Dinosaurs spent an unusually long time inside their eggs - on average, the calves of ancient "horror lizards" were born only 3 or 6 months after fertilization, according to an article published in the journal PNAS.
“One of the oldest and greatest dinosaur mysteries was that we knew nothing about the development of their embryos. Whether their eggs incubated as slowly as the clutches of their closest relatives, crocodiles and lizards, or were they more like their modern descendants, birds whose eggs develop very quickly, said Gregory Erickson of the University of Florida at Tallahassee (USA).
Until recently, scientists knew only a few examples of fossilized dinosaur eggs and fragments of their shells, but in the past 20 years the picture has changed dramatically. Paleontologists have found several "egg graveyards" at once in the north of China and in the Mongolian part of the Gobi Desert, and dozens of eggs of the largest dinosaurs on Earth in Argentina. Thanks to them, we know that some dinosaurs were warm-blooded creatures, hatching eggs in much the same way as modern birds do.
Erickson and his colleagues have uncovered yet another mystery from the early days of these ancient reptiles by studying several highly unusual eggs from Protoceratops andrewsi and Hypacrosaurus stebingeri recently found in Mongolia.
According to the scientist, these eggs contain a very rare and extremely interesting thing - miniature embryonic teeth. These teeth, according to Erickson, can be considered a kind of analogue of the "tree rings" of trees, as they grow in layers, forming one new layer every day. Accordingly, if you cut such a “primary tooth” and count the number of layers, you can find out how long this or that embryo has spent in the womb or in the egg.
With this in mind, Erickson and his colleagues dissected several teeth in ornithischian dinosaur eggs they found. As it turned out, dinosaurs were more like crocodiles in this respect than birds - protoceratops cubs spent an average of about three months in an egg, and hyparhosaurs - about six months.
If the opposite were true, then baby dinosaurs should have hatched in 45-80 days, not three months or six months. On the other hand, dinosaurs nevertheless evolved a little faster than lizards and crocodiles - they were born, according to calculations based on similar "day layers" in the teeth of reptile embryos, 17% faster than them.
Scientists believe that the slow development of the embryo and the need to incubate eggs for a long time could serve as one of the main reasons for the extinction of dinosaurs after the fall of the asteroid on the Yucatan Peninsula 65.5 million years ago. In turn, the ancestors of birds, whose eggs developed many times faster, were able to survive, since they had to spend less time on the nest than their larger and slower relatives, and risk their lives less when raising offspring.
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