China News Agency, Beijing, June 18 (Reporter Sun Zifa) Two new paleontological research papers published in the international academic journal Nature have claimed that scientists have carried out the evolution of the eggs of amniotic animals including birds, mammals and reptiles. Elaboration, research has found conclusive evidence about the evolution of soft-shelled eggs.
Among them, one study believed that the eggs produced by the original dinosaurs may be soft-shelled eggs, which is contrary to the general popular view that dinosaurs produced hard-shelled eggs; another study described a source from Antarctica about 66 million years ago. Large soft-shelled eggs in Cretaceous sediments are also the first fossil eggs found in Antarctica to date.
According to the research paper, the eggs produced by amniotic animals contain an inner membrane or amniotic membrane, which can help prevent the embryos from drying out. Some amniotic animals (such as lizards and turtles) produce soft-shell eggs, while others (such as birds) produce highly calcified hard-shell eggs. This difference shows different evolutionary trajectories, calcified eggs are more resistant to environmental stress, and their evolution is a milestone in the history of amniotic animals because they contribute to the success of reproduction, which in turn promotes the proliferation and differentiation of this branch. However, there are few fossil records for soft-shell eggs, making it difficult to study the transition from soft-shell eggs to hard-shell eggs.
Corresponding author of one of the research papers, Mark Norell of the American Museum of Natural History and others, through the study of embryogenic fossil eggs containing protoceratops and pleurodons, found that they were all soft shells. Researchers believe that calcified hard-shell eggs have evolved independently in dinosaurs at least three times, and may have evolved from a series of primitive soft-shell types. Soft-shell eggs may be buried in moist soil or sand, and then hatched by the heat generated by the decomposition of plant matter, just like some reptiles today.
Julia Clarke and Lucas Legendre of the University of Texas at Austin are co-corresponding authors of another research paper describing a nearly complete football-sized soft shell from Antarctica Eggs, this is one of the largest eggs described to date, and its size is second only to the eggs produced by the extinct elephant bird in Madagascar. The soft shell egg's size and thin shell (lack of a transparent outer layer) suggest that it is viviparous, that is, a "hypoplastic" egg develops in the mother's body and hatches immediately after laying. The soft-shelled egg is classified into a new category. Although its mother is still a mystery, the author of the paper believes that it may be produced by a giant marine reptile like a dragon.
Regarding the study of soft-shell eggs in Antarctica about 66 million years ago, two scholars from Lund University and Uppsala University in Sweden published an opinion article at the same time, and proposed another explanation-it is a kind of dinosaur egg, this hypothesis The basis for the sexual interpretation is that the estimated weight of the soft-shell egg is close to the weight of the largest known egg of birds and non-bird dinosaurs, and the latter two types have left fossils in Antarctica. (Finish)