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



 <20091028142809.f306224d.ee555@ncf.ca>
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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
=20
Mickey Mortimer
The Theropod Database- http://home.comcast.net/~eoraptor/Home.html







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> Date: Wed=2C 28 Oct 2009 14:28:09 -0600
> From: ee555@ncf.ca
> To: DINOSAUR@usc.edu
> CC: dinosaur@usc.edu
> Subject: Re: Ouranosaurus - how many species? Other "spino"-Igaunodontids=
?
>
>
> Hello=2C
>
> In addition=2C to distinguishing tall sail-like structures from humps=2C =
one could presumably further distinguish humps depending on the ratio of fa=
t to muscle content. I'm not arguing that these features were all structura=
lly identical or that they all addressed the exact same combination of sele=
ctive pressures (eg. in cases where a sail may have had an additional role =
in communication=2C in addition to serving for heat dissipation of food sto=
rage).
>
> However=2C the fact that *all* of these humped / sailed species existed d=
uring the early cretaceous would suggest that almost all of these adaptatio=
ns represent cases of convergent evolution in response to some environmenta=
l pressure. It would have to be an environmental pressure that was specific=
 to the early cretaceous and had similar consequences for all of these wide=
ly distributed and distantly related taxa. This would also nicely explain t=
he surprising relative lack of humped or sailed species in other time perio=
ds.
>
> Considering this conjecture it seems plausible that the unusual morpholog=
y of Tenontosaurus may have been a response to the same pressure. Tenontosa=
urs probably had the deepest=2C as well as one of the longest=2C tails=2C r=
elative to body size=2C of any ornithopods.
>
> So=2C I'd tentatively argue that Tenontosaurs should be included in lists=
 of humped or sailed species.
>
> S!
>
> - Jonas Weselake-George
>
> P.S. Modification of the dorsal side of the animal or the tail is less li=
kely to interfere with locomotory or feeding adaptations. So=2C both areas =
may be analogously good candidates for such elongated structures to develop=
. In fact=2C it could further be ventured that the different locomotory beh=
aviour of Tenontosaurs (eg. clearly visible in the structure of the feet) a=
nd habitat requirements either associated with different locomotory behavio=
ur or a need to pass under obstacles=2C may have been deciding factors in w=
hy Tenontosaurs would develop an elongate/deep tail instead of a hump.
>
>
> On Tue=2C 27 Oct 2009 15:26:00 -0700 (PDT)
> Tim Williams wrote:
>
>> Jonas Weselake-George wrote:
>>
>>
>>> If it wasn't for the odd phylogenetic placement=2C one could
>>> also argue that Tenontosaurus fits this category as well. Of
>>> course=2C in this case the equivalent of the "spine" takes the
>>> form of a much enlarged and relatively laterally compressed
>>> tail=2C not a sail/whithers. However=2C 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 anatomic=
al structures: (a) sail=2C (b) ridge or hump. The extremely elongated neura=
l spines of taxa such as _Ouranosaurus_=2C _Amargasaurus_ (paired)=2C and _=
Spinosaurus_ have usually always been interpreted as supporting a membranou=
s sail. But for taxa such as _Acrocanthosaurus_ and _Lanzhousaurus_=2C whic=
h have "moderately" tall spines=2C the spines might have been buried in a m=
uscular ridge or hump. So the latter would be more like the hump of a bison=
 (mostly muscle) than the hump of a camel (fat)=2C where the spines are not=
 elongated for this purpose. For _Tenontosaurus_=2C the enlarged caudal neu=
ral spines were probably enclosed in flesh=2C to produce a strong=2C muscul=
ar tail.
>>
>>
>> Cheers
>>
>> Tim
>>
>>
>>
>>
>
>
> --
> Jonas Weselake-George                                           =