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In a message dated 97-07-14 12:14:12 EDT, firstname.lastname@example.org (Mark
<< Binosaurs is a name I call bipedal thecodonts,
dinosaurs, pterosaurs, and birds. Their bipedal nature freed
up their hands for other purposes. >>
I have a rather different slant on this.
(1) There weren't any bipedal thecodontians.
(2) Pterosaurs were probably not erect bipeds but only got up on their hind
limbs before taking off from level ground, to allow the wings to clear--a
behavior that evolved along with or perhaps somewhat later than the wings
(3) The initial evolution of forelimbs into wings in theropods >compelled<
bipedality in multiple descendant cursorial, ground-dwelling forms, since the
forelimbs could no longer be used for terrestrial locomotion and became
exapted for grasping or vestigialized. This fits the well-known pattern of
forelimb evolution in secondarily flightless birds.
(4) I strongly doubt whether habitual or obligatory bipedality would evolve
>spontaneously< in any terrestrial vertebrate lineage, as is commonly thought
to have occurred in "binosaurs," though I cannot exclude the possibility
completely in small, lightweight cursorial forms where the hindlimbs might
exapt for hopping (for example) or some similar form of locomotion.