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Later, Flower (1883) recognized that the whales have persistent rudimentary and vestigial features characteristic of terrestrial mammals, thus confirming that the direction of descent was from terrestrial to marine species.On the basis of morphology, Flower also linked whales with the ungulates; he seems to have been the first person to do so.Although teeth often occur in fetal mysticetes, only odontocetes exhibit teeth as adults.These teeth are always simple cones or pegs; they are not differentiated by region or function as teeth are in other mammals.To illustrate this approach, I will present the evidence from multiple fields for the origin of the whales from terrestrial mammals.
The elbow joint is virtually immobile, making the flipper rigid.
The rib cage is very mobile - in some species, the ribs are entirely separated from the vertebral column - which allows the chest to expand greatly when the whale is breathing in and allows the thorax to compress at depth when the whale is diving deeply.
The skull also has a set of features unique among mammals.
The odontocetes (toothed whales) have a single blowhole, while the mysticetes (baleen whales) have paired blowholes.
In the odontocetes, there is a pronounced asymmetry in the telescoped bones and the blowhole that provides a natural means of classification.