Baleen whales are the titans of the ocean, the largest animals to have ever lived. The record holder is the blue whale (Balaenoptera musculus), which can reach lengths of up to 30 meters. That’s longer than a basketball court.

However, throughout their evolutionary history, most baleen whales were relatively much smaller, around five meters in length. While still big compared to most animals, for a baleen whale that’s quite small.

However, new fossil discoveries from the Southern Hemisphere are beginning to disrupt this story. The latest is an unassuming fossil from the banks of the Murray River in South Australia.