Biogeography of Australian freshwater fishes : Biogeography of Australian freshwater fishes

The Quaternary ice ages were paced by astronomical cycles with periodicities of 20–100 k.y. (Milankovitch cycles). These cycles have been present throughout earth history. The Quaternary fossil record, marine and terrestrial, near to and remote from centers of glaciation, shows that communities of plants and animals are temporary, lasting only a few thousand years at the most. Response of populations to the climatic changes of Quaternary Milankovitch cycles can be taken as typical of the way populations have behaved throughout earth history. Milankovitch cycles thus force an instability of climate and other aspects of the biotic and abiotic environment on time scales much less than typical species durations (1–30 m.y.). Any microevolutionary change that accumulates on a time scale of thousands of years is likely to be lost as communities are reorganized following climatic changes. A four-tier hierarchy of time scales for evolutionary processes can be constructed as follows: ecological time (thousands of years), Milankovitch cycles (20–100 k.y.), geological time (millions of years), mass extinctions (approximately 26 m.y.). “Ecological time” and “geological time” are defined temporally as the intervals between events of the second and fourth tiers, respectively. Gould's (1985) “paradox of the first tier” can be resolved, at least in part, through the undoing of Darwinian natural selection at the first tier by Milankovitch cycles at the second tier. Show more

The taxonomy of the predominantly Australian fossil dipnoan genus,Neoceratodus,is revised and the Recent Australian lungfish,Neoceratodus forsteri,and two fossil species,Neoceratodus eyrensisandNeoceratodus nargun,are redefined. Two new species of the related Tertiary genus,Mioceratodus,are described on the basis of tooth plates from central and northern localities in Australia. These areMioceratodus diaphorusandMioceratodus poastrus.A new genus,Archaeoceratodus,is erected to include three rare Tertiary species and one Mesozoic species. The Tertiary members of this genus are the type species,Archaeoceratodus djelleh,described originally asNeoceratodus djelleh,and two new species,Archaeoceratodus rowleyiandArchaeoceratodus theganus.The Mesozoic species isArchaeoceratodus avusfrom Triassic and Cretaceous deposits in southeastern Australia, described originally asCeratodus avus.All three genera belong in the family Neoceratodontidae. Show more