John Long
As you walk around Lake Daylesford, spare a thought for the sharks. Yes, that’s right, sharks.
The abundant layers of grey-green slatey and sandstone rocks that are exposed around the lake, especially at the southern end near the bridge, were formed in an ancient sea at a time when Australia didn’t exist. It was just an area within the giant supercontinent of Gondwana, the largest landmass on Earth around 470 million years ago.
The somewhat boring-looking rocks of Daylesford suddenly became extremely interesting when gold was discovered in them throughout the central Victorian district in the early 1850s. This gold would be vital for building up our state as one of the richest colonies in the Empire while also paying off all of Britain’s foreign debt.
The Daylesford rocks yielded gold as placer deposits in streams, or as ore in quartz veins formed within them. These rocks first formed as sandy, silty sediments that were carried out to sea by rivers and eventually built up on the edge of the continental shelf, facing towards what would become the Pacific Ocean in later years.
Earthquakes jolted these continental margins, forcing the sediments to flow rapidly down the continental slope onto the ocean floor. As the slurry of mixed sediments flowed down the slopes they were sorted into varying grain sizes, forming a neat package of layered rocks called turbidites.
When our Daylesford turbidites were building up on the seafloor over 600 metres deep, the dead centre of Australia was covered by a warm, tropical shallow seaway. Australia sat at about 10°-20° north of the equator, as Gondwana spanned from the South Pole to the northern tropics.
This vast inland sea teamed with bizarre forms of life, including some of the world’s first fishes. The oldest known shark, called Tantalepis, lived here. It is identified from just a few tiny scales the size of a pinhead that closely resemble those of some living sharks. It was about 30cm long, but as we have no fossil teeth we don’t much more about it.
Over the next 40 million years sharks developed into sleek, predatory forms with sharp teeth they could replace regularly, just as modern sharks do. This superpower gave sharks an edge over all other fishes. Soon they ruled the oceans and rivers of the world as the top predators.
Their history is a long and complex one, with many twists and turns in the story of how they survived. They endured all five of Earth’s devastating mass extinction events, even the one that killed off the dinosaurs, yet they are now facing their biggest challenge from us today.
So, the next time you walk around our beautiful lake, remember that as these local rocks were being formed at the bottom of the deep ocean, the first sharks on Earth appeared in shallow seas covering central Australia.
Professor John Long is a new resident in Daylesford. He is a retired palaeontologist and the author of “The Secret History of Sharks – The Rise of the Ocean’s Most Fearsome Predators” (Quercus, 2024). Signed copies are available in Paradise Books.
