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RE: dino-lice



Funny how this stuff seems to get brought up:

  Last year, Ed Yong mentioned a curious adaptation for specialized 
snail-eating snakes: 
http://blogs.discovermagazine.com/notrocketscience/2010/12/07/single-gene-creates-snake-resistant-mirror-image-snails-and-maybe-some-new-species/

  The snake, *Pareas iwasakii* (a colubrid) is a snake in which the left and 
right sides of the jaws are dramatically different and identifyiable without 
even having to locate particular bones, due to the increased number of teeth on 
one side. The half of the jaw is the element that more deeply penetrates the 
snail shell due to the helical curvature of the first chamber. Snail eating 
birds, such as the Everglades snail kite *Rostramus sociabilis* (an 
accipitrid), possess an extremely long upper bill which is gradually curved to 
form about 120-degrees of arc. Unlike the snake, this bill is used to penetrate 
the shell directly, where the snail is severed from its attachment and is then 
simplistically easy to remove (Voous and van Dijk, 1973).

  Both animals use elongate, slender devices, both parts of their jaws, to 
enter a small, tight space to extricate a small animal from its shell. In this 
way, the apparati used are no different from that of various shorebirds that 
specialize in removing bivalves from their valves, which is performed by either 
penetration through piercing a tiny space, or prying the valves open (such as 
the oystercatcher *Haematopus* spp.), but both require straight bills or a 
slight curve.

  I am not sure, therefore, that any alvarezsaurid adaptation seems useful for 
extricating snails (or really, any mollusk) from a shell, although egg-eating 
doesn't seem problematic (tool-using animals regularly just smash the egg if 
possible, few animals are adapted to consuming eggs orally and the few snakes 
that do have specialized anatomy for it (e.g., *Dasypeltis* spp. and *Oligodon* 
spp.).

Voous, K. H. & van Dijk, Tj. 1973. How do snail kites extract snails from their 
shells? Ardea 61:179-185.



Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)





----------------------------------------
> Date: Fri, 22 Apr 2011 01:51:38 -0300
> From: augustoharo@gmail.com
> To: ron.orenstein@rogers.com
> CC: dinosaur@usc.edu
> Subject: Re: dino-lice
>
> 2011/4/22 Ronald Orenstein :
> > 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)?
>
> May be, but I was thinking perhaps just a hook is optimal for
> snail-hooking, and that a similar development of other fingers may
> obstaculize it.
>
> > And why would such a
> > strongly-muscled arm be required?
>
> I think the forearm is strong relative to the size of the forearm, not
> so much relative to the size of the entire animal. Perhaps no more
> than in coelurosaurs with longer limbs. Before I wrote (but think it
> did not reach the list), that, so to speak, you choose the size of the
> pincer according to what do you want to pick. You would not use a
> pincer used to remove nails to extract a barely visible splint from
> your skin. So, perhaps if you want to break large termitaria, you use
> a large, strong forelimb, as in anteaters, pangolins, giant armadillo,
> etc. If you need to break something small, you may more economically
> use a smaller version of this. If you need to partially break a small
> thing (I was favouring perforating eggs for the thin snout to enter
> the hole, and to avoid its contents oozing), you need greater
> precision and this is given by a small version ot the same principle.
> For example, a large knife may be useful to get slices of a large
> vegetable, but may crush a small vegetable, where slices may be better
> made with a small knife.
>
> By the way, a question to you, which are an ornithologist: Do all
> birds deposit their eggs in the same season of the year in a given
> place? Because if this is true, then egg-eating (my favourite
> hypothesis) would not be so easy the rest of the year...
>
> > 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 to
> > 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?
>
> These are possibilities... Indeed, they may not be mutually exclusive,
> because many structures can give many good uses, and perhaps looking
> for the one which was selected for implies dismissing the possibility
> that having something good for many uses, instead of specialized for
> the best performance at a unique task, in itself was something to be
> selected for.