Dr Alan Beu reveals some shell fossils in the National Paleontology Collection, stored at GNS Science. Some fossils in a rock can indicate the environment that rock was formed in. Certain shells lived only in shallow water, others only in deep water. Other shells are of less use, as they lived in a range of environments.
DR ALAN BEU
This is one of the most interesting and distinctive fossils at Whanganui. This is a rock borer – it bores itself holes in the rock – and this is a paired whole shell still with the sediment inside it, and these occur only on the sediment planes that represent the glacial periods where the water’s gone right out of the basin and you have this smooth flat surface left and these things are found burrowing in the sediment there.
This is a collection from one of the shallow water brown sands, the Shakespeare Cliff sand. This is a tuatua – very similar to the tuatuas common on sandy beaches today. Dosinia ring shells – these also are on sandy beaches today – and in particular this little topshell Zethalia. The modern one is a bit more brightly coloured but you can see that they’re very, very similar. And these live today only in 2–5 metres of water off sandy ocean beaches. For comparison, there’s a particular shell bed that’s deposited in a lot deeper water, perhaps 20 or 30 metres of water, and the distinctive thing about this shell bed is that it’s got a lot of oysters in it. This is the same as the Bluff dredge oyster today.
The big scallop that’s common has very square ribs with deep obvious grooves between them, but that’s almost entirely limited to this particular shell bed, the Tainui shell bed. This little wee Murex shell with little spiny frills on it is also limited to that shell bed so you can recognise that shell bed all over Whanganui basin by these little Murex shells and that square rib species of scallop.
The mud stone units in general throughout the section also have these very delicate little bivalves and the common little scallop shell Chlamys scallops. Interesting there because it doesn’t actually tell you anything much about their environment. These live today all around New Zealand in a big wide range of environments from just off shore down to hundreds of metres of water.