Paleontologia do desenvolvimento em sinapsídeos: o registro fóssil de ontogenia em mamíferos e seus parentes mais próximos

quinta-feira, março 11, 2010

Developmental palaeontology in synapsids: the fossil record of ontogeny in mammals and their closest relatives

Marcelo R. Sánchez-Villagra*

-Author Affiliations

Paläontologisches Institut und Museum, Karl Schmid-Strasse 4, CH-8006 Zürich, Switzerland
*m.sanchez@pim.uzh.ch

Abstract

The study of fossilized ontogenies in mammals is mostly restricted to postnatal and late stages of growth, but nevertheless can deliver great insights into life history and evolutionary mechanisms affecting all aspects of development. Fossils provide evidence of developmental plasticity determined by ecological factors, as when allometric relations are modified in species which invaded a new space with a very different selection regime. This is the case of dwarfing and gigantism evolution in islands. Skeletochronological studies are restricted to the examination of growth marks mostly in the cement and dentine of teeth and can provide absolute age estimates. These, together with dental replacement data considered in a phylogenetic context, provide life-history information such as maturation time and longevity. Palaeohistology and dental replacement data document the more or less gradual but also convergent evolution of mammalian growth features during early synapsid evolution. Adult phenotypes of extinct mammals can inform developmental processes by showing a combination of features or levels of integration unrecorded in living species. Some adult features such as vertebral number, easily recorded in fossils, provide indirect information about somitogenesis and hox-gene expression boundaries. Developmental palaeontology is relevant for the discourse of ecological developmental biology, an area of research where features of growth and variation are fundamental and accessible among fossil mammals.

heterochrony    modularity    palaeohistology   growth   allometry   skeletochronology

Footnotes

Received November 4, 2009.
Accepted December 17, 2009.
© 2010 The Royal Society

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