Question

6. Discuss how the fin-fold theory explains the structural similarity/homology of bones of the pelvic and pectoral fins of fish and the forelimbs and hindlimbs of Tetrapods. What is the function of fins? What is the function of limbs? What is the basic bone organization of fish fins? What is the basic bone organization of Tetrapod fore/hind limbs?

Answer 1

The paired fins in fish and limbs in tetrapods are a good example of homologous organs. They were derived from locomotive organs in common ancestors of vertebrates, and they share many developmental processes and genetic networks.

The transition of fishes to land animals required the development of paired pelvic fins and their muscles to eventually form weight-bearing hindlimbs. The transition of paired pelvic fins to tetrapods hindlimbs is characterised by gradual progession from posterior and ventrally placed slender pelvic fins articulated to pelvic girdle to dorsally located robust pelvis and hindlimb.

Function-

fins-Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids.

​​​​limbs- fore limbs or upper limbs in human are used for grasping, holding, writing and eating and hind limbs are lower limbs are used for running walking etc.

bone structures-

fins-

the fin skeleton can be divided into three domains: proximal radials, distal radials, and fin rays.

limbs-

Tetrapod limbs can be clearly divided into three domains: stylopod, zeugopod, and autopod.

Stylopod- single long bone like humerus.

Zeugopod- 2 long bone like radius and ulna

Autopods- small elementary bones like carpels, metacarpels and Phalanges.