| Topic: |
Religions > Atheism |
| User: |
"NILS BÖRJESSON" |
| Date: |
15 Jun 2006 01:50:34 PM |
| Object: |
4. Reptiles 1. Amniotic egg |
http://members.iinet.net.au/~sejones/PoE/pe13anml.html#nmlsrptls
4. Reptiles
1. Amniotic egg
Evolution has no adequate explanation for the origin of the amniotic egg.
"There are innumerable examples of complex organs and adaptations which are
not led up to by any
known or even, in some cases, conceivable series of feasible intermediates.
In the case, for example,
of the flight feather of a bird, the amniotic egg, the bacterial flagellum,
the avian lung, no convincing
explanation of how they could have evolved gradually has ever been provided"
(Denton, 1998, p.274).
"Reptiles, birds, and mammals have additional terrestrial adaptations that
distinguish them from
amphibians. One of these is the amniotic egg, a shelled, water-retaining
egg. The amniotic egg functions as
a `self-contained pond' that enables these vertebrates to complete their
life cycles on land. Although most
mammals don't lay eggs, they retain other key features of the amniotic
condition. In recognition of this
important evolutionary breakthrough, reptiles, birds, and mammals are
collectively called amniotes."
(Campbell, Reece & Mitchell, 1999, p.634)
"Some specialized amphibians have virtually cut free from the ties of water
both for everyday life and for
breeding, but they do so with difficulty. The reptiles on the other hand
have made the transition, in a major
evolutionary jump, to an entirely land-based life. Their bodies and eggs are
much more waterproof than
those of amphibians, and the embryo completes its development in the egg -
no reptile goes through a larval
stage. Compared with the amphibians, therefore, reptiles are independent of
the environment and have the
potential to take up ways of life denied to their amphibian forebears. ...
Part of this success is a result of the
evolution of the egg, or more precisely its container, from the simple
jelly-covered amphibian egg. The
reptile egg is called 'cleidoic', meaning 'boxlike', and is the forerunner
of the bird egg, although the details
of its construction vary between groups. .... The most important features of
the reptile egg are the three
membranes surrounding the embryo: the amnion, chorion and allantois. These
act as a life-support system
for the embryo, making it independent of the environment, and are a major
adaptation for terrestrial life.
Reptiles, birds and mammals are called amniotes, to distinguish them from
amphibians and fishes which do
not have these membranes. The embryo of a reptile or a bird survives on dry
land because these membranes
provide a water-filled bath, act as lungs for exchanging oxygen and carbon
dioxide with the atmosphere,
and form a reservoir for waste products." (Burton, 1987, p.34)
"Every textbook of evolution asserts that reptiles evolved from amphibia but
none explains how the major
distinguishing adaptation of the reptiles, the amniotic egg, came about
gradually as a result of a successive
accumulation of small changes. The amniotic egg of the reptile is vastly
more complex and utterly different
to that of an amphibian. There are hardly two eggs in the whole animal
kingdom which differ more
fundamentally. ... some of the main distinguishing features of the amniotic
egg [are] the tough impervious
shell, the two membranes, the amnion which encloses a small sac in which the
embryo floats, and the
allantois in which the waste products formed during the development of the
embryo accumulate, and the
yolk sac containing the food reserve in the form of the protein albumen.
None of these features are found in
the egg of any amphibian. The evolution of the amniotic egg is baffling. It
was this decisive innovation
which permitted for the first time genuinely terrestrial vertebrate life,
freeing it from the necessity of
embryological development in an aquatic environment. Altogether at least
eight quite different innovations
were combined to make the amniotic revolution possible: the formation of a
tough impervious shell; the
formation of the gellatinous egg white (albumen) and the secretion of a
special acid to yield its water; the
excretion of nitrogenous waste in the form of water insoluble uric acid; the
formation of the amniotic cavity
in which the embryo floats (This is surrounded by the amniotic membrane
which is formed by an outgrowth
of mesodermal tissue. Neither the amniotic cavity nor the membrane which
surrounds it has any homologue
in any amphibian; the formation of the allantois from the future floor of
the hind gut as a container for waste
products and later to serve the function of a respirator organ; the
development of a tooth or caruncle which
the developed embryo can utilize to break out of the egg; a quantity of yolk
sufficient for the needs of the
embryo till hatching; changes in the urogenital system of the female
permitting fertilization of the egg
before the hardening of the shell. The problem of the origin of the amniotic
system is even more enigmatic
considering that the basic problem it solves, in freeing reproduction from
dependency on a pool of water,
has been solved in the amphibia by much less radical means, by merely
exploiting the basic amphibian egg.
