37GHz methanol masers: Horsemen of the apocalypse for the class II methanol maser phase?

We report the results of a search for classII methanol masers at 37.7, 38.3, and 38.5GHz toward a sample of 70 high-mass star formation regions. We primarily searched toward regions known to show emission either from the 107GHz classII methanol maser transition, or from the 6.035GHz excited OH transition. We detected maser emission from 13sources in the 37.7GHz transition, eight of these being new detections. We detected maser emission from three sources in the 38GHz transitions, one of which is a new detection. We find that 37.7GHz methanol masers are only associated with the most luminous 6.7 and 12.2GHz methanol maser sources, which in turn are hypothesized to be the oldest classII methanol sources. We suggest that the 37.7GHz methanol masers are associated with a brief evolutionary phase (of 1000-4000years) prior to the cessation of classII methanol maser activity in the associated high-mass star formation region.