SANTINI, F.; University of Toronto: Osteology and phylogeny of the smooth pufferfishes (Tetraodontidae: Tetraodontiformes: Teleostei).

The family Tetrodontidae (Tetraodontiformes, Teleostei) comprises over 120 species of mostly coral reef fishes, with some taxa found also in brackish waters. Commonly known as smooth pufferfishes, these morphologically very derived teleosts possess the smallest genome (in DNA content per cell) among vertebrates. Recently two species, Takifugu rubripes and Tetraodon negroviridis, have been selected as model organisms for the study of the vertebrate genome, and full genome sequencing projects have just been completed. At the present time, however, no cladistic hypothesis for the phylogeny of this important family is available. The preliminary results of my study of the comparative osteology of the fossil and extant taxa of this clade indicate that the first known fossil tetraodontid, the Middle Eocene genus Eotetraodon, represents the sister group to all the other tetrodontids. Several other extinct taxa appear in the fossil record in the Oligocene, and these fossils show very close resemblance to the extant lineages. The data presently available indicate that the radiation of the modern lineages probably took place between 35 and 5 million years ago. Using the phylogeny obtained from osteological data for the extant and fossil tetraodontids, and published data on the genome size of Tetraodontiformes, I will also discuss hypotheses regarding the much higher species richness of tetraodontids with regard to their sister group, the spiny pufferfishes of the family Diodontidae.