Scientists have discovered a "shark graveyard" deep on the sea floor of the remote Western Australian coast containing hundreds of fossilised teeth, including those of a close relative of a fearsome prehistoric predator — the megalodon shark.
The surprising discovery was made by a team of scientists on board the CSIRO's research vessel Investigator, during a biodiversity survey at the new Cocos (Keeling) Islands Marine Park.
Museums Victoria Research Institute senior collections officer Dianne Bray, who was on board the voyage, said when the team first dragged up the net from their final trawl it looked disappointing.
"When we put these nets down hoping to get animals, we are surveying biodiversity," she said.
"So initially we thought it was just full of sediment and manganese nodules."
But soon they realised what they had found.
'Amazing' discovery
"Then we started going through it and one of my colleagues spent at least an hour just going through it picking shark teeth," she said.
"It was amazing, it really was.
"Not all were fossils, some were relatively recent mako sharks and two species of great white shark relatives."
Over 750 teeth were pulled from the area, which was near the base of the Muirfield Sea Mountain, south west of the Cocos (Keeling) Islands.
The haul included the tooth of a megalodon shark, or its closest ancestor.
The prehistoric predator, which died out more than three million years ago, was the largest shark to ever live, and grew to between 15 and 18 metres in length.
WA Museum Curator of Fishes Glenn Moore said the "graveyard" was a remarkable find.
"I don't know of any obvious explanation of why they might all be together other than perhaps it was a low point in the ocean floor, so they would eventually make their way down," he said.
"I have never seen anything like this, or heard of anything like that, it's a unique opportunity to have an almost complete collection from one spot.
"And when the palaeontologist get their hands on them I'm sure they'll be very happy."
Dr Moore is currently on board the second marine park biodiversity study, underway in the Gascoyne.
Like the Cocos Islands trip, it is being undertaken for Parks Australia, who manage Australia's marine parks network.
The trip is designed to understand the biodiversity of the area, and provide a baseline knowledge of the biodiversity.
New records of species discovered
Dr Moore said they had found a huge diversity of animals already.
"We're getting some amazing fish, crustaceans, molluscs and soft corals," he said.
"Off the deep waters, at 5,000 metres, is stuff you just can't imagine."
He said because a survey hadn't been done in that part of WA before, they were also finding species in new areas.
"A 'new record' is a known species that has been described and found elsewhere around the world, but has never been recorded in Australian waters before, or in West Australian waters," he said.
"Those species are really important because it helps us to complete the global map of where these species are distributed, and allows you to build management protocols for how to protect them."
Among the "exciting" finds was a new species of hornshark, already known to scientists, but yet to be described.
CSIRO shark expert Will White, who is the deputy chief scientist of the trip, said it would be of great benefit to their study.
"My current thinking is that it's endemic to Western Australia, possibly also the Northern Territory, and it's a new species," he said.
"And to get a fresh specimen is a real boost to that study, it can be allocated as the holotype, which is the primary species you base all your description on which is the most important one," he said.
"So it's exciting to get one in such good condition. "
Dr Bray said they had likely discovered several new species during their trip to the Cocos Islands, too.
"It won't be until we've looked at them seriously under a microscope that we will know that they are different," she said.
"But we know we have at least a couple of new species."
