Ano 2011 - Volume 31, Número 12

Character transformations and their functional significance as a key to the evo­lu­tion of hystricognath Rodentia, 31(12):1108-1115

ABSTRACT.- Mess A. 2011. Character transformations and their functional significance as a key to the evo­lu­tion of hystricognath Rodentia. Pesquisa Veterinária Brasileira 31(12):1108-1115. Department of Research, Museum of Natural History, Humboldt-University Berlin, Invalidenstr. 43, D-10115 Berlin, Germany. E-mail:
Hystricognathi represent a monophyletic taxon within Rodentia. Since phylogenetically analyzed morphological systems are essential for revealing evolutionary processes, this study identifies evolutionary character transformations on the stem lineage of Hystricognathi as derived from the author’s own work and the literature. Data so far indicate that evolutionary transformati­ons in the rostral head region, the loss of tactile ability in the outer nasal skin and the mobile arrangement of the associ­ated cartilage, were allied with a switch from om­ni­vorous to her­bi­vo­rous and fiber-rich nutrition. Additional character trans­­­formations in the skull assist in digesting such food. Structures associated with re­pro­­duc­tion and placentation show a remark­able pro­portion of derived character con­di­ti­ons: the chorioallantoic placenta has a ring-shaped organization and growth struc­ture which optimizes the capa­ci­ty for passive diffu­s­ion, a subp­lacenta occurred as a speci­a­lized region responsible for pla­cental invasion and the in­verted yolk sac facilitates sub­stance exchange with the main placenta. Fi­n­al­ly, pre­co­cial new­borns evolved as a derived condition within Rodentia. All things considered, a mode of reproduction is indicated, which does not demand excessive additional en­ergy intake by the mother and is in accor­dance with her low energetic diet. Hy­stri­cognathi possess major character trans­for­ma­ti­ons that represent prerequisites for their successful radiation at the time when more open ecosystems and grasslands evolved dur­ing Earth history. The analysis resulted in the re­con­struction of a life-near picture of the hystricognath stem species pattern with high ex­pla­natory power in terms of changes in spa­ce and time and their interdependence with bio­­diversity.
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