Figure 23. Functional morphology of feeding in North American paddlefish, Polyodon spathula. The top photograph shows a juvenile too
small to filter feed; at this size, the gill rakers are not yet developed and reeding is raptorial. Such individuals can eat surprisingly large food
items relative to their size including other juvenile paddlefishes (Yeager & Wallus 1982). The bottom figures show a filter feeding juvenile
with the jaws closed (left column) and open (right column). The bright white objects in the photographs are individual Daphnia; one can
be seen directly in front of the open mouth in the upper right photograph. The tracings of the photographs show in dotted outlines the
positions of the major visible bony elements. Note that unlike the Chinese paddlefishPsephurus(shown in Fig. 7), the upper jaw of
Polyodonis fixed at its anterior contact with the neurocranium. This fixed condition is clearly derived within Polyodontidae (see Grande
& Bemis 1991) (bb = basibranchial series, cb = ceratobranchial; see Figure 7 for other abbreviations).
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