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Re: Archosaur Origins...was:MESENOSAURUS ERRATA.

> And for that matter, if "birds" did get their start from the
> group, and theropod dinos were their flightless descendants, dosen`t this
> imply that the other dino groups (Sauropod and Ornithischian) also had
> prolacertiform ancestry???

Prolacertiformes incl. Pterosauria looks quite holophyletic -- and so does
Archosauriformes which is the sister group to Prolacertiformes.

Michael J. Benton: Vertebrate Palaeontology. 2nd edition, Chapman & Hall

has the following on the pages 149 and 137 (I'm paraphrasing):

            `--Archosauriformes ( = non-crown-group Archosauria)

Archosauromorpha: notochordal canal absent in adults, cervical ribs all have
two heads, entepicondylar foramen in humerus absent, medial centrale in
carpus absent, concave-convex articulation between astragalus and calcaneum
(this is not the croc-reverse ankle joint, or is it? ~:-| )
1: external nares close to midline, premaxilla extends up behind naris,
quadratojugal located mainly behind lower temporal fenestra (vertebral
pneumaticity evolved here or earlier)
2: long snout and narrow skull, nasals longer than frontals, recurved teeth,
extensive participation of parasphenoid/basisphenoid in lateral wall of
braincase, long thin tapering cervical ribs with two or three heads and an
anterior process
Archosauriformes: antorbital fenestra, laterally flattened teeth with
serrations, ossified laterosphenoid in braincase, lateral mandibular foramen
in posterior lower jaw bones.
A subgroup of Prolacertiformes (see www.pterosaurs.net, which %$/&&%?§
doesn't work at the time) has 3 antorbital fenestrae that apparently fused
in pterosaurs.

Well, dinosaurs primitively have the synapomorphies of Archosauriformes,
while prolacertiforms including pterosaurs don't (I don't know whether
pterosaurs have a laterosphenoid). So we can be pretty sure IMHO that
dinosaurs are not prolacertiforms. (Whatever Prolacertiformes really