97
Chapter five: Feeding mechanisms
regions (Slijper 1962; Gaskin 1982). Several other odontocete lineages (oceanic dolphins,
Delphinidae; porpoises, Phocoenidae) also feed on both fish and cephalopods, although
narwhals and belugas (Monodontidae) may also feed on crustaceans and benthic invertebrates (Dahl et al. 2000). These generalized and perhaps opportunistic feeding preferences
reflect the flexibility of feeding strategies afforded by echolocation, a key evolutionary
innovation that is a hallmark of toothed whale life history and functional ecology.
Odontocete (and all cetacean) skulls are perhaps the most derived among mammals.
The morphology of the rostrum, nares, cranium, ear bones, and mandible and biomechanics of jaw adduction have been drastically modified (Rommel 1990). The unusual morphology of cetacean skulls is due to overlapping and telescoping of bones that shorten the
cranium and the elongation of the facial region by lengthening of the maxilla and premaxilla, and mandible. Such modifications of the skull are linked to feeding, respiration, and
the generation and reception of sound used for echolocation (Rommel 1990; Marshall 2002).
Variation in the ratio of facial length versus cranial length is variable among cetaceans and
results in species with very short blunt skulls (e.g., Kogia and Globicephala) or long narrow
rostra (e.g., platanistids; Werth 2006b). Dentition of odontocete jaws varies from virtually
edentulous (e.g., ziphiids) to several hundred simple homodont teeth (e.g., platanistids).
These traits are related to diet. It is thought that constraint of the genetic component in
early dental development has been released in cetaceans (Armfield et al. 2013). Changes
in the development of teeth can drive morphological evolution as observed in odontocetes. Concomitantly, their feeding mechanisms are among the most specialized and varied
among mammals. They range from ram and raptorial feeding to suction feeding, whereas
mysticetes are generally categorized as filter feeders. In odontocetes and many secondarily
aquatic tetrapods, there is a dichotomy of cranial morphology associated with feeding
mode. Piscivory tends to be associated with long narrow rostra and mandibles, and jaws
filled with numerous teeth. This ecomorph has evolved independently several times among
several aquatic vertebrate groups (e.g., extinct marine reptiles, gharials, and some odontocetes) and is an adaptation for high velocity of the jaw tips to capture elusive prey, at the
expense of bite force. On the other extreme, teuthophagy (squid-eating) in toothed whales
is associated with short, blunt rostra and mandibles, a reduction in tooth number (or function), expanded basihyoid bone, and the use of suction as the primary feeding mode.
However, important exceptions to this dichotomy, as observed in sperm whales (Physeter
macrocephalus) and beaked whales, exist. Suction in marine mammals is generated by the
rapid depression and retraction of the tongue (but in some cases by the addition of fast jaw
opening velocities), which results in a rapid increase in buccal volume and concomitant
decrease in pressure (Gordon 1984; Werth 2000, 2006a,b, 2007; Marshall et al. 2008, 2014;
Marshall 2009). It is thought that the muscles associated with the enlarged basihyoid bone
of the hyoid apparatus (Reidenberg and Laitman 1994; Heyning and Mead 1996; Werth
2007) result in a greater force of lingual depression that presumably increases subambient pressure (Heyning and Mead 1996; Werth 2006b). However, orofacial morphology and
tongue shape may be just as important in directing the subambient pressure anteriorly
(Bloodworth and Marshall 2007; Marshall et al. 2008, 2014, in press; Kane and Marshall
2009). Such traits and correlated performance measures are well known for teleost fish
(e.g., Lauder 1985; Wainwright and Day 2007; Wainwright et al. 2007; Van Wassenbergh
and Aerts 2009).
To acquire prey, toothed whales use two primary mechanisms: ram and suction.
