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Re: Mei example
> > So... if short-tailed birds were shown to either form a single clade or
> > be closer to dromaeosaurs, scansoriopterygids or suchlike, or both, this
> > character would disappear from this list.
Nonsense -- I meant long-tailed ones, including *Archaeopteryx*, instead of
short-tailed ones; and I unconsciously excluded the (...probably remote)
possibility of dromies being closer to Pygostylia than to long-tailed birds.
> The incorporation of caudals into the sacrum is indeed a problem with this
> character. Unfortunately, birds were lowering both dorsal and caudal
> counts, so determining how many sacrals were originally caudals is
True -- but not all sacrals are equally fused (at least in said chicken).
The oldest sacrals are probably somewhere between the acetabula... more or
less in the middle of the sacrum.
> Then there's the issue of how many caudal vertebrae are in the
> pygostyle, and if this number differs between pygostyles of different
> (eg. Confuciusornis vs. Hesperornis). These issues do combine to make the
> character tenuous.
There is that number (I forgot the source...) of 18 to 23 caudals in embryos
of living birds, most of which end up in synsacrum and pygostyle. This
suggests that the pygostyle has secondarily lost vertebrae in Euornithes.