15
Chapter one: Hydrodynamics
surface swimmer constructively interfere and limit maximum swimming speed by effectively trapping the animal between two wave crests (Fish 1982; Fish and Baudinette 1997).
In submerged swimming for underwater foraging, wave drag is negated and
swimming speed can be higher than surface swimming (Williams 1999). The platypus
(Ornithorhynchus anatinus) and muskrat swim underwater by reorienting the limbs laterally and using a rowing motion (Fish 1996, 2000). Rowing can generate thrust, while
simultaneously exerting a downward force to counter buoyancy. A further transition from
rowing to pectoral oscillation requires only elongation of the forelimb, with a power phase
of the stroke directed posteriorly and ventrally. Employing simultaneous strokes of the
winglike forelimbs could lead to the lift-based pectoral oscillatory stroke of the sea lion
Zalophus (Feldkamp 1987a,b; Fish 2000). Alternatively, rowing of the pelvic limbs could
have lead to other pinniped swimming mode lateral pelvic oscillation displayed by phocids and Odobenus. By control of the angle of attack, the hind flippers can act as a hydrofoil
for lift-based propulsion (Fish et al. 1988). The lumbar vertebrae in an early fossil pinniped,
Enaliarctos mealsi, allowed swimming by lateral movements of the trunk along with propulsion by the limbs (Berta et al. 1989).
Simultaneous pelvic paddling is another swimming mode used for submerged swimming by otters (Fish et al. 1997). This mode transitioned to undulatory swimming as the
body and tail are thrown into waves due to movement of pelvis (Fish 1996). The combination of limbed and axial propulsion would allow the powerful back muscles to aid in
powering strokes of the hindlimbs. The undulations of the tail contributes thrust production and helps to compensate for the periodic increased drag as both hind limbs are in the
recovery phase. Although this mode of swimming is observed in modern otters (Tarasoff
et al. 1972; Fish 1994), the fossil quadrupedal cetaceans Ambulocetus and Rhodhocetus, and
the quadrupedal sirenian Pezosiren might have used this transitional mode (Gingerich
et al. 1990; Thewissen and Fish 1997; Domning 2001).
Further increases in performance would occur in adoption of fully undulatory swimming in conjunction with abandonment of limbs and distal expansion of the tail (Fish 1996).
A reduction in the limbs would reduce the drag on the animal. The increased surface area
and large amplitude of oscillation at the tip of the tail work against more water, increasing
total momentum, as traveling waves move along the body with increasing velocities (Webb
1975). An oscillatory mechanism is made possible by progressively restricting the propulsive
wave in the tail and establishing a controlled angle of attack at a pivot point toward the tail
tip. This leads to the evolution of a high-efficiency caudal hydrofoil, with a lift-based oscillatory motion like that employed by cetaceans and sirenians (Fish 1996). With the change
from surface to subsurface and drag-based to lift-based swimming in the evolution of a fully
aquatic lifestyle, buoyancy control could be improved by abandoning fur for blubber.
1.3.5 Surface versus submerged and buoyancy control
The evolution from a terrestrial to fully aquatic lifestyle in mammals required the development of buoyancy control mechanisms for stabilization in water (Stein 1989; Fish and
Stein 1991). Buoyancy control has major implications on locomotor energetics with respect
to the ability to float at the water surface and dive and surface easily (Johansen 1962).
Such activities are associated with foraging and escaping predation. For semi-aquatic and
aquatic mammals, a distinct division exists in use of fur and blubber for buoyancy control.
This division is associated also with the insulatory capacity of fur and blubber in the different environments in which they operate.
Chapter one: Hydrodynamics
surface swimmer constructively interfere and limit maximum swimming speed by effectively trapping the animal between two wave crests (Fish 1982; Fish and Baudinette 1997).
In submerged swimming for underwater foraging, wave drag is negated and
swimming speed can be higher than surface swimming (Williams 1999). The platypus
(Ornithorhynchus anatinus) and muskrat swim underwater by reorienting the limbs laterally and using a rowing motion (Fish 1996, 2000). Rowing can generate thrust, while
simultaneously exerting a downward force to counter buoyancy. A further transition from
rowing to pectoral oscillation requires only elongation of the forelimb, with a power phase
of the stroke directed posteriorly and ventrally. Employing simultaneous strokes of the
winglike forelimbs could lead to the lift-based pectoral oscillatory stroke of the sea lion
Zalophus (Feldkamp 1987a,b; Fish 2000). Alternatively, rowing of the pelvic limbs could
have lead to other pinniped swimming mode lateral pelvic oscillation displayed by phocids and Odobenus. By control of the angle of attack, the hind flippers can act as a hydrofoil
for lift-based propulsion (Fish et al. 1988). The lumbar vertebrae in an early fossil pinniped,
Enaliarctos mealsi, allowed swimming by lateral movements of the trunk along with propulsion by the limbs (Berta et al. 1989).
Simultaneous pelvic paddling is another swimming mode used for submerged swimming by otters (Fish et al. 1997). This mode transitioned to undulatory swimming as the
body and tail are thrown into waves due to movement of pelvis (Fish 1996). The combination of limbed and axial propulsion would allow the powerful back muscles to aid in
powering strokes of the hindlimbs. The undulations of the tail contributes thrust production and helps to compensate for the periodic increased drag as both hind limbs are in the
recovery phase. Although this mode of swimming is observed in modern otters (Tarasoff
et al. 1972; Fish 1994), the fossil quadrupedal cetaceans Ambulocetus and Rhodhocetus, and
the quadrupedal sirenian Pezosiren might have used this transitional mode (Gingerich
et al. 1990; Thewissen and Fish 1997; Domning 2001).
Further increases in performance would occur in adoption of fully undulatory swimming in conjunction with abandonment of limbs and distal expansion of the tail (Fish 1996).
A reduction in the limbs would reduce the drag on the animal. The increased surface area
and large amplitude of oscillation at the tip of the tail work against more water, increasing
total momentum, as traveling waves move along the body with increasing velocities (Webb
1975). An oscillatory mechanism is made possible by progressively restricting the propulsive
wave in the tail and establishing a controlled angle of attack at a pivot point toward the tail
tip. This leads to the evolution of a high-efficiency caudal hydrofoil, with a lift-based oscillatory motion like that employed by cetaceans and sirenians (Fish 1996). With the change
from surface to subsurface and drag-based to lift-based swimming in the evolution of a fully
aquatic lifestyle, buoyancy control could be improved by abandoning fur for blubber.
1.3.5 Surface versus submerged and buoyancy control
The evolution from a terrestrial to fully aquatic lifestyle in mammals required the development of buoyancy control mechanisms for stabilization in water (Stein 1989; Fish and
Stein 1991). Buoyancy control has major implications on locomotor energetics with respect
to the ability to float at the water surface and dive and surface easily (Johansen 1962).
Such activities are associated with foraging and escaping predation. For semi-aquatic and
aquatic mammals, a distinct division exists in use of fur and blubber for buoyancy control.
This division is associated also with the insulatory capacity of fur and blubber in the different environments in which they operate.