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Re: Ouranosaurus - how many species? Other "spino"-Igaunodontids?

Jonas Weselake-George <ee555@ncf.ca> wrote:

> If it wasn't for the odd phylogenetic placement, one could
> also argue that Tenontosaurus fits this category as well. Of
> course, in this case the equivalent of the "spine" takes the
> form of a much enlarged and relatively laterally compressed
> tail, not a sail/whithers. However, it is likely that what
> ever drove the unique sail/whithers development in other
> ornithopods and large theropods during this period is behind
> this oddity as well.

Elongation of neural spines has been tied to two very different anatomical 
structures: (a) sail, (b) ridge or hump.  The extremely elongated neural spines 
of taxa such as _Ouranosaurus_, _Amargasaurus_ (paired), and _Spinosaurus_ have 
usually always been interpreted as supporting a membranous sail.  But for taxa 
such as _Acrocanthosaurus_ and _Lanzhousaurus_, which have "moderately" tall 
spines, the spines might have been buried in a muscular ridge or hump.  So the 
latter would be more like the hump of a bison (mostly muscle) than the hump of 
a camel (fat), where the spines are not elongated for this purpose.  For 
_Tenontosaurus_, the enlarged caudal neural spines were probably enclosed in 
flesh, to produce a strong, muscular tail.