RE: Strange thoughts on PN - was Re: BAD vs. BADD

[John Scanlon <riversleigh@outbackatisa.com.au>]

Scott wrote:

> By the way, I *always* refer to snakes as lizards.  They are, after
> all.  The interesting question is" Are they near igaunians, as some
> olecular studies have suggested, or are they closer to (or even
> withing) varanoids, as most other studies have found?  I suspect the
> latter, but time and more data will hopefully clear this up.

That's funny, I often refer to non-ophidian squamates as "snake food" -
members of a highly polyphyletic assemblage of animals, there.  There is
room for many different usages involving both formal/scientific terms, and
informal/folk terms, either within scientific discourse or outside it.
After all, one of the most useful and beautiful features of English is the
wealth of near-synonyms resulting from the ease of borrowing or coining
words and definitions, which allows us the freedom to convey precisely what
we mean by choosing the right words, and to be scientific and playful at the
same time.  (For example: Call this the Humpty Dumpty property of the
language.)

Personally, I would regard 'lizard' as synonymous for most purposes with the
phrase I used above, i.e. 'non-ophidian squamate', and choose either an
apomorphy-based or stem-based definition of Ophidia such that it includes
all those squamates that share common ancestry with the crown-group
(Serpentes) after last common ancestry with any extant clade of 'lizards'
AND have lost the forelimb and shoulder girdle (as far as presently known
fossils are concerned, these definitions would refer to the same group).
Evidence to date suggests this would render 'dolichosaurs' paraphyletic,
leaving mosasauroids as a monophyletic sister group to dolichosaurs+Ophidia,
together forming the clade Pythonomorpha; this in turn is either within, or
the sister group to Anguimorpha.  The molecular support for 'Toxicofera' by
no means implies that snakes could be closer to Iguania than to Anguimorpha
(I don't refer to morphological support, because presence of venom and venom
glands has been demonstrated in very few iguanians or non-ophidian
anguimorphs), but is shocking because it drags Iguania from the 'bottom' to
near the 'top' of the squamate tree (the pinnacle of which, I frankly admit,
lies within Serpentes).

'Dinosaurs' can obviously include or (at least implicitly) exclude birds at
various times, even within a single sentence (e.g. when explaining to a
child that the fossil evidence shows that birds are descended from
dinosaurs, so they really are living dinosaurs).  But for reasons Scott and
others have repeatedly argued, we'd better agree that if birds really are
descended from (i.e. cladistically nested within) dinosaurs, they are
definitely and for all time members of Dinosauria. 

Cheers,
John
 
-----------------------------------------------
Dr John D. Scanlon
Palaeontologist, 
Riversleigh Fossil Centre, Outback at Isa
19 Marian Street / PO Box 1094
Mount Isa  QLD  4825
AUSTRALIA
Ph:   07 4749 1555
Fax: 07 4743 6296
Email: riversleigh@outbackatisa.com.au
http://tinyurl.com/f2rby


> -----Original Message-----
> From: dinoboygraphics@aol.com [mailto:dinoboygraphics@aol.com]
> Sent: Wednesday, August 23, 2006 1:52 AM
> To: martin.baeker@tu-bs.de; david.marjanovic@gmx.at
> Cc: dinosaur@usc.edu
> Subject: Re: Strange thoughts on PN - was Re: BAD vs. BADD
> 
> Martin Baeker wrote: "Everybody here agrees that group
> A=(Megalos.+Iguanodon) is useful, as is B=(Passer+Archaeopteryx) -
> where () denotes MRCA - despite the fact that these are also quite
> arbitrary - there will be a critter looking *almost* like the first
> member of A that is not a member of it (like Lagosuchus), but still,
> the concepts are useful, albeit arbitrary.
> 
> Why is then A\B (A without-B) such a big no-no? From the frequency we
> hear "non-avian dinosaur", this gouping is *useful* for many purposes,
> except, of course, when discussing phylogeny, so, what is *useful* may
> get a name, at least a vernacular name."
> 
> 
> In my opinion ths would be a disaster, not just for science education,
> but for science research.  Allowing yourself to slip into the "Group B
> took a "significantly different evolutionary direction" from group A"
> mode of thinking (as Jason did explicitly when he said "This is
> confusing and disconcerting because it assumes no real change occured
> between the groups...") is what hindered us so long in understanding
> dinosaur biology.  Because people (including scientists) "knew" that
> dinosaurs were reptiles, while sparrows and Archaeopteryx were "birds",
> we took over a century to start to form a consensus on the avian-style
> respiratory system that saurischians use.  Many are still having a hard
> time grasping that some non-avian theropods had not just dino-fuzz, but
> actual wings.  It prevented (most) researchers from seriously
> considering that non-avian dinosaurs had an elevated metabolism.
> 
> Giving arbitrary non-monophyletic groups names is heuristically
> damaging for the same reason that using Linnean ranks is a
> heuristically poor practice; naming them encourages people to think
> that the name or ranking is "real" in some ontologically valid sense.
> It may be "unwelcome" to some (maybe even most) people to have to use
> terms like "non-avian dinosaurs" or "non-human primate", but using them
> encourages us to be intellectually honest, by reminding ourselves that
> the group is arbitrary, and that we must be careful to ensure that the
> characters under discussion are actually restricted to the group at
> hand, not simply an illusory lumping of characters from animals we
> asssume are "alike" in some way.
> 
> By the way, I *always* refer to snakes as lizards.  They are, after
> all.  The interesting question is" Are they near igaunians, as some
> olecular studies have suggested, or are they closer to (or even
> withing) varanoids, as most other studies have found?  I suspect the
> latter, but time and more data will hopefully clear this up.
> 
> Scott Hartman
> Science Director
> Wyoming Dinosaur Center
> 110 Carter Ranch Rd.
> Thermopolis, WY 82443
> (800) 455-3466 ext. 230
> Cell: (307) 921-8333
> 
> www.skeletaldrawing.com
> 
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