; cohort Mutica, order Cetacea)
A suborder of marine mammals that comprises ancestral forms, known from the upper Eocene, and the four superfamilies: Squalodontoidea (extinct forms), Platanistoidea (river dolphins), Physeteroidea (large whales), and Delphinoidea (smaller whales, dolphins, and porpoises). Teeth are always present, and may be numerous (e.g. squalodonts, which possessed up to 180 teeth, one porpoise which had 300, and the river porpoise Platanista, which has more than 50), or reduced to a single tooth (Monoceros). The teeth are simple and peg-like and are not differentiated into incisors, canines, etc. There is a single nasal opening and the nasal bones do not form part of the roof of the nasal passage.
Subjects: Zoology and Animal Sciences.