96
Marine Mammal Physiology: Requisites for Ocean Living
The investigation of feeding mechanisms among any vertebrate group is an integrative and comparative endeavor that involves morphological, physiological, developmental,
behavioral performance, and ecological studies. In addition to understanding the evolution of mammalian feeding in aquatic environments, understanding prey-capture tactics
and feeding performance are important considerations for trophic ecological questions
since such behavior can determine prey choice due to energetic constraints (Emlin 1966;
Schoener 1971; Bowen et al. 2002; Wainwright and Bellwood 2002). Feeding has a direct
bearing on the fitness of an organism by determining the behavioral capacity of an animal to exploit its resources (Arnold 1983; Wainwright and Reilly 1994). Performance is an
important link between morphology and ecology because morphology is a primary predictor of performance and performance is a predictor of ecology.
Marine mammals represent the most recent vertebrate guild that underwent a major
evolutionary transition from land to sea (Pyenson et al. 2014). This macroevolutionary shift
from a terrestrial to a primarily aquatic lifestyle required a complex suite of feeding adaptations, which today are exhibited among several diverse lineages of cetaceans (whales
and dolphins), sirenians (manatees and dugongs), and pinnipeds (seals, sea lions, and walruses). Collectively, these extant species feed on a wide variety of resources that span all
trophic levels including marine algae, aquatic angiosperms, small zooplankton (such as
krill and copepods), fish, squid, and even marine amniotes including other marine mammals. Therefore, marine mammals are important consumers in diverse ocean ecosystems
worldwide through the use of multiple innovations that enable highly successful feeding
mechanisms.
5.2 Knowledge by order
5.2.1 Order Cetacea: Whales and dolphins
Cetaceans (whales and dolphins) represent a radiation of carnivorous marine mammals
descended from terrestrial even-toed ungulates (artiodactyls) that diversified approximately 50 Ma during the establishment of the circum-Antarctic current system in the
Southern Ocean (Fordyce and Barnes 1994). Given our current understanding of the
Southern Ocean as a whale feeding hotspot (Nowacek et al. 2011), this restructuring of
the oceans presumably changed the abundance and diversity of oceanic resources in a
dramatic way (Fordyce 1980; Steeman et al. 2009; Marx and Uhen 2010; Slater et al. 2010;
Pyenson et al. 2014). Extant cetaceans are represented by two major clades that exhibit very
divergent feeding strategies: toothed whales (Odontoceti) and baleen whales (Mysticeti).
Odontocetes possess adaptations of the skull (and other systems) for the integrated dual
functions of prey capture and echolocation to target single prey items, whereas baleen
whales feed in bulk on aggregations of prey using baleen as a filter (e.g., Slijper 1962; Werth
2001, 2004). Both echolocation and bulk filter feeding represent major evolutionary innovations that underlie the ecological success of this adaptive radiation of marine mammals.
5.2.1.1 Cetacea: Odontoceti
It is thought that toothed whales evolved echolocation to feed at night in shallow waters on
diel migrating cephalopods, and later this physiological adaptation was exapted in many
odontocete lineages to exploit deep prey that were also available during the day (Lindberg
and Pyenson 2007). The deepest diving toothed whale lineages are indeed largely teuthophagous (Clarke 1996), as exemplified by beaked (Ziphiidae) and sperm whales
(Physeteridae), but their diets can also be supplemented with fish in many geographic
Marine Mammal Physiology: Requisites for Ocean Living
The investigation of feeding mechanisms among any vertebrate group is an integrative and comparative endeavor that involves morphological, physiological, developmental,
behavioral performance, and ecological studies. In addition to understanding the evolution of mammalian feeding in aquatic environments, understanding prey-capture tactics
and feeding performance are important considerations for trophic ecological questions
since such behavior can determine prey choice due to energetic constraints (Emlin 1966;
Schoener 1971; Bowen et al. 2002; Wainwright and Bellwood 2002). Feeding has a direct
bearing on the fitness of an organism by determining the behavioral capacity of an animal to exploit its resources (Arnold 1983; Wainwright and Reilly 1994). Performance is an
important link between morphology and ecology because morphology is a primary predictor of performance and performance is a predictor of ecology.
Marine mammals represent the most recent vertebrate guild that underwent a major
evolutionary transition from land to sea (Pyenson et al. 2014). This macroevolutionary shift
from a terrestrial to a primarily aquatic lifestyle required a complex suite of feeding adaptations, which today are exhibited among several diverse lineages of cetaceans (whales
and dolphins), sirenians (manatees and dugongs), and pinnipeds (seals, sea lions, and walruses). Collectively, these extant species feed on a wide variety of resources that span all
trophic levels including marine algae, aquatic angiosperms, small zooplankton (such as
krill and copepods), fish, squid, and even marine amniotes including other marine mammals. Therefore, marine mammals are important consumers in diverse ocean ecosystems
worldwide through the use of multiple innovations that enable highly successful feeding
mechanisms.
5.2 Knowledge by order
5.2.1 Order Cetacea: Whales and dolphins
Cetaceans (whales and dolphins) represent a radiation of carnivorous marine mammals
descended from terrestrial even-toed ungulates (artiodactyls) that diversified approximately 50 Ma during the establishment of the circum-Antarctic current system in the
Southern Ocean (Fordyce and Barnes 1994). Given our current understanding of the
Southern Ocean as a whale feeding hotspot (Nowacek et al. 2011), this restructuring of
the oceans presumably changed the abundance and diversity of oceanic resources in a
dramatic way (Fordyce 1980; Steeman et al. 2009; Marx and Uhen 2010; Slater et al. 2010;
Pyenson et al. 2014). Extant cetaceans are represented by two major clades that exhibit very
divergent feeding strategies: toothed whales (Odontoceti) and baleen whales (Mysticeti).
Odontocetes possess adaptations of the skull (and other systems) for the integrated dual
functions of prey capture and echolocation to target single prey items, whereas baleen
whales feed in bulk on aggregations of prey using baleen as a filter (e.g., Slijper 1962; Werth
2001, 2004). Both echolocation and bulk filter feeding represent major evolutionary innovations that underlie the ecological success of this adaptive radiation of marine mammals.
5.2.1.1 Cetacea: Odontoceti
It is thought that toothed whales evolved echolocation to feed at night in shallow waters on
diel migrating cephalopods, and later this physiological adaptation was exapted in many
odontocete lineages to exploit deep prey that were also available during the day (Lindberg
and Pyenson 2007). The deepest diving toothed whale lineages are indeed largely teuthophagous (Clarke 1996), as exemplified by beaked (Ziphiidae) and sperm whales
(Physeteridae), but their diets can also be supplemented with fish in many geographic