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> Avepoda was first proposed in DA, not PDW
Yes, but the name Avepoda first *appeared* in PDW:
"...the bird foot - in which the inner cannon bone does not reach the
ankle - is especially distinctive. It is not proven to appear
anywhere else, and may have evolved only once, so it is a good minimum
definition of the Theropoda. (In this regard, the name Theropoda,
which means beast-footed, is most inappropriate. Avepoda would be
much better, but it is too late for that.)"
So Avepoda was originally mentioned as a replacement name for
Theropoda (Paul, 1988), before being formally applied to a less
inclusive clade (Paul, 2002).
The lack of contact of metatarsal I with the ankle was used as the
defining apomorphy in the definition of Avepoda. This is an
interesting feature, because I'm not sure what adaptive mechanism
drove the detachment of metatarsal I from the distal tarsals, and its
subsequent descent down the metatarsus. As GSP notes, the loss of
contact of metatarsal I with the ankle likely occurred only once in
theropod evolution. But the theropod pes remained functionally
tridactyl - at least from the perspective of locomotion.