RE: Parts & Non-Recreation (was: Ceratonykus)

[Jaime Headden <qi_leong@hotmail.com>]

Vivian Allen wrote:

<It's been brought up a couple of times (By Jason and myself at least, 
apologies if I've missed anyone), but no-one seems to be that interested in 
discussing it.>

Pfft. I'm interested in discussing it. 

  First, note something odd about alvarezsaurs, their hips: they have widely 
flaring postacetabular ala of the ilia; virtually no fusion of the pubic 
symphysis and certainly not of the ischiadic symphysis, instead adopting a 
broadly approaching distal ends neatly conjoined, but not actually fused; a 
developed supracetabular crest of the ilium that extends cranially above the 
pubic peduncle; and an ilium generally longer caudally than cranially to the 
acetabulum's midpoint viewed laterally (if the lateral face of the ilium was 
perpendicular to the sagittal, even though it wasn't). Hip musculature is 
unusual, but it seems to favor the caudofemoralis brevis and iliofibularis 
muscles over the iliofemoralis. This implies the leg extensors were dominant 
over the leg protractors, and more so than in tyrannosaurs or ornithomimosaurs, 
so I hardly think this is phylogenetic or just about speed. The same is true 
for all birds, of course, but the developed supracetabular crest implies the 
femur was probably not held subhorizontally, but rather vertically.

  Second, the feet are cursorially adapted, which relatively short toes 
compared to pes length, a _very_ derived arctometatarsus, and elongated distal 
limb segments (excluding the toes). But these features don't necessarily 
exclude digging. The pedal unguals are higher than wide in *Mononykus 
olecranus* at least, but still appear to possess a developed ventral platform, 
extending into lateral and medial "spurs," as they do in "hoofed" ornithischian 
unguals. Perle et al.'s osteology doesn't say much about range of motion in the 
toes, and developed dorsal (extensor) processes are not apparent (which would 
extend far proximally above the condyle of the preceeding phalanx), but this 
also doesn't exclude digging capability.

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: Sun, 1 May 2011 10:36:28 +0100
> From: mrvivianallen@googlemail.com
> To: dinosaur@usc.edu
> Subject: Re: Parts & Non-Recreation (was: Ceratonykus)
>
> It's been brought up a couple of times (By Jason and myself at least,
> apologies if I've missed anyone), but no-one seems to be that
> interested in discussing it.
>
> On 1 May 2011 09:35, Jaime Headden  wrote:
> >
> > Tim Williams wrote:
> >
> Note something that hasn't been brought up: why did alvarezsaurs use
> their arms for digging, when they have perfectly good legs that other
> avian diggers use instead (wing-shoveling loose soil or snow, but
> foot-based digging)?
> >
> > 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)
> >