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Fossil whales in the very rare, primitive, extinct cetacean family Aetiocetidae are small, relict, toothed mysticetes that persisted into Late Oligocene time after more highly derived baleen-bearing mysticetes had already evolved. No known aetiocetid could be ancestral to baleen-bearing mysticetes, but aetiocetid morphology is in many ways intermediate between archaeocetes and baleen-bearing mysticetes, demonstrating the probable transitional steps passed through in the evolution of baleen-bearing mysticetes. Their discovery indicates that mysticetes evolved from Archaeocetes, and supports theories of the monophyly of Cetacea. Late

A 30-year renaissance in research on fossil marine mammals has brought advances on several fronts and suggests potential directions for future study. Gingerich and Russell have described Pakicetus, the most primitive archaeocete cetacean. Mchedlidze has described a diverse assemblage of late Oligocene/early Miocene cetaceans from the Caucasus and Georgia, S.S.R. Barnes and Fordyce, respectively, have outlined sequences of fossil cetacean assemblages in the northeast and southwest Pacific. Much remains to be done on origin and definition of cetacean suborders, diversification and systematics of families, and relationships among infra-familial taxa.New material has been recovered of the most primitive desmostylians, and other new specimens, especially ones from Japan studied by Inuzuka and others, give a relatively complete picture of their anatomy. Material now exists for phylogenetic analysis.Domning has proposed a phyletic lineage of the sirenian subfamily Hydrodamalinae and has outlined patterns of Late Cenozoic manatee evolution. With Morgan and Ray he reviewed Eocene sirenians in the northwest Atlantic. Numerous new specimens are being actively studied in attempts to reassess relationships within the Sirenia.Mitchell and Tedford described the most primitive otariid, Enaliarctos. Repenning and Tedford reviewed the otarioids. The primitive taxa and their origin near or in the amphicynodontine ursids have been identified. The zoogeography of true seals, the phocids, has been analyzed recently by Repenning, Ray and Grigorescu, and by de Muizon. Most taxa are based on a few fragmentary specimens, and much work needs to be done on basic descriptions, interspecific comparisons and phyletic analysis. However, major progress has been made in the southern hemisphere through description of extensive new materials from Peru and South Africa.Many important phylogenetic gaps in the fossil record of marine mammals have been filled recently, and further advances continue at a rapid rate. Studies lnvited plenary session paper presented at Fifth Biennial Conference on the Biology ofMarine Mammals, November 2 7-December 2, 198.3,

True porpoises are a morphologically distinctive and evolutionarily old group of odontocete cetaceans classified as the family Phocoenidae. They are distinct from members of the family Delphinidae, with which they have sometimes been classified. Re-examination of all living and fossil species of phocoenids yields new information on the evolution of the family and indicates the need for significant taxonomic changes. Two separate lines of descent within the group are classified as the subfamilies Phocoeninae and Phocoenoidinae.The living southern hemisphere spectacled porpoise, Phocoena dioptrica, is actually more closely related to the North Pacific Dali's porpoise, Phocoenoides dalli, than to other species of Phocoena. It therefore belongs in the subfamily Phocoenoidinae with Phocoenoides but represents a separate genus, Australophocaena (new genus). The earliest unquestioned fossil phocoenids have been found only in rocks around the Pacific basin. They include latest Miocene and Pliocene species of Piscolithax and the Late Miocene Salumiphocaena stocktoni (new genus) in the Phocoenoidinae, and an undescribed latest Miocene species in the Phocoeninae. World climate has influenced past and present distributions of phocoenids, andAustralopbocaena dioptrica is possibly the antitropical counterpart of Phocoenoides dalli. All species of living phocoenids show similarities caused by convergent evolution, resulting in part from the phenomenon of paedomorphosis.

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