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A few new Triassic-ish papers....

Maidment, S.C.R., and L.B. Porro. 2009. Homology of the palpebral and origin of supraorbital ossifications in ornithischian dinosaurs. Lethaia, 10.1111/j.1502-3931.2009.00172.x.

Abstract - The palpebral is a small ossification that projects across the orbit in some ornithischian dinosaurs and its presence is considered a synapomorphy of the clade. By contrast, other ornithischians lack the palpebral but possess accessory ossifications, commonly termed supraorbitals, which form the dorsal margin of the orbit. The homology of the ornithischian palpebral to one or more of the supraorbitals is widely accepted in the literature, but this homology has never been explicitly tested and no hypotheses have been proposed regarding the function of the palpebral or why it was incorporated into the orbital margin. As homology is synonymous with synapomorphy, incorrect homology statements can lead to incorrect hypotheses of relationships being obtained during cladistic analysis. The primary and secondary homologies of the ornithischian palpebral and the anterior supraorbital of more derived members of the major ornithischian clades are tested and we demonstrate that these homology hypotheses can be accepted. Osteological correlates indicate that the palpebral supported a layer of connective tissue that roofed the orbit; ossification of this connective tissue resulted in the incorporation of the palpebral into the skull roof and gave rise to additional supraorbital elements, which are neomorphic ossifications. Large-scale structural changes in the ornithischian skull, including dermal ossifications associated with display or defence and the development of complex feeding mechanisms, may have led to the incorporation of the palpebral into the skull roof.

Nicolas, M., and B.S. Rubidge. 2009. Changes in Permo-Triassic terrestrial tetrapod ecological representation in the Beaufort Group (Karoo Supergroup) of South Africa. Lethaia, 10.1111/j.1502-3931.2009.00171.x.

Abstract - For more than a century, large collections of fossils from the Beaufort Group have been built up at various museums in South Africa and have been handled as separate databases in the individual museums. Because of the unique time-extensive record of continental vertebrate biodiversity represented by the fossils of the Beaufort Group, a single standardized database has been compiled for the fossils collected from the Beaufort Group housed in South African museums. This unique data set has enabled the determination of terrestrial tetrapod ecological representation from the Middle Permian to Middle Triassic Beaufort Group of South Africa.

Korte, C., Hesselbo, S.P., Jenkyns, H.C., Rickaby, R.E.M., and C. Spotyl. 2009. Palaeoenvironmental significance of carbon- and oxygen-isotope stratigraphy of marine Triassic–Jurassic boundary sections in SW Britain. Journal of the Geological Society, London 166:431–445. doi: 10.1144/0016-76492007-177.

Abstract - Carbon-isotope stratigraphy is a useful tool for stratigraphic correlation, especially for strata deposited during major perturbations of the carbon cycle that affected the marine, terrestrial and atmospheric reservoirs. For the Triassic–Jurassic boundary, effectively defined by a first-order mass extinction, major fluctuations in carbon-isotope values have been well documented, but these datasets have generally been derived from bulk-rock samples. Hence, the extent to which features of the isotopic curve reflect diagenetic alteration or changing proportions of constituent materials is unconstrained. Here, carbon- and oxygen-isotope
data are presented from well-preserved oyster shells (Liostrea) comprising low-magnesium calcite, a mineral species relatively resistant to diagenetic alteration. Samples were obtained from Lavernock Point, Glamorgan, Wales, a coastal section close to a candidate stratotype for the base of the Jurassic at St Audrie’s Bay, Somerset, England. The carbon-isotope signature from St Audrie’s Bay, previously defined on the basis of analysis of bulk organic matter, is confirmed by our new data. Major features are (1) the upper part of an ‘initial’ negative isotope excursion in the lowest part of the section, followed by (2) a pronounced positive excursion, and (3) an extended ‘main’ negative isotope excursion in the highest part of the section. The data
confirm that the carbon-isotope stratigraphy previously documented from bulk organic matter in SW England records the chemical composition of the contemporaneous seawater. Bulk carbonates sampled over the same interval near Lyme Regis, England, show similar trends to those from oyster calcite in the lower part of the study section, but there are more 13C-depleted values up-section. These lower values probably result from an admixture of primary and diagenetic carbonate. Palaeotemperatures calculated from oxygen-isotope values from Lavernock Point oyster shells are relatively cool at the beginning of the positive carbon-isotope
excursion, and increased by up to 10 8C during the main negative carbon-isotope excursion. The new results are compatible with the view that positive carbon-isotope excursions correspond to times of low atmospheric carbon dioxide content, whereas negative carbon-isotope excursions correspond to times of high atmospheric carbon dioxide content, as is also found to be the case during the Early Jurassic (Toarcian) Oceanic Anoxic Event. The Mg/Ca and Sr/Ca ratios and 18O of investigated Liostrea hisingeri show no correlation, supporting data from modern bivalves that indicate that incorporation of Mg and Sr is controlled mainly by factors other than temperature.

1 comment:

  1. That palpebral paper sounds interesting. I've always wondered about that bone in ornithischians. It's pretty quickly "absorbed" by the surrounding skull bones in virtually all large ornithischian groups.


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