The California Collection/TheCaliforniaCollection.cdr/his065/arch_2.arj/ARCH-2.TXT

Text File | 1991-02-14 | 6KB | 112 lines

                     Archaeopteryx  part 2

 Let's   say  we  decide  that  the  bone  structure  of   the
Archaeopteryx is definitely reptilian, from which line of reptiles
is it related? Surely, there would be traces of one or the other.

Martin, Stewart, and Whetstone, "The Auk" (Ornithological Journal)
January 1980 page 86 "The Origin of Birds: Structure of the Tarsus
and Teeth"

     "...virtually   every  major  group  of  reptiles  has   been
purported to be closely related, if not ancestral to birds."

     In the report they briefly mention two hypotheses  concerning
Archaeopteryx  and proceed to push their own-  crocodile  ancestry
based on teeth.  The hypotheses are:

     1)  A theory  of their ancestry  from  Triassic  pseudosuchian
         archosaurs.
     2)  A  theory  of direct derivation of  birds  from  theropod
         dinosaurs.
     3)  A close relationship between birds and crocodilians.

     It  should  be noted that in their report  that  altho'  they
concentrated on the Archaeopteryx, the authors clearly related the
teeth of this bird to the teeth of later Mesozoic birds and  spoke
of  them as one in the same.   They were mainly dealing  with  the
origin of teeth in all teeth-bearing birds.

     In  another report that I mentioned a while back in  "Nature"
Sept 8 1983 pp99-100 entitled "No consensus on Archaeopteryx"  The
author  Dr.  Michael Benton (not to be confused with  Dr.  Michael
Denton) concerning the different theories:

     "   The relationships of Archaeopteryx and the origin of  the
birds are controversial.   In a recent review, Thulborn and Hamley
identified   seven   hypothses  concerning   the   affinities   of
Archaeopteryx,  three  of  which  appear  to  have  supporters  at
present."

     Just  prior  to this,  Dr.  Benton discusses the  results  of
Archaeopteryx cranial studies:

     "In  the  new  work that has been done on  the  braincase  of
Archaeopteryx   by  Whetstone,   the  cranium  of   the   'London'
specimen has been removed from its limestone slab and painstakingly
prepared  by mechanical means.

  This has shown that the skull  is much broader
and more bird-like than had been thought.  Details of
the  braincase and associated bones at the back of the skull  seem
to  suggest that Archaeopteryx is not the ancestral bird,  but  an
off-shoot from the early avian stem."  He goes on for the rest  of
the paragraph discussing very briefly how it is primitive in  some
respects and advanced in others.   But basically the Archaeopteryx
has been,  according to him,  relagated from the lofty position of
being  the transition between reptile and modern bird to  that  of
just another "side branch" of evolution.

     So you see,  the reptilian features of the Archaeopteryx  are
so  obscure  and ambiguous that trying to pin down  its  ancestral
relationship is just about impossible.  Forcing  the Archaeopteryx
into  the  role  of  transition has proved to  be  nothing  but  a
fruitless exercise.

     But   let's   say  for  the  sake  of  arguement   that   the
Archaeopteryx's bony structure can be related to reptiles as  well
as birds.   Does this still necessarily force us to conclude  that
it is transitional?

     "Evolution:  Nature and Scripture in Conflict?" by  Dr.  P.T.
Pun copyright 1982

     Archaeopteryx  has been cited frequently as the  transitional
type between reptiles and birds. It has a birdlike skull and wings
with  feathers.   The reptile features are presented  by  clawlike
appendages, the possession of teeth, and the long vertebral column
that extends to the tail.   The flying power of this organism  was
presumably  slight,  for the wingspread is much less than that  of
the poor flyers among modern birds.

     Since most skeletal features of birds can be matched by  some
archosaurian  reptiles,  feathers  have been considered  the  only
distinctive feature of birds.  Feathers are essential to birds for
insulation against loss of body heat,  and this contrasts  greatly
with   reptiles   since   they   are   cold-blooded.    Therefore,
Archaeopteryx  was definitely bird.

   However the  presumed  small sternum, the
primitive reptilian structure of  wing  bones,  and
especially the long tail set Archaeopteryx apart from most  modern
birds,  requiring a separate subclass to represent  it.   However,
some  reptilian  structures  of this fossil  are  shared  by  some
modern-day   birds.    For  example,   the  juvenile   stages   of
Opisthocomus  hoatzin of South America and Touraco cory  thaix  of
Africa possess claws, and both are flyers...

     ...More specifically, L. de Nouy, an evolutionist, commenting
on the status of Archaeopteryx  has made a very succinct statement
concerning the establishment of "true links" between major groups.
While recognizing the morphological similarities of  Archaeopteryx
to reptiles and birds, he nevertheless concluded:

          "By  link,  we  mean  a necessary  stage  of  transition
     between  classes  such  as Reptiles  and  Birds,  or  between
     smaller groups.  An animal displaying characters belonging to
     two  different  groups can not be treated as a true  link  as
     long as the intermediary stages have not been found,  and  as
     long as the mechanism of transition remains unknown."