[Taxacom] What taxon corresponds to "birds'?

[Stephen Thorpe]

If we consider extant taxa only, then there is a large morphological gap between birds and (other) reptiles. On the other hand, if we had full access to the complete fossil record, that gap could completely disappear into a continuum. As long as all extant birds are included in a named taxon (of whatever rank), where to draw the line in terms of fossils is going to be arbitrary and unimportant. The main issue is rank. Should Aves be subordinate to Reptilia, or can we tolerate paraphyly? Some say yes, some say no. That is the problem!

Stephen

--------------------------------------------
On Wed, 30/11/16, John Grehan <calabar.john at gmail.com> wrote:

 Subject: Re: [Taxacom] What taxon corresponds to "birds'?
 To: "Kenneth Kinman" <kinman at hotmail.com>
 Cc: "taxacom at mailman.nhm.ku.edu" <taxacom at mailman.nhm.ku.edu>
 Received: Wednesday, 30 November, 2016, 9:31 AM
 
 One could well sympathize
 over the uncertainties of how inclusive to make a
 particular taxonomic category, but it seems to
 me to be disingenuous to
 assert that there
 is a problem of establishing a bird category because
 "cladists
 have so abused
 that taxon name with very different definitions" since
 the
 inclusiveness of a taxonomic category
 has nothing to do with cladistics.
 It's
 a basic principle of cladistics that relationships matter,
 not the
 inclusiveness of a category (other
 than it being a monophyletic entity). It
 matters not a cladistic hoot whether we decide
 to group birds into a class
 Paraves or an
 expanded Aves, whether we include Archaeopteryx or not.
 Such
 choices are inherent problems for any
 kind of taxonomy (as demonstrated by
 Ken's own uncertainty as to what choice to
 make) - or am I mistaken?
 
 John Grehan
 
 On
 Mon, Nov 28, 2016 at 11:44 PM, Kenneth Kinman <kinman at hotmail.com>
 wrote:
 
 > Hi All,
 >        For thousands of years (or
 longer), there has long been a
 >
 classificatory distinction between reptiles and birds,
 although
 > Archaeopteryx eventually
 showed that birds are clearly reptile
 >
 descendants.  This was reflected in both informal and
 formal
 > classifications as Classes
 Reptilia and Aves.  But the more recent
 > discovery of fossil intermediates has
 blurred where to draw the line
 > between
 reptiles and birds.  And around the same time we had
 adherents of
 > phylogenetic
 nomenclature  concluding that both paraphyly and ranked
 > classifications are somehow
 "unnatural".  And yet decades later the
 > PhyloCode is still extremely controversial
 and perhaps not likely to be
 >
 implemented anytime soon (if ever).
 > 
       In the meantime, even among strict cladists, the
 meaning or
 > definition of Class Aves has
 become increasingly muddled, between those who
 > would make it a crown group (and thus a
 synonym of Neornithes) or
 > alternately
 based on a group including Archaeopteryx, crown-group
 birds,
 > and all of their descendants.
 >        Given this muddled situation, I
 have long favored expanding that
 > Class
 (for birds) to include avian dinosaurs that seem to have
 preceded the
 > common ancestor of
 Archaeopteryx and modern birds.  Given the importance of
 > flight in the concept of
 "birds", I have come to the conclusion that
 > asymmetical flight feathers are a primary
 evolutionary development in what
 >
 constitutes a "bird".
 >     
   Therefore, given the muddled debate whether Aves is the
 crown group
 > or anchored instead on
 Archaeopteryx, I would perhaps suggest that we
 > recognize a Class Paraves for
 "birds" rather than a Class Aves.  The
 > discovery of Archaeopteryx long before all
 the other intermediates between
 >
 reptiles and modern birds long made it a convenient anchor
 for a very long
 > time, but it no longer
 seems to be so important given all the other forms
 > since discovered (some older) with
 adaptations for flight (the asymmetic
 >
 flight feather being a primary synamorphy, although even
 though its gradual
 > developmental can be
 problematic given problems inherent in fossil
 > specimens).
 >     
   Therefore, should we start calling it Class Paraves, or
 expand
 > Class Aves to become a synonym
 of Paraves.  I'm not sure which would be the
 > best choice.  However, I am convinced
 that we need to expand the concept of
 >
 "birds" as a Class separate from Class Reptilia. 
 Whether we call that
 > Class Paraves or
 an expanded Class Aves is the question.
 >                           
        ----------------------Ken
 >
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 >
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