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Re: Cretaceous loons

>      Is there any credible published information that loons (Gaviidae)
> actually existed in the Cretaceous?

If that's published meanwhile...
www.cmnh.org/fun/dinosaur-archive/2001Jun/msg01056.html also mentions the
species name: *Polarornis gregorii*.
Otherwise: Sankar Chatterjee: The Rise of Birds. 225 Million Years of
Evolution, Johns Hopkins 1997
It's pretty thoroughly illustrated and very convincing. Much more so than
the "parrot" or *Protoavis*.

> Neogaeornis may be a hesperornithiform.

Or not. Some seem to be very sure about this. Anyway it would be the only
southern hesperornithiform, separated from all others by something like
10,000 km.
        BTW, sorry, it's from Chile, not Argentina.

>      Doesn't that just leave Polarornis?  Is there anything besides the
> shape of the cnemial crest and skull (both subject to convergence)

Not subject to much convergence because there are several methods for how to
get such a cnemial crest. Three have been realized: using the patella alone,
the tibia alone, or both together. One is seen in hesperornithiforms,
another in podicipediforms, another in loons including *Polarornis*.