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On the subject of chamaeleon limb posture and its relationship to
what dinosaurs did, Ralph Miller III wrote...
> Right. Old World tree chameleons do set down their feet directly
> under their bodies when they walk along narrow branches-- eschewing
> the typical reptilian sprawl -- but they do not walk with straight
If you are saying this makes them different from 'erect stanced'
dinosaurs, think again because no one is saying that dinosaur legs
are necessarily held out straight beneath the body. An erect stance
does not preclude legs/arms bowing outward and in fact numerous
erect-stanced tetrapods - birds including ratites and anseriforms
are great examples - actually have legs that bow outwards when their
skeletons are viewed cranially or caudally. The important thing is
that the body is perpetually raised off the ground during all modes
of terrestrial locomotion. Thus reptiles like crocs and varanids,
which can assume erect-stanced postures, are not fully
erect-stanced.. any distinction has become blurry since we have
learnt more of biomechanics and tetrapod gait however (e.g. sprawling
limbs in MTBs). Pillar-like erect legs that really don't bow outwards
are seen, not surprisingly, in big graviportal tetrapods like
sauropods and elephants.
What is important and superficially dinosaur-like about chamaeleon
forelimbs is that they have a slab-sided thorax where the scapula is
stuck flat against it and the glenoid fossa is not directed
laterally, but more ventrocaudally (actually, it is kind of
lateroventrocadually in the chamaeleons I've seen..). It's well known
that some quadrupedal dinosaurs have elbows that articulate in a
flexed position, and not in a straight vertical line perpendicular to
the spine. Chamaeleons approach this complex better than other
What chamaeleons do not have, and what ceratopians apparently do, is
a lateral lip to the glenoid fossa which prevent lateral torsion of
the humerus. If this is correct, it shows that ceratopian forelimb
motion is not totally like that of chamaeleons. I only know the
basics of ceratopian anatomy so I'll leave it at that.
"Look at me, I'm a kitty kat: meoww-moww!!"