No description available.

Thesis (D.Sc.1976) from the Department of Geology, University of Adelaide.

Thesis (B.Sc. Hons.) - Dept. of Geology, University of Adelaide, 1974. / Typescript (carbon copy).

The rudist bivalves were one of the many and varied groups of organisms to be extinguished at the end of the Cretaceous Period. They were a group of bivalves which evolved during Late Jurassic times to dominate the carbonate shelves on the margins of the Tethys Ocean during the Cretaceous Period. Through Late Cretaceous times their diversity climbed to a peak and then entered a period of rapid decline, resulting eventually in the complete extinction of the group. Theories as to the cause of that extinction should clearly be based upon a knowledge of the detailed pattern of the decline. Most important is the question of the timing of the extinction: How long did it take from the peak of diversity to the elimination of the entire group? Is there one main extinction event - or are there several - or is the pattern a gradual decline? In answering these questions this work adopts a new approach to dating end Cretaceous strata by using strontium isotope stratigraphy. The method works by measuring the 87 Sr/86Sr of palaeo-seawater preserved in marine carbonate, such as the thick low-Mg calcite layer of rudist shells. The 87Sr/86Sr of seawater was changing fairly rapidly through time in the latest Cretaceous. The pattern of change has been established in detail using samples from Boreal sequences of which the ages are known with respect to the belemnite stratigraphy. Using this as a standard graph, Tethyan rudist samples have been dated by a comparison of the Sr isotope ratio. The use of Sr isotope stratigraphy has enabled a time axis to be established, against which the ranges of rudist bivalves and of their facies have been ploued. From these data it can be clearly seen that the ranges of many of the established biostratigraphic markers are in error and that the stage boundaries, as defined by the belemnite and planktonic foraminiferal stratigraphies, are offseL When the pattern of rudist diversity is plotted against this time scale it can be seen that, at a specific level, the rudists were at their most diverse at the Campanian/Maastrichtian boundary. Their decline lasted until I almost the end of the Maastrichtian after which the only survivors are Tertiary forms. The decline is related to the disappearance of rudist facies with the end Cretaceous regression, though that graph is slightly displaced from that of rudist diversity. This shows that the rudist extinction is not merely due to non-exposure of terminal Maastrichtian strata.

Palaeo-ornithology has been dominated by taxonomy. To try and redress the balance and help palaeoecologists interpret fossil birds in a biological and ecological perspective, the taphonomy of birds needs to be fully understood. The taphonomy of birds is concerned with all processes from death to the collection of the fossil bird. Between these two points (the transfer of the organism from the biosphere to the lithosphere) a variety of forces and processes affect the bird/fossil. By means of experiments in the natural environment and in controlled conditions in the laboratory, and subsequent comparisons of the results with case studies of fossil assemblages, the processes leading to preservation can be deduced and the former living community restored on the basis of the fossil evidence. The research involved two main approaches: 1. experimental taphonomy / observational taphonomy; and 2. case histories of fossil communities and their interpretation. Experimental work was carried out in the natural environment. Two field sites were chosen in southern Florida, a freshwater environment and a marine environment. The monitoring and controlling of these experiments required knowledge and techniques in zoology, botany, ecology, sedimentology, limnology, marine biology, microbiology, pathology and forensic science. Results obtained included the effects of scavenging, anoxia, transport, rate of burial, and temperature on rates of decay, the causes of bird mortality, the processes resulting in disarticulation, and the effects of decay upon feathers. Once the experimentaVobservational data had been collected they allowed a series of taphonomic thresholds (a decay sequence) to be defined. These data were then applied to case studies of fossil bird assemblages from different sedimentological environments. The following LagersHitten were investigated: Messel (Eocene, Germany) = restricted lacustrine; Green River (Eocene, USA) = lacustrine; Solnhofen Lithographic Limestone (Jurassic, Germany) = restricted marine; La Meseta Formation (Eocene, Antarctica) = marine; Rancho La Brea (Pleistocene, USA) = terrestrial "trap". The biases in each environment were assessed (e.g. birds in an aquatic ten-estrial environment had a higher preservation potential than birds from a tenestrial environment). The fossil record of birds is not as depauperate as previously thought but is heavily biased, depending on the proximity of the bird's habitat to that of the preserving sedimentary environment. Marine and littoral birds are poorly represented even though they inhabit sedimentary environments with a high preservation potential. This reflects low densities of birds per unit area. Aquatic birds (and terrestrial birds that inhabit the ecotone surrounding freshwater together with some larger fOlIDS from further away) are much better represented. This is because they inhabit the only terrestrial environments with a high preservation potential, coupled with the high densities of individuals per unit area. The bias towards large terrestrial birds is due to their large bones being more resistant to transport induced damage. These results have implications for the understanding of the evolution of birds. Patterns of evolution in birds can not be fully resolved on fossil evidence alone; biases in the taphonomy of birds only permit a small proportion of species from certain environments to be preserved. The taphonomy of feathers was investigated and it was discovered that the "organic trace" that commonly represents the outline of the feather trace is the diagenetically altered glycocalyx of the bacteria that were degrading the feather. In several localities these feather-degrading bactelia are preserved in authigenic minerals. The taphonomy of bats and pterosaurs was also investigated. The similarity of anatomical structures of birds, bats and pterosaurs results in similar taphonomic pathways.

