Why is evolution hiding?

[Esquilax]

Shouldn't we still have half reptile/half mammal?

Well, that depends. With those reptiles that became the mammalian lineage, what we find is that the mammalian traits were so conducive to the environment they were born into that they were selected for, while the reptilian traits were selected against; one breeds out, the other stays in and grows more pronounced. That's just a product of the environment that lineage had to survive in.

Now, it's entirely possible that today a reptile could evolve mammalian traits, or vice versa, and those traits would be selected for. But as of right now? that hasn't been the case. But lineages do die off; we don't see every last creature to ever exist around today. In fact, most of the animals that have ever lived on earth are now extinct.