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

["Colin McHenry" <cmchenry@westserv.net.au>]

----- Original Message ----- 
From: "Mickey Mortimer" <Mickey_Mortimer111@msn.com>
To: <dinosaur@usc.edu>
Sent: Friday, May 30, 2003 7:42 PM
Subject: Re: Spinosaurus questions and the presence of air-sacs in
Dinosauria (quite long)


>
> 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.

 > 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...


> > And why is it not present in other groups of
> > large theropods living in the similar climate conditions
> > (Ceratosaurian Abelisauroids, Spinosauroid Megalosaurids, various
> > Coelurosaurians).
>
> Surely one animal can be more efficient than another.  It clearly wasn't
> necessary for Spinosaurus et al. to be humped/sailed to survive, just
> useful.

Precisely - lide in Cretaceous North Africa was undoubtedly possible for all
sorts of animals, but the hump/sail may have provided their owners with a
lever that allowed them to exploit certain niches without much competition.
For example, a few modern deserts have species which can, by some trick or
another, be active at times of the day which allow them to avoid predators
or competitors (or even catch prey which cannot become active).  Emus seem
to do this, and I think there is an ant (in the Namib?) which is active for
a couple of minutes at midday, when all predators are hiding from the sun.

By the way, concerning an earlier thread, since when did emus have feathered
legs?  And as for ostriches being the only ratites to live in treeless
environments....?  Not all the treeless landscapes over here are a result of
land clearing - some of them haven't had tress for at least a few million
years.  And those places (e.g. Simpson desert) are full of emus....

>
> > 3.) Given the facts that are obvious (the size of now destroyed _S.
> > aegyptiacus_ holotype remains and also MNHN SAM remains), why are all
> > studies refer to _G. carolinii_ as the largest theropod ever to have
> > lived? It's estimated to be "just" 12.5 m long and some 8 tons heavy,
> > while Spinosaurus holotype was clearly larger by both measures,
> > though unfortunately, this is not testable nowadays.
>
> Because people like the more complete remains of Giganotosaurus, which get
> more press coverage than Stromer's Spinosaurus holotype.  And because no
one
> seemed to try to accurately determine Spinosaurus' length before I did.

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.

 SNIP
> Any hump would be a muscular hump, like in bison, not a fatty (water
> reserve) hump, like in camels.

At a superficial level, muscle and fat are almost equally effective at
increasing thermal inertia, so the hump theory could probably cope with
either a fatty hump, a muscular hump, or some combination thereof.


 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).


Colin