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Levels Of Classification?


RyanDye

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So I've been reading about paleontology for awhile now, I've read all sorts of books and articles and theses, but the one thing I don't understand is what is the complete list of levels of classification? The average example usually shows eight, in this order: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. But since this is only basic taxonomy there are more than just eight; the ones I know are: Domain, Kingdom, Phylum, Subphylum, Grandclass, Class, Subclass, Infraclass, Legion, Cohort, Grandorder, Order, Suborder, Family, Subfamily, Tribe, Genus, Species, and Subspecies; but then I remembered seeing the clade with dinosaurs and birds was shared, so where is clade in the list, and are there more classifications than I mentioned? If so, then what are they and how many do paleontologists typically actually use, and are classifications used in that order all the time, or are there some classifications that have no specific order?

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To my recollection*, clades are used in cladistics, and are more like a family tree than a way of splitting up organisms that may be contemporaneous. Cladistics is very useful in understanding evolutionary branching according to shared characteristics tracing back to the "root" ancestor. A brief Wiki on cladistics: https://en.wikipedia.org/wiki/Cladistics

 

These days, this can be done by relying on genetic information through computation. The challenge arises when it comes to organisms for which we do not have any genetic information, and thus have to rely on more observational, morphological features.

 

In terms of classic taxonomy, in most papers I've seen it has generally been the old mnemonic of King Potato Came Over For Good Soup, although I've also seen superorder, subclass etc., used in formal descriptions if there is sufficient purpose to distinguish at that granular level. 

 

Technically speaking, we could subdivide any continuum further if necessary, but at a certain point that could get absurdly impractical! :D 

 

* - To be taken with a grain of salt. Our much more seasoned experts can probably be more precise and correct any errors and infelicities in my explanation. :P 

...How to Philosophize with a Hammer

 

 

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You have to remember that the Linnaean classification scheme is an artificial system for organizing species into groups.  Several of the levels, especially Class, Order, Family, and Genus do not really exist as well distinguished "steps", they tend to grade into one another.  To the extent that they appear to be distinct, that is largely due to the fact that intermediate steps are mostly extinct.  Consider, for example, that all the genera within a Family are more closely related to one another than they are to any genera from any other Family, and that if the Family is monophyletic (as all well defined taxonomic categories are supposed to be) then all the genera within that family share a common ancestor.  That means that if you go back in time the genera will be more and more alike, until they are indistinguishable when you reach the common ancestor of the whole Family.  The point at which they differ enough to be called different genera is arbitrary, there is no sudden jump from all belonging to the same common ancestor species to a bunch of distinct genera.  How "different" is enough to say two species belong to different genera?  That is a judgement call, up to the expert who studies those species.  To reflect the fact that one category may gradually blend into the next, taxonomist can (and do) name a variety of intermediate levels.  "Infra" ("above") and "Sub" ("below") are very commonly used, as in Infraorder (a level below Phyllum, but that includes multiple orders) or Subgenus (a group of species that are more closely related to one another than they are to other members of the genus).  In some cases "Super" is used more commonly than "Infra", as in Superfamily.  There is no formal list of names that are the only levels that can be used.  On the other hand, although researchers can propose groupings and come up with new names, those names may not be accepted.  Ultimately you would have to convince other experts that your proposed name and level is the best way to classify whatever group of organisms you are studying.  Some of the names you listed, such as Grandclass, Grandorder, and Legion, are not commonly accepted; their use seems to be limited to the biologists who originally proposed them.  

 

A "clade" is just a group of organisms, it is not confined to one taxonomic level.  For example, one could refer to a group of genera as a "clade", or one could refer to a collection of Orders as a "clade".  It is just a shorthand way of referring to a set of related organisms you want to discuss.  As Kane said, the term comes from cladistics, a type of analysis that groups organisms in terms of shared characters.  

 

Don

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generally, it is Kingdom, Phylum,Class, Order, Family, Genus, Species.

"Absence of evidence is not evidence of absence"_ Carl Sagen

No trees were killed in this posting......however, many innocent electrons were diverted from where they originally intended to go.

" I think, therefore I collect fossils." _ Me

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth."__S. Holmes

"can't we all just get along?" Jack Nicholson from Mars Attacks

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2 hours ago, Kane said:

To my recollection*, clades are used in cladistics, and are more like a family tree than a way of splitting up organisms that may be contemporaneous. Cladistics is very useful in understanding evolutionary branching according to shared characteristics tracing back to the "root" ancestor. A brief Wiki on cladistics: https://en.wikipedia.org/wiki/Cladistics

 

These days, this can be done by relying on genetic information through computation. The challenge arises when it comes to organisms for which we do not have any genetic information, and thus have to rely on more observational, morphological features.

 

In terms of classic taxonomy, in most papers I've seen it has generally been the old mnemonic of King Potato Came Over For Good Soup, although I've also seen superorder, subclass etc., used in formal descriptions if there is sufficient purpose to distinguish at that granular level. 

