<<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.>>
That's the $64,000 question!
To buy the evolution story, you have to believe:
"The evolution of air-breathing organs occurred several times [!!] within
different lines of bony fishes. These organs include vascularized swim
bladders, parts of the digestive tract, specialized compartments to the gill
chamber, and in dipnoans, lungs." [Kardong, Vertebrates, pg. 435]
This is hard to, er, swallow, so the official story is that lungs were
"pre-adaptive." That is, they did not evolve in anticipation of life on land,
but as supplements to gills when oxygen in water became inadequate. Then, when
the little fellas were ready to go onto dry land looking for worms, voila!
They had lungs all ready for them!
Convenient, eh?
And remember, it is not just the lungs. It is a host of adaptive changes that
have to be accounted for:
"The major problems with life on land relate to weight and structural support
as much as to the physiology of breathing air. A fish is buoyed up by the
water and its body weight may be effectively zero. On land, however, the body
as to be held up by some form of limbs, and the skeleton as all the internal
organs have to become structurally modified in order to cope with the new
downward pull of gravity. The backbone of a fish is adapted for the stresses
of lateral stretching and bending during swimming, but the main forces to
which a tetrapod is subject are caused by gravity. The vertebrae and the
muscles around the backbone have to become modified to prevent the body from
sagging between the limbs. The mode of locomotion of a tetrapod on land is
generally different from that of a fish in water." [Benton, Vertebrate
Palaeontology, Chapman & Hall 1990, pp. 46-47]
Once again, a whole host of changes had to occur simultaneously. Like a
protective pectoral girdle and new skin. And bone! This is a real corker:
"It is obvious that the creation of bone required not one but a whole burst of
mutations, all integrated to a single end--an incredible thing to happen by
chance even if nothing else had been going on." [Taylor, The Great Evolution
Mystery, pg. 56]
So in answer to your question, Randy, no one can explain it.
Jim