Coelacanths and lungfish are collectively known as the lobe-finned fishes, and have fins containing similar arrangements of bones to those seen in tetrapod limbs. Which of the following statements about this relationship is TRUE?
A. Because the fins of the lobe-finned fishes and the limbs of tetrapods are used for different purposes, they can not be homologous.
B. Coelacanths and lungfish are considered to be the first tetrapods.
C. This relationship is an example of a morphological similarity reflecting a likely evolutionary link.
D. Despite the similar morphology of lobe fins and tetrapod limbs, genetic evidence suggests that coelacanths and lungfish are only distantly related to the tetrapods
The Correct Answer and Explanation is:
The correct answer is C. This relationship is an example of a morphological similarity reflecting a likely evolutionary link.
Explanation:
Lobe-finned fishes, which include coelacanths and lungfish, are considered to be closely related to the ancestors of tetrapods (four-limbed vertebrates). This relationship is supported by similarities in the structure of their fins and the limbs of tetrapods. Both the fins of lobe-finned fishes and the limbs of tetrapods have a similar internal structure, with bones arranged in a similar manner. This feature is known as homology, meaning these structures are derived from a common evolutionary ancestor. The shared skeletal structure in the fins of coelacanths and lungfish and the limbs of tetrapods suggests that these two groups share a common evolutionary lineage. This morphological similarity reflects an evolutionary link, meaning that the ancestors of modern tetrapods likely had fins with similar bone arrangements to those seen in the lobe-finned fishes today.
Why the other options are incorrect:
- A. “Because the fins of the lobe-finned fishes and the limbs of tetrapods are used for different purposes, they cannot be homologous.”
This statement is incorrect. Homology refers to the common ancestry of structures, not their current function. While the fins of lobe-finned fishes and the limbs of tetrapods may serve different functions today, their similar internal structure points to a shared evolutionary origin. The different uses do not negate their homology. - B. “Coelacanths and lungfish are considered to be the first tetrapods.”
This is incorrect. Coelacanths and lungfish are lobe-finned fishes, not tetrapods themselves. The first tetrapods evolved from lobe-finned fish-like ancestors around 375 million years ago, but they are not the same as modern coelacanths and lungfish. - D. “Despite the similar morphology of lobe fins and tetrapod limbs, genetic evidence suggests that coelacanths and lungfish are only distantly related to the tetrapods.”
This statement is also incorrect. Genetic evidence supports the idea that coelacanths, lungfish, and tetrapods share a relatively recent common ancestor in the evolutionary tree, making them more closely related than distant. The similarity in fin structure and genetic data both suggest a closer evolutionary link than a distant one.
In summary, the shared structural similarities between the lobe fins of coelacanths and lungfish and the limbs of tetrapods reflect an important evolutionary connection, demonstrating that the relationship is best understood as homologous structures pointing to a common ancestry.