What was the first; the egg or the chicken? Scientists think they’ve finally cracked it!
- A new study has found that the ancestor of the chicken may not have laid eggs
- Scientists have long believed that this practice was crucial in evolution.
- But the team of academic thinkers now believes that the amniotes gave birth to live young.
It’s a question that has racked the brains of everyone from academics to schoolchildren, and now scientists may have provided an answer to this perplexing evolutionary puzzle.
A study has now unleashed a new theory on the chicken-and-egg question after finding that the earliest ancestors of modern birds and reptiles may have given birth to live young.
In evolutionary terms, the distant dinosaur ancestors of the chicken laid eggs millions of years before the first chickens evolved.
This was thought to put an end to the age-old question of whether the chicken or the egg came first.
But did it come before the chicken? A new study suggests it may not be so simple after all.
But a research project has now found that the chicken’s earliest reptilian ancestors, dating back millions of years before dinosaurs evolved, may not have laid eggs as previously thought.
Scientists have long believed that laying eggs with hard shells played a crucial role in the early evolutionary success more than 300 million years ago of amniotes, a group of vertebrates that undergo embryonic or fetal development inside an amnion, a protective membrane inside the egg.
A new study of 51 fossil species and 29 living species that could be classified as either oviparous (laying hard or soft-shelled eggs) or viviparous (giving birth to live young) suggests otherwise.
Experts say that while the hard-shelled egg has often been seen as one of the greatest innovations in evolution, this research implies prolonged embryo retention – when the mother holds the young for a variable length of time, actually gave this particular group of animals maximum protection.
Professor Michael Benton, from the University of Bristol’s School of Earth Sciences, said: “Before amniotes, the earliest tetrapods to develop limbs from fish fins had generally amphibian habits.
“They had to live in or near the water to feed and reproduce, just like modern amphibians like frogs and salamanders.
“When amniotes appeared on the scene 320 million years ago, they were able to separate themselves from water by developing waterproof skin and other ways to control water loss.
New research may have sent the classic textbook egg model to the trash can.
But the amniotic egg was the key.
“It was said to be a ‘private pond’ in which the developing reptile was protected from drying out in hot climates and allowed the amniote to wander away from the water’s edge and dominate terrestrial ecosystems.”
He added: “Our work, and that of many others in recent years, has sent the classic textbook ‘reptile egg’ model to the trash can.”
Project leader Professor Baoyu Jiang added: ‘This standard view has been challenged.
Biologists had noted that many lizards and snakes displayed a flexible reproductive strategy through oviparity and viviparity.
“Sometimes closely related species display both behaviors, and it turns out that living lizards can re-lay eggs much more easily than previously assumed.”
Conducted by researchers from Nanjing University and the University of Bristol, the study is published in Nature Ecology & Evolution.
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