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RE: At long last! Turner, Makovicky & Norell on dromaeosaurids



  I do not think the current evidence suggests the sterna of 
*Protarchaeopteryx robusta* present a good base for which large 
pectoralis muscles may be supported. I, of course, haven't done the modeling -- 
I am willing to be corrected, and viciously. My understanding is that they 
*might* be stable if there was some method which kept the plates from moving 
relative to one another, rather than kept them working together. There may be 
such a novelty as a hinge between them, controlled by unknown ligaments or 
muscles, and which would thus bring them from states of instability (being 
skewed) into stability (mirrored).

  Until description of the Thermopolis specimen, *Archaeopteryx lithographica* 
had a fairly well conserved spot for pectorals to be supported with, which 
helped negate the distortion in the girdle. It wouldn't have mattered how small 
the sternum was, as it can form the base of more extensive surfaces, as in 
bats. But we may project that what can be there is simply not recovered. In 
this way, missing data is missing data. *Microraptor zhaoianus* (going by 
Hwang's referred specimens, and partially by *Microraptor gui* -- regardless if 
it's *zhaoianus* or not) had at least partially-fused sterna. This cannot be 
the case for *Protarchaeopteryx robusta* (and indeed, for *Caudipteryx zoui* as 
well), where the sterna are separate and do not even have similar medial shape, 
implying they are without secure contact to one another, even if the space 
between them is filled by cartilage (it would be cartilage of each sternum 
individually, but not one cohesive certilage from which the bone is ossified, 
due to taxa like *Ingenia yanshini* in which the sternal plates show a 
well-ossified appearance, but are separate, partially overlapping, and not that 
significantly different from other oviraptorid sterna (e.g., MPC-D 100/42).

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)


----------------------------------------
> Date: Mon, 27 Aug 2012 10:35:26 +1000
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: At long last! Turner, Makovicky & Norell on dromaeosaurids
>
> I wrote:
>
> > But this was difficult for cursorial animals that still had a
> > fairly cranial center of mass, and hip-based stride generation, and
> > needed a long tail for balance.
>
>
> Oops, that should be "caudal", not "cranial".
>
>
>
> Jaime Headden <qi_leong@hotmail.com> wrote:
>
> > Consider at least that, if Senter's analysis is correct (as has been 
> > followed since), *Incisivosaurus gauthieri* should have a postcrania much 
> > like that of *Protarchaeopteryx
> > robusta*: short tail, longish neck, lanky legs, and relatively long arms. 
> > Compared to the body proportions of microraptorians, which have a very long 
> > tail to compensate their
> > total body length. I'm not quite sure about the effectiveness of even large 
> > sterna when they are not fused to one another, and if we presume this is 
> > the adult condition (size
> > disparity may suggest this wasn't the case), the shoulder apparatus would 
> > have been highly unstable for holding the limbs out for any sort of 
> > sustained flapping or even
> > gliding.
>
>
> But is the shoulder apparatus of _Protarchaeopteryx_ any less stable
> than that of _Archaeopteryx_ and _Microraptor_? I wouldn't have
> thought so. They're all about the same. It is isn't until the level
> of _Jeholornis_ that we see any real reinforcement of the shoulder
> apparatus.
>
>
>
>
>
>
>
> Cheers
>
> Tim