Forwarded Cladistics Nonsense from CIS

[jdharris@csn.net (Jerry D. Harris)]

Hi All! -

        As a sysop in CompuServe's Dinosaur Forum, I occasionally have the
questionable pleasure of reading & responding to some...er, interesting
messages.  Lately, two people have simulataneously popped up in our forum
in a very, very strong anti-cladistic stance -- in fact, I think that they
are against using the fossil record in _any_ form to try and determine
interrelationships between organisms.  I thought that many of _this_
forum's membership would be interested in these two people:

        The initial string began as follows, from a Dr. Ruben Safir, who
can be reached at   75762.2332@compuserve.com

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>>As an outsider looking in, I never understood this arguement that
>>dinosaurs evolve into birds.  Two things bother me about it.  First,
>>there seemed to be mass extiction of large numbers of species.  No
>>dinosaur species seemed to survive.

And seconded - what does evolved mean!

It was my understanding that mammals and birds both evolved from dinosaurs.
They certainly didn't spring from a rock.  They either evolved from
dinosaurs or evolved from reptiles or amphibians directly.  So what's the
issue here.  Birds are not dinosaurs, and neither are mammels.

Dr Safir<<

-----------------------------------------

        My reply, including whatever gross generalities and errors I have
inadvertently included:

-----------------------------------------

>>Dr Safir -

>>As an outsider looking in, I never understood this arguement that
>>dinosaurs evolve into birds.  Two things bother me about it.  First,
>>there seemed to be mass extiction of large numbers of species.  No
>>dinosaur species seemed to survive.<<

        This is a somewhat common error, that dinosaurs mysteriously and
virtually instantaneously evolved into birds just as the dinosaurs were
becoming extinct -- this error stems from the now-common phraseology that
"dinosaurs did not become extinct, because they evolved into birds."  Taken
literally, yes that's what it says, but that isn't the meaning intended by
those words.

        Common consensus is that birds began to evolve sometime in the
latter half of the Jurassic era, between 140-155 million years ago.  The
earliest definitive bird (and the most primitive one known thus far) is
_Archaeopteryx_, found in Germany -- the 7 known skeletons are roughly 145
million years old.  Slightly younger -- and more derived -- birds have been
found in Spain and China.

        All of these birds lived at the same time as the dinosaurs --
remember that dinosaurs did not go extinct until the end of the Cretaceous
era, 65 million years ago.  Lots of birds also went extinct at this
boundary, but some made it through the extinction event, and went on to
rediversify and repopulate the world with feathered creatures!  Exactly why
some birds (and many other animals) made it through the extinction event
while dinosaurs did not is a matter of rather intense study.  There isn't a
good answer yet.

>>And seconded - what does evolved mean!

It was my understanding that mammals and birds both evolved from dinosaurs.
They certainly didn't spring from a rock.  They either evolved from
dinosaurs or evolved from reptiles or amphibians directly.  So what's the
issue here.<<

        Evolved means "underwent the process of evolution."  For birds, we
can look at the earliest bird again, _Archaeopteryx_, to see a good example
of this.  Unlike modern birds, _Archaeopteryx_ has a long bony tail, three
separate fingers with claws, belly ribs, a U-shaped wishbone and either no
sternum or a tiny sternum, and a skull full of teeth.  However, all of
these traits are shared with many dinosaurs, specifically some kinds of
smaller predatory dinosaurs.  However, _Archaeopteryx_ has feathers -- most
of the specimens have good feather impressions; the specimen housed in
Berlin has such detailed fossil feathers, that paleontologists can examine
them in microscopic detail.  No known dinosaur had feathers that we know
of, and feathers are still considered a definitive trait of birds.  Thus,
_Archaeopteryx_ was a bird, despite its otherwise primitive set of
characteristics.

        The aforementioned slightly younger birds from Spain and China,
demonstrate the evolution of birds' next stage:  many retain toothed
skulls, but they also show that the three fingers in the hand have begun to
fuse up (they are entirely fused in modern birds), but they retain claws.
The tail has shortened into the small knob seen in modern birds.  The
sternum has gotten a bit bigger, and the wishbone is Y-shaped, as in modern
forms.  Even younger birds have giant sterna, like modern birds, and by the
Late Cretaceous, we have essentially modern birds slying around (some, even
at this point, retained teeth!)  The evolution of birds, as demonstrated by
the fossil record, is rapdily becoming very clear.

