New Perspectives on the Evolution of Late Palaeozoic and Mesozoic Terrestrial Tetrapods

Abstract

Palaeobiology, like all sciences, progresses by a combination of the discovery of new 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.