COMPARATIVE ANATOMY

COMPARATIVE ANATOMY: THE PENTADACTYL LIMB All tetrapod animals (amphibians, reptiles, birds, mammals) show variations in the same basic skeletal structure, which may be modified in various ways depending on the tetrapod group the animal belongs to and the requirements of the animal’s way of life. Some bones may become vestigial or absent in adults, while others may be highly modified, and groups of bones develop differently in different tetrapod groups. We will examine this process by looking at the limbs of tetrapods. All tetrapods possess a bone structure in their limbs based on the pentadactyl (five-fingered or five-toed) limb (see Fig: 21.13 in Mason et al., 2020). This limb is hypothesized to have been evolutionarily derived from the bone structure of the fins in lobe-finned fishes, the putative ancestors of tetrapods. The basic unmodified structure of the pentadactyl limb is the same in all tetrapods. Write the names of the bones involved in the pentadactyl limbs in the table below, matching the bones of the forelimb with those of the hind limb. Table 5.07: Bones of the pentadactyl limbs. (6 points) Names of equivalent bones Region Forelimb Hind limb Closest to body Humerus 2nd closest (one of pair) Ulna 3rd closest Radius 4th closest Carpals 5th closest Metacarpals Phalanges Q5.41.01 Q5.41.02 Q5.41.03 Q5.41.04 Q5.41.05 Q5.41.06 The hind limb equivalent of the humerus in the forelimb is the femur. (FIBQ. point) The hind limb equivalent of the ulna in the forelimb is the radius. (FIBQ. point) The hind limb equivalent of the radius in the forelimb is the tibia. (FIBQ. point) The hind limb equivalent of the carpals in the forelimb is the tarsals. (FIBQ. point) The hind limb equivalent of the metacarpals in the forelimb is the metatarsals. (FIB

The Correct Answer and Explanation is:

The pentadactyl limb, which all tetrapods possess, exhibits a similar basic skeletal structure in both the forelimbs and hind limbs. However, these bones have been modified to suit the specific needs and lifestyle of each tetrapod group. Below is the table of bones in the forelimb and hind limb, with their corresponding equivalents:

Explanation:

1. Humerus vs Femur: The humerus is the bone closest to the body in the forelimb, while its counterpart in the hind limb is the femur. Both are the main upper bones of their respective limbs, serving as support and enabling movement.
2. Ulna vs Radius: In the forelimb, the ulna is on the inside of the limb (closer to the body), and the radius is on the outer side. In the hind limb, however, the radius plays the role of the ulna, positioned to help support the structure and function of the hind limb.
3. Radius vs Tibia: The radius, in the forelimb, works with the ulna to provide the necessary structure for the forearm’s movement. In the hind limb, this function is largely performed by the tibia, which is a major weight-bearing bone in the leg.
4. Carpals vs Tarsals: The carpals in the forelimb are the wrist bones, whereas in the hind limb, their equivalent is the tarsals, which are the ankle bones. Both serve to support and allow flexibility in the movement of the limbs.
5. Metacarpals vs Metatarsals: The metacarpals in the forelimb correspond to the metatarsals in the hind limb. Both connect the proximal parts of the limb to the phalanges (fingers or toes), contributing to support and movement.
6. Phalanges: These are the finger (or toe) bones that are the same in both the forelimb and hind limb, facilitating the movement and manipulation of objects (in some species) or support of weight (as in the hind limbs).

This structure provides a functional basis for movement, adaptation to the environment, and support in different tetrapod species. Evolution has led to modifications in these bones to suit specific lifestyles, such as flight in birds or swimming in marine mammals.