Re: SWIMMING ANKYLOSAURS

[Betty Cunningham <bettyc@flyinggoat.com>]

Has anyone resolved whether ankylosaurids had air sacs similar to birds?
(ie: their own natural flotation devices?)

-Betty

darren.naish@port.ac.uk wrote:
> Matt Bonnan wrote....
> 
> > Hippos not only have specially adapted limbs and splayed feet, but
> > also do not have armor and have large, dorsal nostrils.
> 
> Also, aquatic hippos have a particularly high SG because of dense
> bones. Of course, the idea that certain ankylosaurs may have been
> amphibious or semiaquatic is not new: Mehl (1936) published on it.
> 
> However, the evidence for it is entirely circumstantial: based on
> little more than the presence of certain nodosaur fossils within
> marine sediments. In the MS of a book I'm co-writing, I note that
> aquatic habits for these 'coastal' nodosaurs is very unlikely given
> that they seem pretty much the same as their definitely non-aquatic
> relatives found 1000s of km from the marine environment. A criticism
> set to me by a reviewer was that aquatic/amphibious taxa are _not_
> always distinguishable from closely related non-aquatic taxa (mink
> and other mustelids were cited as an example).
> 
> In fact, though, this is not correct and, certainly in mammals, there
> _are_ strong indicators of aquatic habits in the skeleton. Aquatic
> hippos have particular limb proportions and a 'gorgops' type skull
> (where the eyes and nostrils are above an imaginary water line)
> whereas terrestrial hexaprotodont hippos don't. Mink, beaver, coypu
> etc etc., _Thalassocnus_ (the now speciose Pisco Fm. 'swimming
> sloth') all have larger transverse processes on their proximal
> caudals and more elongate metatarsals than their close, terrestrial
> relatives. Ergo, the swimming taxa are distinguishable based on
> comparative morphology. However, little work of this kind has been
> done on reptiles. Bummer.
> 
> "This is getting out of hand - now there are two of them"
> "We should not have made this bargain"
(matt's part)
> While you do find Euoplocephalus in Judith River sediments which suggest a
> deltaic environment, how do we know that they aren't the carcasses of poor
> suckers who drowned in a river or estuary and then were transported to and
> buried in the deltas?  The heavily armored carcass may have prevented it
> from breaking up as quickly as others and may have protected it from
> smashing into rocks on the way to its final burial place.
> 
> I dunno, but I would take a long hard look at the limbs and feet (as you
> would predict), but also the teeth to get some ideas about diet.  Also, most
> mammals have relatively flexible vertebral columns that flex in a
> dorsoventral plane which may allow hippos (I don't know for sure, so check
> me on it) to "bound" or "run" under water.  The armored thyreophorans, in
> contrast, seem rather limited in their body movements by their armored
> bodies, squat limbs, and heavy tails.  It would appear to me that the only
> time armored dinos like Euoplocephalus went into the water was when it was
> shallow enough to drink or bathe in, or when they drowned.

-- 
Flying Goat Graphics
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