>I was wondering if you could explain to me how fish which had gills and no
>lungs could develop lungs loose their gills and still survive. I am not
>debating eye witness accounts of fish climbing out of the water and
>walking on dry land.
In the case of the amphibians, the latest fish in the amphibian/tetrapod
transition had both lungs and gills. The lung is determinable from the bones
by the presence of nostrils and an internal connection through the palate so
that breathing can take place. The gill support bones are also found. The
earliest amphibians have both gills and lungs. Later amphibians lost the
gills. Here is something I am working on. These are the traits of the various
animals in the transition.
Pandericthys--These are lobe-finned fish.
Panderichthys was a rhipidistian,osteolepiform fish. The skull
bones of these fish are bone for bone equivalents to the skull
bones of the earliest tetrapods. (Carroll 1988, p. 160). These
are the only fish whose fin bones fit the tetrapod pattern of
humerus, ulna and radius in the forelimb and femur, tibia and
fibula in the hindlimb.(Thomson, 1991, p. 488), Yet these limbs
still have fins on them (Coates, 1994,p. 174).
Their brain case is so much like that of the earliest tetrapod,
they were originally classified as tetrapods until a complete
skeleton was found. Then is was proven that they were really
still fish. (Ahlbert and Milner, 1994, p. 508). This fish also
had lungs and nostrils (Vorobyeva and Schulze, 1991, p.87) but
also had gills. These things really looked like tetrapods until
you see the fins. The teeth had infolding enamel which is
identical to that of the earliest tetrapods. Unlike all fish but
like the tetrapods, the Panderichthys have lost the dorsal and
anal fins, leaving 4 fins in the place where legs would be in the
Tetrapods.(Ahlberg and Milner, p.508). This contradicts Gish's
claim that there is no fossil which shows loss of fins. (Gish,
1978, p. 78-79). Unlike fish, Panderichthys had a tail, like the
amphibians with the fins stretched out along the top and bottom (Carroll,
1995, p. 389; Carroll, 1996, p. 19).
Panderichthyds and all other osteolepiform fish had a
choana, a hole between the nasal passage and the mouth. This hole
is missing in all other lobe-finned fish. It is what we use to
breathe through our nose. But Panderichtys also had external
nostrils which were in the same position as those of the early
tetrapods. (Schultze, 1991, p. 58)
Ichthyostega-- Is the first animal with feet but they
are different than most tetrapod feet. They are much like
Acanthostega but has 7 digits on his hindlimb. He has lungs. His
legs were only good for being in water. They could not support
his weight. (Coates and Clack, 1990, p. 67) These are half
evolved legs since they have more digits than the normal tetrapod
but fewer bony rays than the fish and they are unable to support
the weight. This contradicts Gish's statement that there are no
half-evolved feet. (Gish, 1978, p. 79) Ichthyostega had external
nasal openings and a choana like that of the Panderichtys
(Schultze, 1990, p. 35). His tail was long with fins above and
below like that of Panderichthys and Acanthostega. (Carroll,
1992, p. 46). His legs were tetrapod having humerus, ulna and
radius in the forelimb and femur, tibia and fibula in the
hindlimb. (see diagram Carroll, 1992, p. 46).
Hynerpeton-more advanced legs and pelvic girdle than
Ichthyostega. (Carroll, 1996, p. 19)
Acanthostega- has four legs, lungs but still has
internal gills. (Coates and Clack , 1991, p. 234) He has 8 digits
on his front leg; seven on his back feet. (Carroll, 1995, p. 389)
His legs could not support his weight either. (Coats and Clack,
1990, p. 66-67). Ahlberg (1991, p. 301) points out that the front
legs were more fish-like than the back legs. He has fishlike
lower arm bones (Coates and Clack 1990, p. 67). Once again,
contrary to Gish (1978, p. 79), these are still half-evolved
legs. He also retains a caudal fin (Coates, 1994, p. 175) and an
elongated tail with fins stretched out along the top and bottom. (Carroll,
1995, p. 389). The stapes, the bone which eventually became part
of the hearing aparatus in tetrapods was still used for
ventilation of the gills (Clack,1989, p. 426).
Note that the loss of gills would be a deleterious mutation since
an animal that can live in both land and sea is more fit. Yet
this did not kill the tetrapods.
references
Ahlberg,P. E. 1991, "Tetrapod or Near-tetrapod fossils from the
Upper Devonian of Scotland," Nature, 354:298-301.
Alberg and Milner, "The origin and Early Diversification of
Tetrapods," Nature April 7, 1994.
Carroll, Robert L. 1988, Vertebrate Paleontology and Evolution,
(New York: Freeman).
Carroll, Robert L.,1992. "The Primary Radiation of Terrestrial
Vertebrates," Annu. Rev. Earth Planet. Sci. 1992: 20: 45-84.
Carroll, Robert, 1995, "Between Fish and Amphibian", Nature, 373,
pp 389-390.
Carroll, Robert L., "Revealing the Patterns of Macroevolution",
Nature, 381, May 2,1996.
Clack, J. A. 1989."Discovery of the Earliest-Known Tetrapod
Stapes," Nature, 342:424-427.
Coates and Clack, "Polydactyly in the earliest Known Tetrapod
limbs," Nature, Sept 6, 1990, p. 66-67
Coates and Clack, "Fish-like Gills and breathing in the earliest
known Tetrapod," Nature, 352, July 18, 1991, p. 234-236
Coates,M.I., 1994. "The Origin of Vertebrate Limbs," Development
1994 Supplement, 169-180, p. 174
Gish, Evolution: the Fossils say No. 1978.
Thomson, Keith Stewart 1991. "Where Did Tetrapods Come From?"
American Scientist, 79(Nov/Dec 1991), p. 488-490, p. 488
Schultze, "Controversial Hypotheses on the Origin of Tetrapods,"
in _Origins of the Higher Groups of Tetrapods_, ed H.P. Schultze
and L. Trueb, 1991, pp 29-67.
Vorobyeva and H.P. Schultze, "Description and Systematics of
Panderichthyid Fishes with comments on Their Relationship to
Tetrapods," in Schultz and Trueb, 1991. Origins of The Higher
Groups of Tetrapods, Comstock Publ. Assoc., p. 68-109
glenn
Foundation,Fall and Flood
http://members.gnn.com/GRMorton/dmd.htm