It’s a shame these aren't around in some form or another anymore. I loved these cards as a kid and my daughter loves cards of all kinds so this was another good resource for us. I managed to find a good set on ebay and, as a bonus, this set contains a lot of cards of extinct animals that I don’t remember having in my original set.
We began by looking through the cards to find the ones of animals we see around us; common birds, deer, squirrels, skunks.
Next, we sorted the cards into the mammals, birds, reptiles, and so on. Of course this provides some great early lessons in taxonomy and some basic ideas in evolution such as variety and adaptation. Never hurts to begin laying a foundation.
So much of what we learn connects with everything else we learn and this is another good example. Talking about animals leads to talking about extinct animals which leads to talking about things that happened in the past.