Marine Mammal Locomotion

MARE 390Dr. Turner

LocomotionSwimming by marine mammals is derived from:Paired flipper movements – pinnipeds & sea otters

Vertical movement of caudal flukes – cetaceans & sirenians

Pinniped MechanicsTerrestrial & aquatic locomotion achieved differently

Aquatic - three distinct patterns:1. Pectoral Oscillation – forelimb swimming used by otariids; flapping2. Pelvic Oscillation – hindlimb swimming in phocids; alternating3. Pelvic Oscillation (variant) – hindlimb swimming in odobenids; forelimbs also

Pectoral OscillationAquatic – flapping forelimbs, no hindlmbs

Pectoral OscillationOtariidae

Pectoral OscillationOtariidae

Pectoral OscillationTerrestrial – posture (hind facing forward) allows for weight on all four limbs

Pectoral OscillationOtariidae

Pelvic OscillationAquatic – alternating hindlimbs, forelimbs for steering

Pelvic OscillationAquatic – alternating hindlimbs, forelimbs for steering

Pelvic OscillationPhocidae

Pelvic Oscillation (Variant)Aquatic – hindlimbs used in alternating force; forelimbs either as rudders or paddles

Pelvic Oscillation (Variant)Odobenidae

Pelvic Oscillation (Variant)Terrestrial – hindlimbs can be rotated forward (like otariids)

Belly supports more of body than limbs

Pelvic Oscillation (Variant)Odobenidae

Cetacean LocomotionVertebral column – cervical, thoracic (rib attachments), lumbar regions (chevron bones)

Cervical VertebraeAll cetaceans have 7 cervical (neck) vertebraeDifferent from other mammals – flat, fused

Sperm whale – 6 fusedMost others – 2+ fused

Adaptation to high-speed swimming

SCTSSubdermal Connective Tissue Sheath

Collagenous sheath that restrains thoracic & lumbar vertebrae and gives rigidity to thorax & ↑ surface area for muscle connections of the back & tail

ZygopophysesAnterior & posterior facing articular processes on vertebrae

Work to link vertebrate togetherstiffens vertebral column

Ligaments alignvertebrae

Flippers & LocomotionIn cetaceans – forelimb proportions altered

Pectoral fin is forearm & hand – elbow not external

Also seen in marine reptiles, ichthyosaurs, mosasuars

Pelvic Girdle & LocomotionPelvic column reduced to innominate bones

Portions of femus, tibia, or foot

No direct connection to vertebral column

Tail Fluke LocomotionFollowing basic components:1. Cutaneous layer – like rest of body2. Blubber layer – far thinner than rest3. Ligamentous layer from caudal keels 4. Extremely dense fibrous material within ligamentous envelope

Tail Fluke ShapeThe shape of the flukes differs among cetaceans in response to varying hydrodynamic parameters

Trailing edges of most are slightly convexOther straight (Sperm whales)Curved (Humpbacks)Falcate (sickle-shaped; rorquals)Biconvex (narwhals)

Dorsal Fin ShapePredominant in most cetaceans

Supported by tough fibrous tissue – similar to flukes

Provide additional surface for balance & maneuverability, thermoregulation, & conspecific recognition

Mechanics of LocomotionModern cetaceans are caudal oscillators; swim by vertical movements of the flukes by alternate actions of epaxial & hypaxial muscles

Similar to billfishes & tunas except plane

Cetacean LocomotionDelphinidae

Cetacean LocomotionBalaenopteridae

Cetacean LocomotionPhyseteridae

Cetacean LocomotionPhocoenidae

Cetacean LocomotionMonodontidae

Cetacean LocomotionIniidae

Evolution of Cetacean LocomotionEvolved from an initial quadruped, pelvic phase, caudal undulation phase, & caudal oscillation

Evolution of Sirenian LocomotionCaudal oscillation

Poor swimmers compared to cetaceans

Unable to reach sustained high speeds

Evolution of Sirenian LocomotionTerrestrial quadrupeds – alternate thrusts of limbs

Aquatic quadrupeds – dorsal ventral spinal undulation & thrusts of hind limbs

Completely aquatic animals swimming with tail alone

Sirenian LocomotionTrichechidae

Sirenian LocomotionDugongidae

Evolution of Mustelid LocomotionHind limb much larger than forelimbs - terrestrial locomotion slow

Walking & bounding

Mustelid Locomotion

Evolution of Mustelid LocomotionAquatic locomotion achieved by pelvic paddling (surface) & pelvic undulation (submerged)

Mustelid Locomotion

Evolution of Ursid LocomotionPolar bears have few adaptations to the aquatic environment

Ursid Locomotion

Evolution of Ursid LocomotionSwim with crawling motion – only use forelimbs; hindlimbs trail behind

Ursid Locomotion