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Geologists to unearth the missing body of a giant fossil fish

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Posted August 20, 2013

CASEY HAMILTON packed her hammer and joined a group of ANU geologists as they set out to unearth the missing body of a giant fossil fish on the NSW South Coast.

If you saw me trekking through coastal bushland carrying a sledge hammer and a crowbar, you might think I’m up to no good, but I am actually off to see an old friend. A really old friend.

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I’m joining a research team from the ANU Research School of Earth Sciences as they search for the fossilised body of Edenopteronkeithcrooki, a 360 million-year-old giant predatory fish. The team uncovered the skull of the new species and is returning to the site in the hope of uncovering the rest of their fossil friend.

Wearing borrowed hiking boots and layers of polar fleece and enthusiasm,  I bundle myself into the car in the NSW town of Eden. Bob Dunstone, a plant scientist who moved from working with living plants to fossilised ones in his retirement, is in the driver’s seat; former ANU Geology Department staff member Dr Keith Crook (for whom the Edenopteron fossil was named) and his wife Dr Anne Felton, an ANU geology graduate, are along for the ride too.

Throughout the sixties and seventies, Crook supervised ANU geology student fieldwork, mapping much of the coastal geology from the Victorian border right up to Ulladulla. In 1978 they came across something unexpected.

“We were finding objects in the shale that clearly were not modern material – they were animal fossils,” says Crook.

They had discovered a hotbed of fossils from the Devonian Period. Spanning from about 420 to 360 million years ago, this ‘Age of Fishes’ was when lobe-finned fish like Edenopteron first appeared, and armoured placoderm fish crowded the waters. But the most exciting thing about the Devonian Period is that it saw marine life first start to explore land.

“The rocks here on the south coast span a time when marine animals like fish were beginning to use their fins to crawl out of the water and move around on land. It was a time when plant life on land diversified and atmospheric oxygen increased. From those points of view, this is a scientifically significant and challenging place to study,” says Crook.

As we pull up in a clearing at the end of a fire trail, we meet the second carload of the research team. Dr Gavin Young – a student of Crook’s in the sixties and leader of the Edenopteroteam – is here, along with his son Ben, Professor Tim Senden from the Research School of Physics & Engineering, and Bega Valley Shire Councillor Liz Seckold.

“We originally visited this site in 1979 using one of Keith’s student’s maps but then lost it – there wasn’t GPS back then,” Gavin says as we begin the trek to the site. “Luckily we had photos of us working at the site, so we were able to relocate it from landmarks.

“The fossil bones at this site are quite spectacular, but years ago we decided to keep the locality secret and leave the fossils in place. We couldn’t dig them out for study because they would break into tiny pieces, so we traced the fossil layer into the tea tree scrub and discovered a new excavation site.”

As we reach the site, I can see why they want to keep it secret. The martian-red rocks that once formed an ancient riverbed have been thrust out of the ocean, exposing hundreds of fossilised fish. Some are little more than grey strips of crushed bone running in lines through the red rock, but others are in exceptional condition.

“There was a lot of geological movement in this area so it’s a miracle they haven’t been destroyed,” explains Felton, pointing across the bay at the distinct coloured layers in the cliff face which warp closer to the shore, showing the immense forces at play. We follow the sound of a power drill up the hill, signalling that the other half of the team has started the dig.

Digging fossils is not like you see in the movies, with fine layers of dirt painstakingly removed with a paintbrush. These fossils are buried within a thick layer of rock, and power tools are the only way to reach them.

The team is drilling holes in which to pour expanding cement in order to crack the slab along its weakest points, a new technique they are testing after the method they used to excavate the skull ofEdenopteron in 2006 didn’t cut it. Or rather it did – it cut right through it!

Unaware of the remnants of the scaly giant beneath their feet, the research team was cutting through the rock with a circular saw to extract a placoderm specimen with the tail

still intact. When the block was lifted out, Ben made the surprising discovery.

“We pulled out this big bit of rock and saw a large tooth. Placoderms don’t have teeth, so we knew we were onto something,” he says.

Back at the lab, the team realised the circular saw had cut right through the jaws, making the task of piecing the bones together more difficult than usual.

“It was huge,” exclaims Gavin when I ask him about the skull. “The bottom jaw was about 50 centimetres long. Initially we thought it had a flat skull, because things of this size that have been found overseas have crocodile-shaped skulls. However Edenopteron was a high and narrow fish. It was probably out in the main river channel as ‘top predator’ gobbling up placoderms for lunch.”

Compared to similar Devonian fish fossils in the Northern Hemisphere, Edenopteron had a few unusual features, including extra bones in its palate and strange ornamentation on the scales.

“The Eden site is only the fourth place in the world where Devonian fish show these unusual features,” says Gavin.  “They were first identified in fish from another fossil site in central NSW, then at the Jemalong Range near Forbes, and in similar-aged rocks in Australian Antarctic Territory.”

Back in Devonian times these areas of Australia and Antarctica were joined together as part of the supercontinent Gondwana.

“It was always assumed that the Devonian fish found in Australia were immigrants from the Northern Hemisphere. Now we have identified a group of lobe-finned fish that actually evolved here and were closely related to the ancestors of the first land animals whose fleshy fins evolved into legs.”

Today the team has lifted a large section of rock, revealing a patchwork of placoderm fossils beneath, but no trace of the two- or three-metre-long body of Edenopteron. It will be a few days before the next expanding cement slab cracks, so we pack up and trek back to the cars.

The team wants to show me another fossil site on the way back to town. The track is rough, with collapsed drains and branches covering the road and Gavin is trying to find the site by memory.

“We could pull out a map, but that’s cheating,” he jokes.

We’re soon pulled over, crowded around a map on the bonnet of the Hilux.

After several minutes of discussion, we drive a little further, stopping beside an innocuous rocky outcrop.

“The Devonian plant beds in this area have hardly been studied, but this is an exceptionally important fossil site,” says Gavin.  “There is evidence here of some of the oldest known land plants and even some creepy crawlies that lived among the leaf litter – these were perhaps the first forests to have evolved on the planet.”

Dunstone hands me a hammer and encourages me to have a go. Feeling out of place,  I pick up a likely looking rock and gently tap it with the hammer. It reveals nothing. I pick up another and it crumbles in my hands.  I keep picking up rocks for a few minutes, beginning to wonder what all this fossil fuss is about.

The next rock I pick up looks just like the rest. I give it a half-hearted tap. I turn to Felton: “I think I have  something”.

She inspects the rust-coloured impressions in my rock.

“You’ve found an impression of some reed-like plant stems,” she says. “This site is full of plant fossils; it used to be a still lake. The vegetation nearby would fall into the water and settle, leaving impressions like this.”

It turns out my own discovery was a dime a dozen, but that doesn’t bother me: I now understand the team’s passion. The thrill of the find. The wonder of how old something is. Piecing together the clues of how we came to be standing on this land as it is now.

“You always think, ‘maybe tomorrow, maybe over that ridge, we will find something’,” Dunstone had said to me earlier in the day and now it rings true. I turn back to the outcrop with my hammer. Maybe the next rock I pick up will be the next big find.

Source: Australian National University

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