SANTINI, F.: Origin and Evolution of the Tetraodontiformes (Teleostei, Pisces), with an Analysis of the Patterns of Speciation of the Family Triacanthodidae.

Fossil evidence seems to point towards an origin in shallow waters, during the upper Cretaceous, of several lineages of Acanthopterygian fishes, which now are widely distributed in deep waters. Among these groups, we find the Zeiformes, the Caproiformes, and the Tetraodontiformes. This distributional shift probably happened after the K/T mass extinction. Possible scenarios regarding the origin of one of these clades, the Tetraodontiformes, are presented and discussed. In addition to this, a phylogenetic systematic analysis of one of these groups, the family Triacanthodidae (Tetraodontiformes, Teleostei) is being utilized to test the applicability to marine taxa of methodologies that rely on phylogenetic hypotheses and biogeographical distributions to study patterns of speciation. A variety of pioneering studies seem to suggest that the vast majority of speciation processes in terrestrial and freshwater taxa might be due to vicariant events. By contrast very preliminary work on marine organisms seems to indicate that different modes of speciations might be predominant in the sea, perhaps due to important differences in the reproductive biology of many marine organisms. The results of this study are presented and discussed.