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Re: Family Ties

At 06:27 PM 5/13/97 -0400, you wrote:
>Bronson Barton wrote:
>I just have two short questions on the features that separate the 
>Camarasauridae from the Brachiosauridae?
>Isn't it something to do with differently shaped skulls?  I also think that
to be classified as Brachiosauridae, a dinosaur would have to ridiculously
long front arms in proportion to its back ones, like the one the family is
named for, Brachiosaurus.

There are many differences between the two families.  If Brian Curtice or
one of our other sauropod experts has time, perhaps they could highlight
some of them.

>And also, what separates the 
>Sinraptoridae from the Allosauridae?  I often see many genera 
>"interchangeable" between these families.
>I don't have an answer for that one, I'm not familiar with Sinoraptoridae.

Until 1993/4, NOTHING was placed in the Sinraptoridae, because it hadn't
been named yet.  Since then, Sinraptoridae has had a pretty constant
membership: the two species of Sinraptor and the two species of
Yangchuanosaurus.  Unlike other allosauroids, sinraptorids have: several
extra accessory openings in the antorbital fossa connected to the maxillary
sinus, a low lacrimal horn (okay, the same is in carcharodontosaurs), and
the ventral margin of the axial intercentrum rotated above the ventral
margin of the axial centrum.

Or, in layman's terms, very little of interest separates Sinraptoridae from
other allosauroids, but there are enough differences to keep specialists
happy that they are distinct!

>It seems to me that if the above mentioned families should be 
>separated, that the Lambeosaurinae deserves family status.

This has been argued.  However, it has been argued at about the same time
that many dinosaur taxonomists are joining most other taxonomists in
abandoning the "rank" concept (i.e., the metaphysical reality of 'family'
versus 'subfamily' versus 'infraorder' versus what have you), so I don't
expect these names to change...

>Is there another dino besides Lambeosaurus itself that fits in that
category?  Maybe Corythosaurus, but that's kind of a long shot IMHO.

Among others: Parasaurolophus, Tsintaosaurus, and Hypacrosaurus are all very
distinctive lambeosaurines.  Others (Bactrosaurus, Barsboldia, etc.) are
less well-known.

I might suggest a perusal of the Weishampel and Horner chapter on
hadrosaurids in The Dinosauria or the chapter on Ornithopods in Fastovsky
and Weishampel's textbook for a discussion of duckbill systematics.  There
are a LOT of lambeosaurine taxa, and they have a whole host of features
which distinguish them from hadrosaurines (and, despite common perception to
the contrary, not all of the distinguishing features are in the skull!).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661