124
T.w. Cranford
present in all odontocete groups. They also reasoned (and rightly so in my
opinion) that it was unlikely for vastly different sound generation mechanisms to be in effect in different groups of toothed whales. This was unlikely
regardless of their phylogenetic relationships, especially since at least some
of the homologous relationships between structures in the foreheads of dolphins and sperm whales were evident to them. At the same time, Schenkkan
and Purves did raise important questions about which structures were
involved. Their objections needed to be addressed, but their arguments
failed, in any convincing way, to disprove the nasal phonation hypothesis.
Oddly enough, it was Norris and Harvey's work (1972) with the sperm
whale that proposed a sound generation function for the world's largest
nose and suggested a likely scenario for how it might be accomplished.
Richard Ellis (1981) later added to this suggestion by reporting that he was
able to feel pulsed sounds emanating from the anterior surface of the forehead in a live sperm whale, supporting the Norris and Harvey proposal.
3. Recent Work
The debate finally ended in the 1980s. Although evidence had been accumulating that dolphins produced biosonar signals within the nasal apparatus, the exact site remained a mystery. Ridgway and his colleagues (1980),
and Amundin and Andersen (1983) recorded air pressure changes and electromyographic events during phonation by T. truncatus and P. phocoena.
Both groups showed muscle activity in forehead structures and changes in
air pressure within and above the superior bony nares, simultaneous with
sound production. Ridgway's group also found an absence of concordant
activity in the larynx. Both groups showed that air pressure changed in the
nares just before the onset of sound production. They also corroborated
earlier findings of Norris and others (1971) that air is directed, during sound
generation, into the supracranial nasal air sacs, particularly the paired
vestibular sacs. Collectively, these observations pointed to the same indisputable and unequivocal conclusion, that sounds were being generated in
the tissues above the superior bony nares (i.e., they originated in the nose).
Mackay (1980) and Mackay and Liaw (1981) conducted ultrasound
studies on the heads of phonating dolphins. They also confirmed the results
of Norris and colleagues (1971) and reported activity in the nasal sac region
during phonation, as well as an absence of movement in the larynx. Investigators could then be certain that dolphin sonar signals were produced
using pressurized air in the supracranial nasal passages but there was still
the issue of exactly where and by what mechanism the pneumatically driven
apparatus functioned.
Attention was still focused on the nodes of the nasal plugs, even though
definitive proof for their function or involvement was lacking. Additional
confusion grew from the fact that several other structures had, at one time
or another, been implicated as part of the sound generation apparatus: the
T.w. Cranford
present in all odontocete groups. They also reasoned (and rightly so in my
opinion) that it was unlikely for vastly different sound generation mechanisms to be in effect in different groups of toothed whales. This was unlikely
regardless of their phylogenetic relationships, especially since at least some
of the homologous relationships between structures in the foreheads of dolphins and sperm whales were evident to them. At the same time, Schenkkan
and Purves did raise important questions about which structures were
involved. Their objections needed to be addressed, but their arguments
failed, in any convincing way, to disprove the nasal phonation hypothesis.
Oddly enough, it was Norris and Harvey's work (1972) with the sperm
whale that proposed a sound generation function for the world's largest
nose and suggested a likely scenario for how it might be accomplished.
Richard Ellis (1981) later added to this suggestion by reporting that he was
able to feel pulsed sounds emanating from the anterior surface of the forehead in a live sperm whale, supporting the Norris and Harvey proposal.
3. Recent Work
The debate finally ended in the 1980s. Although evidence had been accumulating that dolphins produced biosonar signals within the nasal apparatus, the exact site remained a mystery. Ridgway and his colleagues (1980),
and Amundin and Andersen (1983) recorded air pressure changes and electromyographic events during phonation by T. truncatus and P. phocoena.
Both groups showed muscle activity in forehead structures and changes in
air pressure within and above the superior bony nares, simultaneous with
sound production. Ridgway's group also found an absence of concordant
activity in the larynx. Both groups showed that air pressure changed in the
nares just before the onset of sound production. They also corroborated
earlier findings of Norris and others (1971) that air is directed, during sound
generation, into the supracranial nasal air sacs, particularly the paired
vestibular sacs. Collectively, these observations pointed to the same indisputable and unequivocal conclusion, that sounds were being generated in
the tissues above the superior bony nares (i.e., they originated in the nose).
Mackay (1980) and Mackay and Liaw (1981) conducted ultrasound
studies on the heads of phonating dolphins. They also confirmed the results
of Norris and colleagues (1971) and reported activity in the nasal sac region
during phonation, as well as an absence of movement in the larynx. Investigators could then be certain that dolphin sonar signals were produced
using pressurized air in the supracranial nasal passages but there was still
the issue of exactly where and by what mechanism the pneumatically driven
apparatus functioned.
Attention was still focused on the nodes of the nasal plugs, even though
definitive proof for their function or involvement was lacking. Additional
confusion grew from the fact that several other structures had, at one time
or another, been implicated as part of the sound generation apparatus: the