The adorable little penguins (Eudyptula minor) of southern Australia, the continent's only surviving penguin species, manage to support a large tourism industry single-flippered. Once, however, Australia was blessed with many of the flightless birds, and a new study suggests giant penguins survived there long after they had died out everywhere else.

Australia and Antarctica separated from each other around 80 million years ago, opening up plenty of ocean. The first penguin species appeared around the time the dinosaurs became extinct, and made good use of both shores of this widening gulf, diversifying dramatically. After a while, however, many of these birds, particularly the larger ones, died out.

Travis Park, a Ph.D. student at Monash University, has been trying to piece together Australia's role in this, publishing his findings in PLOS One, a day after World Penguin Day.

Central to Park's work is a single bone retrieved from the limestone of western Victoria. This comes from a species described in 1959 named Anthropodyptes gilli. Based on the size of the bone, the penguin it belonged to would have been 1.4 to 1.5 meters (4.7 to 5 feet) tall, which Park pointed out to IFLScience is 50 percent taller than the largest penguin alive today.

^{Travis Park with the humerus of an A. gilli, an emperor penguin and a modern little penguin. Ben Healley}

Such giant penguins were common on every southern continent 23 million years ago, but Park told IFLScience that previous studies of the bone had failed to “put the find in context.” At 18 million years old, A. gilli indicates that Australia's giant penguins outlasted their counterparts by at least 5 million years.

"The past 20 years has seen a renaissance in our understanding of penguin evolution,” Park said in a statement. “However, Australian fossil penguins have, until now, been left out of this global picture and no-one has known where they fit into the story. Our paper is the first attempt at putting the missing piece of this puzzle in place.” 

Park concluded that rather than penguins arriving in Australia once before diversifying, there were several dispersals where new species arrived from elsewhere over the course of millions of years. “There is no evidence suggesting that any of the Australian taxa are more closely related to each other than to other taxa, although more complete remains of these taxa may reveal a sister group relationship between some species,” the paper reports.

“Several different types of giant penguin colonized Australia before eventually disappearing around 18 million years ago. Since then smaller penguins have been the norm, although modern penguins do not appear to have reached Australia until relatively recently,” Park said.

The disappearance of other giant species coincided with the loss of many marine mammals, something Park said may have been related to major changes in sea levels at the time. Australia's isolation possibly protected A. gilli for a long while, and Park told IFLScience it was not clear why the species finally died out.

Relics of other giant penguins might have survived with A. gilli, but they remain undiscovered in the less explored parts of Australia's southern coastline.