CVA - Appendicular skeleton

• In a lamprey, the fins and tail are the axial skeleton
• agnathans have no appendicular skeleton, but the do have paired fins
• lamprey and hagfish possess fin folds along their backs
• Fin fold theory: Balfour and Thacher (1876) - Proposes that they evolved from a trunk bilateral fin fold
• Fin spine hypothesis: Westoll (1958) - Spinal separation of fin folds evolved into median paired fins overtime
• Gill Arch Theory: Gegenbaur's (1878) - The most posterior gill arch developed into a limb, similar to how anterior gill arches may have developed into jaws
• Gill arches and fins develop similarly
• Fins have girdles, long bone (basal) and fin rays
• Lepidotrichia are made of bone, where actinotrichia are made of keratin and ray-finned. Both are digit-like formations
• From lobed-fin fish to tetrapods, lepidotrichia was lost and phalanges developed from the rest of the skeleton
• Birds either have lengthened digits or they made be reduced entirely. Ungulates can be similar
• Pectoral girdle

  • scapula
  • clavicle
  • coracoid
• Pelvic girdle parts:

  • ilium
  • ischium
  • pubis
• It is those in the fossil record that some animals may have reduced digits for swimming, flying, and running