Traditional taxonomic rankings

Everyone on here is probably familiar with the old taxonomic ranks of kingdom, phylum, class, order, family, genus and species that was a mainstay of school biology classes and of course was a fundamental part of taxonomic work for, well, pretty much centuries. However, with the advent of cladistics more and more specific groupings of taxa were possible based on branching nature of phylogenetic trees. While there were sub-ranks of subfamilies, superorders, tribes and the like, these were rarely invoked and I think people shied away from them because they implied a level of detail that couldn’t really be inferred based on how these groups were generally formalised.

However, many of the intermediate ranks are rapidly falling by the wayside because they simply are no longer useful or don’t make sense. Kingdoms and phyla are still useful and major groups of taxa that represent fundamental divisions, and of course genera and species are the basis of all taxonomy, but that stuff in the middle? Doesn’t fit.

To take an excellent example (floated my way by Mike Taylor, despite the fact that it should have been obvious to me) birds are in Class Aves, we now accept that birds are dinosaurs but more specifically that means they sit within the traditional Superorder Dinosauria, Order Saurischia, Suborder Maniraptora and (depending on your favoured phylogeny / family definition) Family Paraves. So a Class ends up sitting in half a dozen groups that are supposed to be subordinate to it. And all the various orders and families of birds also sit in there. Oh.

We are increasingly getting close to building the Tree of Life – a single vast and unified trees that put whole phyla together at the species level in clades that most experts generally agree on. No longer are new or odd species somewhat arbitrarily assigned to families or have new families erected for them because they are special. We simply don’t think of trees and relationships in those terms anymore – not everything has to sit in a family, and it’s no longer the case that just a couple of researchers look at their clade and split up the taxa with no reference to related clades or other, wider patterns. As such, while at a conversational level, it still makes sense to use and discuss things like the ‘cat family’ or ‘dog family’ increasingly these are being abandoned for their formal names (Felidae and Canidae in this case) though the endings of various names betray their origins as the –idea, -inae, -oidea, and so on demonstrate. These now represent successive ranks rather than ‘families’ and ‘tribes’ as once they would.

1 Response to “Traditional taxonomic rankings”


  1. 1 Mark Robinson 15/04/2011 at 5:11 am

    I think the old-style taxonomic groupings still work fine when restricted to today’s animals because they and their relationships are essentially static. It’s really only when you try to force species separated over time into one or other of these artificial categories that you start running into problems.

    Of course, it’s not perfect. Some of today’s animal families have members who are quite closely related to each other while other families are more disparate. There are also other anomalies like crocodiles being more closely related to birds than tortoises but being grouped with tortoises as “reptiles”.

    Some classification issues will always remain. We humans like to put everything into nice neat little boxes but the natural world is often a continuum and at some point an arbitrary decision will need to be made. Boxes are fine for classifying rocks but at exactly what frequency does “red” light become “orange”?

    Even “species” isn’t as real as we often seem to treat it. If you have three partially-isolated populations of a creature and individuals from Group 1 can successfully breed with those of Group 2, and Group 2 with 3, but not Group 1 with 3, are they three separate but closely-related species or three sub-species?

    Sorry about the length of my comment, Dave – it’s an interesting topic!


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