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Re: Alvarezsaur spurs (was Re: dino-lice)



Dann Pigdon <dannj@alphalink.com.au> wrote:

> The problem I have with envisaging them as specialised diggers is that 
> anything within reach of
> those stumpy forelimbs would seem to have been also out of sight. Not being 
> able to see what you
> are digging into would appear to be a major disadvantage.


Yes - especially if you're disturbing an insect nest.  After the nest
is breached, the ants or termites will go on the attack.


The other problem with the ant-/termite-eating hypothesis is that
modern myrmecophagous mammals (i.e., those that specialize in eating
ants and termites) tend to have low body temperatures and BMRs - at
least those mammals that weigh more than I kg.  Although some
alvarezsaurs weighed less than this (like _Parvicursor_), most weighed
more than 1 kg.  I don't want to extrapolate too much from this,
because alvarezsaurs are not mammals; but an exclusively
myrmecophagous diet is hard to accord with the high BMRs indicated by
the highly cursorial proportions of alvarezsaurs.


> Having such long legs would also seem
> to require them to be in some sort of prone position in order to dig.


The exception to this would be if alvarezsaurs targeted dampwood
termites nesting within a living tree.  Or if the termites were housed
inside large termitaria (if they existed back in the Cretaceous).



> Perhaps they were useful for scraping out nest hollows while the animal was 
> lying prone, done
> mostly by feel rather than sight. Otherwise they'd have been quite 
> inconvenient excavation tools.
> Neither would they seem to have been much good for defense, since any 
> predator close enough to
> be in range of the forelimbs had probably already bitten into the head or 
> neck.


True.  Modern anteaters (including the little silky anteater,
_Cyclopes didactylus_) use their sharp manual claws as a defense
against approaching predators.  But again, they have long forelimbs


> They do remind me somewhat of platypus spurs though, which are used almost 
> exclusively in
> intraspecific combat (platypus don't produce much, if any, venom outside of 
> the breeding season,
> so the spurs aren't much use as a general year-round defense against 
> predators).


And as you know, only male platypuses have spurs.



Cheers

Tim