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In the collective imaginary, the eggs of dinosaur they are huge, with a hard layer of which as we have shown films, there were dinosaurs. And despite the fact that these images are part of the science fiction, most of the scientific theories supporting this idea. However, a new study published in “Nature” comes to remove those foundations of all we took for granted. What if the first egg of a dinosaur, in fact, was a kind of soft dough? This is the point scientists at the American Museum of Natural History (EE. UU.).
Birds, reptiles and mammals have in common that our first moments of life were protected by an inner membrane , call amnion , which among other things prevented us secáramos in our embryonic stage, in addition to creating a comfortable “cushion” of liquid in which to spend our first moments of life. But this “layer” is different to each other: while the mammals stored in its interior, the other the expelled, in the form of egg . And among these last, there are two types: amniotes with soft shell, such as lizards or turtles ; and those that lay eggs with hard shell, like the bird . These two variations represent two evolutionary paths different.
“The evolution of the eggs calcified -with hard shell-which offer greater protection against environmental stress, represents a milestone in the history of the amniotes , which probably contributed to the reproductive success and, therefore, to the spread and diversification of this clade,” write the researchers, those who point out that that was possibly one of the factors of survival in the extinction of the Cretaceous (66 million years ago), and that the greater part of the ovíparos present present eggs with hard shell. However, the eggs are “soft” exist, while there is a gap in his historical study due to their rarity within the fossil, “which hinders the study of the transition of shells, soft to hard” indicate.
at The beginning were soft
despite the fact that today it is much easier to find species of eggs with hard shells that soft, previous studies show that the first ambiotas and tetrapods laid eggs of the latter type . In fact, some theories indicate that the pterosaurs , from the group “brother” of the dinosaurs and the first vertebrates to conquer the sky, they had this feature. However, the remains of dinosaur eggs found in deposits such as Djadoktha or Tugrugeen Shireh (both in Mongolia) did think that all the young dinosaur were born, breaking a hard shell.
But the researchers of the study suggest that these fossils are not representative of all species. “Up until now, have only been discovered hadrosauridos, some egg-shells of sauropodomorfo and tetanurano; the scarcity of the fossil record and the lack of intermediate types of egg shells defy the efforts to standardise structures of shell in all of the dinosaurs”, they write. That is to say, although there are remains of dinosaur eggs, these are limited to species highly specific it is possible not to represent the whole family.
therefore, Mark Norell , lead author of the study, along with colleagues from the American Museum of Natural History analyzed from different perspectives, eggs, fossil embryos belonging to two species of dinosaur: Protoceratops and Mussaurus . Thanks to different analysis and reconstructions, they could see that their eggs were divided into strata that were closer to soft eggs, as the turtles. “By using a reconstructed ancestral state of composition, and ultrastructure, we compare the shells of eggs of Protoceratops and Mussaurus with the other diápsidos, revealing that the first egg of dinosaur was soft shell”, they write in the study.
in Addition, the research suggests that the eggs hard shell evolved independently at least three times in the dinosaurs, and were probably developed from a variety of ancestral types of soft shell. That is to say, first came the eggs “soft” and, from them, evolved into what today we all know . In terms of its form of incubation, the experts point out that, surely, the eggs were buried in the wet ground or in sand, where it is incubated with the heat from the decaying plant material, as occurs with the reptiles of today.
