Rainbow Fossils from the Eromanga Sea Quiz

Answer: Silica

Opal fossils are particularly rare, as they rely on a series of particular events to occur. Inland seas, such as those found during the Cretaceous period in Australia needed to recede, leading sediments to mix with reactive minerals to form a type of sandstone.

These rocks began to weather, leading to the presence of silica. Opal is formed from a solution of silicon dioxide and water. As water ran down through the earth, it picked up silica from sandstone, and carried this silica-rich solution into cracks and voids caused by natural faults or decomposing fossils.

Answer: Cast

A mould or impression fossil is formed when the organism material decays completely but leaves behind an impression of itself. Air needs to be present for decomposition of the organism which prevents fossilization of the organism. These fossils are are normally in sand or clay.

Cast fossils are similar in formation, however, minerals are deposited into the hole left by the rotting organic material, creating a three-dimensional replica. The silica fills the space where the plant or animal was buried. This fossil resembles the outside of the deceased organism. The level of detail can vary from very intricate to little detail at all. Some examples of these types of fossils are shells and plant fossils.

Trace fossils show aspects of a particular species, for example, dinosaur footprints such as those found in Lark Quarry in Queensland.

True form fossils occur when the organism does not decompose.

Answer: Perimineralisation

Perimineralisation occurs when the organic material becomes saturated with silica rich groundwater, and causes the organic material to be dissolved and replaced by the silica mineraloid. The original shape of the organism remains but the composition is different and heavier.

Petrification fossils form when the organic matter is entirely replaced by minerals and turns to stone, petrified wood is an example of petrification.

Answer: Lightning Ridge

Australia is the only country in the world where black opals are found. While Coober Pedy in South Australia is also an opal mining town, most black opals are mined in Lightning Ridge in NSW, and this is where many significant opalised fossils have been found.

Andamooka in South Australia, and White Cliffs in New South Wales also produce opals and opalised fossils have also been found in these towns.

All towns listed are country towns in New South Wales, Australia. While Broken Hill is also a mining town, silver, zinc and lead are mined here. Cobar located in central New South Wales is a copper mining town.

Answer: Monotreme

The Steropodon galmani fossil found by the Galman brothers in Lightning Ridge is held by the Australian Museum. It consists of part of the jaw with several teeth. Apart from being one of the few fossils of mammals, it was the first mammal fossil from the Mesozoic era found in Australia. Mammal fossils are rare as most mammals present in prehistoric times were small and their fossils delicate and easily damaged.

Monotremes are rare, and the only current known species are echidnas and platypus. Monotremes are the only mammals to lay eggs. Marsupials are also mainly found in Australia, and are mammals who carry their young in pouches.

Answer: Hot cross bun

Kollikodon is derived from two Greek words, kollix, meaning bun and odon meaning tooth. The Kollikodon specimen includes molars, which are described as looking like hot cross buns.

Like Steropodon galmani, it is another ancestor of monotremes. Scientifically, the discovery of Kollikodon ritchiei and Steropodon galmani supports the theory that monotremes were originally located in the part of Gondwana that later split to form Antarctica and Australia, helping to explain why marsupials are limited to this part of the world today.

Answer: Fish bones

'Eric', as this plesiosaur was nicknamed, was nearly sold for jewellery. A fundraising campaign by the Australian public, and supported by Akubra hats, ensured that 'he' remained in Australia. 'His' nickname comes from a Monty Python song, 'Eric the Half-a-bee'.

The fish bones found with 'Eric' were named 'Wanda' after the movie 'A Fish Called Wanda'.

Answer: Dinosaur herd

Fostoria dhimbangunmal were plant eaters, and this group of fossils is the first evidence of a dinosaur herd to be found in Australia. Many of the bones were juvenile or immature, suggesting that these were a herd grazing and living together.

Bob Foster found the first group of fossils in 1986. He had previously found similar 'rocks' which he had broken up to find opal. One of these rocks he thought might be a fossil of a horses hoof, so took them to be examined at a museum in Sydney. Members of the Army Reserve were sent to help excavate further remains, after the fossils were identified as a new species.

This new species is named in Foster's honour with dhimbangunmal, taken from the language of the local Yuwaalaraay and Yuwaalayaay Aboriginal languages, meaning 'sheepyard' the name of the area where Bob was mining.

Answer: Lightning claw

Rob and Debbie Brogan found a number of bones including a 25cm claw, part of a forearm, a metatarsal, a rib and parts of a hip and lower leg in 2005, on the Lightning Ridge fields. It is estimated that this meat eater was up to 7m long, and its claw around 25 cm long (slightly shorter than one ruler).

A meat eater, it is likely that the large claws would have been used to grapple with prey.

Answer: Virgin Rainbow

On display in the South Australian Museum, the Virgin Rainbow is valued conservatively at AUD $1 million. The specimen is 6cm and 72-carats. It has a stunning range of colours and its discoverer, John Dunstable, states that it glows in the dark, with dark rooms highlighting its vibrancy.

The Olympic Australia is the largest opal discovered to date in Australia. Named for the Melbourne Olympics, it was found in 1956. The other two opals are also famous Australian opals.