Lower Triassic Temnospondyli of Tasmania
Amphibians of the superorder Labyrinthodontia, order Temnospondyli, form a prominent component in a fossil vertebrate fauna collected from exposures of the Lower Triassic Knocklofty Formation in central and southeastern Tasmania. The four identified species described in this paper include: a brachyopid, Blinasaurus townrowi; a lydekkerinid, Chomatobatrachus halei; and two rhytidosteids, Deltasaurus kimberleyensis and Derwentia warreni. Deltasaurus kimberleyensis is also found in the Cluan Formation of north-central Tasmania as well as in the Blina Formation of the West Kimberley District, Western Australia (Cosgriff, 1965). Blinasaurus townrowi is closely related to B. henwoodi of the Blina Formation and to B. wilkinsoni of the Gosford Formation of New South Wales (Cosgriff, 1969). The other two forms, Chomatobatrachus halei and Derwentia warreni, are new, monotypic genera. All three of the temnospondyl families of the Tasmanian Triassic are also represented in other areas of the world widely separated from the Australian region by present-day geography. Their distributions thereby strongly suggest land connections linking most of the continental areas during the late Paleozoic and (or) early Mesozoic. This, in turn, supports the hypothesis of continental drift, a phenomenon for which abundant and convincing geophysical evidence has been accumulated in recent years. Blinasaurus is most closely related to Batrachosuchus of the Cynognathus Zone of South Africa, to Brachyops of the Mangali beds of India, and to Boreosaurus of the Sticky Keep Formation of Spitzbergen. Chomatobatrachus closely resembles Lydekkerina and Limnoketes of the Lystrosaurus Zone of South Africa. The two rhytidosteids, Deltasaurus and Derwentia, resemble both Rhytidosteus of the Cynognathus Zone and Peltostega of the Sticky Keep Formation. Fossil vertebrate and palynologic evidence, taken together, indicate that the faunas from the Knocklofty and Blina Formations are closely synchronous in the earliest part of the Triassic and that they are somewhat older than the vertebrate fauna from the Gosford Formation. In reference to the standard stratigraphic scale of the Beaufort Series of South Africa, the Knocklofty-Blina horizon appears to be above the Lystrosaurus Zone but below the Cynognathus Zone. Habitus and lithologic evidence, together with considerations of relative abundance in the localities and the environments in which related species in other areas have been found, provide the tentative conclusions that: B. townrowi and C. halei were more proximal to the sites of deposition than D. kimberleyensis and D. warreni; that B. townrowi was a benthonic pond dweller that fed on large prey such as lungfish and other temnospondyls; that C. halei was a stream or stream-bank dweller that fed on insects or fish; and that D. kimberleyensis and D. warreni were actively swimming fish-eaters, inhabiting a downstream or estuarine habitat. The over-all aspect of the vertebrate fauna indicates a climate that was at least temperate, that lacked a marked cold season, and that was humid enough to maintain standing and flowing water during the entire year.