All organisms in group 2(birds, fish, mammals, echinoderms, amphibians) except _______ are thought to share a common ancestor that possessed many of the same characterisitcs as the modern lancelets.
A)echinoderms
B)fish
C)amphibians
D)birds
E)mammals
The correct answer is C) amphibians.
Amphibians are the only organisms in group 2 mentioned (birds, fish, mammals, echinoderms, amphibians) that are thought to share a common ancestor with lancelets. They are believed to have evolved from a common ancestor that possessed many of the same characteristics as the modern lancelets, such as a notochord and a dorsal nerve cord.
To determine the answer to this question, we need to identify which organism in group 2 is not thought to share a common ancestor with the modern lancelets, as the rest of the organisms in the group are believed to have similarities with lancelets.
To find the answer, let's go through each option and consider whether it is plausible that the given organism shares a common ancestor with the modern lancelets.
A) Echinoderms: Echinoderms are not likely to share a common ancestor with the modern lancelets, as they belong to a different phylum (Echinodermata) than lancelets (Chordata).
B) Fish: Fishes are vertebrates and belong to the phylum Chordata, which also includes lancelets. Therefore, it is possible that fish and lancelets share a common ancestor.
C) Amphibians: Amphibians, such as frogs and salamanders, belong to the phylum Chordata, which suggests that they share a common ancestor with lancelets.
D) Birds: Birds are also vertebrates and belong to the phylum Chordata. Therefore, it is plausible that birds and lancelets share a common ancestor.
E) Mammals: Mammals, including humans, are vertebrates and belong to the phylum Chordata. Hence, it is likely that mammals share a common ancestor with lancelets as well.
After considering all the options, we see that the only organism remaining is the answer. Therefore, the correct answer is:
A) echinoderms