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16th June 2023
01:44pm BST
It's a question that has confused people of all ages and backgrounds, prompting a evolutionary debate in the human mind: what came first - the chicken or the egg?
Well, it seems like we may finally have the answer, thanks to a new study carried out by a group of scientists.
Scientists have known for a long time that eggs were being laid by dinosaurs millions of years before chickens had evolved, and this seem to form the basis of the answer to the question - it seemed obvious that eggs came first.
But the new research - conducted by experts from Nanjing University and the University of Bristol, and published in Nature Ecology & Evolution - has suggested that the chicken's earliest reptilian ancestors may have actually given birth to live young.
The egg is seen as one of the most significant evolutionary developments ever, and the long-held theory is that eggs played a big role in the success of amniotes in the animal kingdom. This is the term given to a group of vertebrates that undergo foetal development within the protective membrane in an egg, the amnion.
The new research saw scientists take 51 fossil species and 29 living species, and split them into two categories for examination: oviparous (laying hard or soft shelled eggs) and viviparous (giving birth to live young).
The findings implied that extended embryo retention - when the young are retained by the mother for a varying amount of time - actually gave this particular group of animals more protection that an egg would.
This meant that the chicken's earliest reptilian ancestors were viviparous.
Professor Michael Benton from the University of Bristol's School of Earth Sciences, said: "Before the amniotes, the first tetrapods to evolve limbs from fishy fins were broadly amphibious in habits.
"They had to live in or near water to feed and breed, as in modern amphibians such as frogs and salamanders.
"When the amniotes came on the scene 320 million years ago, they were able to break away from the water by evolving waterproof skin and other ways to control water loss.
"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 the warm climates and enabled the Amniota to move away from the waterside and dominate terrestrial ecosystems."
Project leader Professor Baoyu Jiang added: "This standard view has been challenged.
"Biologists had noticed many lizards and snakes display flexible reproductive strategy across oviparity and viviparity.
"Sometimes, closely related species show both behaviours, and it turns out that live-bearing lizards can flip back to laying eggs much more easily than had been assumed."
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