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Re: Did pterosaurs feed by skimming?



>  I think there's lots of alternatives, but I think
>  a lot of them are hard to test with Pteranodon bones being so horribly
>  flattened. 

True, but with the few unflattened Pteranodon bits that we do have, combined 
with comparisons to relatives of similar morphology (but better preservation), 
some additional alternatives can be tentatively ruled out (or at least rendered 
very unlikely).  Further thoughts inserted below...


>  I guess we're left with plunge diving, surface diving, dip-feeding or
>  dull-old alighting on the water surface to grab fish being bait-balled
>  by marine reptiles below. On diving: maybe, but not in the manner of
>  sulids - these fellas have all sorts of diving signatures across their
>  skulls and necks (rounded skull profile in anterior view, streamlined
>  skull in lateral view, super-robust cheek bones and neck vertebrae),
>  none of which we see in Pteranodon. 

Not to mention the fact that Pteranodon would probably destroy itself diving 
like a sulid.  So, I guess it could do it once...


>  Pteranodon lacks a
>  frigate bird-like hooked bill, and I wonder if this might be important
>  for dipping. If anyone knows any different, let me know.

It could be; most dip-feeders have hooked bills.  However, some have only very 
small hooks, and tropicbirds can dip feed and have an unhooked bill.  Gulls can 
also dip feed, I think, and lack much of a hook.

Personally, I tend to caution against using frigates as a major source of 
comparison for other flying vertebrates; they have a very unusual ecology 
(albeit an awesome one) and more of their morphology is adapted to piracy than 
is generally given credit (example: their extremely low wing loading probably 
has as much, or more, to do with piracy than marine thermal soaring.  More on 
that sometime later).

 
>  What's next? Surface diving: although many albatross surface dive
>  nowadays, I'm not sure how plausible this is for any pterosaur, really,
>  as their wings don't appear to fold up as neatly as those of birds.
>  Swimming with only half-folded wings underwater would be a real drag 
> (ho
>  ho), so I might put it on the 'doubtful' pile.

I don't really see any adaptations related to surface diving in any pterosaurs, 
and they are pretty obvious in diving birds.  This goes for surface diving 
propelled by the forelimbs or the hind limbs.  I have not done any careful 
analysis of Pteranodon mechanics yet, but some quick and dirty math suggests 
that they could not sustain either set of loads (hind or forelimb propelled).  
So, I agree with placing this one on the doubtful pile.


> However, Pteranodon feet are certainly very big for their
>  body size and suggest to me that they'd be absolutely ace at punting 
>  a floating Pteranodon around the water surface. Their feet were almost
>  certainly webbed, so big feet in any pterosaur would be handy for
>  pedaling their way through the water. This is my favourite idea,
>  actually: Pteranodon alighting on the water surface, feeding simply by
>  dunking its long jaws into the water to snatch up little fish and other
>  pelagic critters. 

I see two possible problems with this otherwise very cool idea.  The first is 
that the rest of the Pteranodon hind limb does not seem to show any signal of 
aqueous propulsion, and morphologic signals related to fluid medium show up 
very clearly in birds (though, admittedly, most of the available limbs are 
flattened beyond all recognition, making this conclusion tentative).  
Pterosaurs don't have to follow the same patterns as birds, but enough of the 
mechanics would be consistent that I find it doubtful that pterosaurs could be 
swimming and not have to deal with loads at least somewhat similar to those 
experienced by swimming birds.

The other potential problem is that I'm not sure Pteranodon could take off from 
the water.  Same goes for other wide-spanned pterosaurs with gracile hind limbs 
(such as Anhanguera, though that is a considerably more extreme example than 
Pteranodon).  Again, I need to work out the precise numbers, but a quick and 
dirty run implies that such pterosaurs are pretty poorly adapted for hind limb 
launch from the water (or hind limb launch at all), just looking at relative 
structural strengths.  Add the issues of required launch speeds and launch 
kinematics, and it becomes increasingly unlikely.

Of course, Pteranodon must have been doing *something* to eat, so maybe I have 
missed a critical detail.  Nonetheless, that's what I have been able to come up 
with thus far, though it is all very preliminary.


Cheers,

--Mike H.