron and zygapophyeal caudal
>> rods of dromaeosaurids evolved in an aerial/arboreal context (as in
>> rhamphorhynchoids).  In other words, the specialized stiffened tail of
>> dromaeosaurids evolved "on the wing" to assist in gliding or flying.
>> Therefore, the highly specialized tail of large, and presumably fully
>> terrestrial dromaeosaurids (such as _Deinonychus_ and _Velociraptor_)
>> would be a relict of an aerial/arboreal ancestry (represented by basal
>> dromaeosaurids such as _Microraptor_)... according to this hypothesis.
>> I'm not convinced.  Little _Mahakala_, which comes up as the most
>> basal dromaeosaurid, lacks the elongate prezygapophyses and chevrons
>> present in more derived dromaeosaurids; but it nevertheless has an
>> underdeveloped fourth trochanter.  So unless _Mahakala_'s caudal
>> features are a reversal (like the short forelimbs), then the presence
>> of rod-like prezygapophyses and chevrons in more derived
>> dromaeosaurids is not necessarily correlated with the proposed
>> reduction in femoral retraction (i.e., a more bird-like locomotor
>> style).
>> Both "Groucho running" and caudal rods are regarded by this study as
>> indicators of aerial behavior (or descended from ancestors that
>> exhibited aerial behavior).  I'm still extremely skeptical that
>> deinonychosaurs had a bent-legged locomotor style ("Groucho running").
>>  I'm still extremely skeptical that deinonychosaurs had a bent-legged
>> locomotor style ("Groucho running").  And as for the caudal rods:
>> _Deinonychus_, _Velociraptor_ and _Achillobator_ had these specialized
>> caudal rods, even though they were not likely to have been aerial
>> gliders (or fliers!)  Presumably these highly specialized rods had a
>> purpose in these large, derived dromaeosaurids that had nothing to do
>> with aerial behavior.  If so, maybe the original purpose for these
>> caudal rods also had nothing to do with aerial behavior.
>> The authors aver: "A thin light-weight tail with reduced caudofemoral
>> musculature that preferentially retains lateral flexibility while
>> increasing dorsoventral rigidity is well suited for a flying or
>> gliding animal."  I don't doubt that this is true.  But that doesn't
>> mean such a tail couldn't be used for other behaviors.  The
>> biomechanical pressures might have been similar between the tails of
>> dromaeosaurids and rhamhorhynchoids; however, the behavioral pressures
>> may have been quite different.  Ostrom's hypothesis that _Deinonychus_
>> attacked prey much larger than itself has been criticized by some
>> (e.g., Darren Naish), but I'm more supportive.  Perhaps the
>> specialized tail of dromaeosaurids was associated with predation -
>> more in line with what Ostrom proposed in 1969 for the tail of
>> _Deinonychus_.
>> Cheers
>> Tim