Field of Science

More Triassic Articles From the "New Aspects of Mesozoic Diversity" Book

Kemp, T. 2010. New Perspectives on the Evolution of Late Palaeozoic and Mesozoic Terrestrial Tetrapods; pp. 1-26 in S. Bandyopadhyay (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7

Abstract - Palaeobiology, like all sciences, progresses by a combination of the discovery of new information, in this case fossils, the application of new techniques, and the development of new concepts with which to generate novel kinds of hypotheses. Research in the field of Late Palaeozoic and Mesozoic terrestrial tetrapods has involved major advances in all three of these over the last decade or so. Several new discoveries fill in gaps in the evolution of higher tetrapod taxa such as Tetrapoda, Dicynodontia, and birds, while others add significantly to the understanding of patterns of faunal turnover and palaeo-community structure.

The molecular revolution in biology is having a profound effect on several aspects of palaeobiology, in particular the use of large amounts of sequence data for phylogenetic studies and estimating branching dates. In some cases, notably placental mammals, this has produced results that highlight the limitations of purely morphological evidence in this, and probably other cases, and points to the desirability of seeking other kinds of evidence of relationships. Molecular developmental biology is starting to suggest new evolutionary hypotheses about the molecular genetic basis of the evolutionary transitions that can be inferred from the fossil record, such as how the tetrapod limb arose. In the field of functional analysis of fossils, CT scanning has opened the way to the application of such methods as finite element analysis for studying the mechanical design of fossil tetrapod skulls and skeletons. Geochemistry has also introduced new methods, notably stable isotope analysis, that have a direct bearing on the interpretation of the palaeoenvironmental background of major evolutionary events such as mass extinctions.

The principal new concept in palaeobiology arises from a shift towards the systems view that it is the interactions of the parts of a complex system, rather than the nature of the parts themselves that provide the main key to understanding how the system works. Correlated progression is a model based on this concept which offers a more realistic view of major evolutionary transitions such as the origins of tetrapods, mammals, and potentially all the higher taxa of tetrapods. Earth sciences are also moving more towards a systems way of thinking, such as when seeking explanations for mass extinctions.

Ray, S., Bandyopadhyay, S., and R. Appana. 2010. Bone Histology of a Kannemeyeriid Dicynodont Wadiasaurus: Palaeobiological Implications; pp. 73-89 in S. Bandyopadhyay (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7

Abstract - Examination of the bone microstructure of several skeletal elements shows that the cortex comprises fibrolamellar bone tissue suggesting rapid osteogenesis and overall fast growth for Wadiasaurus, a kannemeyeriid dicynodont from India. Three distinct stages have been identified in the ontogeny of Wadiasaurus. In the juvenile stage, when up to 30% of adult size is attained, growth was fast and sustained, whereas in the sub-adult stage when up to 60% of adult size is attained, growth was fast but periodically interrupted as evident from the presence of growth marks. During the adult stage the bone microstructure is characterized by the presence of peripheral parallel-fibred bone that suggested considerable slowing down of growth, possibly with the onset of sexual maturity. A flexible and indeterminate growth strategy is proposed for Wadiasaurus. The cortical thickness (RBT) and the correspondingly low optimal k values of the various limb bones of Wadiasaurus were comparable with that of the land vertebrates such as Ceratotherium, suggesting that the limbs were selected for impact loading.

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