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Dinosaur Eggs Developed Slowly Like Reptiles, Not Like Birds

Dinosaur eggs

Dinosaur eggs took a long time to develop, far longer than birds. Jaroslav Moravcik/Shutterstock

It is suggested by the latest evidence that it would take dinosaurs three to six months to develop in the egg, just like modern reptiles rather than birds. The researchers estimate that slow developers were put at the disadvantageous position  when the environment was greatly changed at the end of the Cretaceous period, and this could be the cause of their extinction.

It is quite different between birds and reptiles in regard to egg laying. Generally speaking birds produce fewer eggs in a clutch, in most cases, only one, however make them bigger relative to the size of the parents. Their incubation periods would be between eleven days to eighty-five. As for reptiles, they can lay far more eggs at one time – for example, hatching sea turtles – but their eggs wold be quite smaller. Less obviously, it takes longer time for them to hatch.


A research group headed by Dr Gregory Erickson of Florida State University set out to look at the way dinosaurs were compared, using the fact that teeth contain age lines just as tree rings show. Mankind develop their teeth through a process of layering with daily mineralization, that might be calculated to demonstrate how long their development has been carried on. It could be thought that day-night cycles don’t matter in the egg, but embryonic teeth from crocodiles and their relatives illustrate show the same pattern, termed as incremental lines of von Ebner. With the help of  the incremental lines, Erickson and his team took measurement of the incubation periods for two dinosaur species at their large nesting sites, where scientists have discovered suitable fossils to study.


At average, It took Protoceratops andrewsi 48 days to produce an embryonic tooth. That was reported by Erickson in Proceedings of the National Academy of Sciences. According to the ratios found in related species, Erickson’s team estimated that an incubation time would be least 83 days. As for Hypacrosaurus stebingeri, such time would be 99 and 171 days.

H. stebingeri was a dinosaur in the late Cretaceous period. It grew much larger than any bird, even if on hatching it was 1.7 meters (5.6 feet) long. therefore there is no obvious avian comparisons to make regarding its long incubation time. However, P. andrewsi is quite different. Although it was a late Cretaceous species as well, its size was just like an ostrich.


Compared with or similar-sized avian eggs, P andrewsi’s incubation period was at least two times longer. When the scientists modeled the time, it would take to hatch a bird’s eggs of similar size to those of H. stebinger, they got figures half as long, with crocodiles even shorter.


Erickson’s team was surprised to have such findings, because dinosaurs were thought to be more closely related to birds rather than crocodiles and resemble crocodiles in this way. It is proposed that rapid incubation evolved around the time when toothless dinosaurs came into being . Long incubation times would have been disastrous when food became so dear because of the drastic events that ended the Cretaceous, forcing parents to spend too long time in nesting.


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