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At 03:08 PM 12/6/98 -0500, Alan Edels wrote:
> 1) Do any other archosaurs (non-dinosaurs) have the acetabulum (a
>hole in the hip girdle, created by the intersection of the three hip bones)
>as a character?
Mixup in the terminology here: acetabulum = hip socket. We've got 'em,
frogs go 'em, crocs got 'em, any tetrapod with hindlimbs attached to the
pelvis has got 'em.
What dinosaurs have is a perforate acetabulum. This is much rarer. Despite
early reports to the contrary, basal dinosauromorphs like _Lago/Marasuchus_
does not have a perforate acetabulum. _Herrerasaurus_ has sort of a
> 2) Does the description/definition of a dinosaur indicate that the
>supra-acetabular crest must be present?
Definition, no. Definition is "all descendants of most recent common
ancestor of birds and _Triceratops_".
Even if it is part of the diagnosis (still debated), NO character MUST be
present in any taxon. Membership in a taxon is based on ancestry, not
diagnosis. If a mammal were, through evolution, to lose lactation, it would
still be a mammal.
> 3) Are there instances in dinosauria where the acetabulum has
>closed/sealed up (i.e fused the hip bones together), as we see the closure
>of fenestrae in Ceratopsians, and Ankylosaurs?
Ankylosaurs are a good example where it did close over.
> 4) Did ALL dinosaurs have digitigrade stance (i.e. they walked on
>"tiptoe")? - Or were some "flat-footed"?
All known dinosaurs were digitigrade skeletally, although some (sauropods,
instance) cheated by adding fleshy tissue under the hindfeet, and others
walked plantigrade at least some of the time.
Remember, everyone: evolution happens. All characters are subject to
Thomas R. Holtz, Jr.
Vertebrate Paleontologist Webpage: http://www.geol.umd.edu
Dept. of Geology Email:firstname.lastname@example.org
University of Maryland Phone:301-405-4084
College Park, MD 20742 Fax: 301-314-9661