Long bone microanatomy, lifestyle in extant tetrapods, and the conquest of land by vertebrates
UMR 7207 (CNRS/MNHN/UPMC), Department ‘Histoire de la Terre’, CP 48, 43 rue Buffon, F-75231 Paris Cedex 05, France
Fecha y lugar: 15 de diciembre de 2010 a las 16 hs. Auditorio del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Av. Angel Gallardo 470 - C1405DJR - Buenos Aires - Argentina.
Resumen: A correlation between long bone microanatomy and lifestyle (aquatic to terrestrial) in tetrapods was suggested early in the 20th century. However, quantitative tests of this hypothesis based on extensive comparative datasets (representing dozens of species) were done only in the 1980s, and the first phylogeny-informed tests were published in 2004. The first study that used a new mathematical model of compactness profile was published the same year (2004). Since then, several more quantitative studies have confirmed the presence of a significant ecological signal in long bone microanatomy. Return to an aquatic lifestyle in lissamphibians results in increased bone compactness. In amniotes, increased compactness is usually observed in shallow water inhabitants, especially if these are sluggish swimmers, such as sea cows (Sirenia). Pelagic forms, that are active, deep divers, tend, on the contrary, to have spongy bone. This is seen in extant cetaceans, but also in plesiosaurs and mosasaurs. Finally, amphibious forms that are suface swimmers, such as Capybara, show no microanatomical adaptations to aquatic life.
Large comparative databases on long bone microanatomy (typically between 45 and 100 species of known lifestyle) have been used to produce mathematical inference models using linear discriminant analysis. These models have been made accessible through Excel spreadsheets to facilitate paleobiological inference. Application of these models to several early stegocephalians produces some surprising results (such as an amphibious lifestyle in Captorhinus and in Placodus), or, in other cases, confirms long-held hypotheses (such as an aquatic lifestyle in Mesosaurus and in Neusticosaurus).