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

[Tim Williams <tijawi@yahoo.com>]

Michael Mortimer <mickey_mortimer111@msn.com> wrote:


> Don't forget Late Cretaceous taxa like Hypacrosaurus and
> Barsboldia.  Then =
> you have some 'protoceratopsian' tails too=2C and Jurassic
> metriacanthosaur=
> ids and Ceratosaurus had somewhat tall spines. 
> Really=2C taxa with tall ne=
> ural spines were common=2C it's just that only a few are
> famous for it. =20


Those dinosaurs that are most famous for having tall neural spines tend to be 
those that show the most extreme development of this condition -  such as 
_Spinosaurus_, _Amargasaurus_ and _Ouranosaurus_.  In these forms, as with 
_Dimetrodon_ and _Edaphosaurus_, the extreme elongation of the spines suggests 
that they supported a membranous sail.  


For those taxa that have 'tall-ish' spines, it's a much more open question 
whether the spines supported a sail, or a ridge or hump.  For example, the tall 
spines of _Altispinax_ and _Metriacanthosaurus_ might have supported epaxial 
musculature, rather than a sail.


Bailey (1997) proposed that ALL tall-spined dinosaurs had a "buffalo-style" 
hump, for the purposes of fat storage.  He even included restorations of 
_Ouranosaurus_ and _Spinosaurus_ sporting giant humps!  However, as fat-storing 
devices, these humps would make them more like camels (which do *not* have tall 
spines to support the adipose hump) than buffalos (where the hump is muscular, 
and helps support the head).  I think most workers would agree that a muscular 
hump is a possibility for some dinosaurs with moderately tall spines; but it's 
a stretch for the very tall-spined ones.


Ref:

Bailey, Jack Bowman (1997). Neural spine elongation in dinosaurs: sailbacks or 
buffalo-backs?  J. Paleontol. 71: 1124-1146.


Cheers

Tim