-- DanielSantos? - 30 Jun 2003

Geometry of Claws and how it relates to Climbing Ability


Dai, Z., Gorb S., Schwarz, U.. "Roughness-dependent friction force of the tarsal claw system in the beetle Pachnoda marginata (Coleoptera, Scarabaeidae)" The Journal of Experimental Biology, Vol 205, pgs 2479-2488.

Link: http://jeb.biologists.org/cgi/content/abstract/205/16/2479

The above paper looks at the geometry and structure of beetle claws. SEM photos of the claw show 3 distinct structural layers. Experiments were conducted on the breaking stress (in bending) of a single claw and it was found to be approximately 143-684 MPa. Also, experiments were conducted to determine the amount of force that a single beetle could apply in the direction it was walking while on different substrates. The substrates used were sandpaper of a range of grit sizes. The experiments correlated the radius of the claw tip and the mean radius of the sandpaper particles with the amount of force that could be generated in the walking direction. It was found that little force could be generated (< 50 mN) when the mean particle size was much smaller than the claw tip radius. When the claw tip radius was of comparable size to the mean particle size then forces on the order of 200-400 mN could be generated in the walking direction. Increasing the mean particle size past the claw tip radius did not result in significantly larger forces generated in the walking direction.


Feduccia, Alan. "Evidence of Claw Geometry Indicating Arboreal Habits of Archaeopteryx" Science, Vol. 259, Issue 5096, pgs 790-793.

http://dart.stanford.edu:88/Get/File-4669/ClawGeometry.pdf

The above paper looks at the shapes of claws in a large number of birds ranging from ground-dwelling to tree-climbing. The conclusions drawn were that mainly tree-climbing birds had claws with a greater claw arc than mainly ground-dwelling birds. Specifically, the author found that ground-dwelling birds tended to have claw arcs of around 60 degrees, and not more than around 90 degrees, while tree-climbing birds tended to have claw arcs of around 150 degrees, and at least around 120 degrees. The author was using this information to argue that the Archaeopteryx dinosaur had been a tree-climbing dinosaur.


Zani, P.A.. "The comparative evolution of lizard claw and toe morphology and clinging performance" The Journal of Evolutionary Biology, Vol 13, no. 2, pgs 316-325.

The above paper analyzes claw and toe shape in a large number of different species of lizards (including geckos). The author finds two correlations between claw/toe shape and climbing performance. Increases in claw curvature, toe width, and adhesive lamella number were found to be correlated with increases in clinging performance on smooth substrates. Increases in claw height (vertical thickness of claw measured at the base of the claw) and decreases in toe length were found to be correlated with increases in clinging performance on rough substrates.

 
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