Polymorphism, variation and evolutionary change in early vertebrates from the Gogo Formation, Western Australia

The imperfection of the fossil record was used by Charles Darwin to explain the lack of evidence for 'organs of extreme perfection and complication', which under his theory of natural selection must have evolved through a series of gradual transitions. In addition, a major premise in the theory of natural selection is that variation between organisms is required so selection for particular traits can occur. The fossil record has subsequently revealed a small number of sites comprising fossils of exceptional preservation including the Gogo Formation of Western Australia. Here a unique Late Devonian (Frasnian) reef fauna, with exceptional three-dimensional preservation of macrofossils combined with unprecedented soft-tissue preservation has preserved examples of the transitional forms and morphological variation Darwin predicted. The most significant discoveries have contributed: insights into reproductive biology, including the oldest known vertebrate embryos and evidence of sexual dimorphism with internal fertilization; the anatomy and variation present in the earliest gnathostomes, the placoderms, provides evidence of directional selection; some of the earliest morphological changes required in the transition from an aquatic to land environment are seen in the primitive tetrapodomorph, Gogonasus

Upper Devonian microvertebrates from the Canning Basin, Western Australia

A diverse microvertebrate fauna is described from the Virgin Hills and Napier formations, Bugle Gap Limestone Canning Basin, Western Australia. Measured sections at horse Spring and Casey Falls (Virgin Hills Formation) and South Oscar Range (Napier Formation) comprise proximal to distal slope carbonates ranging in age from the Late Devonian Frasnian to middle Famennian. A total of 18 chondrichthyan taxa are identified based on teeth, including the first record of Thrinacodus tranquillus, Cladoides wildungensis, Protacrodus serra and Lissodus lusavorichi from the Canning Basin. A new species, Diademodus dominicus sp. nov. is also described and provided the first record of this genus outside of Laurussia. In addition, the upper range of Australolepis seddoni has been extended to Late Devonian conodont Zone 11, making it the youngest known occurrence for this species. The Virgin Hills and Napier formations microvertebrate faunas show close affinities to faunas recovered from other areas of Gondwana, including eastern Australia, Iran, Morocco and South China, which is consistent with known conodont and trilobite faunas of the same age

The significance of 24-norcholestanes, 4-methylsteranes and dinosteranes in oils and source-rocks from East Sirte Basin (Libya)

The present paper involves a detailed evaluation of specific steroid biomarkers by gas chromatography-mass spectrometry (GC-MS) and GC-metastable reaction monitoring (MRM) analyses of several crude oils and source rocks from the East Sirte Basin. 24-Norcholestanes, dinosteranes, 4a-methyl-24-ethylcholestanes and triaromatic steroids have been identified in both source-rocks and crude oils of the East Sirte Basin. Diatoms, dinoflagellates (including those potentially associated with corals) and/or their direct ancestors are amongst the proposed sources of these biomarkers. These biomarker parameters have been used to establish a Mesozoic oil-source correlation of the East Sirte Basin. Hydropyrolysis of an extant coral extract revealed a similar distribution (although immature) of dinosteranes and 4a-methyl-24-ethylcholestanes also observed in the Sirte oils and source-rocks. This is consistent with the presence of dinoflagellates present during the deposition of the Mesozoic aged East Sirte Basin Formations.A good data correlation for the rock extracts revealed a similar distribution of 3,24-dimethyl triaromatic steroids, 3-methyl-24-ethylcholestanes, 4-methyl-24-ethylcholestanes and 2-methyl-24-ethylcholestanes observed in one of the oil families and associated source-rocks for the East Sirte Basin

Assessing the fidelity of marine vertebrate microfossil δ18O signatures and their potential for palaeo-ecological and -climatic reconstructions

Conodont biogenic apatite has become a preferred analytical target for oxygen isotope studies investigating ocean temperature and palaeoclimate changes in the Palaeozoic. Despite the growing application in geochemically-based palaeoenvironmental reconstructions, the paucity or absence of conodont fossils in certain facies necessitates greater flexibility in selection of robust oxygen-bearing compounds for analysis. Vertebrate microfossils (teeth, dermal denticles, spines) offer a potential substitute for conodonts from the middle Palaeozoic. Vertebrate bioapatite is particularly advantageous given a fossil record extending to the present with representatives across freshwater to fully marine environments, thus widening the scope of oxygen isotope studies on bioapatite. However, significant tissue heterogeneity within vertebrates and differential susceptibility of these tissues to diagenetic alteration have been raised as potential problems affecting the reliability of the oxygen isotope ratios as palaeoclimatic proxies. Well-preserved vertebrate microfossils and co-occurring conodont fossils from the Upper Devonian and Lower Carboniferous of the Lennard Shelf, Canning Basin, Western Australia, were analysed using bulk (gas isotope ratio mass spectrometry, GIRMS) and in-situ (secondary ion mass spectrometry, SIMS) methodologies, with the latter technique allowing investigation of specific tissues within vertebrate elements. The d18Oconodont results may be interpreted in terms of palaeolatitudinally and environmentally sensible palaeo-salinity and -temperature and provide a baseline standard for comparison against vertebrate microfossil d18O values. Despite an absence of obvious diagenetic modification, GIRMS of vertebrate denticles yielded d18O values depleted in 18O by 2–4‰ relative to co-occurring conodonts. SIMS analysis of dentine tissues exhibited significant heterogeneity, while hypermineralised tissues in both scales and teeth produced d18O values comparable with those of associated conodonts. The susceptibility of permeable phosphatic fossil tissues to microbial activity, fluid interaction and introduction of mineral precipitates post-formation is demonstrated in the dentine of vertebrate microfossils, which showed significant heterogeneity and consistent depletion in 18O relative to conodonts. The hypermineralised tissues present in both teeth and scales appear resistant to many diagenetic processes and indicate potential for palaeoclimatic reconstructions and palaeoecological investigations

Evidence for Placoderms from the Mid-Palaeozoic Sandon Beds of North-western New South Wales, Australia

Armoured jawed fishes known as placoderms are a well-documented group with a fossil record spanning the Silurian to end-Devonian. They have a global distribution and a marked diversity within Devonian deposits of Australia. Despite their notable Gondwanan fossil record, new material is occasionally identified and can present important stratigraphic information for otherwise under-explored deposits. A unique find from the so-called Sandon beds is presented here and expands the record of placoderms from New South Wales. This specimen presents insight into a previously unknown macrofossil record from the deposit and suggests a more Devonian age for the unit, rather than the previously suggested Carboniferous date. We also summarise the macrovertebrate record of Devonian placoderms from Australia, highlighting and discussing changes in their Gondwanan taxonomic diversity across the time period

Theoretical Studies on Small Ring Heteropropellanes. Oxapropellanes

Oxa(l.1.l)propellane (2), dioxa(l.1.l)propellane (3), and trio-· xa(l.l.l)propellane (4) have been studied by means of ab initio SCF MO technique at 6-31G* level. The geometry optimization is carried out for these molecules and the parent hydrocarbon (1.1.l)propellane. The bond between the two bridgehead carbon atoms is predicted to be in (2) : 1.503 A, (3) : 1.474 A, and (4) : 1.456 A. These are shorter than the calculated central bond (1.543 A) in (1.1.l)propellane