Miniaturization and heterochrony in Homoeorhynchia meridionalis and H. cynocephala (Brachiopoda, Rhynchonellidae) from the Jurassic of the Iberian Range, Spain

摘要: The miniaturization of shells, often observed in Mesozoic brachiopods, is analyzed two species the well-known genus Homoeorhynchia. We investigated shell development context recent works that consider growth as a function size, shape, and age. results from heterochronic disturbances during development. Although these shells exhibit large morphological plasticity, architectural constraints limit their morphogenesis, so small adult specimens are not exactly reduced replicas ones. Adult morphology depends largely on pattern rib formation, with arising by different processes affecting this pattern: predisplacement appearance ribs H. meridionalis acceleration cynoceph- ala. first case seems to be reversible process without evolutionary consequences, but second occurs within an trend. In both cases, related environmental influences. Study pathway allows recognition basic characters variation populations.