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Re: Bipedality



Guy Leahy wrote:

> It's difficult to think of any clear advantage bipedalism would have.

Shine and Lambeck (1989) note that "_Chlamydosaurus_ may be unique among
reptiles in its use of bipedal locomotion for routine foraging. Many other
lizards adopt a bipedal gait at high speeds (e.g. Snyder 1962), and varanids
us this stance for surveillance as well as for threat displays (personal
observations).  We speculate that bipedal locomotion may also be advantageous
in elevating the head and thus providing a better field of view for the
lizard."

_Chlamydosaurus_ [the Australian frillneck lizard] is pugnacious and highly
territorial, aggressively chasing men carrying 16mm cameras out of its
"zone".  It spends 95% of its time hanging vertically on tree trunks, waiting
for prey (caterpillars or massed swarms of bees, wasps and winged termites)
and surveying for rivals. The trees give it a better view. Standing upright
does as well when they descend.

So rather than ventilation, surveillance and intimidation may be the
important factor in originating bipedality.  Also, note that the anatomical
features which separate _Chlamydosaurus_  and other lepidosaurian bipeds from
the quads are exagerated in pterosaurs (longish neck, reduced caudal
transverse processes and reduced hemal arches, anterior projection of the
ilium). 

David Peters

Shine and Lambeck (1989) Ecology of Frillneck Lizards, _Chlamydosaurus
kingii_ (Agamidae) in Tropical Australia
Aust. Wildl. Res., 1989, 16, 491-500.