I study fossil whales. This here is a fossil skull - a 25 million-year-old fossil of a whale called Janjucetus. Next to it here is the skull of a living species of dolphin called the Common Dolphin which lives in Victorian waters today.
One thing I'm interested in trying to work out is exactly how these extinct fossil whales ate, and also what they ate. One method we can use to try and work this out is a simple ratio. That ratio is the length of the upper jaw, here, to the total skull length, here.
The total skull length. And here's that upper jaw.
This ratio of upper jaw length to total skull length is important in living whales and dolphins because those whales and dolphins that have a relatively long upper jaw tend to specialise on eating fast-swimming fish, and smaller fish at that.
However, those living whales and dolphins that have much shorter and more massive jaws as a ratio of total skull length tend to specialise on feeding on larger fish and squid and are more active predators.