Scientists Believe They Have Found Evidence That Reptiles Came Before Eggs
On of the more infantile creationist "Gotcha!"s is to ask which came first; the chicken or the egg, in blissful ignorance of the fact that eggs predate chickens by tens of millions of years and hens evolved from egg-laying ancestors, so the real question is, when did eggs evolve as a reproductive strategy in multicellular organisms? But of course, that would give the scientific answer; what creationists want is a superstitious answer - "God made the first chicken and designed it to lay eggs!"
Sadly for creationists, the fossil evidence flatly contradicts that superstition, but, since creationism is a counter-factual superstition, mere evidence is ignored if it isn't what the cult wants its dupes to believe.
Since the evolution of the amniotes, which includes all reptiles, mammals and birds, there have been several instances of the evolution of extended embryo retention (EER), most notably in all the mammals, but also in some reptiles such as lizards and snakes, although not in birds.
And now a combined team of researchers from Bristol University, UK and Nanjing University, China, led by Professor Baoyu Jiang, of the State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing, China, have discovered fossil evidence the a reptilian common ancestor of mammals and bird had evolved EER and had become viviparous.
The earliest reptiles, birds and mammals may have borne live young, researchers from Nanjing University and University of Bristol have revealed.The team have published their finding, open access, in the journal Nature, Ecology & Evolution:
Until now, the hard-shelled egg was thought to be the key to the success of the amniotes - a group of vertebrates that undergo embryonic or foetal development within an amnion, a protective membrane inside the egg.
However, a fresh study of 51 fossil species and 29 living species which could be categorised as oviparous (laying hard or soft-shelled eggs) or viviparous (giving birth to live young) suggests otherwise.
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.
Professor Michael J. Benton, co-author
School of Earth Sciences
Bristol University, Bristol, UK.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 favourable.
Whether the first amniote babies were born in parchment eggs or as live, snapping little insect-eaters is unknown, but this adaptive parental protection gave them the advantage over spawning earlier tetrapods.
Professor Michael J. Benton.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.
Professor Baoyu Jiang, senior author & project leader State Key Laboratory for Mineral Deposits Research
School of Earth Sciences and Engineering and Frontiers Science Center for Critical Earth Material Cycling
Nanjing University, Nanjing, China.
Also, when we look at fossils, we find that many of them were live-bearers, including the Mesozoic marine reptiles like ichthyosaurs and plesiosaurs. Other fossils, including a choristodere from the Cretaceous of China, described here, show the to-and-fro between oviparity and viviparity happened in other groups, not just in lizards.
Dr Armin Elsler, co-author
School of Earth Sciences
Bristol University, Bristol, UK.EER is widespread among vertebrates today, where the developing young are retained by the mother for a lesser or greater span of time. EER is common and variable in lizards and snakes today.
Their young can be released, either inside an egg or as little wrigglers, at different developmental stages, and there appears to be ecological advantages of EER, perhaps allowing the mothers to release their young when temperatures are warm enough and food supplies are rich.
Dr Joseph N. Keating, co-author
State Key Laboratory for Mineral Deposits Research
School of Earth Sciences and Engineering and Frontiers Science Center for Critical Earth Material Cycling
Nanjing University, Nanjing, China
The findings, published today in Nature Ecology & Evolution, show that all the great evolutionary branches of Amniota, namely Mammalia, Lepidosauria (lizards and relatives), and Archosauria (dinosaurs, crocodilians, birds) reveal viviparity and extended embryo retention in their ancestors.
Extended embryo retention (EER) is when the young are retained by the mother for a varying amount of time, likely depending on when conditions are best for survival.
While the hard-shelled egg has often been seen as one of the greatest innovations in evolution, this research implies it was EER that gave this particular group of animals the ultimate protection.
Fig. 2: Structure of the choristodere egg (MES-NJU 57004).
Fig. 3: CT scans of the choristodere skeleton (Ikechosaurus sp.) and its reconstruction.
AbstractThis finding is a problem for creationists for several reasons, and not just because there is no suggestion in their work that the scientists think magic by an invisible, supernatural magician is a better explanation than that provided by the Theory of Evolution. It also gives the lie to the creationist excuse that common design shows a common designer. If there was an intelligent designer at work here, it couldn't make up its mind which was best - eggs or live birth.
The amniotic egg with its complex fetal membranes was a key innovation in vertebrate evolution that enabled the great diversification of reptiles, birds and mammals. It is debated whether these fetal membranes evolved in eggs on land as an adaptation to the terrestrial environment or to control antagonistic fetal–maternal interaction in association with extended embryo retention (EER). Here we report an oviparous choristodere from the Lower Cretaceous period of northeast China. The ossification sequence of the embryo confirms that choristoderes are basal archosauromorphs. The discovery of oviparity in this assumed viviparous extinct clade, together with existing evidence, suggests that EER was the primitive reproductive mode in basal archosauromorphs. Phylogenetic comparative analyses on extant and extinct amniotes suggest that the first amniote displayed EER (including viviparity).
Jiang, B., He, Y., Elsler, A. et al.
Extended embryo retention and viviparity in the first amniotes. Nat Ecol Evol (2023). https://doi.org/10.1038/s41559-023-02074-0
Copyright: © 2023 The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
On the other hand, this is exactly what the TOE predicts because different species would be expected to have different survival and reproductive strategies according to local conditions, and mindless, undirected evolution can only respond to the conditions as they are, not what they will be in the future - which is exactly what we see.
And of course there is the little discrepancy between the age of this fossil evidence and when creationist superstition insists Earth was created.
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