Question

If you are interested in the evolutionary relationship of animals that have four limbs, which of the following would be the outgroup? Group of answer choices Sharks Ray-Finned Fish Amphibians Crocodiles Dinosaurs

Answer 1

Answer:

• First outgroup → Ray-Finned Fishes
• Second outgroup → Sharks

Explanation:

The outgroup is the most distant taxonomic group that shares no traits or characters with the lineages of interest, which compose the ingroup. You can compare the outgroup with the ingroup to determine the evolutive relationship and which characters are primitive or derived.    

Even though the outgroup shares a common ancestor with the ingroup, this is placed far away in evolution, making the outgroup to be the taxonomic group less related to the other lineages. The lineages in the ingroup share another common ancestor that is more recent in history.

To select the outgroup, you need to focus on what you are interested in. There might be several outgroups, but you should choose the one that is more related or closer to the ingroups. This selection is important because you need to make comparisons to understand the evolution of specific traits.  

In the exposed example, we need to focus on animals that have four limbs. Then, we might assume that the ingroup is composed of Amphibians Crocodiles Dinosaurs. Sharks and Ray-Finned Fish do not have four limbs, so they might be considered outgroups.

From these two outgroups, sharks have a cartilaginous skeleton, while Ray-Finned Fishes have a bony skeleton. This fact makes ray-finned fishes more related to the ingroup than the sharks. So,

• First outgroup → Ray-Finned Fishes
• Second outgroup → Sharks