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Mononykus & Parvicursor
I would like to expand a little on my idea that Mononykus stripped bark in order
to capture insects. First, let us consider this criticism by Peter Buchholz:
"This is also not very likely to me (though more likely than the first idea
[digging]) because the claws are not very coordinated as one would expect to dig
out insects in bark ..." Diane Farish has this to say in Dinosaur Discoveries
#2, p. 11: "The bone surfaces suggest the clawed forearms moved inward towards
the center of the body." It is not likely that the claws were used like those
of the Aye-Aye since they are so remote from the head. I imagine that the claws
were inserted on either side of a targeted strip of bark, dug in towards one
another, then pulled down with the aid of a backward movement of the animal.
This would strip off a long piece of bark, exposing scrambling insects. At this
point, Mononykus, having pulled back in the process of stripping bark, would
then place its head to the exposed area and consume the insects with its tongue
(etc.). Pulling backwards with the body might put some stress on back muscles,
but if most of the action is accomplished by forelimb power, then this would be
a minimal stress.
There are partial remains (no forelimbs) of a Mongolian relative of M. called
"Parvicursor remotus" (DinoDisc #3, p. 6). However, there are three vertebrae
from the lower back that are of a ball and socket design, the same design found
in the necks of most theropods and in the upper backs of some. I assume that
the theropods have them because of the stress of pulling back the neck in
connection with tearing out chunks of flesh, the ball and socket being a
protection against dislocation of the vertebrae. The ball and socket vertebrae
of Parvicursor would suggest similar stress to the lower back, which is
consistent with the theory of bark stripping and similar activities, only with
Parvicursor relying more on back pull than Mononykus.
Also consistent: the only tooth thus far found for Mononykus is described (loc.
cit.) as "... small, laterally compressed, and spatulate." We know that
spatulate teeth can be used for gripping as well as cutting, as we see from the
use of incisors in "primitive" contemporary cultures of our own species. In
Mononykus and its kindred, a certain amount of bark pulling by gripping the
strip in the teeth would be expected once the head became engaged. This is a
matter of "fine tuning," in which gripping teeth could be used and far less
force applied to peel back the already separated bark.
The following activities seem to be consistent with what is so far known of
Mononykus and its kin: 1. stripping bark; 2. pulling fallen branches and small
logs to expose insects (etc.); 3. stripping the outer parts of the trunk of
certain kinds of trees to get at the pith (useful in an arid environment); 4.
shaking bushes and small trees to knock down fruit; 5. pulling down bushes or
fragile small trees to get at edible items in the higher branches; 6. in
scavenging, hooking detached pieces of meat (as suggested by Bruce Thompson),
and running off to safety with them; 7. flipping over flat rocks to get at grubs
(secondary function); and, 8. as suggested by Roger Compton, tearing up insect
mounds (secondary function).