It was believed before that an asteroid collided on the Earth which impact totally extinguished dinosaurs. Or it might be by a volcanic eruption that caused massive climate change and when the sunlight was blocked by dust thrown out they did not adapt the colder climate.

But new discovery suggests that they were the most endangered to be wiped out during that time since their babies took so long to hatch. This would put both babies and their parent easy prey for predators, starvation and flood.

Researchers from Florida State University, Calgary University and the American Museum of Natural History came to the idea when they analyzed rare fossils of dinosaurs' embryos. The embryos' teeth, like three rings of Hypracrosaurus, a large duck-billed dinosaur, helped determine their age, as Washington Post reported.

The belief before that they might similar to birds like ostrich when hatching which took 42 days before the hatchling totally got out from the shell, was superceded by the new discovery.

It was confirmed that dinosaurs' eggs would take twice as long as bird eggs. They were more like as reptiles when hatching egg is considered.

According to Mail Online, the embryo of Protoceratops, a sheep-sized dinosaur and Hypracrosaurus were examined and gave them the idea on how to determine how long each dinosaur had been developing. This study was published in the journal Proceedings of the National Academy of Sciences.

This time as the result shows Hypracrosaurus eggs are totally hatched within 171 days. And that the study suggests that it would be applied to all dinosaurs with teeth.

Such discovery made Mark Norell Macaulay, Curator of Paleontology at the American Museum of Natural History to say: 'With the help of advanced tools like CT scanners and high-resolution microscopy, we're making discoveries that we couldn't have imagined 20 years ago. This work is a great example of how new technology and new ideas can be brought to old problems.'

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