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Megadesmus and Eurydesma

posted 2 Mar 2017, 21:21 by Jamie Derkenne   [ updated 2 Mar 2017, 21:26 ]

Bought a box of fossils from Lawsons Auctioneers, late November 2012. They were bivalves - the line of symmetry runs along the hinge line. The auctioneer said they were from near Branxton in the Hunter Valley of NSW.




Wee Jasper

posted 1 Mar 2017, 15:33 by Jamie Derkenne   [ updated 21 Mar 2017, 15:05 ]

Wee Jasper, north west of Canberra, Australia, is rolling sheep country, presently gripped by drought. From the hills you can see panoramic views of the Murrumbidgee and Goodradigbee valleys and Burrinjuck Dam with outcrops of grey limestone dotted along the ridges. 
The limestone is completely fossiliferous. Pick any of it up, and you are bound to see a fossil of some sort - mainly early Devonian  corals, shells, but also of lung fish and placoderm fish.

Coprolites

posted 1 Mar 2017, 15:30 by Jamie Derkenne   [ updated 1 Mar 2017, 15:30 ]

Coprolites - Nundle New South Wales
Now rock, these strange looking objects were once the droppings of prehistoric animals which roamed the Nundle area millions of years ago.

  
By Jamie Derkenne and Danja Nieminen

What's brown and curly, pinched at one end, formed after a tummy rumble millions of years ago, and found throughout the Nundle area? 
`They say they are bloody droppings from bloody prehistoric animals,' says Nundle publican Robert Schofield. According to scientists, he could well be right.

Nundle is a geologically tortured area. It's as if the ground was picked up by a giant hand and scrunched up like a piece of paper. Layers of chert - sediments laid down in the sea millions of years ago - stand almost on their end. Basalts and other volcanic rocks meet with sandstones and river gravels on the side of cliffs. Geologists at the University of New England routinely refer to the area in the best traditions of scientific description: a `real mess' is how geology students are told to describe the area. 
No wonder then that the area, in rugged, mountainous country 65 kilometers south-west of Tamworth, was famous for its gold. At the nearby village of Hanging Rock, the Great Serpentine Belt, a huge rock formation of serpentine that winds its way along the Northern Tablelands meets cherty siltstones, laid down deep in the ocean hundreds of millions of years ago. 
The ground is littered with shafts burrowing deep into where the two rock groups meet: that's where the gold was to be found. The old miners, while digging their shafts through ancient gravels and sands, would sometimes come across rocks totally different to the gold they were seeking. 
It's that rock which is giving Nundle a notoriety it hasn't experienced since the gold rush days. These strange looking rocks, often found in ironstone formations or in the soft white clay beds around Hanging Rock are called pineapple stones by the locals. It's not hard to see why. 
But many scientists think these rocks may have their unusual shape because they were once the excretement from prehistoric animals such as diprotodons - giant marsupials which looked like wombats, but were the size of well fed rhinoceros - long before the Aboriginal dream-time. 
In search of prehistoric poo, we scoured Hanging Rock recently to see if we could find any of the dinosaur dung. 
On the first day, we had no luck. We figured we were looking in the right spot, though, because the ground was sticky with white clay. The next day, after a thunderstorm had washed clay way from some of the stones sitting on the surface, we fared better. 
No doubt about it, they sure did look like your average Fido find. It's after rain too, when the locals, nearly all of them rock-hounds, have found the best specimens. A Nundle local, Tom Melvaine remembers townsfolk in years gone by picking up prehistoric poo by the bag full. The stones have been sought avidly by American tourists, but no-one's ever been game enough to ask why. 
Dr Peter Flood, a paleontologist with the University of New England, has examined some of the `pineapple' stones, and has an eloquent explanation as to what they are all about. 
`They are fossil shit,' he said. 
`They are always pinched at one end like the real thing - upon drying out they crack up a bit.' 
So that's why they look like pineapples. Scratch that theory as to why the dinosaurs died out. 
But how does a bit of soft, steamy dropping become a hard rock? 
It seems many of the fossils - scientists call them coprolites - were `deposited' by large animals in what geologists call the tertiary period, that is, up to about 65 million years ago. 
Some scientists think the animals concerned defecated near rivers and lakes. The droppings would crack and dry out in the sun, but would eventually be covered by river and lake sediments. Compression, mineral percolation and millennia all combined to make the material into a hard rock - so hard in fact, it resists much of the weathering of surrounding rocks. 
Theories of what made these stones abound. Talk to any one in Hanging Rock or Nundle, and they'll let you in on their own ideas. 
Local rock-hound Shirley Ryan remembers miners years ago telling her they had come across great gobs of the stuff, sometimes 20 metres deep. 
`It's definitely not dinosaur dung, but it's from a prehistoric animal,' she said, `and is found mainly in one spot at Hanging Rock. 
`A Californian university professor told me it was from giant, soft boned sloths, and that the only other sites are in America and India,' she said. 
Shirley explained that no fossils remain of the sloths themselves, because the soft bones soon rotted away. 
She said the droppings were percolated with ironstone and eventually over millions of years, became rocks themselves. 
However Tom Melvaine isn't so sure. He believes the stones are in fact stalactites from ancient caves, and have somehow survived all the geological upheaval of the area. It's not an idle opinion. Tom's father was one of the founders of the first lapidary club in Sydney. And Tom himself has been a keen rock hound all his life. 
But certainly these rocks look like what many say they are. 
Some of the coprolites look so real that if you put one down on the ground, you'd swear that Fido had fouled the carpet. 
Other locals are pretty sure the droppings belong to diprotodons. And, unlike the other theories, plenty of fossils of the huge animals, mainly their tusk-like teeth, can be found throughout the New England area. 
Perhaps they come from a range of animals - after all, they come in all sizes and shapes. The only common characteristic is the pinched end - a sure sign that they are coprolites, and the swirly shape, which some scientists think could even be an indication of the animals' intestinal structure. 
Robert Schofield has seen a few tourists come through his pub in search of the coprolites. If he's got a theory, he's not giving the game away. 
`Someone found a real big one the other day - it must've been three foot long,' he said. 
`I guess the animal must've been constipated at the time.' 

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