I am trying to find information on the pangolin evolutionary tree and saw some information claiming they are more closely related to reptiles, is this true?
https://en.wikipedia.org/wiki/Pholidotamorpha
I don’t see how any placental mammal can be closer related to reptiles than others.
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Agreed. There’s no evidence that any of the currently recognized clades within Mammalia are more closely related to any reptile lineage than they are to other mammals. That would make Mammalia paraphyletic. Pangolins apparently are most closely related to the cat clade.
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Thats what I thought, thank you!
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Not at all, but there’s something similar.
Lobe finned fishes, like the Queensland lungfish and the West Indian coelacanth are more closely related to humans than they are to ray finned fishes
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i wonder how this is measured exactly? i know that the shared ancestor between humans and coelacanths is closer to coelacanths in the evolutionary tree than the shared ancestor between coelacanths and ray-finned fishes.
but suppose:
A = the evolutionary distance between humans and the human / coelacanth ancestor
B = the evolutionary distance between coelacanths and the coelacanth / ray-finned fishes ancestor
C = the evolutionary distance between a non-Teleost member of ray-finned fishes and the coelacanth / ray-finned fishes ancestor
could it be possible that A > B + C?
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Likely a genetic distance between common ancestors? Molecular clock or something like that.
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General pages on wikipedia be a good basis for discussion
see
https://en.wikipedia.org/wiki/Pangolin#Phylogeny
Where the essence says that modern studies favour them being closely related to Carnivora (https://en.wikipedia.org/wiki/Carnivora)
(i.e. cats, hyenas, dogs, bears, seals, etc.)
Here’s a decent overview on how ideas of where pangolins fit into the scheme of mamals has changed over recent times. https://blogs.scientificamerican.com/tetrapod-zoology/refined-fine-tuned-placental-mammal-family-tree/#
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thats a strange claim to make considering there mammals that literally lay eggs and pangolins are not them
If you draw yourself a cladogram (picture of a family tree connecting these organisms) it should have two main branches, with humans and coelacanths on the two sub-branches of a single branch, and all ray finned fishes as sub-branches of the other main branch. Relatedness in phylogenetics is defined as time since most common recent ancestor, and looking at your cladogram, you should see that the common ancestor of humans and coelacanths is more recent than that of either of these and any ray-finned fish. So A< B+C.
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aren’t they the closest relative to carnivorans? I think I heard that.
As long as we measure evolutionary distance by time since the last common ancestor, then no, this can’t happen. If we break down B, then it consists of the distance between coelacanths and the human/coelacanth ancestor + the distance between that ancestor and the coelacanth / ray-finned ancestor. (We’ll call that D.) But the first part of this is just A – the same as the distance between humans and the human / coelacanths. Every ancestor prior to that human / coelacanth ancestor belongs to both humans and coelecanths. So the distance between humans and any such ancestor will be the same as that between coelecanths and that ancestor. (In mathematical terms, for both species, the distance to any ancestor is A + D, if we define D as the distance between our common ancestor and the other species we’re interested in.)
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Whoa, that is a pretty awesome construction! I don’t really have the background to even fully appreciate it, but I am amazed.
Convergent evolution, ho!
Sorry. I messed up the definition of B and C in my earlier example. Let me try again…
Suppose we have the following ancestry, where “evolutionary distance” between 2 nodes is represented as the horizontal distance between them:
Is it possible for T1+T2+T3 < T4?
What I’m getting at is: Is it possible for some descendants to have evolved much more than their siblings? (For example, is it possible that G is much more distant from C than F is from C? And therefore could F be closer to D than to G?)
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The distances as measured on the tree are less important than shared common ancestry. Did humans and coelacanths share a common ancestry in which Ray-finned Fish were not involved? If so they are more closely related.
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It is possible to come up with situations depending on the metric of “evolutionary distance” which you use where those conditions might be met. For instance, you’ll see trees where branch lengths are based on base pair differences or something similar.
However, as @jnstuart notes, the key concept is common ancestry - this is what “relatedness” refers to. In the case of comparing G and F on your diagram, it could be valid to say that G has diverged more from C than F has from C. In this comparison though, C is the common ancestor of F and G. F wouldn’t be considered more closely related to D than G however, regardless of branch lengths, because F and G share a common ancestor (C) that D does not. If you had a trichotomy where F,G, and D all shared the same common ancestor, some types of comparisons would be valid.
If you’re really interested in this, I would recommend an undergrad or grad level Evolution textbook - and that’s not meant in any kind of negative way. I bet you’d find it really interesting, and the authors will certainly do a better job explaining the concepts than most of us on the forum will!
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ok. i’ll take your word for it.
it’s just unintuitive to me that something like
ABCDX
would be considered more closely related to
ABCDEFGHIJKLMNOPQRS
than to something like
ABCYZ
… maybe one day i’ll sit down and read something to see why folks decided to look at things that way.
Evolution and differentiation can occur at very different rates across lineages. So some lineages show greater differences among their members than others— think whales and deer within Artiodactyla. The thing that binds them is when that lineage - which gave rise to all members - split off from an ancestral form.
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