I considered keeping this photo for a puzzle, but I thought it might be a little unfair.
It's the tip of the tail of a Rio Fuerte beaded lizard (Heloderma horridum exasperatum). The rest of the lizard was underground in a burrow it was digging. This exhibit was renovated before Christmas, so the soil is obviously good for digging and there must be plenty of it as I estimate that at least 40 cm of lizard and tail was underground. I don't know if it is significant that 2 beaded lizard eggs hatched at the zoo last month.