The most obvious example of an approximately monthly biological cycle is the human menstrual cycle. My questions are the following:
Is it known when and where this cycle or one like it arose?
What exogenous cue(s) (if any) is/are this cycle based on? The moon's orbit around the earth is seemingly obvious however the only cue that I can think of that would be easily sensed by organisms is variance in night-time illumination, which seems like a very weak phenomenon when compared to day/night and seasonal cycles. King and neap tides may be a suitable cue however they have a half-monthly modulation.
The moon has been steadily retreating from the earth over the course of its history, which means that months have been slowly getting longer. Is there any fossil (e.g. biogeochemical) evidence of organisms with biological cycles in synchrony with a 'short month'?
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