Question at position 2 Ichthyosaur was a large aquatic reptile of the Mesozoic, some 150 million years ago. Fossils show that it had a dorsal fin and a tail just as fish do, even though its closest relatives were four-legged terrestrial reptiles that had neither dorsal fins nor aquatic tails. The dorsal fins and tails of ichthyosaurs and fish areanalogous.homologous.examples of genetic drift.vestigial.Clear my selection单项选择题
A
analogous.
B
homologous.
C
examples of genetic drift.
D
vestigial.

Question

Question at position 2 Ichthyosaur was a large aquatic reptile of the Mesozoic, some 150 million years ago. Fossils show that it had a dorsal fin and a tail just as fish do, even though its closest relatives were four-legged terrestrial reptiles that had neither dorsal fins nor aquatic tails. The dorsal fins and tails of ichthyosaurs and fish areanalogous.homologous.examples of genetic drift.vestigial.Clear my selection单项选择题

A

analogous.

B

homologous.

C

examples of genetic drift.

D

vestigial.

BlackTom AI · Accepted Answer

The question presents a comparison between a dorsal fin and a tail found in ichthyosaurs and those in fish, asking you to classify their relationship as analogous, homologous, an example of genetic drift, or vestigial.
Option 1: analogous. This is correct. Dorsal fins and aquatic tails in ichthyosaurs and fish serve similar functions (streamlining and propulsion in water) but arose independently in their respective lineages. Their structures did not come from a common ancestral fin, so they are the result of convergent evolution rather than shared ancestry.
Option 2: homologous. This would be true if the fins/tails were inherited from a common ancestor with those same features. However, ichthyosaurs are not closely related to modern fish, and their dorsal fins and tails did not originate from a trait carried down from a common ancestor with fish. The similarity is due to similar needs in an aquatic environment, not shared origin, so this choice is incorrect.
Option 3: examples of genetic drift. Genetic drift refers to random changes in allele frequencies that can affect traits over time, not to the similarity of structures due to function or their evolutionary origin. The dorsal fins/tails’ similarity is best explained by adaptive, convergent evolution, not drift, making this option inaccurate.
Option 4: vestigial. A vestigial trait is one that remains from an ancestral feature that no longer serves its original function. The ichthyosaur fins and tails functioned for aquatic locomotion, so labeling them vestigial is incorrect.