Triassic continental sediments in south-east Queensland were deposited in a number of discrete basins, of which the Esk Trough (Middle Triassic) and Ipswich Basin (Upper Triassic) have yielded abundant plant fossils. Conchostracans are common at several localities in the latter basin.
A number of genera from the flora have been described in detail, either because of their intrinsic interest or biostratigraphic significance. The descriptions of the species of Dictyophyllum are expanded in the light of new material collected; Thaumatopteris is synonymized with Dictyophyllum. A new species of the marattialean genus Marantoidea, M. acara sp. nov., is erected, and Danaeopsis is regarded as a junior synonym of Marantoidea. The monotypic genus Ogmos gen. nov. with type species O. adinus sp. nov., is based on specimens from the Esk Trough, and.may be of marattialean affinities.
An extensive review has been undertaken of the Australian Triassic species of the pinnate genera Nilssonia, Pseudoctenis, Zamites and Anomozamites, and the simple genera Yabeiella, Linguifolium and Taeniopteris, with particular emphasis on the species occurring in south east Queensland. Graphical analysis was used to help differentiate the species (26 in all), and the following new species are described: Nilssonia stalsis, N. dissita, ?Pseudoctenis contracta, ?P. stenygra, ?P. dinmorensis, Yabeiella intermedia, Y. crebra, Y. arta, Y. patula, Linguifolium ascium, Taeniopteris adunca and T. apleta. A number of nomenclatural changes are made to other species, including the synonymy of Pterophyllum multilineatum Shirley 1897 with ?Pseudoctenis abnorme (Etheridge) comb. nov., the reduction of the number of previously described species of Linguifolium and Yabeiella to two each [L. lillieanum Arber 1913 and L. tenison-woodsii (Etheridge) comb. nov.; Y. mareyesiaca (Geinitz) Oishi 1931 and Y. brackebuschiana (Kurtz) Oishi 1931], and the transferral of Otozamites queenslandi Walkom 1917 to Zamites. The species Anomozamites anomozamoides (Bonetti) comb. nov. is recognized for the first time in Australia. A principal component analysis performed on the conifer shoots found in Esk Trough sediments shows that only one species, Rissikia media (Tenison-Woods) Townrow 1967, is present.
A study of the time ranges of the species described reveals that three floral zones can be distinguished in eastern Australia, being roughly Early, Middle and Late Triassic in age. The species of Taeniopteris are particularly useful in differentiating these zones.
Conchostracans are small phyllopod crustaceans enclosed in a chitinous bivalved carapace. The valves usually show a wide variation in morphology, and a series of measurements seems to be the best method of description. The measuring schemes of previous authors usually rely on the hinge line, which can be difficult to recognize, so a new system of measurements is developed, based around an origin on the umbo. This scheme is applied to conchostracan populations from the Blackstone and Mt Crosby Formations in the Ipswich Basin, and successfully differentiates two quite similar species, one of them very variable.
While modern conchostracans are restricted to small, temporary freshwater pools, some of the fossil species seem to have lived in brackish or even marine environments. The occurrence of closely related fossil species in the same pool is also in contrast to modern associations, which hardly ever contain more than one species per genus. The suggestion that this reflects excessive splitting of fossil species rather than a change in occupancy over the years would invalidate conclusions about the duration of pools and sedimentation rates in fossil examples.