So... I'm fiddling with Yet Another Bipedal Digitigrade Species. There is tons of material on the legs, but seemingly not so much on the hands.
So... I'm wondering; is it possible to design a "hand" that can function as both a digitigrade 'foot' and be useful to a civilized tool-user?
As we know, digitigrade forepaws have extended metacarpals, and the range of motion between the metacarpals and proximal phalanges is from roughly in-line to about 90° forward/out. In humans and most other species with grasping fingers, the range is from roughly in-line to about 90° backward/in.
Another challenge is claws, especially the retractile variety, which effectively 'eat up' a useful joint. That said, I'm not sure how much it would really inconvenience most people if the last two digits of their fingers were fused.
An obvious solution is to provide the MC/PP joint with a greater range of motion. Is this plausible? If not, is it plausible that a species with such 'fingers' would be able to grasp objects anyway? (What might the thumb look like?) Or is there any other 'hand' design that could be used?
- 'Hands' should be able to grasp objects well enough to plausibly be able to survive in any period of development (assume technological progression similar to human).
- Should be able to grasp a pencil / thin rod. Bonus points if they can use chopsticks.
- Should be able to grasp a tool handle / thicker rod.
- Should be able to grasp a ball / apple / etc.
- Okay if they need to use two hands more often than humans.
- Should be able to 'stand' on forelimbs with weight partially carried by the metacarpals. Should ideally be able to walk like this, but okay if they can't run (on all fours) very well.
- Phalanges are probably longer than otherwise; closer to human proportion.
- There is definitely a thumb, although I'm not entirely sure what it looks like or how it stays out of the way for walking-on-hands. Ideally it is opposable, at least to the tips of the other fingers when said fingers are curled. (Maybe not to each finger joint.)
- Should be able to have "retractable"¹ claws.
(¹ For you pedants out there, yes I know claws are really protractile.)