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Thread: Modern Taxonomy

  1. #1 Modern Taxonomy 
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    Just curious as what the current status of today's accepted system is...

    Still 6 Kingdoms? Is "Chromista" an official kingdom yet?

    It's sort of hard to get a straight answer from Googling.


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    Most people tend to speak about domains (normally a three domain system, but there are others), then use some other high-level group that can be above or below the traditional kingdom. As far as I understand it, the traditional kingdoms (Animals, Plants, Fungi, Archaea and Bacteria) don't really map very well on to the current tree of life and don't have much value as a result. Pretty much abandoned I think, although still often taught at school-level.


    As for Chromista, I think that has fallen by the way side now. Sort of merged and/or replaced by Chromalveolata.


    The last tree I seriously studied (see below) had the eukaryotes split into six supergroups (kingdoms): Ophistokonta, Amoebozoa, Plantae, Chromalveolata, Rhizaria and Excavata. Over half these kingdoms just contain single-celled organisms - a truly diverse group of organisms that very few people even know exist. Here's one from a brief article that appeared in Current Biology a while back:
    "The Real Kingdoms of Eukaryotes":




    At 8 years old it's probably out of date already.
    Note that in this system, the kingdoms are a feature of eukaryotes only. Not sure why most authors ignore the other two domains, since they probably exhibit even more diversity than protists.


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    Zwirko, thanks. Is that diagram a general taxonomic tree or is it phylogenetic? If that diagram's right, then my understanding is way outdated. So Fungi and Animalia are now subkingdoms? Why would they be placed in the same taxon? And I'm assuming Chromista and "Chromalveolata" are related. And green algae are now plants?!

    Not sure why most authors ignore the other two domains, since they probably exhibit even more diversity than protists.
    Possibly because we're more interested in what's more closely related to us. Not impartial, but that's what we would do. Also, it would be better to trace our evolutionary history backwards.
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    Forum Professor Zwirko's Avatar
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    Note that the tree I included is by no means the last word. It's only really a hypothesis at best and could well have been superceded already because I don't exactly have my finger on the pulse as it's hard to keep up. There are numerous other competing trees as well just to make it all very confusing, so don't take this one as gospel. The concept of supergroups, as in the tree I presented, may (or may not) be replacing the older idea of Kingdoms. I get the sense that kingdoms are somewhat historical and may be on the way out. They are still used as valid groups though. The six supergroup concept of the eukaryotes is slowly gaining popularity. How it pans out in the future is anybody's guess.

    At an ecological level fungi and animals are all strictly heterotrophs, while at the level of cell structure, as well as at the molecular level, they have a great deal of similarities with each other and have many crucial differences from the other groupings. And sequence data strongly supports the relatedness too, of course. Fungi and animals diverged from each other an incredibly long, long time ago. That they appear very closely related in that diagram is an illustration of just how different from each other these supergroups are and how deep down in the tree taxonomists can go these days to find evidence of common ancestry. Toadstools and sharks seem to have absolutely nothing in common, yet there they are sitting on two little twigs right next to each other amidst a forest of unicellular eukaryotes.

    I don't think Chromista is dead as such; it is still widely used in fact. From what I've read I don't think the group is very well-supported by the data. I think the Chromalveolata is effectively a reduced Chromista.

    I'm far from expert on this topic (a million miles off it if truth be told) so don't assume anything I've said is 100% true. Hopefully I didn't mess up too much - I'm still learning all this stuff myself.
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