No description available.

The evolution of the Metazoa is among the greatest success stories in Earth history. From modest origins, probably in the Cryogenian (~720 - 635 Ma), metazoans had acquired hard parts, and a vast range of life strategies and body plans by the middle Cambrian (around 520 Ma). This leaves a long delay between the origin of the Metazoa and their rise to ecological dominance. A popular explanatory hypothesis for this delay is that atmospheric oxygen levels, low in the Proterozoic (< 0.001 % PAL), began to rise towards modern levels towards the end of the Neoproterozoic. Among the earliest known putative metazoans are Namacalathus, Namapoikia and Cloudina, calcified marine invertebrates abundant in the latest Ediacaran (~ 548-541 Ma) Nama Group, Namibia. Although they were pioneers of metazoan biomineralisation, little is known of their affinities or palaeocology. The Nama Group, a well-characterised, relatively undeformed mixed carbonate and siliciclastic succession, provides a rare opportunity to investigate the palaeoecology of these important organisms in their environmental context. New geochemical data from the Nama Group confirm the heterogeneity of Ediacaran redox conditions. These contextualise in situ fossil assemblages which reveal diverse ecological strategies among the calcified metazoans of the Nama Group, and offer constraints on their affinities. Based on its large size (< 1 m), modular body plan and internal structure of interlinked tubules, Namapoikia was a long-lived specialist and possible Poriferan. I show that Namapoikia colonised both lithified and living microbial substrates in oxic, mid-ramp reef crypts. By contrast, size and occurrence data show that Namacalathus was an environmental generalist, forming large, thick aggregations in persistently oxic, mid-ramp reef environments but opportunistically exploiting the transiently oxic, inner ramp setting. Bilaterally symmetrical, asexual budding and a microlamellar skeletal ultrastructure suggest that Namacalathus may have been an early lophophorate, and had flexible growth depending on environmental setting, showing a cup diameter of 2 – 35 mm, and size distributions varying with substrate type, redox and water depth. In oxic mid-ramp reefs, Cloudina constructed large (> 20 m) reefs showing mutual attachment and consistent orientation in life position, making it the earliest known reef-building metazoan and suggesting that it was a passive suspension feeder. I further present food webs based on fossil assemblages from Ediacaran to Cambrian Stage 4 carbonate successions and evaluate their usefulness in tracking metazoan trophic diversification in the early Cambrian. Ediacaran redox conditions were a major control on the ecologies of the earliest metazoans. A requirement for oxygen made persistently oxic conditions a prerequisite for complex and long-lived ecologies, while highly flexible life strategies were used to exploit changeable environments. Ediacaran metazoans represent a phylogenetic and ecological foreshadowing of the complexity of the Phanerozoic, but it was not until much later that the Metazoa would attain their evolutionary potential.

