The topic of ‘What came first: chicken or egg?’ is one of the most perplexing evolutionary puzzles. The subject has perplexed everyone from intellectuals to schoolchildren, but scientists appear to have found a solution.
According to The Times, experts from the University of Bristol believe that the ancestors of current birds and reptiles may have given birth to live offspring rather than laying eggs. The discovery was detailed in a paper published in the journal Nature Ecology and Evolution.
Together with Nanjing University academics, scientists dispute the long-held view that hard-shelled eggs were essential to the survival of amniotes – animals whose foetuses develop inside an amnion (membrane or sack) inside the egg.
“The amniotic egg is very different from the anamniotic egg of extant amphibians, which lacks an eggshell and extraembryonic membranes. The amniotic egg consists of a suite of fetal membranes, including the amnion, chorion, and allantois, as well as an external shell that can be either strongly mineralized (as in rigid-shelled eggs) or weakly mineralized (as in parchment-shelled eggs),” the study said.
According to the source, the study looked at 51 fossil species and 29 extant species classified as oviparous, meaning they lay hard or soft-shelled eggs, or viviparous, meaning they give birth to live young.
According to the findings, all Amniota branches, including mammals, show symptoms of maintaining embryos within their bodies for extended periods of time.
While the hard-shelled egg is widely regarded as one of the greatest evolutionary breakthroughs, this study suggests that it was the protracted embryo retention that provided this group of animals with the ultimate protection.
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Professor Michael Benton, from the University of Bristol, said: “Our work, and that of many others in recent years, has consigned the classic ‘reptile egg’ model of the textbooks to the wastebasket. The first amniotes had evolved extended embryo retention rather than a hard-shelled egg to protect the developing embryo for a lesser or greater amount of time inside the mother, so birth could be delayed until environments become favorable.”
“Sometimes, closely related species show both behaviors, and it turns out that live-bearing lizards can flip back to laying eggs much more easily than had been assumed,” Project Leader Professor Baoyu Jiang added.
