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I'm creating a large ungulate that is likely a part of the suborder Anclyopoda. Suspension of disbelief is expected, but there's a detail with the current design that's really bugging me.

The creature is meant to be related to the odd-toed ungulates, but the current iteration of its anatomy has three toes and a fourth as a vestigial-looking thumb. This happened because the animal is meant to be a good climber in order to thrive in their environment.

Should I remove the smaller toe or one of the large ones? Should I just add another thumb? How important is it for the ungulate to keep an odd number of toes through their evolution?

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    $\begingroup$ Tapirs are perissodactyls and have four digits on their forelimbs. The characteristic of perissodactyls is not that they have an odd number of digits, but that the weight-bearing axis passes through the 3rd digit, contrasted with the artiodactyls where the weight-bearing axis passes between the 3rd and the 4th digit. The question is asking for an answer to a non-existent difficulty. $\endgroup$ – AlexP Jun 30 at 19:58
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It isn't important at all.

We call them the odd-toed ungulates, but really it's just a group of related animals that, for the most part, have odd numbers of toes. This tends to happen because the common ancestor of these animals placed most of its weight on one particular digit, so unless there's a reason not to its descendants tend to have the other toes evenly distributed around that one.

It's not universal though. Tapirs have four digits on their front legs, and if this particular group is adapted for climbing - which represents a significant change from their ground-dwelling ancestors - all bets are off.

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Remember as well that lots of animals have either vestigial digits or even tiny bits of subdermal bone that once were toes. Your animal could easily fall into one of those categories and still be strictly a (2N+1)-toed family member.

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