Re: Croc classification (was Re: Sarcosuchus and Dumbing things down)

[chris brochu <christopher-brochu@uiowa.edu>]

>>      The broader term "crocodylian" should apply to members of Crocodylia,
>> but we still are faced with two different concepts of what Crocodylia
>> includes.  The traditional concept is Crocodylia sensu lato, used by Alfred
>> Romer, Robert Carroll, Encyclopaedia Britannica, and lots of other
>> references, and relatively recently in Mike Benton's 1997 classification.
>
>Contrary to the assertions of several cladists, Owen did not use the term
>'Crocodylia' (with a 'y' instead of an 'i') when he emended Gmelin's
>Crocodili in 1842 to additionally encompass fossil taxa.


I don't recall cladists (including myself) referring to Owen for taxonomic
principles; most of us refer straight to Gmelin, whose usage was limited to
extant crocodylians (which were all he knew about - and to Gmelin, crocs
were all species of Lacerta).  And in any case, terms like "eusuchian" and
"mesosuchian" were coined by Huxley (who DID use Crocodilia), not Owen.



 The latter
>spelling was introduced in 1973  by Rodney Steel, who considered it to be in
>accord with the correct spelling of Crocodylus (note that Steel's motivation
>had nothing to do with the establishment of a crown group)


The reason this spelling has been resurrected is to emphasize the usage of
the newer taxonomy - it has nothing to do with Steel's work.



  Up until 1973,
>Crocodilia was broadly equivalent to what most cladists now call
>Crocodylomorpha.  About the only point of contention prior to 1973 (and
>indeed for about a decade after) was whether Sphenosuchia should be placed
>in Crocodilia or Thecodontia.


Crocodylomorpha = "sphenosuchians" + crocodyliforms.  I think you mean "in
the older usage, Crocodilia meant "Crocodyliformes."


I think some posters to this list have the misimpretion that "Crocodilia"
had a stable meaning before the crown-group definition was published in
1988 - and Ken, you'd be VERY surprised at who the senior author of that
paper was.  If it did, there'd not have been a need for a revised
definition. Most people agreed that things like dyrosaurids and
notosuchians should be "crocodilians," but what about Gracilisuchus?  or
Terrestrisuchus?  Were these "crocodilians" or "thecodonts?"  The lower
bounds of "Crocodilia" in the former usage were absolutely unclear and
ambiguous.  This is the point Steve makes above, but the very fact of the
undefined lower bound emphasizes the need for a stable phylogenetic group
name.  One might prefer to define "Crocodilia" as Steve proposes, but that
definition would be a junior synonym of Crocodylia sensu Benton and Clark
1988.







>
>The usage of Crocodilia as an ordinal taxonomic term from 1842 to 1973 is
>the reason these animals are referred to as crocodilians (with an 'i').
>Eusuchians, mesosuchians (such as pholidosaurids) and protosuchians are all
>crocodilians.  Within a traditional Linnean classification, Crocodylia is an
>invalid term, since Crocodilia has priority, having been used consistently
>for over 130 years.

In the context of the Linnean system, perhaps.  But we no longer use the
Linnean system (or shouldn't), so whether one spelling or the other in the
Linnean system has priority is irrelevant to the crown-usage currently in
place.




>
>I therefore fully endorse Sereno when he calls Sarcosuchus a crocodilian.
>Only one problem: he's a cladist.
>


I know - those people who use organismal information to reconstruct the
phylogenetic relationships necessary to do things like the evolution of
functional morphology are a menace to society.



chris

------------------------
Christopher A. Brochu
Assistant Professor
Department of Geoscience
University of Iowa
Iowa City, IA 52242

christopher-brochu@uiowa.edu
319-353-1808 phone
319-335-1821 fax