 

Technically speaking, we could subdivide any continuum further if necessary, but at a certain point that could get absurdly impractical! :D 

 

* - To be taken with a grain of salt. Our much more seasoned experts can probably be more precise and correct any errors and infelicities in my explanation. :P 

 

1 hour ago, FossilDAWG said:

You have to remember that the Linnaean classification scheme is an artificial system for organizing species into groups.  Several of the levels, especially Class, Order, Family, and Genus do not really exist as well distinguished "steps", they tend to grade into one another.  To the extent that they appear to be distinct, that is largely due to the fact that intermediate steps are mostly extinct.  Consider, for example, that all the genera within a Family are more closely related to one another than they are to any genera from and other Family, and that if the Family is monophyletic (as all well defined taxonomic categories are supposed to be) then all the genera within that family share a common ancestor.  That means that if you go back in time the genera will be more and more alike, until they are indistinguishable when you reach the common ancestor of the whole Family.  The point at which they differ enough to be called different genera is arbitrary, there is no sudden jump from all belonging to the same common ancestor species to a bunch of distinct genera.  How "different" is enough to say two species belong to different genera?  That is a judgement call, up to the expert who studies those species.  To reflect the fact that one category may gradually bled into the next, taxonomist can (and do) name a variety of intermediate levels.  "Infra" ("above") and "Sub" ("below") are very commonly used, as in Infraorder (a level below Phyllum, but that includes multiple orders) or Subgenus (a group of species that are more closely related to one another than they are to other members of the genus).  In some cases "Super" is used more commonly than "Infra", as in Superfamily.  There is no formal list of names that are the only levels that can be used.  On the other hand, although researchers can propose groupings and come up with new names, those names may not be accepted.  Ultimately you would have to convince other experts that your proposed name and level is the best way to classify whatever group of organisms you are studying.  Some of the names you listed, such as Grandclass, Grandorder, and Legion, are not commonly accepted; their use seems to be limited to the biologists who originally proposed them.  

 

A "clade" is just a group of organisms, it is not confined to one taxonomic level.  For example, one could refer to a group of genera as a "clade", or one could refer to a collection of Orders as a "clade".  It is just a shorthand way of referring to a set of related organisms you want to discuss.  As Kane said, the term comes from cladistics, a type of analysis that groups organisms in terms of shared characters.  

 

Don

 

58 minutes ago, Herb said:

generally, it is Kingdom, Phylum,Class, Order, Family, Genus, Species.

Thank you for all your responses, and yes I'm familiar with cladistics and all of this reasoning cleared up alot for me, after seeing so much information and so many different names to classify organisms I got confused on how scientists even used all of it, once again, thanks alot! :)

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As I’ve heard it put before, nature hands you a loaf of bread, and you can cut as many or as few slices as you want. Nature doesn’t adhere to our labels. 

4 hours ago, FossilDAWG said:

as all well defined taxonomic categories are supposed to be)

And everyone in the room looks at Carcharocles.

“...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin

Happy hunting,

Mason

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I miss the word "plesion" in all of this:ptero:(with or without "crownward(etc)"

And O(perational)T(axonomic)(U(nit)B)

"Traditional"(Linnean)taxonomy is (was?)based on morphology/anatomical characters,mostly ,if not solely , adult morphology.

 

Developmental(ontogenetic) data didn't (yet)enter into the systematic fray.

 

There are other data(ethological,eg,species-specific songs of birds),immunological(species-specific responses to threats to the immune system),endocrinological,genetic,

ecological.

So it was based on an incomplete subset of taxononomical useful data right from the word "go".

The data used are anatomical,but what about them?

Basically they are: topology(what is/or rather "goes" where ,shape,connectivity,colour,material and structural properties,function,metrics).

The problem lies with the intrinsic properties of the biological world:all data are basically multidimensional(it starts already at the (single)organismal level,think e.g. organelles/cell/organ tissue.,let alone higher "categories";multidimensional data are hard to capture linguistically, semantically,and mathematically.

Morphological data are idiotypical,in the sense that the basic assumption is that there is a organism with well-defined properties.(BTW,one just has to think of sexual dimorphism

to know that that basic assumption is wrong)

(There may be some among us who have wondered about subspecies,"forma ","var",and their putative usefulness/validity)

The descriptive terminology is insufficiently objectified,and very,very worker-based.

There have been experiments where systematists where given specimens to classify,with some very mixed results.

As repeatedly pointed out above,taxonomy is a very human endeavour,with a pretty large subjective element

The problems are gigantic:how to make biological sense of e.g.siphonophores,or ant colonies("superorganisms") ?

(I have to mention PHYLOCODE and its influence on nomencalture/ methodology,BTW)

(NOTE:every classification has an evolutionary model at its root,but it is SELDOM stated which model is used,I mentioned the Yule tree before)

 

 

The data generated by molecular phylogenetics on the affinities and placement of taxonomical entities do not automatically corroborate the data derived from an analysis of morphology!

The fossil record is an extremely limited subset of the data necessary to generate useful ideas on phylogeny.The amount of missing (useful)data is HUGE

variability of body parts,a fish example:

 

 

jplsei554px-Augen_8gneiss_est.jpg

 

 

 

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