Jurassic marine ecosystems (ca. 201-145 million years ago) were dominated by three different lineages of reptiles - plesiosaurians, ichthyosaurs and thalattosuchian crocodylomorphs. Stratigraphic and fossil evidence indicates that these animals, like their modern counterparts, were able to coexist in the same environment for over ~50 million years from the Early Jurassic (~180 million years ago) to the Early Cretaceous (~130 million years ago). Marine reptile ecosystems were often very diverse, and included animals from different lineages, of disparate body-size and inferred ecology living alongside each other in the same environment. This unusual diversity suggests that marine reptiles formed complex ecosystems, and may have occupied analogous ecological roles today held by large fish, sharks, crocodiles, sirenians, and cetaceans. However, these comparisons are essentially qualitative, as they are based on the recurring convergent morphologies of skulls, mandibles and dentitions in aquatic tetrapods. Yet, they have never been quantitatively tested. Furthermore, although we have a comprehensive understanding of the anatomy, systematics, phylogenetic relationships, physiology and feeding ecology of these extinct animals, little is still known about the structure and evolution of their ecosystems. Thus, we do not understand what enabled marine reptiles to form complex assemblages, how their fauna changed through time, and more importantly how climatic and environmental changes shaped their long-term evolution. Answering these questions is essential because understanding past marine ecosystems may inform on whether and how modern ones can adjust to changes in the ocean temperature, chemistry and sea-level. In order to establish the reliability of these comparisons, in this project, I consider the evolution of the diverse marine reptile fossil assemblage of the Jurassic Sub-Boreal Seaway (JSBS) of the UK. The fossil record of the JSBS is an ideal case-study for many reasons. Firstly, it is a well-documented, high-diversity ecosystem, represented by hundreds of well-preserved specimens collected from the world-famous Oxford Clay Formations (OCF Callovian-early Oxfordian, late Middle to early Late Jurassic) and Kimmeridge Clay Formation (KCF - Kimmeridgian to Tithonian, Late Jurassic). These specimens have been intensively collected since the XIX century, and are available in museum collections. Secondly, the fossil record of the JSBS covers a continuous interval of ~18 million years (middle Callovian-early Tithonian ~166-148 million years ago) of marine reptile evolution, in a single seaway, during a time of well-documented environmental changes. These changes in sea-level, temperature and chemistry happened in concert with drastic changes in the composition between the OCF and KCF marine reptile faunas across the Middle-Late Jurassic boundary. Unfortunately, to date, the attempts to understand whether there is a correlation between these events have been hampered by the scarcity of fossils material from the intermediate layers of the Oxfordian 'Corallian Gap'. After a brief introduction (Chapter I), this project articulates in two parts. In the first descriptive section (Chapters II, III and IV), I set the bases for the second part by reviewing the fossil record of ichthyosaurs, plesiosaur and thalattosuchians of the JSBS. Particular emphasis was put on the systematics of thalattosuchian crocodylomorphs, and the fossil assemblage of the 'Corallian Gap'. The second part of this thesis is an analytical section (Chapters V and VI), in which, using a suite of numerical techniques, I investigate the ecology, evolution and feeding ecology of marine reptiles through time. A summary of the main conclusions and future directions are presented in Chapter VII. Chapter II is a description of a new genus and species, Ieldraan melkshamensis, a metriorhynchid thalattosuchian from the Callovian of England. The stratigraphic occurrence of this new taxon demonstrates that all the macrophagous lineages of Late Jurassic metriorhynchids originated in the Middle Jurassic, earlier than previously supposed. This also has important implications for the evolution of macropredatory features (particularly the dentition) in this group. In Chapters III and IV, I review the scarce fossil record of the Oxfordian 'Corallian Gap', the least studied stage of the considered ~18 million-year interval. The results show that despite the scarcity and poor preservation of materials compared to the underlying and overlying fossil-rich OCF and KCF, a large variety of marine reptiles lived in the JSBS during the 'Corallian Gap' (middle-late Oxfordian). The study confirms a drop in marine reptile diversity in the Oxfordian, exemplified by the demise of several OCF taxa, but partially counterbalanced by the contemporaneous radiation of some KCF lineages. This review confirms that a faunal turnover severely affected the composition of the JSBS across the Middle-Late Jurassic boundary, and I hypothesise that these faunal changes may have been driven by environmental perturbations during the Oxfordian. In Chapter V, I use the most common marine reptile fossils - teeth - and the revised stratigraphic occurrences of the JSBS (from the previous Chapters), to investigate the evolution of marine reptile groups, through time. Using a multivariate approach I established a quantitative system to assign species to dietary guilds based on dentition features that together with the availability of teeth, allowed examination of diversity and disparity patterns at unprecedented time, and systematic resolutions. The results show that different taxonomic/dietary groups did not overlap, suggesting partitioning of resources based on diet/feeding strategy. The analyses show a decline of shallow-water specialists, the diversification of macrophagous species, deep-diving taxa, and increasing body-size in concert with a deepening of sea-level across the Middle-Late Jurassic boundary. These trends are not accompanied by drops in disparity, but by a selective decline/increase of specific ecological guilds, that mimic the transition from shallow/nearshore to deeper/offshore habitats in modern cetacean coastal assemblages. In Chapter VI, I use a variety of multivariate techniques to present a quantitative assessment of the feeding behaviour of marine reptiles. The aim of this study is investigating the morphological and functional variation of ichthyosaur, plesiosaur and thalattosuchian lower jaws. This is done using a variety of multivariate techniques, and a biomechanical comparative approach. The analyses confirm previous qualitative observations that the ecosystems in the OCF and KCF were markedly distinct in faunal composition and structure. Phylogenetically closely related taxa preferentially cluster together, with minimal overlaps amongst groups in the morphospace. Focus examinations of key morphofunctional complexes reveals that marine reptile subclades are characterised by different combinations that are consistent with their inferred feeding ecologies (based on tooth morphology). Overall, the present quantitative results validate previous qualitative hypothetical feeding ecologies, and reveal multiple instances of morphofunctional convergent evolution. Overall my results also show that, like in modern ocean ecosystems, complex mechanisms of niche and habitat partitioning may have facilitated the coexistence of diverse marine reptile assemblages over tens of millions of years of evolutionary time.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Geology, 1981.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.