Fossil Plants of the Darling Range and Beyond

DRB Nats March Meeting

There was excitement at the DRB Nats when over 90 people arrived to hear Professor Ken McNamara talk about plant fossils. He had worked as a palaeontologist at the WA Museum for over 30 years and been the Director of the world’s oldest geological museum, the Sedgwick Museum. He introduced us to the evolution of our flora.

We began in Kununurra, where a giant club moss about 30 metres tall inhabited the area about 380 million years ago. Next we saw tracks of a giant scorpion-like creature about 2 metres long in the 440 million year old Tumblagooda sandstone in Kalbarri. South of Kalbarri, near Red Bluff, some younger fossils—formed about 130 million years ago—were found in paler-coloured rock called silcrete. They were formed when plant leaves fell onto sand and the greenhouse climatic conditions and rising groundwater caused the sand to get wet, and then dry winters caused it to crystallise, much like a wet teaspoon in sugar. The fossils were made up of 45 per cent ferns, 25 per cent conifers similar to Bunya Pines, Monkey Puzzle trees, and Araucarean seed ferns, 25 per cent cone cores, and the remainder unidentified leaves, seeds, and spirals. There is also silcrete on the top of the Kennedy Range in the Gascoyne region. The oldest fossil Banksia fruit, Banksia archaeocarpa was found here, by Ken. It had some of the follicles missing or broken which suggests the presence of prehistoric cockatoos or similar.

The Walebing (near Moora), West Dale (Brookton Highway) and Kojonup silcrete fossils include possible Grevillea species which are amazingly similar to modern species, and many rainforest species (including Nothofagus, Gymnostoma, Araucarea) similar to those now occurring only in rainforest areas in Tasmania, Queensland, New Caledonia and South America. These were in the same habitat as Banksia and Grevillea. There were also many mystery fruits and leaves.

A landowner near West Dale found fossil leaves in silty brown rock called goethite, with remarkably preserved cell structure. These were Agathis, which are similar to New Zealand Kauri trees, Podocarps, and Callicoma and Rose Myrtles now only found in Fiji, New Caledonia, Southeast Asia and South America, and Macadamia (no longer found in WA.) There is also evidence of fossil plants adapting to the drying climate, shown by the sunken stomata in the leaves of Banksia paleocrypta, which would slow water loss. There are also many myrtles and Proteaceae with narrow, thick leaves to adapt to dry climate and poor soils. This shows the climate has dried and the rainforest plants became extinct, which is sad for those who would like WA to have a macadamia industry!

As a raffle prize, one of our long-standing members, Lesley Brooker, was excited to win a bee’s nest fossil—kindly donated by Bill Fitzgerald. Joff Start won a stunning trilobite sketch drawn by Noah Červenka.

The talk is now available for all to see on the DRB Nats YouTube channel.

Shelley Campbell