# How can I make these feet spikes more sturdy?

The bone is three inches circumference at the joint and one-millimeter circumference at the tip. How might this bone support the front of an animal weighing one-hundred pounds? It runs with its legs below the body (I'm not sure what that's called). Its body structure is comparable to Earth animals such as leopard and mountain lions. It is a quadrupedal predatory animal that actively hunts prey. It must be able to run quickly. It hunts by chasing down prey, then jumping onto them and piercing the prey's hide with its feet spikes. If there are no possibilities of an animal running on such spikes I can always turn to the bipedal running idea. I have put a reference below.

The bone shaded in blue is a fusion of the phalanx and metacarpus bones.

This image used above is a poorly edited maned wolf skeleton (I suck at drawing complex anatomy)

• How much can the spikes be altered?
– Rob
May 3 '19 at 15:44
• @Rob I would prefer if the overall look stayed relatively similar but I'm open to changing the design a bit just so long as the needle-like tip remains. May 3 '19 at 15:46
• Imho, we need more information about the creature. Is it a bipedal creature? What is the creatures gate and how do these legs attach to the hip?
– Rob
May 3 '19 at 15:51
• Would it be possible for the "claw" to be curled back and the animal's weight is supported by the joint where the claw connects to the leg?
– user39548
May 3 '19 at 16:05
• @Hosch250 Yes, that could be an option, but the claw still needs to be strong enough to pierce through flesh and bone without damage to the spike. May 3 '19 at 16:10

Ironically, the question is how to make anything else strong enough to support that leg?

The formula to calculate the psi your creature generates by resting on those legs evenly is 25 / ((circumference / 2 / pi)^2 * pi) * 645. Let that sink in a minute (pun intended.)

1 millimeter circumference gives you a psi of ~200k just by standing still with evenly-distributed weight. For reference, 1,500k psi can make diamonds, 16k psi can break deep-sea submarines and 1.7k psi will cleanly break a femur. Your animal is literally going to punch through rocks just by walking.

Solution #1 - don't actually support weight with those legs. Plenty of creatures are bipedal or semi-bipedal. Kangaroos are a good example. Or you could go for six legs, with these two pointy ones held off the ground while running.

Solution #2 - more of the same legs. Doesn't work, sorry. Even 8 still leaves you with 50k psi, which is too much.

Solution #3 - less pointy of a leg. Increasing the circumference to 16 millimeters drops the psi to a much more manageable ~800 psi while still leaving the tip smaller than a US dime.

The spiky legs are going to be a hindrance for regular running, since they're going to sink in and take extra effort to pull out. However, they could be useful on difficult/sloped terrain where the spikes can act as pitons to guarantee solid footing on anything but solid rock. You just have to adjust the gait so that they don't risk snapping it in half by "stubbing" their toe.

• I like the idea of increasing the size of the point, pretty much my only criteria there is that the feet claws can pierce animal hide and flesh. May 3 '19 at 16:37
• @ShimmeringCosmos if your animal can actually punch with these spikes it'll definitely pierce hide and flesh, even with 16 mm circumference. If it can even punch with ~55 pounds of force it'll crack femurs. May 3 '19 at 16:52

An example of a way to keep the bone spikes out of the way whilst running would be the giant sloth:

As you can see from the picture, the joints with the claws keep them bent backwards in line with the foot when locomoting, but can be rotated forward for when climbing trees ( or fighting in the case of your creature).

It is apparent that these sloths used the side of the foot (the blade as it were) as the surface to contact the ground, this possibly fits in with the adaptation for wrapping the feet around trees when climbing. Your creature, needing to run fast could instead run on the underturned "finger" as a chimp walks on all fours:

sciencemag.org

The way that you've illustrated the spike - with a curve, it's apparent that the part of the spike in contact with the ground would be the upper part of the curve, perhaps a suitable pad of callus would grow there from abbrasive pressure from the ground.

• +1, just fold it out of the way. Gives you more contact area on the ground for lower ground pressure and keeps the spike intact and sharp. May 3 '19 at 20:23

Leave your dog its paw. Make your spike out of the dewclaw.

https://en.wikipedia.org/wiki/Dewclaw

A dewclaw is a semi-vestigial digit. Dogs can use them a little to grab things and possibly for traction when climbing. If your spike is a modified claw, the dog can keep it up out of the way when running on its regular paw and claws. It will extend the sharp dewclaw for attacking. This setup is a better approach to the cat system - cats (except cheetahs!) give up the traction of claws in favor of extending them as weapons. Your dog can have regular traction claws and then a single weapon claw.

If you curve your spikes a little bit more, then you can have the creature effectively run on the side of the spike rather than running directly on the tip.

Having the spike slightly flattened and designed slightly like a leaf spring would increase its surface area to sensible sizes to run on, while also providing increased durability if it is made of semi-flexible materials: Being naturally able to bend along its curve will decrease the probability of the spike snapping from being hit on the side, still give it good stiffness when striking with the tip, but also allow some give if it attacks and hits something hard.

It can then still use the tip to 'dig in' for added grip in many materials to aid movement.

A creature with such a weapon on its forelegs would probably also only be semi-quadruped, and be able to maintain good mobility with its forearms raised to strike. Shifting the hindlegs more towards that of a rabbit or kangaroo [animals that rely on powerful leaps mainly from the hind legs] rather than wolves [animals that tend to leap from all four legs] may also make a lot of sense to get the most out of its piercing claw attacks.

Since your creature has a similar skeleton to a maned wolf, I'll assume it has similar evolutionary traits etc. In our real world, animals pass down traits down the line as evolution progresses. Lines branch off as mutations and environmental changes occur. I'm unclear as to behaviour though. It chases prey and then pounces. It sounds like a solitary predator so I assume it's a sprinter and not a long distance runner. It chases prey so I'll assume it's not an ambush predator so stealth it probably not too much of a factor. As a result, I'll assume from your description that it's a akin to a cheetah...Fast in a sprint but not much endurance or stamina. Such a lifestyle would require the spikes to perhaps be a modified middle toe (instead of a dewclaw) that flips back up against the paws while in a rest position and extends out when the animal is in mid leap,attacking its prey. To make it easier to picture, imagine your middle finger bent backwards onto the back of your hand while your fingertips are on the table. This would increase the striking power as the claw is snapped forward.