The animal mired here was Diprotodon, the largest marsupial that ever lived. Picture a wombat scaled to the size of a rhinoceros: up to four metres from nose to tail, standing nearly two metres at the shoulder, and weighing as much as 2,800 kilograms. They moved across the inland plains in small herds, browsing on saltbush and shrubs, and when drought drove them toward Lake Callabonna's vanishing water, the mud took them one by one. Their carcasses sank where they stood. The salt and silt sealed them. What makes Callabonna extraordinary is not just the number of animals but the way they were preserved: complete, articulated skeletons, the bones still lying in the positions the living animal held, many caught upright as though frozen mid-stride.

European science learned of the bones almost by accident. Aboriginal people of the region had long known the lake held the remains of huge creatures, and in 1892 an Aboriginal station hand named Jackie Nolan showed the giant skeletons embedded in the dry surface to the lessee of Callabonna Station, F. B. Ragless. Word reached the South Australian Museum in Adelaide. The following year, in 1893, the museum dispatched the geologist Henry Hurst to the site, and what he found astonished the scientific world. Across only a few hectares of salt pan lay the remains of hundreds of Diprotodon. Later work would put the count at some 360 individuals, the largest assemblage of these animals found anywhere on Earth.

The Callabonna fossils did more than fill a museum. They solved a mystery that had defeated the greatest anatomist of the age. When the English scientist Richard Owen first reconstructed Diprotodon, he could not work out the shape of its feet, and famously had his artist hide them behind tufts of grass. The skeletons drawn from the Callabonna mud, described in scientific papers in 1899, finally revealed the front and hind feet in full and completed the picture of the animal. The lake gave up other treasures too, including the bones of Genyornis newtoni, a flightless bird taller than a man that shared this drying world and met the same fate in the same mud.

Recognising what lay beneath the surface, the colony set the lake aside as a Fossil Reserve in 1901, a protection that still stands. The lake was added to the South Australian Heritage Register in 1997 for its palaeontological significance, and administrative responsibility rests with the South Australian Museum. Access is restricted, and for good reason: the skeletons remain in the salt where they fell, vulnerable to anyone who might disturb them. The northern end of the lake falls within the Strzelecki Regional Reserve. When floodwaters do reach Callabonna, the white pan briefly becomes a shallow lake again, drawing waterbirds in numbers that earned it a place within the Strzelecki Desert Lakes Important Bird Area. The same drying that doomed the megafauna still rules here: water arrives, life floods in, and the salt reclaims it all when the heat returns. The difference is that today the lake gives up its dead instead of taking them, surrendering one of the richest windows we have into the lost giants of Ice Age Australia.