On Friday I gave you one of the specimens on display at the Horniman Museum, photographed from an unusual angle, as the mystery object:

I thought it might prove tricky, but jonpaulkaiser managed to identify it within 16 minutes of it being posted. Impressive stuff! Matt King also managed to spot what general type of beastie this bit of bone belonged to; a turtle, more specifically a snapping turtle – Chelydra serpentina (Linnaeus, 1758) according to its label, but given the size I wouldn’t be surprised if it was actually the larger Alligator snapping turtle Macrochelys temminckii Troost, 1835.

Of course the fact that the specimen is sectioned probably made this harder than it might have been – here’s what it looks like from the other side:

These are among the largest freshwater turtles in the world and they are called ‘snapping turtles’ for a good and rather obvious reason. Their jaws close very rapidly and the sharp bill that covers their toothless jaws makes these turtles a worthy of caution if you want to keep all of your fingers.

The reason that these turtles snap is because they are ambush predators – the inside of their mouth is camouflaged and their tongue has a wriggly appendage that acts as a lure. They sit in the murky water with their mouths open and wait for fish and other aquatic organisms to come and investigate their lure, at which point it’s game over.