TOURISMINTERNET
[ Up ]

Up
Earth

The fossil site at Limestone Road, Yea, Victoria

has been gazetted as part of the National Estate

                   because it contains the

     most ancient leafy foliage so far found on earth.

This is derived from a plant named Baragwanathia longifolia in honour of the Director of the Geological Survey of Victoria at the time of discovery.

The Baragwanathia plant formed scrubby cover over tidal flats in the latter part of the Silurian Period, a time of earth history almost inconceivably long ago (400 million years).

Above is a drawing by Mrs C Healy, which is an interpretation of the evidence provided by the rocks and the fossils at the Yea site.

Explanation of the Drawing

Silt and sand banks in a tidal estuary support the world's earliest leaf bearing land plants. The dark plants depicted across the centre of the picture presents Baragwanathia forming a thick growth to 3 metres in height with prostrate elements in semi submerged areas.

In the foreground one of the much smaller, and as yet unnamed accompanying plants flourishes on a sandy stretch, and on the bottom left hand corner the kelpy fronds of a seaweed reach the shallows. An arid landscape spreads dismally to low sandstone hills in the distance.

The most ancient leafy foliage so far found on earth.

The Baragwanathia plant formed scrubby cover over tidal flats in the latter part of the Silurian Period, a time of earth history almost inconceivably long ago (400 million years).

At the time Central Victoria was part of a submarine trench bounding the east of the continent. According to the plate tectonics theory this was itself part of an enormous land mass called Pangaea, comprised of the continental masses prior to separation into their present day entities.

The rocks at the Yea site are sandstone and shale, alternating in very clearly defined beds that have been deformed and significantly tilted from their original horizontal aspect. The Baragwanathian fossils are present only in some of the beds, generally as pieces of stem 10 to 50cm in length with attached long narrow leaves.  Deep burial for millions of years has resulted in drastic alteration of the stem, which is now evident as impressions, often made clearly visible by iron staining on the more weathered surfaces.

As mentioned above, the rocks in the Yea area were deposited under an ancient sea now long departed. This means of course that the Baragwanathia plant must have either grown on the shore line or has been washed out to sea by stream or other action, to ultimately attain the fossil condition.

Large vascular land plants (plants with woody tissue) like Baragwanathia have not been found elsewhere in rocks of Silurian age.  The vegetation at this time principally existed in the sea as algae like the kelp and seaweed common in the oceans of today. Land plants are known from overseas beds of similar age to those of this Yea site, but they were small erect naked stems a few centimetres in height (often with a fertile extremity), quite unlike the large vegetative body of Baragwanathia.

Baragwanathia is not the only fossil plant found at Limestone Road, about a dozen others have been recognised, but less than half of these have so far been described and named.  One or two are possibly relatives of Baragwanathia but most are not vascular land plants.

There are also animal fossils at the site.  A mollusc fossil, called Orthoceras is even more common than Baragwanathia, and divalve shells are occasionally found.  At least one fish, affiliation not yet determined, has also been collected.

More important from the point of view of establishing the age of the beds are members of an extinct Order, the Graptoelites. These are important because the species present are used as the criterion for the confirmation of the Silurian age.

Baragwanathia is found at several other parts of Central Victoria but these localities are all in younger ( Devonian ) rocks.

Registration in the National Estate (after application by interested parties) is approved only after close scrutiny into the merit of the application.  This Yea locality is one of only two fossil localities so far accorded this status in Victoria.

The other fossil locality is the Koonwarra Fish Bed locality in South Gippsland, of Cretaceous age. It contains a renowned fish, insect, crustacean, bird feather, and plan fossil assemblage.

W Baragwanath was Director of the Geological Survey of Victoria from 1920 to 1943.

Isabel Cookson (Melbourne) and William Lang (Manchester) described Baragwanathia in 1935.

The species name “longifolia” literally means that it is the “long leaf” Baragwanathia.

In the photo above you can see the sedimentary rock which makes up this fossil site.

On the rectangular rock, above the number 1, you can clearly see the layers where the sediment has been collected and then turned into stone. On the same rock you can see a thicker line, number 2, running through the rock. The rocks are easily pulled apart on these lines.

On the rock on the left, the number 3 indicates a line or crack which has occurred in this rock. The part of the rock numbered 4 easily lifts off, just like a tile or a jig saw piece.

It is in these rocks where these important 400 million year old fossils are entombed.

The Up Button takes you to the Home Page