Let me start with an explanation. Science believes life is abundant in the Universe. I believe, life is abundant in the solar system.
Now Mars is a planet and does not offer a lot of hideaways for animals. On earth we have extended woods, rainforrests, deep oceans.
What does that mean for life? They need camoflage! Like animals on earth. If they life in the open, they are quite often camoflagued so spotting them becomes hard.
I think the same applies to Mars animals - Thinking about that, what would be the best camoflage an animal can have on such an open planet? The anser is quite easy, appear as if you were a rock.
Secondly Mars is much smaller than earth is, so we'd expect the animals being quite small as well.
Today I found proof of Mars bears. Have a look at this:
Clearly a Mars bear on the hunt. Deliberately looking away from the camera so we cannot spot it by its eyes.
As always, the above is slightly contrast enhanced for the effects. the original can be found in this picture a lil bit right and down from the middle: 0109MR0684019000E1_DXXX.jpg
hope you have phun - comments and conspiracy theories welcome