Re: Alvarezsaur Polarity and Features

["David Marjanovic" <david.marjanovic@gmx.at>]

> There are two choices for the evolution
> of the [meta?]tarsus that a matrix like PAUP would not resolve, and this
is essentially an
> evolutionary complex that only the human brain can come up with:
>
>   1) the [meta?]tarsus of *Alvarezsaurus* is basal to _all_ alvarezsaurs,
thus the condition in
> mononyki[ne]s are derived and convergent to the condition in other
arctomet theropods; the arctomet
> is essentially only a complex of advanced theropod cursorial adaptations,
rather than indicating
> any real phylogenetic signal.
>
>   2) the tarsus of *Alvarezsaurus* is unique to Maniraptoriformes,
indicating that the [meta]tarsus of
> the Mononyki[n]ae is the plesiomorphic condition; the arctomet pes is
plesiomorphic to the group,
> and appears to indicate a phylogentic signal [...].
>
>   Either condition is plausible, one is more parsimonious than the other
based on reduction of
> transformations (reversals or acquisitions).

IMHO, while both are equally parsimonious, 2) is much less plausible because
it requires *Alvarezsaurus* to lose the arctomet while obviously staying
cursorial (the metatarsus is long and compressed like in *Archaeopteryx*,
more than in *Coelophysis* or IIRC *Compsognathus*). Judging from the line
drawing in Glut's Encyclopedia, it looks a lot like that of *Archaeopteryx*
in general.