Considering the vast number of non-human animals compared to humans, the probability of being a human is vanishingly low. Therefore, chances are that if I could be an animal, I would be. This makes a strong anthropic argument that it is impossible for me to be an animal.

You assume that you have equal probability of being any conscious being. The internal subjective experience of humans stands out in its complexity; perhaps more complex subjective experiences have higher weight for some reason.