Re: Spinosaurus questions and the presence of air-sacs in Dinosauria (quite long)

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Colin McHenry wrote-

> > Who says it didn't eat dinosaurs too?  Baryonyx has Iguanodon bones in
its
> > stomach.
>
> Interesting. I had thought the only known stomach content contained fish.

Nope.  Charig and Milner (1997) state "the disarticulated remains of a young
Iguanodon showing some evidence of abrasion (and/or eching)" were found in
the stomach region.  These included a supraoccipital, cervical vertebrae,
dorsal vertebrae, proximal caudal centrum, neural spine, humerus, manual
phalanges, distal femora, indeterminate limb fragments, metatarsals II, III
and IV, and four phalanges.

>  > Sice the dorsal sail evolved also in basal hadrosauriform
> > > _Ouranosaurus nigeriensis_ living in about the same time and
> > > geographical area of central northern Gondwana, was the climate
> > > somehow specific in requiring this morphology?
> >
> > No, because Carcharodontosaurus and Lurdusaurus lacked humps/sails.
>
> Except if the climate was such that an animal with a hump/sail could gain
> some competitive advantage over non-hump/sailed sympatrics....for example,
> the hump/sail may have allowed spinosaurs and Ouranosaurus (this was an
> iguanodont last time I looked.  When did it switch teams?) to have been
> active at times of the day when the others had to shelter from the heat.
> Alternatively, it may have allowed to hump/sailed animals to range into
> areas not accessible to the non-hump/sailed animals at certain times of
the
> year.  Or something else.  I think that this is what Mickey is getting at
> below...

I was just saying humped/sailed forms possibly had an advantage in that
environment, but sails/humps obviously weren't required to live there.
As for Ouranosaurus, Iguanodontia includes Hadrosauriformes.  I think
Hadrosauriformes is defined as "The common ancestor of Hadrosaurus and
Iguanodon and all its descendents", though I don't have Sereno 1999 on hand.
However, this seems to be a useless renaming of Iguanodontoidea, defined
identically.  In any case, the most recent phylogenetic analysis of
dryomorphans (Norman, 2002) finds Ouranosaurus to be both an iguanodontian
and an iguanodontoid/hadrosauriform.

> Just want to make absolutely clear that my earlier point about
mythological
> spinosaur palaeobiology was most definitely not aimed at Mickey's work on
> the beast.

Don't worry.  My estimates were nothing more than extrapolations based on
dorsal centrum and tooth row length of Spinosaurus, and estimated total
length of Suchomimus and Baryonyx.  They're more accurate than any other
estimates I've seen, but who knows....

>  Humps also increase the surface area to mass
> > ratio (for thermoregulation) and could have been brightly colored.
>
> Do you mean decrease?  Actually, now I think of it, maybe I've got my
> increase and decrease in ratios muddled.  When I wrote that the hump would
> decrease the SA:vol ratio, I meant that there would be less surface area
as
> a proportion of the total mass.  Which is to say that the hump would
> increase total surface area slightly, but not as much as the increase in
> mass caused by the hump, and thus overall surface area to volume ratio
would
> decrease.
>
> There would be a confuiguration of the sail/hump that would be neutral
with
> respect to changing the animal' SA:vol ratio.  At a guess, I would imagine
> that this would be equivalent to a very fat sail (or a skinny hump,
> depending on whether the bottle is half empty or half full).

Yes, this is an important observation.  Judging by past posts between Jaime
and myself, Spinosaurus seems to have one of the more sail-like humps among
high-spined dinosaurs (specifically due to the lack of spine tables).  I
would think it would be difficult to determine the width needed to start
decreasing the surface area to volume ratio.  Whatever width ended up making
the hump/sail's sa/v ratio smaller than the sa/v ratio of the hump/sailless
body, right?  I picture Spinosaurus' hump/sail raising the sa/v ratio
primarily due to its great height.  This would make the hump/sail equivalent
to a triangle of <10 degrees in cross section.  Now we just have to adjust
for the varying height of the hump/sail and figure out the sa/v ratio of a
megalosauroid....

Jean-Michel wrote-

> BTW, if *Baryonix* was a sub-adlut (as mentionned often onlist), what size
would it have > reached, and what height for the sail?

Dinosaurs grew continuously, right?  So there was no maximum adult size
except that imposed by lifespan.  Naish reported onlist (1998) that Hutt has
some very large Baryonyx manual phalanges.  Are these in the Isle of Wight
volume?
Baryonyx really had quite short dorsal neural spines.  The sacral and
proximal caudal neural spines are longest, but even these barely reach over
the ilium.  Comparable to Allosaurus, shorter than sinraptorids and
Suchomimus, and not even comparable to Spinosaurus.

Mickey Mortimer