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Climbing Mononykus



Betty CunninghamÕs recent post is stimulating: 

ÒI am looking closely at a reconstruction of Mononykus (from a speech by Novak 
in SF) and I am wondering if the shape of the arm-taken out of
context as an arm- looks to anyone else like a ruminant hoof and leg
specializing in rock-climbing?  The reduced area of the point-of-contact
and the very straight support behind it leads me to wonder if they might
have used it as an aid to rock-climbing or hill-traversing. The rest of
the animal could have stayed in relatively stable areas of ground, and
the fore-limbs and long neck could have been used to search for food in
and around rocks in the area-maybe for lizards and bugs?  Richard's
description of a very powerful forelimb seems to support (sorry) this.
DinoGeorge, would that lend support to your arboreal dino if it's a
rock-climber?Ò  

Your thesis is isomorphic to mine in several respects, under certain 
assumptions.  If you imagine the animal gripping rocks on a hill of steep grade,
the idea has an air of plausibility.  This visualizes the animal using a pincer 
movement of the arms in a more or less upright position.  But this doesnÕt 
really seem to be what you are suggesting.  You seem to be saying that we should
view the arms as front legs, and the claws as analogous to the hooves of goats 
(etc.).  I would suggest that the following are serious problems for this view: 
(1) the muscle attachments indicate that the power of the arms was directed 
inward; (2) the claws were also pointed inward; (3) ex hypothesi, the front legs
have undergone radical adaptive changes to rock-climbing while the back legs and
feet remain, even by Theropod standards, relatively primitive and not obviously 
specialized for rock-climbing; and (4) if we are to imagine Mononykus as 
quadrupedal, how could we then explain the peculiar foreshortening of the front 
legs?  Also, is it not true that mountain goats primarily locomote in rocky 
terrain by leaping?  I sure would hate to land on two stubs terminating in 
giant, pigeon-toed claws.  However, even in the bipedal, upright climbing model,
the arms are so small in relation to the legs, one wonders how the two sets of 
limbs would coordinate in this enterprise.  The same holds for climbing trees.