Some amphibian eggs have a tough gelatinous skin which will stand a certain
degree of desiccation, others
are live bearing. Certain amphibia are therefore quite independent of water
for reproduction. The origin of
the amniotic egg and the amphibian - reptile transition is just another of
the major vertebrate divisions for
which clearly worked out evolutionary schemes have never been provided."
(Denton, 1985, pp.218-219)
"Not that life was easy for the first amphibians. They had gravity to
contend with-a factor several times
greater on dry land than in the buoying water as well as desiccation, the
drying-out action of the air.
Nevertheless they flourished. ... These newcomers to the land, however,
never succeeded in wholly
freeing themselves from the water. Although they learned to rely fully on
their lungs, and to amble
along the swampy riversides on sturdy legs derived from their ancestral
fins, they always returned to the
water to lay soft, jelly-coated eggs. Reproduction tied them to the past,
and to the water. In the fullness
of time, mutation and selection again performed their wonders. Some of the
amphibians developed an
egg which was encased in a firm, leathery shell and was thus far better
protected than the soft eggs of
the fish and the other amphibians. This new and better egg was internally
fertilized and deposited in
some safe place until the young were hatched. With its perfection, the
egg-laying animals won their full
freedom from the water. A well- protected embryo could develop in its own
private pool, the amniotic
cavity of the egg, guarded not only from dryness but also from the hazards
of the land world outside.
The new and freer group which was evolving in this way, from amphibian
ancestry, was the reptiles.
The oldest fossil eggs ever found come from sediments in Texas dated at
about 280 million years ago.
When the eggs were laid the reptiles were already well advanced. (Moore,
1964, pp.113-114)
"THE LAND EGG or reptilian egg, as it is also called has a very special
place in the story of life as it lived
on earth. The land egg is one of nature's greatest innovations. It made
possible the conquest of the land, first
by reptiles and then by birds and mammals. If the land egg had not
developed, the land would have
remained largely empty except for plants, invertebrate life and amphibians.
As we have seen, amphibians
are not strictly land animals; they cannot venture far from water, and most
must return to the water to lay
their soft, jelly-coated eggs. Some time after the first amphibians
developed, evolution took a decisive leap
forward. The first reptiles invaded the land. ... These first reptiles,
which had evolved from the amphibians,
were able to do so because they had acquired an egg that could be laid and
incubated on land. This land or
reptilian egg was much more complicated than the simple amphibian egg. The
water cradled and protected
the amphibian. The developing amphibian got its oxygen and most of its food
from the water, and its waste
matter was discharged into the water. A land egg if it was to be successful
had to provide everything the
water had. Let us look closely at the extraordinary solution-the land or
amniotic egg, as biologists often call
it. ... Enclosed in the calcareous shell is a rich supply of food-the
yolk-which, in a fertilized egg, is
connected to the digestive tract of the embryo. ... Enclosing the developing
embryo is a large sac, the
amnion, which is filled with liquid and protects the embryo from injury and
desiccation. The amnion is thus
the embryo's own private pond. At the back end of the embryo is a tube and a
sac, the allantois, which
functions both as a bladder for waste matter and as a lung. Enclosing the
amnion is a membrane charged
with blood vessels, which takes in oxygen and discharges carbon dioxide
through the porous calcareous
shell which encloses the egg. Another sac contains egg white (albumen).
