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Re: Land of the Lost review-spoiler?



2009/6/5  <dinoboygraphics@aol.com>:

> This is all fine reasoning, but has nothing to do with EPB; EPB basically
> informs you of the best null hypothesis, and then outlines what degree of
> uncertainty a specific inference is (i.e. how strong the data should be
> before assuming a given condition).  Given the bracketing on dinosaurs for
> lips, there isn't a condition shared by both, so the issue will have to rise
> and fall on the strength of osteological correlates.  At this point there is
> no consensus as to what the bones are telling us (although Witmer's group
> has suggested more beaks and less lips).

True, that was an additional comment which was not intended to have
not to do with EPB methodology.

I think that using extant taxa we can hypothesize the most
parsimonious possibility (admitting bony correlates are not decisive
yet), by taking into account the condition in more basal tetrapods and
perhaps fishes: if we found that the lepidosaur condition is
restricted to the Lepidosauria, then it would be likely autapomorphic,
and then we should not extrapolate the condition in this taxon to
dinosaurs, because we would have to hypothesize extra-steps.

On the other side, I am not sure we can put birds aside from
consideration when hypothesizing an EPB, for we consider lip muscles
cannot be associated with beaks mainly because we do not know of
beaked animals with muscles between the epidermis and bone (I mean,
the reason is distribution of both features), but at the same time,
the distribution of the lack of lip muscles and presence of beaks is
not coincident (example: crocodiles), so at least with crocodiles the
features were not correlated (but it is true that two features can be
correlated in some cases, but not in others).

This is not to deny that it is equally parsimonious to admit lip
muscles were lost in Archosauria (or some ancestor basal to
Archosauria within Archosauromorpha) and then beaks appeared in
Neornithes, than that some crurotarsan ancestor of crocodilians lost
lip muscles and some avialan Neornithes ancestor gained a beak,
automatically losing the muscles, if by some reason beaks can not
coexist with lip muscles.

> FWIW, dicynodonts had beaks, so evolving beaks is not archosaur-specific,
> although you are right that archosaurs seem to exhibit a higher incidence of
> beak origins.

Right, you have them also in turtles, tadpoles and... can we consider
the horny premaxillary cover of artiodactyls a beak?? (that would be a
beak associated with lip muscles)