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Re: Quadraped Sailbacks-All non-dinos?



>     I was recently talking to an Earth science high school teacher about
>     how he teaches his kids about what makes a dinosaur different from
>     other prehistoric animals.  He told me that he uses "quadraped
>     sailbacks" (i.e. Dimetridon) as one discrimination as to what is _not_
>     a dinosaur.  I told him that there were other (better) ways to
>     discriminate a dinosaur such as: (1) Lived only in the Mesozoic Era,
>     (2) Walked with legs directly under the body (not sprawled), (3) Lived
>     primarily on land, (4) Had unique anatomical structure (i.e. hips,
>     etc), and (5) All dinos were reptiles.
>
>     Although he uses some of the above, he still put in "Quad. Sailbacks".
>     Are there any quadraped sailback dinos?  I think the five
>     qualifications above are enough to qualify for dinosaurian without the
>     confusion of "Quad. Sailbacks".  What do you think?  Thanks!

Okay - Dimetrodon, Edaphosaurus, and its relatives are not dinosaurs, nor
reptiles (under cladistic taxonomy), but are primitive representatives of
the synapsids (mammals and their ancestors).  The general name for the
early sailbacks is "pelycosaur", but a) this is a paraphyletic group (a
common ancestor but not all descendants); b) not all "pelycosaurs" were
sailed; and, c) there were sailbacked amphibians from the same time, which
of course were neither synapsids nor reptiles.

Good for the teacher for recognizing that Dimetrodon is not, nor ever was,
a dinosaur, despite the fact that this interesting genus graces the cover
of maybe a fifth of all chldren's dinosaur books.

However, there are some definite dinosaur quadruped sailbacks (i.e., true
dinosaurs which were quadrupedal and sailbacked).  These are sauropods from
the Early Cretaceous, especially Amargasaurus (okay, maybe it was
"spine-backed") and Rebbachisaurus (or whatever genus the tall-spined
northern African sauropod winds up in).  There is a sailbacked bipedal
dinosaur (Spinosaurus) and a sailbacked facultative biped (up on two legs
sometimes, down on four others) named Ouranosaurus.

Your diagnosis for dinosaurs is pretty close to most peoples (although some
of us would recognize 9000 living species of dinosaurian).

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.