Enclosing everything inside the
shell is yet another membrane, the chorion. ... The shell is porous in a
special way-it lets gases in and out
but sheds a reasonable amount of water. However, if you submerge a
developing egg in water, its embryo
will surely drown. Thus, with its own food supply (yolk sac), its private
pond (amnion), waste disposal and
lung (allantois) and protective shell, the tiny reptile was freed from its
dependence on water, and the
conquest of the land could be attempted." (Stivens, 1974, pp.168-170)
"As happened many times, life rallied; evolution responded to ecological
challenges by appropriate
adaptions. It even turned disaster into success, driven by the great Permian
crisis to accomplish one of its
most decisive advances. While seed plants took over the cold, dry swamps
left barren by the decimation of
sporulating plants, some obscure amphibian suddenly soared into prominence
by developing the animal
equivalent of the seed: the fluid-filled egg. Instead of delivering
fertilized egg cells for development in some
body of water-the normal amphibian mode-the female of this key transition
species enclosed its fertilized
egg cells in a fluid-filled sac, the amnion, within which the embryo could
pursue its normal aquatic
development. After Claude Bernard's milieu interieur to bathe all cells and
tissues, here was a re-created
milieu exterieur to shelter the developing embryo. A hard, porous shell
protected this substitute marine
incubator, while a highly vascularized membrane, the allantois, produced by
the embryo and lining the inner
face of the shell, served in gas exchanges and waste disposal. Another sac,
filled with a richly nutritious
yolk, provided the embryo with necessary foodstuffs. Thus, the complete
development of the organism up to
a stage where it could survive on land took place within the protective,
well-stocked, and appropriately
renewed environment of the amniotic fluid. True terrestrial reproduction was
initiated. The first reptile was
born." (de Duve, 1995, p.207)
"One of the greatest evolutionary advances-the amniotic egg-occurred among
the deuterostomes. This
type of egg, exemplified by that of a chicken ... first appeared in reptiles
about 255 million
years ago. The amniote egg allowed vertebrates to roam on land, far from
existing ponds. Whereas
amphibians must return to water to breed and to enable their eggs to
develop, the amniote egg carries
its own water and food supplies. The egg is fertilized internally and
contains yolk to nourish the
developing embryo. Moreover, it contains two sacs: the amnion, which
contains the fluid bathing the
embryo, and the allantois, in which waste materials from embryonic
metabolism collect. The entire
structure is encased in a shell that allows the diffusion of oxygen but is
hard enough to protect the
embryo from environmental assaults. A similar development of egg casings
enabled arthropods to be
the first terrestrial invertebrates. Thus, the final crossing of the
boundary between water and land
occurred with the modification of the earliest stage in development, the
egg." (Gilbert, 1994, p.31).
"Here, if this were a textbook, I should have to tell you how the amphibians
gave rise to the reptiles, but I
shall confine my account to a single feature of reptilian innovation, the
egg - or rather, since fishes lay eggs
of a sort, the amniotic egg without which of course we cannot begin to
understand how the birds contrived
to emerge. It is one of the wonders of evolution. ... a minor miracle. ....
Besides being smooth it is rigid
enough to protect its cargo while not being so hard that the chick will be
unable to peck its way out. The
shell also is pervious to gases, so that the chick can breathe ... Suspended
in the middle of the egg is the
yolk, supported by threads. You can rotate the shell of the egg twenty times
without disturbing the yolk: the
threads just wind up. The medium in which the yolk floats, the white or
albumen, is remarkable too. ... I am
speaking of course of the bird's egg as it exists today. The reptilian egg,
as it first emerged, was slightly
different. It contained the large yolk which served to nourish the
developing embryo. It also contained two
sacs, the amnion, filled with liquid and containing the embryo, and the
allantois, which receives the waste
products produced by the embryo while it is in the egg. It was however very
different from the egg of fishes.
From the shell, constructed of crystals of hydroxyapatite and waxed over, to
the altered chemistry, based on
fat rather than protein, the amniote egg was in a different class
altogether, a stunning advance on the simple
blob of jelly that constituted the egg of frogs and fishes - a saltation if
ever there was one." (Taylor, 1983,
pp.62-64).
"A major difference between modern amphibians and the remaining tetrapods is
the occurrence of an
amniotic egg in the latter group. The amniotic (or cleidoic) egg is
sometimes referred to as the `land egg,'
but this is a misnomer. .... Nonetheless, the amniotic egg is a derived
character that distinguishes the two
major groups of tetrapods amniotes and nonamniotes. The amniotic egg, as we
know it, is characteristic of
turtles, squamates, crocodilians, birds, monotremes, and in modified form,
of therian mammals as well. ...
An amniotic egg is a remarkable example of biological engineering (Figure
10-19). The shell, which may be
leathery or calcified, provides mechanical protection while allowing
movement of respiratory gases and
water vapor. The albumin (egg white) gives further protection against
mechanical damage and provides a
reservoir of water and protein. The large yolk is the energy supply for the
developing embryo. .... The
significant differences [from the anamniotic eggs of amphibians and fishes]
lie in three other
extraembryonic membranes the chorion, amnion, and allantois. The chorion and
amnion develop from
outgrowths of the body wall at the ends of the embryo. These two pouches
spread outward and around the
embryo until they meet At their junction, the membranes merge and leave an
outer membrane, the chorion,
which surround the embryo and yolk sac, and an inner membrane the amnion,
which surrounds the embryo
itself The allantoic membrane develops as an outgrowth of the hind gut
posterior to the yolk sac and lie
within the chorion. It is a respiratory organ and a storage place for
nitrogenous wastes produced by the
metabolism of the embryo. The allantois is left behind in the egg when the
embryo emerges, and the
nitrogenous wastes stored in it do not have to be reprocessed." (Pough,
Heiser & McFarland, 1989,
pp.363-365).
