It was crawling up this large rock covered with lichens and browning moss. It is a squatty thing, not so typical of other ground beetles and just over a centimeter long. Its shape reminded me of the snail-eating carabids in the genus Dicaelus but this resemblance is superficial. In fact the beetle belongs to the primitive ground beetle subfamily Paussinae, a group that is much more diverse in the tropics. Many species are associated with ants in some way. This species may as well although I am unfamiliar with any work confirming this.
The habitat picture is from the spot where I found it, but on the following day.