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Re: Land of the Lost review-spoiler?



Noticeably, beaks appeared many times in Archosauria, including
poposaurs, some pterosaurs, Silesaurus, Ornithischia, some basal
Sauropodomorpha, and many coelurosaurs. May it be that archosaurs have
something which made it easy for them to acquire beaks? I would think
of lack of lip muscles even in beakless, toothed archosaurs, as
before, but do not really know.<<<

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).

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.

Scott


Scott Hartman Science Director Wyoming Dinosaur Center 110 Carter Ranch Rd. Thermopolis, WY 82443 (800) 455-3466 ext. 230 Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: Augusto Haro <augustoharo@gmail.com>
To: dinosaur@usc.edu
Sent: Fri, 5 Jun 2009 5:58 am
Subject: Re: Land of the Lost review-spoiler?






According to Bakker 86', cocodiles lack lip muscles, but lizards have them. Lizard lip muscles seem to be non homologous with ours, however, and not striated, unlike the lip musculature of ours, and likely not innervated by nerve VII, unlike our facial muscles.

We should go down to turtles and lissamphibians, and even "fishes" to
see if they have the muscle kind present in lizards (I suppose turtles
may not have the muscles because they have a beak, except perhaps for
tryonichids); if not, the lizard condition may be autapomorphic.

Noticeably, beaks appeared many times in Archosauria, including
poposaurs, some pterosaurs, Silesaurus, Ornithischia, some basal
Sauropodomorpha, and many coelurosaurs. May it be that archosaurs have
something which made it easy for them to acquire beaks? I would think
of lack of lip muscles even in beakless, toothed archosaurs, as
before, but do not really know.

There are two main points in which beaked archosaurs emerged, one in
the early history of Dinosauriformes -Late Trias, Early Jura- and
other in Coelurosauria. I do not know if this means anything.