MORPHOFUNCTIONAL ANALYSIS OF SVOBODAINA SPECIES (BRACHIOPODA, HETERORTHIDAE) FROM SOUTH-WESTERN EUROPE

Geometric morphometric methods applied to the ventral muscle field outline of the various species of Svobodaina from south-western Europe identify criteria for discriminating among this key cluster of brachiopod species. These data indicate the close relationship between the patterns of the ventral muscle field in the Svobodaina species and the environmental conditions where each inhabited; the fields are better developed in species related to high-energy environments. For example, S.armoricana, with the smallest diductor scars, would have inhabited the quiet marine environments of the lower offshore or within protected lagoonal settings. S.feisti would have inhabited the upper offshore, a more energetic environment than S.armoricana. Finally, S.havliceki, with the largest diductor scars, would have thrived in the most energetic environments among all the south-western European Svobodaina species, living just above the fair-weather wave base in the lower shoreface. The palaeoecological results suggest a distribution of Svobodaina species during the Late Ordovician along an onshore-offshore transect across the shallow marine platforms of the Mediterranean margin of Gondwana. On the other hand, the occurrence in some localities of several species with overlapping ranges or within the same assemblage indicates that the biostratigraphical efficacy of the genus is restricted. Thus, the previously defined taxon-range biozones characterized by Svobodaina species of the north Gondwanan margin are in need of reassessment. The morphology of Svobodaina may be a considerable aid to environmental analyses rather than to precise biostratigraphical correlations.