It was recently shown that elephants passed the mirror test for self-consciousness. Along with chimps, orangutans, and dolphins, they recognized that they are seeing themselves in the mirror. However, other animals that may not pass the mirror test in its hard form, i.e. a positive recognizing themselves, do pass a softer form of the test in that they do not interpret their reflection as that of another.
Many times I have watched pet dogs and cats walk past a mirror. Occasionally they give their reflection a glance, but mostly they take no notice. In so doing they demonstrate that, although they may not recognise themselves in the reflection, they do know that they are not seeing another dog or cat.
I suspect this more rudimentary “not-other” awareness (as opposed to true self-awareness) is to be found in any animal that drinks from water. As an animal leans forward to drink, it is likely to see its own reflection face to face. if it interpreted this as another animal looming close, it would probably back off (and, if continually repeated, die of thirst). For such creatures, there is a clear evolutionary advantage in the inhibition of the “other” response when seeing their own reflection in water.
This more prevalent “not-other” awareness is probably an important step in the emergence of true self-awareness.