[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: dino-lice

A snail-picking adaptation might have led to a digit such as those in 
alvarezsaurs, but why would the other digits be lost (they might be useful in 
picking the animal out of the shell, for example)?  And why would such a 
strongly-muscled arm be required?  If the arms were used in foraging it seems 
more likely that they would have been used as levers against considerable force 
-- perhaps pulling apart some tangled mass of plant fibres or ripping into a 
cycad trunk, for instance -- if they had access to some sort of trunked or 
otherwise erect plant the difficulty of  them having to stoop to ground level 
burrow might not exist.  Could the arms of alvarezsaurs be analogous to the 
enlarged rooting teeth or tusks of some herbivorous mammals - given that tooth 
modification was not on the cards for them - rather than to any limb structure 
in another animal?

 Ronald Orenstein
1825 Shady Creek Court
Mississauga, ON L5L 3W2

----- Original Message ----
From: Augusto Haro <augustoharo@gmail.com>
To: Dinosaur Mailing List <dinosaur@usc.edu>
Sent: Fri, April 22, 2011 9:42:09 AM
Subject: Re: dino-lice

I just read some news about a new snail-eating marsupial and thought
how possible it may be for the "hook and pull" mechanism of
alvarezsaur forelimbs to open snail opercula and remove the snail
while holding the shell with the kinetic, and possibly very good in
manipulation, jaws. Yes, looks odd, and i do not know how abundant are
snails in xeric habitats... This may also go for crabs or other
hard-shelled but possible to open invertebrates, supposing problems in
swallowing them whole (for example, spikes on the shells).

2011/4/21 Augusto Haro <augustoharo@gmail.com>:
> Regarding the display hypothesis, it is tempting to see that the
> strong musculature in a small limbs as moving a larger structure,
> perhaps as in the endoskeleton of actinopterygian fins. But feathers
> are not particularly heavy. And, long processes generally provide with
> stronger movements, but not fast ones (quite the contrary, faster
> extension is provided by shorter olecrana). So I do not see that the
> forelimb skeleton of an alvarezsaur permitted an especially fast
> display.
> I think the possibility of more than parasagittal movements, overall
> lateromadial ones, as explained by Jaime, indicates that the forelimb
> may have some versatility in dealing with whatever it was trying to
> destroy or penetrate. I think it reduction in size may have to do with
> care while destroying. I mean, to destroy a large thing, or with a
> thicker crust, you generally need a large and powerful extremity, as
> Priodontes has. However, to destroy a relatively small structure, or
> with a narrower crust, as egg or seed, or even small insect nest, you
> may go well with a tiny extremity of similar function, which may be
> more economical, even in if the larger structure is still good for the
> task. But, if you need not to completely destroy what you are
> attempting to modify, you will more imperatively need a tinier
> extremity, capable of greater precision. Perhaps precision can be
> increased with decreased excursion ranges, tinier unguals, and small
> power (small relative to whole animal mass, but strong relative to
> forearm mass). If you want to make a salad with slices from some small
> vegetable, you would use a small knife instead of an axe, which may
> impede you to generate slices without crushing the vegetable.