This is a really odd little fly that looks like a cross between a sciomyzid (snail-killing fly) and a sarcophagid (flesh fly), which isn’t far from the truth because the family Ropalomeridae sits within the Infraorder Muscomorpha and the Superfamily Sciomyzoidea. The family is nearly entirely neotropical, with 1 of the 26 known species occuring in the Nearctic.
I can’t find very much information on their ecology – except that their larvae have been found in rotting substrates and the adults are attracted to molasses and rotting fruit. I can back up the latter observation because I have seen them feeding on rotting banana bait traps.
After a bit of Googling and downloading papers I think mine is a female of the genus Willistoniella (the commonest genus) – based on the shape of the face; one pair of marginal scutellars; and the only slightly curved and laterally compressed hind femur. Unfortunately I don’t think I can go much further with the ID because the key relies on seeing parts of the female genitalia that seem to have been retracted on my specimen.