Ram feeding occurs when the whale’s attack speed and agility outperform that of
t argeted prey, thereby resulting in raptorial capture (Weihs and Webb 1984). In contrast,
suction can be generated from negative intraoral pressures through the rapid depression
Chapter five: Feeding mechanisms
regions (Slijper 1962; Gaskin 1982). Several other odontocete lineages (oceanic dolphins,
Delphinidae; porpoises, Phocoenidae) also feed on both fish and cephalopods, although
narwhals and belugas (Monodontidae) may also feed on crustaceans and benthic invertebrates (Dahl et al. 2000). These generalized and perhaps opportunistic feeding preferences
reflect the flexibility of feeding strategies afforded by echolocation, a key evolutionary
innovation that is a hallmark of toothed whale life history and functional ecology.
Odontocete (and all cetacean) skulls are perhaps the most derived among mammals.
The morphology of the rostrum, nares, cranium, ear bones, and mandible and biomechanics of jaw adduction have been drastically modified (Rommel 1990). The unusual morphology of cetacean skulls is due to overlapping and telescoping of bones that shorten the
cranium and the elongation of the facial region by lengthening of the maxilla and premaxilla, and mandible. Such modifications of the skull are linked to feeding, respiration, and
the generation and reception of sound used for echolocation (Rommel 1990; Marshall 2002).
Variation in the ratio of facial length versus cranial length is variable among cetaceans and
results in species with very short blunt skulls (e.g., Kogia and Globicephala) or long narrow
rostra (e.g., platanistids; Werth 2006b). Dentition of odontocete jaws varies from virtually
edentulous (e.g., ziphiids) to several hundred simple homodont teeth (e.g., platanistids).
These traits are related to diet. It is thought that constraint of the genetic component in
early dental development has been released in cetaceans (Armfield et al. 2013). Changes
in the development of teeth can drive morphological evolution as observed in odontocetes. Concomitantly, their feeding mechanisms are among the most specialized and varied
among mammals. They range from ram and raptorial feeding to suction feeding, whereas
mysticetes are generally categorized as filter feeders. In odontocetes and many secondarily
aquatic tetrapods, there is a dichotomy of cranial morphology associated with feeding
mode. Piscivory tends to be associated with long narrow rostra and mandibles, and jaws
filled with numerous teeth. This ecomorph has evolved independently several times among
several aquatic vertebrate groups (e.g., extinct marine reptiles, gharials, and some odontocetes) and is an adaptation for high velocity of the jaw tips to capture elusive prey, at the
expense of bite force. On the other extreme, teuthophagy (squid-eating) in toothed whales
is associated with short, blunt rostra and mandibles, a reduction in tooth number (or function), expanded basihyoid bone, and the use of suction as the primary feeding mode.
However, important exceptions to this dichotomy, as observed in sperm whales (Physeter
macrocephalus) and beaked whales, exist. Suction in marine mammals is generated by the
rapid depression and retraction of the tongue (but in some cases by the addition of fast jaw
opening velocities), which results in a rapid increase in buccal volume and concomitant
decrease in pressure (Gordon 1984; Werth 2000, 2006a,b, 2007; Marshall et al. 2008, 2014;
Marshall 2009). It is thought that the muscles associated with the enlarged basihyoid bone
of the hyoid apparatus (Reidenberg and Laitman 1994; Heyning and Mead 1996; Werth
2007) result in a greater force of lingual depression that presumably increases subambient pressure (Heyning and Mead 1996; Werth 2006b). However, orofacial morphology and
tongue shape may be just as important in directing the subambient pressure anteriorly
(Bloodworth and Marshall 2007; Marshall et al. 2008, 2014, in press; Kane and Marshall
2009). Such traits and correlated performance measures are well known for teleost fish
(e.g., Lauder 1985; Wainwright and Day 2007; Wainwright et al. 2007; Van Wassenbergh
and Aerts 2009).
To acquire prey, toothed whales use two primary mechanisms: ram and suction.
Ram feeding occurs when the whale’s attack speed and agility outperform that of
t argeted prey, thereby resulting in raptorial capture (Weihs and Webb 1984). In contrast,
suction can be generated from negative intraoral pressures through the rapid depression