Sixty-six million years ago, the Antarctic fossil egg showed
The original dinosaur eggs may be soft-shelled
Science and Technology Daily, Beijing, June 17 (Reporter Zhang Mengran) Two paleontological studies published on the 17th by the British magazine Nature provide evidence for the evolution of soft-shell eggs. One of the studies suggested that the eggs produced by the original dinosaurs may be soft-shelled eggs, which is contrary to the general popular opinion that dinosaurs produce hard-shelled eggs; another study describes a large soft shell from Antarctica Egg, this is also the first fossil egg found in Antarctica to date.
Such as birds, some mammals and reptiles, their eggs contain an inner membrane or amniotic membrane, which can help prevent embryos from drying out, so it is also called amniotic animals. Some of them, such as lizards and turtles, produce soft-shell eggs; others, such as birds, produce highly calcified hard-shell eggs. It is this difference that embodies 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 and thus promote the proliferation of the branch And differentiation. But for a long time, soft-shell eggs rarely have fossil records, so it is difficult for scientists to study the transition from soft-shell eggs to hard-shell eggs.
This time, scientists at the American Museum of Natural History studied embryogenic fossil eggs of protoceratops and saury dragons, and found that they were all soft shells. The team believes 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.
In a separate study, a research team from the University of Texas at Austin described a nearly complete football-sized soft-shell egg from Cretaceous sediments in Antarctica about 66 million years ago. This is also one of the largest eggs described to date, second only to the eggs produced by the extinct elephant bird in Madagascar. The egg's size and thin shell (lacking a transparent outer layer) imply that it is viviparous, ie, an "underdeveloped" egg develops in the mother's body and hatches immediately after laying. This egg is classified as a new category-"A. bradyi"; although its mother is still a mystery, researchers believe that it may be produced by a giant marine reptile, such as a dragon.
In the news and opinion articles attached to the paper, scientists from Lund University and Uppsala University in Sweden proposed another explanation: it was produced by a dinosaur, based on the estimated weight of this egg close to birds The weight of the largest egg is known for non-bird dinosaurs, and the latter two types have left fossils in Antarctica.