https://science.thewire.in/the-sciences/why-humans-dont-lay-eggs-a-viral-story/ago. Named Juraimaia sinesis i.e., the Jurassic mother from China, the fossil revealed a shrew-like mammal, barely 100 mm in length, that had walked upon the Earth alongside the gigantic dinosaurs of the Jurassic era.
"In 2011, a team of scientists led by the paleontologist Zhe-Xi Luo discovered a well-preserved fossil from North-east China that will push back the timeline of the emergence of a very important group of animals by 35 million years to 160 million years
...nutrition supply, efficient exchange of respiratory gases, and a means for waste disposal in the live-bearing mammal.
It has been argued by diverse groups of researchers that in a harsh Jurassic environment strewn with ferocious predators, Juramaia and its offspring would not have had a fair chance to thrive, if not for the placenta. The placenta allows for continuous
...surprisingly is no!
The obvious question is whether acquiring the placenta is a once-in-a-million-years flash in the evolutionary pan, a genetic prerogative that empowered the ancestral Eutherians to get a head start on ensuring the survival of offspring. The answer
...the wall of the uterus, the outermost layer of this ball extends finger-like projections known as placental villi to invade the uterine tissue. A continuous layer of fused cells known as syncytiotrophoblasts line the outermost border of these finger-like
Soon after fertilisation, the embryo implants into the uterine wall, wherein all its future physiological demands will be met through the placenta that begins forming at about week four post-conception for humans. As the ball-like embryo attaches to
Human endogenous retroviruses (HERVs) can be considered as fossil remains of ancient retroviruses (a family of viruses of which the most well-known representative is the human immunodeficiency virus type 1, which causes AIDS) which had infected ourproto-placental ancestors. After gaining entry inside the host cell, retroviruses typically insert themselves into the host’s DNA, hijack the host’s cellular machinery to make thousands of copies of themselves, and then exit to infect more cells.
...proto-placental ancestor of Juramaia. During infection, this retrovirus infected cells in the germ line (eggs and sperms) and owing to some random mutation lost its ability to multiply or exit thereby becoming an endogenous retrovirus. Through millions
So, how did our placental ancestors gain syncytin-1? Paleovirologists estimate that retroviruses started infecting vertebrates around 450 million years ago. Somewhere between 150 and 200 million years ago, an ancestor of HERV-W2 may have infected a
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