Ontogeny in Terebratula species. Functional convergence and allometry but not heterochrony.

The brachiopod genus Terebratula occurred in the circum Mediterranean area during the Miocene-Early Pleistocene period. The four morphotypes we recognize within this genus, are separated by different shell size (larger in stratigraphically older species) and commissure type, the latter being sulciplicate in older forms and uniplicate in youngers. Although this would suggest a consistent evolutionary trend toward larger size and simpler plicatures, our analysis reveals a more complicate pattern in the evolutionary history of Terebratula spp. We found evidence for mosaic character evolution. The affirmation of novel morphologies in younger species is not interpreted as a consequence of any heterochronic change in the ontogeny of older morphotypes, but as a product of the increasing body size –from early stage of development- and of the matching of functional requirements.