Marine Mammal Musculoskeletal Disorders & Orthopedics

Question 1

Describe the vertebral anatomy of marine mammals?

How are their vertebrae different?

What are chevron bones?

How are the ribs different?

What is unique about their muscle anatomy?

Answer 1

• Musculoskeletal:
  
  • Skeletal muscle: very dark red, high in myoglobin
  • Still have 5 main areas of vertebrae (cervical, thoracic, lumbar, sacral, caudal) but less distinctive in fully aquatic animals that have vestigial pelvic bones
    
    • Post-thoracic vertebrae: refers to lumbar, sacral and caudal regions because difficult to differentiate
    • Caudal vertebrae in cetacteans start with chevron bones and extend to tip of tail
  • Chevron bones: ventral intervertebral ossifications in caudal region – juxtaposed in manatees and fused in dolphin at ventral aspects, articulate dorsally with vertebral column – makes triangular channel 🡪 blood vessels run to and from the tail
  • Ribs more flexible to facilitate diving
  • No functional clavicle
  • Olecranon – proximal extension of ulna – increases mechanical advantage of triceps muscle

Question 2

What is unique about the cervical vertebrae of cetaceans?

What is the function of the long transverse processes of cetacean vertebrae?

Which muscles are responsible for the upstroke and downstroke.

What is the function of the pectoral flippers?

Answer 2

• Musculoskeletal
  
  • Ankylosis of 2+ cervical vertebrae is common
  • Some odontocetes have bony sternal ribs
  • Do not have long neural spines on thoracic vertebrae because head weight is carried by water (buoyancy) instead of by spine
  • Long transverse processes to hold the large epaxial muscles needed for upstroke
    
    • Slow deep divers: fast twitch (type II) fibers
    • Sprinting deep divers: 1/3 slow-twitch
  • Cetaceans, sirenians: axial M/S for swimming; epaxial (upstroke) and hypaxial muscles (downstroke) attached to longer vertebral spinous processes
    
    • No recovery phase because two separate muscle groups so more efficient
  • Absence of pelvic limbs
  • Flukes (vs fluke in manatee) - tail
  • Pectoral flippers – help steer

Question 3

How does pinniped swimming differ from cetacean swimming?

What musculoskeletal adaptations enhance this?

How does this differ between otarrid and phocid seals?

Answer 3

• Musculoskeletal
  
  • Appendicular M/S system for swimming (compared to axial for cetaceans)
  • Proximal limb bones shortened to create more powerful lever/stroke, enveloped partially in the body to decrease drag; thicker cross-sectional area of proximal limb muscles
• Otarrids
  
  • Locomotion: walk with pelvic, swim with pectoral
  • Robust olecranon for powerful triceps
• Phocids
  
  • Locomotion: swim with lateral undulation of pelvic flippers; land movement via dorsoventral undulations
  • Tuck heads back against thorax (neck looks shorter than it really is), creates deep “s” shape
  • Manubrium and xiphoid may have an elongated cartilaginous extension with 1 or more articulations with sternal ribs
  • Flippers: long curved nails, thicker keratin layer on weight bearing surfaces

Question 4

Describe the locomotion of manatees.

What muscle groups are responsible for their motion.

How do the tails of manatees adn dugongs differ?

How do they use their pec fins?

Answer 4

• Musculoskeletal
  
  • Cetaceans, sirenians: axial M/S for swimming
    
    • Epaxial (upstroke) and hypaxial muscles (downstroke) attached to longer vertebral spinous processes.
    • No recovery phase because two separate muscle groups so more efficient
  • Dorsoventrally flattened fluke (manatee), flukes (dugong)
  • Pec walk in shallow water using flippers