        You are incorrect when you state that mammals are descended from
dinosaurs.  Mammals, actually, evolved at the same time as dinosaurs!  In
fact, the reptiles that gave rise to mammals predate dinosaurs by about 100
million years!  Those animals, called collectively the Synapsida
(synapsids, for short) evolved in the Pennsylvanian era, and were the
dominant terrestrial vertebrates from the Permian (at the end of which they
survived a mass extinction) and through most of the Triassic.  The reptiles
that gave rise to dinosaurs, and then birds, are called the Diapsida
(diapsids).  They, too evolved in the Pennsylvanian, but did not dominate
in the Permian.  Towards the end of the Permian, some diapsids stemmed off
into another group, the Archosauria (archosaurs), which are the forms that
are ancestral to dinosaurs and birds.  For reasons also not well
understood, the archosaurs were able to "take over" the ecological niches
held by the very advanced synapsids in the Triassic, and by the Late
Triassic (230 million years ago), there are true dinosaurs.  However, just
because the archosaurs "overthrew" the synapsids doesn't mean the synapsids
went extinct!  They were still there -- and got quite small.  They, too,
kept evolving.  By the end of the Triassic, we also find the first true
mammals, but the mammals didn't have quite what it took to compete with the
larger archosaurs, and mammals stayed quite small throughout the Mesozoic
era, and didn't get the opportunity to strongly diversify and "take over"
until after the dinosaurs went extinct, 165 million years or so later.

>>Birds are not dinosaurs, and neither are mammels.<<

        Using the classification system of life forms that seems to be
pervading the paleontological sciences called cladistics, birds are indeed
dinosaurs.  Cladistics uses advanced characteristics of  organisms to unite
those organisms into more closely related groups.  I'm not going to go into
the details of cladistics here -- there may be some files on it in our
libraries for this forum -- but suffice to say, strange as it may seem, if
you made a cladogram (a kind of tree of relationships) of all tetrapods
dating back to their origins, you'd see that birds are dinosaurs, and that
both dinosaurs and mammals are essentially reptiles, and that reptiles are
amphibians, and amphibians are fish.  Thus, dinosaurs and mammals are fish!
But, we don't generally consider them such. It's strange, until you get
used to it.  But it does show that, from this perspective (and rapdily
becoming the most common one in paleontology) that birds are dinosaurs.
Not everyone agrees with this, or this system, though.

        I hope this helps!

                                                -- Jerry

<<

-----------------------------------------

        A second, more vehement posting followed, from "Ellen", who can be
reached at
102051.254@compuserve.com

-----------------------------------------

Please

Cladistics will be accepted by the scietific community - as what - a
replacement for the scientific method.  Relating different animals species
together because the share a common wrist bone or pelvis is absurd -
scientifically speaking.  This is all a bunch of guess work based on what
someone beleives might be the facts.  And to frame it any other way is to
mislead someone.  And birds are NOT dinosaurs, nor are they fish.  That is
a scientifically in accurate statement.  Cladistics will never prove any
species was or is related to any over.  About the only thing Mammals and
fish have in common is that their both cordates.  Was else is simular on a
biochemical, or physialogical level.  When I test a new drug in the lab,
I'm careful about the conclussions I draw from a mouse to a human.  Would
you suggest that I test it on a fish before releasing it to the public.

At best this system is similar the the Linnes clasification system of
naming families and species.  And as any microbiologist can tell you, this
classification system is consently changing, day to day.  What was Neiseria
yesterday today is a whole new family.  What changed - the microb or our
understanding of it.

Until we start to make some serious dents in genone mapping, the only thing
you'll convince me of is that your taking an educated guess.  And even the
most educated and expereinced scientist guess wrong.  But if you guess
wrong, what is the criteria for you hypotheses to fail?

Ellen

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        From the strings of subsequent messages, I have gathered that both
Dr. Safir and Ellen are biochemists who believe that genome mapping of
modern animals, and, to a lesser extent, fossil organisms, is the _only_
method of correctly determining organismal interrelationships.  Despite
being pathetic spellers (a trait that makes me respect them as scientists
all the more...  ;-)  ), they have yet to clearly delineate specifically
why they don't perceive cladistics as being a "scientific" technique -- I
get the impression that they only find things in test tubes to be
"scientific."  Anyone who wants can respond to these two...I can also
forward any other of their messages to this server as well, if anyone wants
to see them -- they get more vehement and less coheret with time!  8-)



Jerry D. Harris
Denver Museum of Natural History
2001 Colorado Blvd.
Denver, CO  80205
(303) 370-6403
Internet:  jdharris@teal.csn.net
CompuServe:  73132,3372

--)::)>   '''''''''''''/O\'''''''''''`  Jpq--   =o}\   w---^/^\^o

Overheard in the Denver Museum's
old Fossil Mammal Hall, from a mother
to her daugher:

"See there?  That's the camel-dinosaur, and
the horse-dinosaur, and the elephant-dinosaur..."

--)::)>   '''''''''''''/O\'''''''''''`  Jpq--   =o}\   w---^/^\^o