While we are talking about marsupials (see previous post), it's a good time to show how to tell the difference between a marsupial and placental mammal skull - you know for those life or death, save the world, situations when you need to be able to tell the difference. There's nothing like being prepared.
There are a few differences between the marsupial and placental skulls, however the easiest by far is the nasolacrimal duct - that's the tear duct to you and me.
Above are the skulls of a Thylacoleo (left) and a Thylacene (right). The tear duct is clearly visible outside of the eye socket, sitting on the cheek.
Now the skull on the right is a dog skull. See the tear duct?
Oh no, that's right, you can't, 'cos it's not visible. In placentals, the tear duct sits inside the eye socket, and so you would have to view the skull from above and look down into the eye socket to see it. Whereas in marsupials, the duct sits outside the eye socket and is clearly visible when viewing the skull from the front or side.
So the next time you have to make a life or death identification, you can spot the marsupial with confidence.