Question

In a comparison of birds and mammals, the condition of having four limbs is

(A) a shared ancestral character.

(B) a shared derived character.

(C) a character useful for distinguishing birds from mammals.

(D) an example of analogy rather than homology.

Short answer

(A) The statement“a shared ancestral character” is true.

(B) The statement “a shared derived character” is false.

(C) The statement “a character useful for distinguishing birds from mammals” is false.

(D) The statement “an example of analogy rather than homology” is false.

Step-by-step solution

Phylum Chordata

The phylum Chordata is one of the clades of the bilaterian group of the animal kingdom. The presence of an endoskeleton structure characterizes it termed the vertebral column. The members of this phylum are further grouped into different divisions based on their anatomical or physiological similarities.

Explanation of option ‘(A)’

The characteristic feature of the presence of four limbs is observed in the members of class Mammalia, class Reptilia, class Aves, and class Amphibia. This feature is not present in all chordates and is thought to evolve from an ancestral tetrapod organism that evolved from a finned fish.

As the character of four limbs (tetrapod condition) is shared among the classes and is also present in their ancestral organism, it is a shared ancestral character.

Thus, four limbs are a shared ancestral character because they are found in mammals and birds along with their ancestors.

Therefore, the given statement is true.

Explanation of option ‘(B)’

A shared derived character can be explained as the trait present between descendant groups of organisms but absent in their common ancestral organism. These characters develop due to evolution and enhance the chance of survival.

Thus, the presence of four limbs is not a shared derived character as it is also present in the ancestral group.

Therefore, the given statement is false.

Explanation of option ‘(C)’

A distinguishing character helps in differentiating between two groups of animals. The character of four limbs is present in mammalian organisms and birds, so it cannot be used for demarking these groups of animals.

Thus, four limbs are a shared character and not a distinguishing character between birds and mammals.

Therefore, the given statement is false.

Explanation of option ‘(D)’

Analogy refers to characters between different groups of organisms that serve the same function but originated from different ancestral organisms. In contrast, homology refers to characters that originated from a single ancestor but served other functions in different groups.

Thus, four limbs are present in both birds and mammals, but the feature serves different functions in different groups.

Therefore, the given statement is false.