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

["Steve Salisbury" <steve_salisbury@bigpond.com>]

----------
>From: chris brochu <christopher-brochu@uiowa.edu>
>To: dinosaur@usc.edu
>Subject: Re: Sarcosuchus & Dumbing things down
>Date: Mon, 29 Oct 2001 10:23 PM

>>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;

Well maybe you should.

>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.

That's just the point.  When Gmelin introduced the term Crocodili in 1788,
the study of crocodilian palaeontology was in its infancy, with only a
single fossil having been documented (see Chapman 1759; Wooller 1759).  The
emendment of Crocodili by Owen in 1842 to additionally encompass fossil taxa
reflects the rapid expansion that occurred within the field of palaeontology
in England, as well as France and to some extent Germany, during the first
half of the nineteenth century.  Not only was there an increase in the
number of fossil crocodilians being collected, but also, and perhaps more
importantly, immense changes were taking place in the social foundation of
science.  Between 1850 and 1875, palaeontology went through a golden age.
When Huxley presented his paper on crocodilians to the Geological Society in
1875, Owen¹s 1842 concept of the Dinosauria had taken hold and Darwin¹s
Origin of species had been published and widely acclaimed by the scientific
community.  Five years earlier, Huxley had put forward the theory for the
origin of birds from dinosaurs following the discovery of the London
specimen of Archaeopteryx lithographica in 1861.  Most groups of animals
were considered to have fossil representatives, and their classifications
had been expanded accordingly.  In Huxley¹s 1875 classification, extant
crocodilians were no longer considered the only members of their group, but
representative of a distinct suborder within it ? Eusuchia.

>  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.

But through its spelling it is inexplicably linked.

>   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."

No.  Some poeple considered spenosuchians members of Crocodilia (hence the
comparison to Crocodylomorpha), whereas others excluded them, placing them
in Thecodontia instead, hence making Crocodilia broadly equivalent to
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.

Is it any different now?  Just compare the works of Clark, Wu, Sues,
Brinkman, Parrish, Sereno and Wild.

>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.

It's not what I propose; I'm just going along with Owen and Huxley.
Taxonomic stability is an unachievable Holy Grail.  In any case, it makes
systematics more enjoyable.

>>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.

Whose 'we'?  Not me.  I'll use which ever system I think is most
appropriate.  And for purely taxonomic purposes, the Linnean system wins
hands down.  Phylogeny is something else.

>>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.

I'll take that as a compliment.

Cheers,

Steve


---------------------------
Steve Salisbury

Palaeontology and Geology, Queensland Museum
PO Box 3300, South Brisbane, Q 4101, Australia

www.Qmuseum.qld.gov.au