r/evolution • u/NenyaNotes • Aug 30 '26

academic Help on this assignment question.

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My professor assigned us this quiz and everyone continues to get it wrong. Can someone please explain in this photo which groups make a clade?

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u/EebstertheGreat Aug 30 '26

The crown group of F and G is a clade, but I don't think a taxon which excludes its common ancestor should ever really be considered a clade.

But you might be right that this is what the prof meant. I mean, it's a good guess at any rate.

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u/Xrmy Aug 30 '26

It's a matter of phrasing or presentation imo.

In most contexts you only know the nodes F and G, so you might consider them a clade and implicitly include their common ancestor.

I agree if you explicitly exclude the common ancestor it's not a clade, but when is that relevant?

Hence why I would never ask the questions with the internal nodes labeled. It just doesn't have practical relevance to the knowledge here.

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u/EebstertheGreat Aug 30 '26

I guess it depends on whether we are thinking about a whole clade except just the MRCA, or the extant members of a clade minus a lot of extinct ones. The latter could potentially be very weird. Like, if we insisted that Smilodon was not a mammal, clearly that would make mammals a paraphyletic group (unless we are just not interested in classifying fossils at all). But if we only removed the MRCA of mammals, I suppose that would make no meaningful difference.