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Re: Dryptosaurus, Deltadromeus, and Bahariasaurus



At 08:48 PM 12/14/97 -0600, Seth Ellestad wrote:
>Lately I've heard conjecture that Dryptosaurus may be very similar to
>Deltadromeus, and Bahariasaurus may also be similar to Deltadromeus.  Which
>leads to a couple of questions:
>
>(A.)  Wasn't Dryptosaurus thought to be a whole lot bigger than
>Deltadromeus, with weights of around one ton or more for full grown
>individuals?

The type of Deltadromeus has a femur length of 740 mm, and a tibia estimated
at 700 mm.  The type of Dryptosaurus has a femur length of 770 mm and a
tibia of 775 mm.  Drypto is thus a bigger animal than the type of Delta, but
see below.

>(B.)  How big was Deltadromeus known to get, and was the specimen found a
>subadult, or a mature individual?  (I ask this seeing that the animal seems
>to already have been prepped and mounted).

Sereno et al. (1996) report a Deltadromeus with a 1220 mm femur, which is
well into the Tyrannosaurus & Daspletosaurus range!

Also, BEWARE OF THE DELTADROMEUS MOUNT! (Or it may come to life and get
you...)  Well, more importantly, it is based on a LOT of conjecture, given
that there is little known for this interesting beastie.  For example, I do
not know of any evidence for the three-pronged ornament on the lacrimal
(given that no skull material has been described for Deltadromeus), so that
is entirely fantasy.

Unfortunately, there is the push by museums and exhibitors to make mounts of
creatures, even if there isn't the fossil material to back up said mounts.
This would be less annoying if the mounts were color-coordinated to show
what parts are based on real bones, and what on conjecture (as some museums do).

>(C.)  And what about Bahariasaurus?  I've seen it described as anything
>from a ~4-ton allosauroid similar to Carcharodontosaurus, to an animal
>almost identical to Deltadromeus.

Sereno et al. (1996) report that most of the bones once refered to
Bahariasaurus are actually from Deltadromeus.  The type (name-holder)
specimen of Bahariasaurus, however, (2 dorsal vertebrae, a neural arch,
three sacral vertebrae, rib fragments, pubes, and the proximal part of the
ischium) are distinct from Deltadromeus and other North African theropods.
The exact affinity of Bahariasaurus has not been worked out.

The 4 ton estimate is primarily based on the femur mentioned above, now
considered to come from a large Deltadromeus.

>(D.)  Finally, what about the idea that these things (and Baryonyx and
>Spinosaurus) were all distant radiations of Celophysis via Dilophosaurus?
>Is that still a current hypothesis?  I always thought that was kinda nifty,
>based on the traits they seem to share, especially the "kinked" snout.

There do not seem to be any characters especially linking Deltadromeus or
Dryptosaurus and either the Spinosauridae or the Coelophysidae.  The
spinosaurid-coelophysid link is weaker than once thought, now that the
anatomy of the former is better known (and is pretty clearly tetanurine).

Hope this helps.

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