"It is easier to understand the stages by which the reptiles evolved
temporal fenestrae and other
distinguishing skeletal characters than to imagine the steps that led to the
development of the `land egg.'
Paleontologists continue to speculate upon the way in which the enclosure of
the embryo came about,
however, because the matter is central to the broad question of reptilian
origins. Study of the eggs laid by
living reptiles has provided little insight into the evolution of the
extraembryonic structures which gave
protoreptiles their first advantage over other tetrapods. Rather than
recapitulating the process of its
evolution, the `land egg' develops in a specialized manner derived, no
doubt, by abbreviation and reordering
of an earlier procedure. ... All the extraembryonic membranes in the `land
egg' of a modern reptile must
complete their formation normally if the embryo is to sustain itself. The
yolk sac is of crucial importance,
because nutritive materials from the yolk mass can enter the body only by
passing through the vessels in its
surface. The allantois also cannot fail: it serves as the respiratory organ
for the embryo, since blood
coursing through it loses carbon dioxide and receives oxygen by diffusion
through the adjacent chorion and
porous shell. In addition, its central cavity stores nitrogenous wastes
produced by the actively metabolizing,
embryonic cells. Blood reentering the embryo from the allantoic vessels
restores to the body water that has
When resorbed from the excreted waste and also adds some that passes into
the egg from the environmental
air. The exterior of the embryo is kept wet by a liquid that accumulates
within the amnion. Unlike pond
water, to which it is often compared, the amniotic fluid does not act as an
oxygen-bearing medium for the
embryo. It is an adaptation for protecting the developing, animal against
shock and for preventing it from
resting against the membranes in the shell and sticking to them. Despite the
difficulty of explaining how the
embryo might have been served while the "land egg" was evolving to its
present state, Szarski has suggested
a series of steps by which the reptilian structure may have arisen." (Stahl,
1985, pp.268-270)
[top]
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| User: "Ph˙ltêr" |
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| Title: Re: 4. Reptiles 1. Amniotic egg |
16 Jun 2006 10:08:56 AM |
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"NILS BÖRJESSON" <borje@ludd.luth.se> had me ROTFL with:
news:_Zhkg.4914$E02.1264@newsb.telia.net:
http://members.iinet.net.au/~sejones/PoE/pe13anml.html#nmlsrptls
4. Reptiles
1. Amniotic egg
Evolution has no adequate explanation for the origin of the amniotic
egg.
Nor does fairy tale belief. ALL of ITS answers are the same, God did it, HOW
scientific...
BTW, don't start using "science" to argue your case for god.
You motherfuckers always come off looking like slack-jawed drooling retards
that overheard something they thought would be cool to say.
--
Ph˙ltêr
Alt.Atheism #1938
Plonked by Fred Stone 17/03/2006
Denizen of Darkness #44 & AFJC Antipodean Attaché
http://www.jesusneverexisted.com
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| User: "Christopher A. Lee" |
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| Title: Re: 4. Reptiles 1. Amniotic egg |
15 Jun 2006 02:00:21 PM |
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On Thu, 15 Jun 2006 18:50:34 GMT, "NILS BÖRJESSON"
<borje@ludd.luth.se> wrote:
http://members.iinet.net.au/~sejones/PoE/pe13anml.html#nmlsrptls
4. Reptiles
1. Amniotic egg
Evolution has no adequate explanation for the origin of the amniotic egg.
What do you imagine that your ignorance and lies about evolution, have
to do with atheism, moron?
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| User: "Ben Kaufman" |
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| Title: Re: 4. Reptiles 1. Amniotic egg |
16 Jun 2006 07:57:20 AM |
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On Thu, 15 Jun 2006 18:50:34 GMT, "NILS BÖRJESSON" <borje@ludd.luth.se> wrote:
http://members.iinet.net.au/~sejones/PoE/pe13anml.html#nmlsrptls
4. Reptiles
1. Amniotic egg
Evolution has no adequate explanation for the origin of the amniotic egg.
<SNIP>
You have an explanation you believe is better? If so, what's your evidence?
Ben
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