Evolution betwee Vivipary placental
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The platypus (Ornithorhynchus anatinus) is a semiaquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth. It is the sole living representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus), though a number of related species have been found in the fossil record.
The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal
Wiki
The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal
Wiki
Jumping from egg to placenta is a big jump for evolution and there must be some transition . Platypus is usually the answer for hard core evolutionists , But there are not many spots on the earth were you find Platypus , but you see many viviparos and placental animals . I hope my confusing question clears up.
Not really. Even today some humans are born in an "egg" (en caul) that doesn't harm them. We still create yolk sacs for our fetuses, so there are certainly eggs in our past. It would be very easy to imagine an oviparous animal living in a benign environment giving birth to thinner and thinner eggs until the egg started to rupture right at birth. This would require the mother to eat less (less eggshell to form) and thus survive better than the other animals who needed to eat more to give birth. As the egg became thinner and thinner, her oviduct would start to supply more and more blood to the walls so that infants that took longer to make it out of the tube would survive a bit better. (An exchange of oxygen and nutrients would be made possible by the thinner shell.) In time that becomes a uterus.
These lizards are an interesting example of this transition:
Evolution in Action: Lizard Moving From Eggs to Live Birth
Evolution has been caught in the act, according to scientists who are decoding how a species of Australian lizard is abandoning egg-laying in favor of live birth.
Along the warm coastal lowlands of New South Wales (map), the yellow-bellied three-toed skink lays eggs to reproduce. But individuals of the same species living in the state's higher, colder mountains are almost all giving birth to live young.
Only two other modern reptiles—another skink species and a European lizard—use both types of reproduction. (Related: "Virgin Birth Expected at Christmas—By Komodo Dragon.")
Evolutionary records shows that nearly a hundred reptile lineages have independently made the transition from egg-laying to live birth in the past, and today about 20 percent of all living snakes and lizards give birth to live young only.
(See "Oldest Live-Birth Fossil Found; Fish Had Umbilical Cord.")
But modern reptiles that have live young provide only a single snapshot on a long evolutionary time line, said study co-author James Stewart, a biologist at East Tennessee State University. The dual behavior of the yellow-bellied three-toed skink therefore offers scientists a rare opportunity.
"By studying differences among populations that are in different stages of this process, you can begin to put together what looks like the transition from one [birth style] to the other."
Along the warm coastal lowlands of New South Wales (map), the yellow-bellied three-toed skink lays eggs to reproduce. But individuals of the same species living in the state's higher, colder mountains are almost all giving birth to live young.
Only two other modern reptiles—another skink species and a European lizard—use both types of reproduction. (Related: "Virgin Birth Expected at Christmas—By Komodo Dragon.")
Evolutionary records shows that nearly a hundred reptile lineages have independently made the transition from egg-laying to live birth in the past, and today about 20 percent of all living snakes and lizards give birth to live young only.
(See "Oldest Live-Birth Fossil Found; Fish Had Umbilical Cord.")
But modern reptiles that have live young provide only a single snapshot on a long evolutionary time line, said study co-author James Stewart, a biologist at East Tennessee State University. The dual behavior of the yellow-bellied three-toed skink therefore offers scientists a rare opportunity.
"By studying differences among populations that are in different stages of this process, you can begin to put together what looks like the transition from one [birth style] to the other."
Com on guy I know you are good in biology but don't stretch the point . You were incubated for 9 months inside of warm human body , You were not buried in the sand of a beach and then you hatched .
I am asking for explanation how did the transition take place , and if you point to a Platypus then my question how come it is only in the southern part of Australia such evolution have take place and perhaps not in other place but one skeleton in southern Aregentina
An other question rises Genesis 1 God created mammals ( Placenta ) after fish and birds ( viviparos )
I know snails lay eggs, but sometimes they keep the eggs in their body for a time until they can lay them. One can imagine a situation where an animal simply holds on to the eggs longer until they hatch inside them. Then the shells wouldn't be necessary and perhaps a womb would evolve.
Right. And platypus eggs are incubated inside a warm platypus body before they are laid. And seahorses give birth to live young. And sharks, after incubating their babies in their bodies up to two YEARS, give birth live. Does that mean they are more advanced than we are?
1) Thinning of shell due to a benign environment
2) Improvement in oviduct circulation. Oviducts already carry oxygen to eggs; improving this will improve survival of young.
3) Improvement in the allantois, the organ in eggs that absorbs oxygen and removes wastes. Again, improving this will improve survival in young.
4) Beginning of adhesion between the allantois and the oviduct, made possible by better nutrition of the egg. At this point the allantois becomes the placenta and the oviduct becomes the uterus. This happened about 60 million years ago.
Platypuses just split off the mammalian line earlier (around 100 million years ago) and thus never developed a true placenta.
In Genesis 2 God created Man first. BTW "viviparous" means "live birth."
You mention sharks , do sharks have a placenta ? Please be a little more open minded , don't us believers in creation so hard
I do not understand Gen 2 well I feel is like a mans explanation, I don't see the 6000 years well.
Fraggle Rocker
Staff member
No, you misunderstand the point. The vagaries of tectonic movement allowed Australia to remain separated from the other, larger continents. The point is not that marsupials and monotremes only throve there; the point is that placental mammals never evolved there. So the marsupials and monotremes had the place to themselves.
Everywhere else in the world, placental mammals evolved and competed for resources. This is the reason that the other types of mammals simply died off before they had a chance to evolve into a richer variety. The opossums, of which there are about 100 species, are the only primitive mammals that survived outside of Australia. Read up on opossums, and you'll see that they have a few unique characteristics that helped them survive the intense competition with more "modern" mammals in many environments.
As for Argentina, apparently South America was the homeland of the marsupials. Many fossils are found there. It was connected to Antarctica, which for a time was also connected to Australia, so the animals migrated to that continent. That land bridge disappeared before the placental mammals evolved, and this is why they never arose on Australia.
A land bridge eventually formed between North and South America (the Isthmus of Panama), so millions of placental mammals migrated into South America, out-competing the marsupials and driving them to extinction. The only successful ones were the opossums, who migrated north, and eventually to the other continents. Opossums are very common in North America and are found in virtually every part of the United States, from the forests of Oregon to the back yards of Washington DC.
Some have none (they lay eggs.) Some have something called a "yolk placenta", a placenta that is created from the former egg's yolk sack. It is a different structure than a mammalian placenta but serves the same purpose.