120
T.w. Cranford
region of the animal, above the level of the mouth" (Norris et al. 1961, page
175). They did not attempt to localize an internal source for the sounds.
Lilly and Miller (1961, page 1692) suggested that dolphins possess "two
separately controllable sonic emitters" whose locus was not pinpointed
beyond being in the head. They also suggested that, "clicks 'shock excite'
the resonant frequencies and harmonics of the air containing cavities in the
head," although they offered no further explanation of this proposal. Lilly
(1966), during the discussion following his paper, indicated that the larynx
might be the source of the ultrasonic or high-frequency components.
Various groups did report the presence of ultrasonic frequencies in the
signals they recorded from T. truncatus (Kellogg et al. 1953; Norris et al.
1961), but most investigators of that time were primarily using limited
bandwidth recording equipment. The use of high-frequency equipment
only came into widespread use ten years later.
Evans and Prescott (1962) forced air through the heads of post-mortem
dolphins and produced sounds they deemed similar to those made by live
phonating animals. Evans and Prescott speculated that, "the tubular sacs
combined with the nasal plug nodes appear to be the site of sound production," though this contention remained otherwise unsupported.
Nonetheless, their paper presented the first idea that could be tested and
so served as a focus for further investigations into the nasal phonation
hypothesis. The premise and design of the Evans and Prescott experiments
were solid enough, but their proposed sound generation site lacked a
comparative foundation because it was based upon the anatomy of only
two modern dolphin species (StenelLa allenuata, spotted dolphin, and
S. Longirostris, spinner dolphin). This invited intense rebuttal by the laryngeal phonation proponents who showed, through standard comparative
anatomy, that some odontocetes lacked nasal plug nodes altogether
(Schenkkan 1973). This combination of factors, in my estimation, increased
the fervor over the question of odontocete sonar signal origins.
In order to avoid confusion it is important to distinguish that we are
tracking two separate but related issues. One general question is whether
sonar sounds were being produced in the larynx or in the forehead. The
other question is which specific structure or structural complex actually produces the sonar signals? The distinction here is that the nasal phonation
hypothesis was, in general, more secure than any particular speculation
about the exact site or mechanism involved. For a time, however, the possibility could not be ruled out that sounds were generated laryngeally and
transmitted or "piped" into the forehead and rostrum.
Lilly (1962) claimed to discover "two separate phonation mechanisms in
the nasal sacs." He indicated that his dolphin apparently clicked predominately from one side of the nasal passage and whistled from the other.
Supporting evidence for these assertions or statements about exactly what
was observed were not given. In retrospect, Lilly's paper, though not providing enough information to allow assessment of all its details, is closer to
what we now believe to be the case (Ridgway et al. 1980; Amundin and
T.w. Cranford
region of the animal, above the level of the mouth" (Norris et al. 1961, page
175). They did not attempt to localize an internal source for the sounds.
Lilly and Miller (1961, page 1692) suggested that dolphins possess "two
separately controllable sonic emitters" whose locus was not pinpointed
beyond being in the head. They also suggested that, "clicks 'shock excite'
the resonant frequencies and harmonics of the air containing cavities in the
head," although they offered no further explanation of this proposal. Lilly
(1966), during the discussion following his paper, indicated that the larynx
might be the source of the ultrasonic or high-frequency components.
Various groups did report the presence of ultrasonic frequencies in the
signals they recorded from T. truncatus (Kellogg et al. 1953; Norris et al.
1961), but most investigators of that time were primarily using limited
bandwidth recording equipment. The use of high-frequency equipment
only came into widespread use ten years later.
Evans and Prescott (1962) forced air through the heads of post-mortem
dolphins and produced sounds they deemed similar to those made by live
phonating animals. Evans and Prescott speculated that, "the tubular sacs
combined with the nasal plug nodes appear to be the site of sound production," though this contention remained otherwise unsupported.
Nonetheless, their paper presented the first idea that could be tested and
so served as a focus for further investigations into the nasal phonation
hypothesis. The premise and design of the Evans and Prescott experiments
were solid enough, but their proposed sound generation site lacked a
comparative foundation because it was based upon the anatomy of only
two modern dolphin species (StenelLa allenuata, spotted dolphin, and
S. Longirostris, spinner dolphin). This invited intense rebuttal by the laryngeal phonation proponents who showed, through standard comparative
anatomy, that some odontocetes lacked nasal plug nodes altogether
(Schenkkan 1973). This combination of factors, in my estimation, increased
the fervor over the question of odontocete sonar signal origins.
In order to avoid confusion it is important to distinguish that we are
tracking two separate but related issues. One general question is whether
sonar sounds were being produced in the larynx or in the forehead. The
other question is which specific structure or structural complex actually produces the sonar signals? The distinction here is that the nasal phonation
hypothesis was, in general, more secure than any particular speculation
about the exact site or mechanism involved. For a time, however, the possibility could not be ruled out that sounds were generated laryngeally and
transmitted or "piped" into the forehead and rostrum.
Lilly (1962) claimed to discover "two separate phonation mechanisms in
the nasal sacs." He indicated that his dolphin apparently clicked predominately from one side of the nasal passage and whistled from the other.
Supporting evidence for these assertions or statements about exactly what
was observed were not given. In retrospect, Lilly's paper, though not providing enough information to allow assessment of all its details, is closer to
what we now believe to be the case (Ridgway et al. 1980; Amundin and