Australia: The Land Where Time Began

A biography of the Australian continent 

Baragwanathia Flora

Based on Baragwanathia and associated plants, this is among the most important terrestrial plant floras of ancient vascular plants in the world. Among one of the best preserved, it is one of the richest with regards to the number of different plants it contains. It was discovered at Yea in Victoria, as long ago as 1875.

Baragwanathia is a genus of Lycopod that derived from Zosterophylls, and is similar to living lycopods in both structure and organisation, in particular Lycopodium squarrosum. There has been much controversy about the age of the the deposits it was first found in because of its high degree of specialisation. The sediments of the deposit are continuous from the Silurian to Early Devonian. In the Yea deposits it occurs with Rhyniophytes and a Zostrerophyll, as well as Graptolites (invertebrates). The Graptolite in this deposit was used to correlate the fossil horizon with the Silurian Ludlow Division of Wales, as well as elsewhere. The original graptolite fossils were of poor quality so not all agreed with the correlation, but more recent finds of high quality fossil Graptolites has confirmed the Late Silurian as the age of the Yea deposits.

The fact that Baragawanathia had such an advanced appearance compared with that of Zosterophylls, that it had evolved from, caused many to doubt the Late Silurian age. The discovery of land plant spores and fragments in rocks from pre-Late Silurian age, has made it increasingly clear that the vascular plants had indeed evolved earlier than had previously been thought.

In the Yea deposit, 1700 m of siltstone separates the lower Late Silurian rocks from the upper assemblages of Early Devonian age. This siltstone was deposited over a period of 30 million years. The Early Devonian rocks contain many more plant species in this upper flora. Among them were Trimerophytes, that had evolved from Rhyniophytes and are members of the group of early plats leading to all higher plants.

The Baragwanathia Flora is closely related to floras from around the world of a similar age, apparently because at this time all the landmasses were combined into the single landmass of Pangaea.

Sources & Further reading

1. Maey E. White, The Greening of Gondwana, the 400 Million Year story of Australian Plants, Reed, 1994