Academic literature on the topic 'Fishes, Fossil Victoria'

Eastern Australia has two major Mesozoic fossil localities. The Talbragar Fish Bed in central west New South Wales contains an assemblage of Upper Jurassic fishes, plants and insects. The Koonwarra Fossil Bed, in South Gippsland, Victoria, has an assemblage of Lower Cretaceous fishes, plants and insects. The geological settings of these localities are described. Each locality has a common genus of fish that was originally described as Leptolepis. The names of both these fish have been changed, the Talbragar one to Cavenderichthys talbragarensis and the Koonwarra one to Waldmanichthys koonwarri. Both of these fish have been placed into the Family Luisiellidae, together with a Patagonian fish, Luisiella feruglioi. Each locality also has a member of the family Archaeomenidae: Archaeomene tenuis from Talbragar and Wadeichthys oxyops from Koonwarra. The relationships of these and other fish have been discussed by various authors over the last 20 years and a summary of these comments is presented, as well as a brief comparison between the plants of both localities. The localities of Talbragar, Koonwarra and the Argentinian fishes during the Mesozoic appear to have similar palaeo-environmental settings, which may explain the similarities in the assemblages. The Australian localities contain well-preserved specimens which shed light on the diversity and extent of fishes in southern Gondwana, a region otherwise poorly represented in the fossil record.

In this study I take advantage of an unusual system of fossil lakes in eastern North America to estimate the time for speciation of endemic semionotid fishes. Twenty-one species are all found in sedimentary cycle P4, the deposits of a single Early Jurassic lake, in the Towaco Formation of the Newark Basin in New Jersey. To determine the degree of endemism in the fauna from this fossil lake and estimate time for speciation, I surveyed more than 2000 museum specimens from 45 named localities in the Newark Basin and related basins of the Late Triassic to Early Jurassic Newark Supergroup. Six species not found in deposits equal in age to P4 or older are considered to be endemics, eight species occurring in older deposits presumably colonized Lake P4, and evidence for whether the remaining seven species were endemics or colonists is equivocal. The time for the formation, decline, and evaporation of Lake P4, in which P4 sediments were deposited, has been estimated at 21,000-24,000 years. Because all endemic Semionotus first occur in the first third of lake history, the estimated time for speciation of endemics is six species in 5000-8000 years. This rate is remarkably similar to that estimated for the five cichlids in Lake Nabugabo that diverged from Lake Victoria cichlids in about 4000 years.

The frequent occurrence of adaptive radiations on oceanic islands and in lakes is often attributed to ecological opportunity resulting from release from competition where arrival order among lineages predicts which lineage radiates. This priority effect occurs when the lineage that arrives first expands its niche breadth and diversifies into a set of ecological specialists with associated monopolization of the resources. Later-arriving species do not experience ecological opportunity and do not radiate. While theoretical support and evidence from microbial experiments for priority effects are strong, empirical evidence in nature is difficult to obtain. Lake Victoria (LV) is home to an exceptional adaptive radiation of haplochromine cichlid fishes, where 20 trophic guilds and several hundred species emerged in just 15 000 years, the age of the modern lake that was preceded by a complete desiccation lasting several thousand years. However, while about 50 other lineages of teleost fish also have established populations in the lake, none of them has produced more than two species and most of them did not speciate at all. Here, we test if the ancestors of the haplochromine radiation indeed arrived prior to the most competent potential competitors, ‘tilapias’ and cyprinids, both of which have made rapid radiations in other African lakes. We assess LV sediment core intervals from just before the desiccation and just after refilling for the presence of fossil fish teeth. We show that all three lineages were present when modern LV began to fill with water. We conclude that the haplochromines' extraordinary radiation unfolded in the presence of potentially competing lineages and cannot be attributed to a simple priority effect.

Neill Alexander graduated in natural sciences at the University of Cambridge in 1955. After a PhD at Cambridge and a lecturership at the University College of North Wales in Bangor, he was appointed to the chair of the Department of Pure and Applied Zoology at the University of Leeds in 1969. At that stage, he switched his research interests abruptly from fishes to the mechanics of legged locomotion. He conducted experiments with a variety of mammals, calculating forces, stresses and strains in muscle fibres, bones and tendons. His speciality became the application of mathematical models to animal locomotion, including repurposing the Froude number, devised by the Victorian engineer William Froude (FRS 1870) for use with ships, to estimate the speed of dinosaurs based on the spacing of their fossil footprints. Subsequent work included modelling the optimization of mammal performance and the minimization of energy costs. In 1992, following an announcement that London Zoo would have to close as a result of shortage of funds, Neill was appointed secretary of the Zoological Society of London. During the period of his secretaryship, the Society's finances recovered, with both its zoos (London and Whipsnade) breaking even in 1993 and the Society returning a surplus in each subsequent year. Neill was awarded the CBE in 2000. The National Portrait Gallery holds his portrait by John Arnison.

ABSTRACTRamsay Heatley Traquair, the eminent Victorian Scottish palaeoichthyologist and museum curator, procured an extensive collection of Palaeozoic fishes from across Scotland with the help of local miners and quarrymen. One very productive locality near Edinburgh was Loanhead. Traquair described numerous fossil fish from this Serpukhovian site, including four lungfish taxa: Ctenodus interruptus, Sagenodus quinquecostatus, Uronemus splendens and Ctenodus angustulus. The first three are now quite well known, but the fourth was only briefly described and never figured. It is based entirely on tooth plates, which are unusual both in their very small size and the arrangement of the tooth ridges. They lack the diagnostic characters of Ctenodus tooth plates and are here renamed Clackodus angustulus. A further taxon, Conchopoma sp., has recently been identified. Represented by a spade-shaped parasphenoid and denticulated jaw elements, it is the earliest known occurrence of the genus, extending its range into the Mississippian. A sixth taxon may be represented by an isolated parasphenoid bearing an anterior process, previously only seen in Devonian lungfish. The presence of up to six lungfish taxa at a single locality is unprecedented in the Carboniferous and indicates that the high level of lungfish diversity encountered in the Tournaisian of the Scottish Borders continued throughout the Mississippian, adding to the growing evidence that post-Devonian lungfish evolution was not as limited as previously proposed. This may have been due to changes in tooth plate growth, enabling greater variation in dentition and diet. In most Devonian taxa, tooth plate growth can be explained by comparison with that in extant forms, but analysis of Carboniferous tooth plates suggest growth was different in many taxa, possibly based on more than one pioneer tooth, allowing for novel patterns of tooth ridges and different types of teeth to develop on the same plate.