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



Perhaps conservation of canines until developing powerful arms with
large claws is a way an anteater can protect itself. Phylogenetically,
conservation of canines makes sense, overall if descending from a
clade where the canines were much used. At least, there is an
intraspecific struggle selective force acting for their conservation,
in absence of other weapon. I once saw a video with an aardvark trying
to bite a cheetah which was trying to play with it. I suppose that
although biting will not be great thing against a larger hyena, lion
or leopard, it may at least diminish the list of predators, because
the similarly sized jackal and Cape badger would likely go for it if
this defense was not present (as far as I was able to observe, no
matter how courageous they are, mammalian carnivores do not prey on
other carnivores not smaller than they one-on-one, probably because
they have canines similar in effect to their own).

Returning to the question of mymecophagy and cursoriality, I think
they are not exclusive, as shown by Proteles, and also the canid
Otocyon, but this is constrained because most myrmecophages today are
quadrupedal mammals, where you cannot specialize the forelimb for
myrmecophagy in the sense of anteaters or pholidotans while keeping
being a cursor. When termites go around without need to break their
nests, a cursor may perfectly feed upon them. The limbs of cursors are
energy-saving because of their longer stride and lesser weight
distally, requiring less force to be moved forwards, so can easily be
used for an energy-saving myrmecophage. It seems that the inactivity
of the specialized Proteles has more to do with the inactivity of the
termites themselves. Likely, if the termites were less seasonally
variable in activity, or active during a larger part of the day, the
aardwolf would be a similarly more active animal.

Now, turning back to alvarezsaurs, they may have simply specialized
their forelimb without need to lose their hindlimb cursorial
adaptations (as many said). Thus, lack of cursoriality in most
myrmecophagous mammals can be explained because of the adaptation of
the forelimb, instead of metabolic rate constraints. Now, if
alvarezsaurids were capable of preying upon termites in their nests,
thanks to their forelimbs, they may have likely enjoyed this food
during a larger part of the year, overall accepting the calid
conditions loved by termites were more common in the Mesozoic.

Other thing: there are birds, like picids, which have a long, sticky
tongue to grab insects. This seems to make them more similar to their
mammalian myrmecophagous counterparts. Tubular mouths are less common
outside mammals because there are no cheeks (oh, well, except for
seahorses and curculionids). We may say it was difficult for
alvarezsaurs to have had a tubular mouth because of phylogenetic
constraints.