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Re: Number of Stegosaurus stenops plates

In a message dated 95-12-02 20:40:35 EST, anarvaez@umd5.umd.edu (Amado
Narvaez) writes:

>If I counted correctly, there seem to be 17 plates on the Stegosaurus 
>sculpture by Czerkas. I counted the same number in a Franczak painting. 
>Is there a best guess about the number of plates based on most recent 
>findings? Is there any relationship to the number of plates and the 
>number of vertebrae? Could a young Stegosaurus start out with x number 
>of plates and then grow more as it matured? 

Ken Carpenter's mount in Denver has an exact count of 17: six on the neck,
six more on the back, and five on the tail. These are visible in photos in
_Dino-Frontline_ #10. This count should be correct, because it is based on
the complete skeleton Ken and co-workers unearthed in 1992. But do not
discount the possibility of individual variation knocking the count off by
one (probably on the neck). I consider _Stegosaurus stenops_ a different
genus from _Stegosaurus armatus_, _Stegosaurus ungulatus_, and _Stegosaurus
sulcatus_, all of which seem to have had smaller, more numerous plates than
_?Diracodon stenops_. But just how much more numerous (maybe 20-22?) awaits
the discovery of a complete specimen like Ken's.

Stegosaur ontogeny is poorly known, but my guess is that the plates were
mainly keratinous in very young animals and that their number didn't change
(increase) as the animal grew. The plates toughened, hardened, and became
ossified by early adolescence: the tail of a half-grown _?Diracodon stenops_
already shows the terminal plate as bone, along with the four tail spikes.
But very small juveniles have no trace of bony plates (which may be due to
scattering rather than the bony plates' physical absence).