The fossil flora - Thinnfeldia odontopteroides, Morr.
The Triassic age of the Hawkesbury Sandstone is supported by the evidence of the fossil fish; though, according to Dr Smith Woodward, they may perhaps be Rhaetic, .'But the fossil plants of which the chief are Taeniopteris daintreei and Thinnfeldia odontopteroides are regarded by Seward as Lower Jurassic. At Talbragar there is a bed containing Jurassic fish, which rests in an erosion hollow in the Hawkesbury Sandstone.
Among the plants, Thinnfeldia and Taeniopteris are common.
Among other well-known Jurassic genera Nathorst has identified the following: Equisetites, Cladophlebis, Todites, Thinnfeldia, Otozamites, Williamsonia pecten, Araucarites.
As examples of these doubtful forms may be mentioned Thinnfeldia, characteristic of Rhaetic and Lower Jurassic rocks; Dichopteris, represented by some exceptionally fine Jurassic specimens, described by Zigno, from Italy; and Ctenis, a genus chiefly from Jurassic beds, founded on pinnate fronds like those of Zamia and other Cycads, with linear pinnae characterized by anastomosing veins.
The close resemblance between specimens from Jurassic rocks placed in one or other of the genera Thinnfeldia, Dichopteris, Cycadopteris, &c., illustrates the unsatisfactory custom of founding new names on imperfect fronds.
It is of interest to note that some leaf-fragments recently found in Permian rocks of Kansas, and placed in a new genus Glenopteris, are hardly distinguishable from specimens of Jurassic and Rhaetic age referred to Thinnfeldia and other Mesozoic genera.