Looking for the title of a sci-fi story about astronauts using their knowledge of evolution to figure out they're in a space zoo

I read it back in junior high, and google isn't helping. From what I remember, a group of astronauts lands on a planet that has a bunch of animals on it. What they observe is that some of the animals have two limbs, some four, some six, some eight. What they eventually found strange was that animals seeming to be of the same level of evolutionary development would have such a disparate number of limbs. Looking at Earth, for example, what we might think of as "upper level" animals have four limbs. Then they notice other things that hint that the animals all may be from different planets. They conclude that they're in some kind of zoo or collection. I don't remember if they get off the planet or anything.