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At school I was taught the Linnaean view of vertebrate life - that vertebrate animals consisted of 5 distinct groups: mammals, birds, reptiles, amphibians, fish.

I learned later however that this was phylogenetically inaccurate, with birds being 'closer related' to crocodiles than other reptiles are, for example.

As such I am curious - since the ideas of these groupings is so strong in popular conceptions of animals:

What is the minimum number1 of clades we would need in order to partition 'Vertebrates', maintaining 'Mammals', 'Amphibians', and 'Birds' as clades?


1. Minimum number = number of leaf nodes

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  • $\begingroup$ How do you define reptile (see this post)? Fish is not a monophyletic groups. Whichever is the number of clades (= monophyletic group) you consider, fish will never be a clade. The same holds true for reptiles if by reptiles, you mean turtles, Rhynchocephalia, Squamata and Crocodilia. You might want to have a look at this answer that offers a quick intro to phylogenetics. $\endgroup$ – Remi.b May 23 '18 at 20:36
  • $\begingroup$ @Remi.b I'm aware of that, I think you misunderstood my question - the fact that 'fish' and 'reptile' (as the terms are commonly used) aren't monophyletic is my point. In my example grouping I didn't say "these 5 clades together make the clade I now call 'Fish'", I meant "What is commonly known as the paraphyletic group 'Fish' can be spit into 5 distinct clades" $\endgroup$ – ukemi May 23 '18 at 20:46
  • $\begingroup$ Indeed, I misunderstood you, sorry about that. It is still unclear to me though what you mean by what is the minimum number of clades we would need to maintain the first 3 as distinct. Mammals, birds and amphibians are three clades. So it takes naming three clades. I am not sure why the answer could be any different from three. $\endgroup$ – Remi.b May 23 '18 at 20:52
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    $\begingroup$ @Remi.b By completely partition I mean, every member of vertebrates belongs to one of the clades, and the clades are disjoint; by minimum I mean make the remaining clades as large as possible given the constraint Birds, Mammals, Amphibians are already clades. e.g. Crocodilians is 1 clade (considering smaller clades e.g. Crocodiles, Alligators & Caimans just increases the amount we need to consider, therefore not minimum), and it cannot be extended to form a larger clade as this would be (at least) 'Archosaurs', and hence absorb 'Birds', breaking one of the conditions. $\endgroup$ – ukemi May 23 '18 at 22:28
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    $\begingroup$ Oh I got it now $\ddot \smile$. Here is the beginning of the tree of vertebrates and as you can see there are already quite of few branches that will need named to "completely partition the clade of vertebrates". One could just screen through tolweb.org (or some other similar ressource) and count. $\endgroup$ – Remi.b May 23 '18 at 22:39
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Eyeballing it from http://www.onezoom.org I have this attempt at a breakdown (11 clades):

enter image description here

Here, what was preivously 'Fish' (the paraphyletic group of non-tetrapod vertebrates) becomes 5 clades, and 'Reptiles' (the paraphyletic group of non-avian Sauropsids) becomes 3.

After doing this it seems the question is equivalent to asking "what is the minimum number of clades necessary to partition Vertebrates while maintaining 'birds' as a clade?".

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