Re: Claws on deinonychosaurs

[Michael Habib <mhabib5@jhmi.edu>]

Since claw shape seems to be featuring in some of these posts, I would 
like to mention that a straight claw would, in fact, be better for 
slashing than a curved claw.

This means the claws of deinonychosaurs remained curved through the 
evolution of the lineage for one of two reasons:

1) Phylogenetic/developmental constraint (claws are ancestrally curved, 
curve is maintained).

2) There was at least some importance to piercing/hooking; either in 
addition to, or to the exclusion of, slashing cuts.

With regards to piercing, from a pure physics standpoint: Using a 
curved weapon that is swung has the advantage of focusing a lever 
movement (the strongest movement of most animal limbs) into a piercing 
action. Piercing with a tip is much more effective at deforming a stiff 
or semi-stiff surface (say, thick skin, scales, etc) than slashing with 
an edge.

Of course, part of the difficulty with looking at fossil claws this way 
is that curvature is somewhat uncertain (owing to a lack of the keratin 
sheath in most fossils).  Then there is the whole issue of how straight 
is 'straight' and how curved is 'curved'.

--Mike