What animal has an unexpected skeletal shape?

 In my opinion, the sperm whale, also known as the box-headed whale, is the largest animal with teeth.

This animal has a square head:

Look at its shape: square, sturdy, and thick. Just like a submarine.

But the skull looks flat and pointed:

It turns out that the extra large head contains this:

These are the spermaceti and melon organs (not the melon fruit, of course). The arrangement of these organs gives the whale its boxy shape. These organs are useful for echolocation. Furthermore, its skull is apparently asymmetrical, allowing it to detect echoes from different directions.

Pay attention to the breath hole located on the left.

So, from the side, a sperm whale's head is square, from the front it's round, and from the top it's triangular, even though its jawbone is rather flat, like a crocodile's. It's a truly difficult 3D shape to visualize.

One more thing. Sperm whales only have teeth on their lower jaws, so their upper jaws are… toothless. But this half-toothless jaw is big enough to eat a giant squid. It's insane.

What animal has the strangest skeleton/skull?

 Toucans are pretty weird when you look at their skull-to-beak ratio:

I was wondering how the bird can even keep its head upright.

But learned the beak is surprisingly lightweight and balanced on their body.

It also helps them with cooling, as it has tiny blood vessels that run through it and release heat when need be.

Apparently the beaks also help them forage in the rainforest, allowing them to reach deeper into trees and crevices to get bugs and fruits, etc.