The pygmy right whale is an oddity, possessing features not found in any other living whale. This makes its origins of particular interest to marine biologists, so the finding of just the sixth fossil ever from this enigma would excite scientific interest on its own. The fact that the latest discovery is easily the oldest relic of Caperea marginata we have has made it particularly noteworthy.

In the 1950s, palaeontologist George Baxter Pritchard found a fossil in the sandstones of Beaumaris, Melbourne and identified it as a whale ear bone, adding it to the Museums Victoria collection. However, Pritchard could not identify the species of whale, and it was only recently when Dr Erich Fitzgerald of the Museum conducted a thorough study of its collection of whale ear bones that he recognized how unusual this one is.

“What began as puzzlement rapidly shifted gears to astonishment as it dawned on us just what we were looking at – the unmistakable periotic bone of a pygmy right whale,” Fitzgerald said in a statement. CT scans, described in PeerJ, confirmed the strong resemblance to living pygmy right whales.

Despite its name, Dr Fitzgerald told IFLScience the pygmy right whale appears only distantly related to true right whales. Its closest living relatives are probably the ocean's giants, the Blue and Humpback whales. Some scientists regard it as the sole survivor of the Cetotheriids, a once diverse group of whales that are now extinct, but Fitzgerald said this remains controversial. We know little about their lifestyle, because they make shorter trips to the surface than most whales.

Besides being the smallest baleen whale, the pygmy right whale has eyesight suited to low light conditions, unusual among whales that feed on krill rather than needing to spot individual prey. Its oddest feature is its ribs, which form a series of overlapping flat blades, rather than a rib cage.

Useful as this shield-like structure would be to a medieval knight, it is hard to see why whales would need protection against stabbing. Fitzgerald thinks the most plausible explanation is that the ribs provide a strong anchor point for the muscles of the upper tail. This relates to the C. marginata’s other odd feature, a swimming style that undulates the whole body, rather than relying on the tip of the tail for movement like most whales.

Pritchard's specimen still had some sediments attached to it, and from these and other clues, Fitzgerald has concluded it came from strata laid down 6-6.2 million years ago, preceding all other Caperea fossils.

The find confirms the pygmy right whales originated in the southern hemisphere, where they still live, despite Fitzgerald’s discovery last year of two specimens showing they crossed the equator in cooler eras.

The Beaumaris site where the fossil was found represents a conundrum of its own. The site has produced one of our richest trove of Southern Hemisphere marine fossils, revealing much about the evolution of penguins and dolphins, as well as whales and pelagornis, a long-lost seabird with an astonishing 5-6 meter (17-20 feet) wingspan.

Unusually for such a good site, it is located at the base of one of Melbourne's more affluent suburbs. Fitzgerald told IFLScience palaeontology has benefited greatly from local amateurs offering the museum the fossils they find. Indeed, with sea level rise likely to drown the lower strata within a few decades, such voluntary efforts help in the race against time to reveal the site’s riches.

On the other hand, Fitzgerald added, many of the site's fossils have been sold to private collections before palaeontologists could examine them, something the accessible location makes hard to prevent.