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Buccal Oscillation Behavior in Amniotes
Elizabeth L. Brainerd

All extant amniotes, with the possible exception of mammals, exhibit rhythmic oscillations of the hyobranchial apparatus which are not associated with lung ventilation. Similar non-ventilatory hyobranchial oscillations are also seen in amphibians, interspersed with ventilatory hyobranchial movements. In amphibians, the non-ventilatory movements are called 'buccal oscillations' to distinguish them from ventilatory 'buccal pumps'. Buccal oscillations are commonly seen in 'lizards' (non-serpentine squamates), turtles, crocodilians and birds. In lizards, buccal oscillation with the mouth closed draws air over the nasal epithelia and may enhance olfaction. Buccal oscillation with the mouth open enhances evaporation from the oral mucosa and may contribute to thermoregulation (this behavior is sometimes called 'gular flutter'). Gular flutter in response to heat stress has been observed in many species of lizards and in birds. In crocodilians, buccal oscillation with the mouth closed is a common behavior, occurring both at rest and during exercise on a treadmill. In some turtles, buccal oscillation with the mouth closed is a common behavior for animals at rest, both under water and in air. Buccal oscillation behavior, if present at all, is least pronounced in mammals. Some mammals perform panting behaviors in which the tongue moves in and out of the mouth in a rhythmic fashion. This panting behavior may be related to the buccal oscillation behaviors seen in other amniotes. Given the overall similarity between buccal oscillation in amphibians and the rhythmic hyobranchial movements seen in amniotes, it seems likely that these behaviors in amniotes represent a retention of the primitive buccal oscillation behavior. The presence of buccal oscillation in extant archosaurs and lepidosaurs suggests that this behavior was also present in non-avian dinosaurs, and depictions of dinosaurs in animations or animatronics should include rhythmic throat movements.

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