Here we have what until now has been the only known specimen and record of a Rough-toothed Dolphin from Victoria. And it's a skull that was collected from a specimen found at Hobson's Bay near Melbourne and that was discovered in the 19th century.
On my left we have a skull of the Bottlenose Dolphin, typically seen in Port Phillip Bay, and on my right is the skull of the Rough-toothed Dolphin. And we can nicely see here some of the key features, which we can use to distinguish between the Rough-toothed Dolphin and the Bottlenose Dolphin.
Firstly, in the Rough-toothed Dolphin, we have a quite a narrow upper jaw and in the Bottlenose Dolphin it's quite broad and flat. Also, if we look at the undersides here of the eye socket, we can actually see that in the Rough-toothed Dolphin there's this long, scroll-like ridge which is absent in the Bottlenose Dolphin.
Lastly, if we look at the join between the two halves of the bottom jaw, we can see that in the Rough-toothed Dolphin this join, or as it's technically known, a symphysis, is quite long whereas in the Bottlenose Dolphin it's much shorter.
It's using characteristics like this on skull specimens in our museum collection that we can use to actually distinguish between closely-related species. One day myself and Dr Kate Charlton were doing some research on Bottlenose Dolphin skulls in the museum's Mammalogy Collection and we came across this one particular skull and we immediately thought this doesn't really look like your typical Bottlenose Dolphin for a number of reasons. And that really gave us that hint that this was in fact a different kind of species. We used these diagnostic features to determine that this was in fact a Rough-toothed Dolphin and therefore the first record of that species from Victoria.