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Re: no marine dinos/no viviparous dinos.
> Given the current distribution of loons/divers in the northern hemisphere
> only, and the recent claims that loons and penguins are sister groups
> have refs?),
Newest I can find is a sequence-based phylogeny in
Marcel Van Tuinen, Dave [sic] Brian Butvill, John A. W. Kirsch & S. Blair
Hedges (email@example.com): Convergence and divergence in the evolution of
aquatic birds, Proceedings of the Royal Society Biological Sciences 268,
1345 -- 1350 (7 May 2001 IIRC)
Also see below.
> is it possible that the Antarctic "loon" (it's *Polarornis*,
> right?) is actually on the penguin branch of the family tree?
It is *Polarornis* (and there's *Neogaeornis* from Chile), and it is a
foot-propelled diver with a cnemial crest neither like those of
hesperornithiforms nor those of grebes but those of loons. I think if
penguins had started as foot-propelled divers they, erm, would be loons.
> Then again, how good is the fossil record for Gaviiformes?
Feduccia (1996 book) p. 174 and 176: "The oldest truly reliable records for
loons [*Polarornis* was unknown] are the two species of *Colymboides*, *C.
anglicus* from the Eocene of England and *C. minutus* from the early Miocene
of France and the former Czechoslovakia [...] The modern genus *Gavia* first
appears in the Lower Miocene of the former Czechoslovakia as *Gavia
egeriana* from deposits that have also yielded the primitive loon
*Colymboides minutus*, thus illustrating that the two lived
contemporaneously". He does not mention in the text the Oligocene loon
*Gaviella* but shows it in a family tree on p. 176 which is copied from a
paper from 1960.
Grebes, BTW, are not known before the early Miocene.
Same page: "On the basis of his extensive study of the fossil loon
*Colymboides minutus*, Storer (1956, 1960) suggested that loons may have
been derived from a shorebird (charardriiform) ancestry. However, the
feather structure and loonlike bill and vertebrae of some Eocene penguins
may point to a 'close common ancestry between the Gaviiformes and
Sphenisciformes' (Olson 1985a, 216), a conclusion that is concordant with
DNA comparisons, which 'support a relationship among loons, penguins, and
procellariids, but not a close relationship between loons and grebes'
(Sibley and Ahlquist 1990, 550)."