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1957:GFI:0068
Trigonotreta stokesi Bruny Is. This is a spiriferid brachiopod. Brachiopods are a separate phylum of shellfish, more ancient than Phylum Mollusca which contains modern scallops and oysters. The spiriferid group of brachiopods are characterised by their “winged” appearance. In the 18th century such fossils were thought to be fossil birds! This specimen is an internal cast, made of sediment which filled the shell and thus shows the internal characters of the shell. The prominent central beak is a feature of internal casts of most spiriferids |
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1957:GFI:0077
Grantonia sp. Granton Another spiriferid brachiopod. While bivalves have a left and right shells, brachiopods have a brachial (uppermost) and pedicle valve (shell). A significant character of spiriferids is the depression in the centre of the brachial valve and the corresponding ridge or keel on the pedicle valve. This specimen is a replacement. It shows the characteristics of the outside of the shell, but the original shell material has been replaced, molecule by molecule, by a mixture of calcite and silica carried in groundwater. |
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1957:GFI:0151
Spirifera strzeleki Derwent Valley Another spiriferid brachiopod –they are very common amongst Tasmania’s Permian fossils. This fossil is in the form of an interior cast of the pedicle valve (see comment on Grantonia) and shows the distinct keel and ribs. Fine detail is not present because this fossil has undergone replacement crystallization by impure calcite and the crystal size is too coarse to permit the retention of fine detail. |
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1957:GFI:0192
Paraconularia derwentensis Bridgewater Conularids were ancient organisms with a shell of roughly pyramidal shape and a soft body something like a sea anemone or a simple member of the octopus group – or something in between. The shell was carried apex upwards, tentacles trailing from the open base. This group has been extinct for nearly 200 million years, so there is much about them we will never know. Paraconularia is characterised by the distinct lines across the shell with the kink at each corner and the vertical line dividing each side into two equal sections. derwentensis is the most common species, but compared with other Permian fossils, these organisms are relatively rare. |
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1957:GFI:0313
Protoretepora ampla Hobart This is an example of a bryozoan fossil. Bryozoans were colonial organisms similar in structure to some corals but a separate phylum of animals with a more advanced soft body biology than coral polyps. You see this fossil as a 'line of bumps' – which are actually the sediment which filled the holes in the colony – called fenestrules. This organism should not be mistaken for the very similar and more common Fenestella. Fossils of bryozoans are usually called imprints, as in this case, because the original organism is very thin or 'somewhat two dimensional'. It is as if something fine had imprinted itself on the rock. |
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1985:GFI:0433
Aviculopecten sp. Latrobe Another pectin bivalve – similar to Deltopecten. This genus had much finer ribs on the shell, a very distinctive shape along the hinge line, and is seldom as large as Deltopecten. Bivalves are described as having left and right valves (shells) when viewed with the hinge line uppermost. That makes this fossil a left valve. The fossil appears as an external mould in the rock, with the process of fossilization assisted by recrystallization in the original limestone. |
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1985:GFI:0513
Fenestella fossula Tas. Another bryozoan – like Protoretepora. This is the most plentiful of all Tasmanian Permian fossils. Dense “forests” of folded fans of Fenestella grew up off the floors of shallow seas, and this saw a high percentage fossilized when they toppled over into the mud and sand accumulating on the sea floor. This specimen is not an imprint, but a replacement. The actual material of the colony has been replaced by impure, fine grained carbonate material, which stands out against the backdrop of the grey limestone. The limestone itself is described as bryozoal, because these organisms were a significant component. |
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1987:GFI:0125
Eurydesma sp. Maria Is. This is a bivalve mollusc, a replacement created when re-crystallizing calcite replaced the original shell. Consequently this fossil shows the details of the shell’s exterior. The fossil shows part of both valves, right valve uppermost. Eurydesma is a common fossil in low grade limestones from the lower Permian, and is best known from the “fossil quarries” on the north end of Maria Is. Although easily identified amongst other Permian bivalves by its shell shape, Eurydesma has minimal markings on its shell exterior, compared to more recent and current life forms of the same type.. |
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2002:GFI:0078 Martiniopsis
sp. Bronte Park A spiriferid brachiopod but quite different from Grantonia & Spirifera. The vast majority of fossils of this organism are internal casts, noted for their very prominent beak. Most internal Martiniopsis have little detail apart from the beak area, so careful consideration of that part of the fossil must be used to separate the species, of which there are a number. If you look carefully around the edges of the fossils you can see a narrow space – where the original shell has been removed from by chemical action. If such specimens are broken apart there is often confusion, as the details of the internal cast are quite is different from those of the external mould, the other side of said gap. |
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2006:GFI:0002
Keeneia platyschismoides Poatina A Permian gastropod (sea snail). All the specimens pictures are internals – “the sediment which filled the shell”. Gastropods first appeared in Ordovician times as shells which were flat coils – planispiral – on the sea floor. As time went by the coil began to spiral upwards so that Permian sea snails like this were almost as high as they were wide. Modern forms often have shells 4 to 5 times as high as they are wide at the base. The first coil of the shell from the aperture is called the body whorl, and is where the animal lived. Some gastropods coil to the left (sinstral) while others coil to the right (dextral). Keeneia is sinstral. |
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2007:GFI:0013
Martiniopsis ingelarensis Tas. This species of Martinioposis is quite different from the one already pictured. It is identified as ingelarensis by the shape of the beak and the features to either side of it. Like the vast majority of Martiniopsis specimens, this fossil is an internal cast of the brachial (upper) valve. Most brachiopods tend to be buried in their normal position, pedical valve downward, which mean brachial valves are far more common amongst fossils of Martiniopsis. |
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2008:GFI:0010
Wyndhamia jukesi Liffey One group of brachiopods called strophomenids had spines on the upper shell, possibly as protection from predators. This particularly large and detailed specimen of Wyndhamia clearly shows the spines on the brachial valve. The fossil is a replacement, formed when the calcium carbonate of the original shell, buried in sea floor sediments, was replaced by silica rich calcium carbonate. This makes the fossil much more resistant than the surrounding rock, promoting survival for us to find. The next most common Tasmanian Permian fossil of this spiny type of brachiopod is Strophalosia. |
