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Re: dinosaur ancestor question...

David Peters (davidrpeters@earthlink.net) wrote:

<Was wondering what the current consensus is on which taxa bridge the 'gap'
between Euparkeria and Marasuchus?>

  All of crocdom, *Lagerpeton* and potentially (but unlikely) *Lewisuchus*.
*Scleromochlus* (following Benton) is also between basal archosauriform
*Euparkeria* and all other non-dinosaurian Archosauria. Note that the most
recent analyses on this subject have been from Benton (1999, _Philosophical
Transactions of the Royal Society of London_ B 354:1423-1446) and work on
general theropod origins which include most dinosauromorph taxa as outliers in
order to root the trees in PAUP OR create the "null hypothesis" of a
non-dinosaur to develop parsimony argument for character evolution (otherwise
called rooting the tree). Sereno (1999, _Science_ 284:2137-2147), and the
recent _The Dinosauria, Second Edition_ emphasize dinosaur origins, and thus
the subject of the origins of Archosauria. Interceding taxa between Archosauria
and *Euparkeria* include proterosuchids like *Proterochampsa* and *Archosaurus*
(Gower and Sennikov, 1997, _JVP_ 17(1):60-73; Gower and Sennikov, 2000, in
Benton et al. _The Age of Dinosaurs in Russia and Mongolia_, pp. 140-159) which
precede the croc-like morphologies of basal Crocodylomorpha/Crurotarsi and
Dinosauromorpha/Avemetatarsalia (i.e., cursorial quadrupeds to bipeds, such as
the basal crocs "Sphenosuchia" and the non-dinosaur [?] *Silesaurus*).


Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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