The Evolution of Modern Flora

Queensland Museum

The Cretaceous Period is an important era in the evolution of Australian flora and much of what is known about plants during this time comes from the exceptional fossil record of the Winton Formation. On a worldwide scale, the first flowering plants on Earth appeared during the Early Cretaceous and this group would later come to dominate most terrestrial environments.

Impression fossil of a cone scale from an araucarian conifer. Winton Formation.  
The southern conifer families, like the Araucariaceae and Podocarpaceae (brown and plum pines), which had emerged during the Jurassic, continued to dominate elements of the Cretaceous flora. Some plant groups, such as pentoxylales and bennettitales, declined and would eventually disappear completely, while other, like the ginkgoes and horsetails vanished from the Australian fossil record, but persisted in the Northern Hemisphere.

Impression of a fossil leaf from a flowering plant.
Winton Formation.

Impression fossil of Phyllopteroides macclymontae (Osmundaceae).
Winton Fromation.
This genus occurs in other Early Cretaceous deposits in Queensland and in Victoria, which shows that it is widespread at this time.

Well preserved plant fossils from the Jurassic Period have given Palaeobotanists new insight into the evolution of Australian flora. This specimen of the fossil tree fern, Cladophlebis australis, comes from the Walloon Coal Measures, near Ipswich in southern Queensland.

Foliage of the Triassic-age cycad, Pseudoctenis eathiensis, from near Esk in south-east Queensland. Cycads are seed plants that resemble tree ferns or palms. They first appeared on Earth more than 200 million years ago.
The Arucariacean Phase
From 178-160 million years ago, during what is called the ‘Arucariacean Phase’ , conifers, pentoxylales, liverworts, lycopods, equisetales and a diverse range of ferns dominated Jurassic vegetation communities. Conifer wood is the most common fossil from this time and the growth rings in the woods from the Arucariacean Phase occur in a wide belt across the Surat Basin and numerous examples have been found on the western Darling Downs in southern Queensland.

Osmundacaulis stems, fractured longitudinally, and showing the central vascular stele and obliquely orientated leaf traces. From the Walloon Coal Measures.

Another plant group recovered from this area include a genus of seed fern, Donponoxylon. In cross-section, the wood is divided into multiple segments, which may exhibit both continuous and discontinuous growth patterns. There are two species of Donponoxylon, but little is known about the affinities of this plant. It differs from conifers and cycads, which typically have single stems. Donponoxylon shares some similarities with the pentoxylales, a group of seed plants that also have complex multiple stem segments.

Stem of Donponoxylon bennettii showing the classic stem structure of this species. The central bundles of vascular tissues are surrounded by multiple smaller bundles.

Conifer leaves from the Burrum Coal Measures in south-east Queensland.

Branch of an araucarian conifer.

Fossils are rare in the Precipice sandstone. This fine-leafed fern is from Mount Morgan, in central Queensland.

Impression of a fossil conifer shoot. Winton Formation.

Leaves from Hausmannia sp. (cf. H. defarrariisii). This fossil was recovered from the Walloon Coal Measures at Mutdapilly in south-east Queensland.
Credits: Story

Images and text from: In Search of Ancient Queensland.
Principle Authors: Dr Alex Cook and Dr Andrew Rozefelds.
Published by the Queensland Museum, 2015.
Photographers: Peter Waddington, Rochelle Lawrence, Jeff Wright.

Credits: All media
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