reptiles, birds, and mammals have one thing in common: they all belong to the amniotes. The members of this group of animals protect their young by means of an additional, inner membrane, the dry amniotic fluid, before the. The allowed this branch of the animal Kingdom, on Land, regardless of breed. While most amniotes lay eggs, the mammals of this principle and to relocate the Egg as the amniotic SAC in the mother’s womb. Their young are born, therefore, usually live – you slip, is practically in the womb. But also in the case of the egg-laying amniotes legends, there are differences: snakes, lizards, and some turtles lay soft-skinned eggs without a lime peel, from which the young hatch shortly after oviposition. Most of the other reptiles and all birds protect their young by a firm eggshell.

Fossil clutches of two herbivores

the same was true for the dinosaurs – or so they thought-at least so far. “The assumption was always that the original dinosaur eggs had hard shells,” says first author Mark Norell from the American Museum of Natural History in New York. Because most of the fossils found of dinosaur eggs had shell, such a Lime. Thoughtful is the fact that these Eisfossilien were only three dinosaur groups made, however, the predatory theropod dinosaurs, the duck-billed dinosaurs, and the last representatives of the great sauropods, the long-necked plant-eaters. Of many other major groups of dinosaurs, however, Eifossilien almost completely absent. “We have found ides of thousands of skeletons of the Ceratops, but almost none of their eggs. But why her eggs were not preserved?”, so Norell.

In answer to your question, two fossil finds came from the researchers to help. One of them is a Nest of the bird-dinosaur protoceratops basin from the late Cretaceous period discovered in Mongolia. Protoceratops was a roughly two-Meter-long, four-legged running herbivores that protected themselves with a powerful header tank and the neck-shield from attacks. “This Nest comprises a scrim of a minimum of twelve eggs and Embryos, six of which are nearly complete skeletons are preserved,” reports Norell and his Team. Most of these young animals are surrounded by a diffuse staining in the egg shape, and her hunched posture indicates that she died in the Egg. As the researchers analyzed the chemical composition of the ultra-thin, fossilized egg shells, showed that they contain fossil humanized proteins, and phosphates – but no relics of a calcareous shell.

“The first Dino Egg was soft-shelled”

To view Norell and his Team, these results suggest that Protoceratops laid soft-skinned eggs without a solid calcareous shell. Similar to the end of the 1970s, discovered the second Fossil find from the Laguna Colorada Formation in Argentina revealed. This is the 210-million-year-old Remains of eggs, Embryos and young animals, attributed to the dinosaur Mussaurus patagonicus. One of these plant-eaters the lizards-dinosaurs (sauropods), and thus to a change in the dinosaur pool-large group of Protoceratops. Also, the membrane of the egg of this dinosaur was closer analysis as a carbon-containing, organic and free of residues of a solid calcareous shell, as the researchers report. In your view, this suggests that the current dominance of hard-shell eggs at the dinosaurs in their better preservation than with an actually wider dissemination.

On the Basis of the chemical composition and characteristics of egg shells of 112 other living and extinct dinosaurs and relatives of reptiles, the scientists reconstructed as a next step, the possible Evolution of the soft – and hard-shelled eggs. Your result: The distribution of the various Eitypen in the dinosaur family tree suggests that the original Form had no calcareous shell. “We have found that the first dinosaur egg was soft-shelled and the solid, calcified eggshells have evolved three times independently in the three major groups of dinosaurs,” conclude Norell and his Team. This view also explains why the fine structure of the calcareous shell in Ornithopoden, sauropods and theropods differed significantly from each other – it was not homologous but convergent evolution, the researchers said.

source: Mark Norell (American Museum of Natural History, New York) et al., Nature, doi: 10.1038/s41586-020-2412-8

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