I have designed an animal that lives on a low-gravity planet. It has bird-like digitigrade legs with raptor-like claws, similar to the image below, except with two wider toes instead of three in the front.

A similar foot design to what I'm shooting for

The toes are designed this way so the creature can perch on surfaces, etc. However, I also wanted to make the creature be able to run quickly. I noticed while researching that ostriches and even velociraptors do not have a back toe, implying that they could get in the way of running quickly. Would it make more sense to remove the back claw, or find some way to have it "retract" while running? Would it necessarily have a big influence on running speed/efficiency, or have a big effect on the gait of the creature?

  • 2
    $\begingroup$ If you are the person behind the other Mark Price accounts, you can request them to be merged, so you can keep all your contribution under a single roof $\endgroup$
    – L.Dutch
    Commented Nov 2, 2021 at 15:49
  • $\begingroup$ @L.Dutch will do. Sorry for the confusion. $\endgroup$
    – Mark Price
    Commented Nov 2, 2021 at 17:49

2 Answers 2


You can get away with them.

The faster you want your creature the lighter you need the ends of the limbs to be, their is a strong push to get rid of anything not useful on the legs of running animals.

That said there is an example of what you want, the roadrunner, which are Zygodactyly. They curl the back toes upwards creating something like a heel when running. they still do a lot of climbing and perching. the Zygodactyly feet are ancestral and since they get a lot of use, they have only modified them not lost or reduced them. As long as you don't need cheetah speed out of your animals it is fine.

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  • $\begingroup$ Exactly what I was looking for. $\endgroup$
    – Mark Price
    Commented Nov 2, 2021 at 17:50

Not necessarily. While there's a strong correlation between not having trailing toes and moving swiftly. There are also lots of examples of creatures who don't move swiftly who also don't have trailing toes. Think the elephant, or the tortoise.

What's probably more likely is that having trailing toes on the hindleg is not useful for all these creatures and as a result there is no evolutionary pressure to preserve the toe. If you look at creatures with trailing toes, there tends to be some advantageous reason for them to exist. Common reasons seem to be grasping things, or distributing pressure over a wider area.

  • $\begingroup$ Uh... elephants can run faster than humans (25 mph / 40 km/hr). I suspect they're limited by sheer bulk more than the shape of their feet. $\endgroup$
    – Matthew
    Commented Nov 2, 2021 at 17:46
  • $\begingroup$ @Matthew elephants can move fast because their limbs are very long, that is it. $\endgroup$
    – John
    Commented Nov 2, 2021 at 17:51

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