I can only assume that some mammals will treat animals from other species as part of their tribe/pack/pride/etc if they get along well enough.

It's hard for me to imagine how this wouldn't be the case. It is a highly non-trivial sensory/processing problem for a cat to look at another cat and think "This creature is a cat, just like I am a cat, therefore we should take care of each other" but, at the same time, to look at a human and think "This creature is a human, it is not like me, therefore it does not share my interests."

This problem is especially more acute for cats than dogs, because cats don't really form tight-knit packs, and they have less available processing power.

I'd like to see some more research on the psychology of pack behavior and how/why animals cooperate with each other though.