Re: As biology goes, sixty million years ago wasn't that long ago and organisms had pretty established patterns.
Life has been on earth for 3 or 4 billion years, I doubt a newcomer who hadn't evolved here could survive here, or compete against the local bugs. Still...you never know. Maybe an invader microbe capable of attacking alien populated worlds has had time to evolve in the thirteen odd billion years the galaxy has been here.
Still, if such a killer critter existed, it should have attacked and destroyed all earth life by now.
We see no hint of any life on earth not descended from the same primordial organism.