Measuring the volume of the fossa indent of bird skulls from a 3D mesh image

New user here :slight_smile:

I am trying to measure the volume of the fossa in bird skulls from a 3D mesh scan, I believe I need to cap the indent with a closed curve and go from there, but I am a little lost. I have 150 skulls to do, any help gratefully received. below is the scan of an Adelie Penguin.

Thankyou