No wonder the dinosaurs died out: They were vulnerable for the SIX MONTHS it took them to get out of their eggs when they were born
Scientists have discovered a new clue as to why dinosaurs died out, after finding their eggs took up to six months to hatch.
It might have been an asteroid or volcano behind the massive climate change which ultimately wiped out the beasts, but new evidence shows why they were so at risk in the first place.
When the dust thrown up from such an event blocked out sunlight, dinosaurs are believed to have failed to adapt to a colder climate and the fewer plants available to eat.
However the latest findings suggest baby dinosaurs also took so long to hatch that they and their parents were extra vulnerable to predators, starvation and floods.
Dr Gregory Erickson (pictured) is professor of biological science at Florida State University
It could be the reason why, unlike more fast-breeding birds and mammals, the dinosaurs did not survive the mass extinction event of 65 million years ago and do not walk among us now.
The first insight into hatching baby dinosaurs was led by Florida State University, Calgary University and the American Museum of Natural History, whose researchers analysed rare fossils of dinosaurs embryos.
As birds are 'living dinosaurs', it was thought dinosaur eggs probably took about the same time to develop as an ostrich hatchling, which emerges from its egg after 42 days.
Instead, analysis of a large duck-billed dinosaur called the Hypracrosaurus found their babies took nearly as long as humans' to be born. This was worked out using growth lines in the embryos' teeth, like tree rings, used to determine their age.
Dr Gregory Erickson, professor of biological science at Florida State University, said: 'Some of the greatest riddles about dinosaurs pertain to their embryology – virtually nothing is known.'
He added: 'We suspect our findings have implications for understanding why dinosaurs went extinct at the end of the Cretaceous period, whereas amphibians, birds, mammals and other reptiles made it through and prospered.'
The scientists found that dinosaur eggs take around twice as long to hatch as bird eggs, whose chicks emerge after between 11 and 85 days. Despite birds having evolved from the dinosaurs, the prehistoric animals' eggs are more like those of reptiles.
The study, published in the journal Proceedings of the National Academy of Sciences, examined the embryo of Protoceratops, a sheep-sized dinosaur found in the Mongolian Gobi desert whose eggs weighed nearly seven ounces (194 grams).
It also looked at Hypracrosaurus, a very large duck-billed dinosaur discovered in Alberta, Canada, with giant eggs weighing almost nine pounds (more than 4kg).
For the first time, they found in the teeth of the dinosaur embryos 'von Ebner' lines, which are growth lines found in the teeth of all animals, including humans. Professor Erickson said: 'They're kind of like tree rings, but they're put down daily. We could literally count them to see how long each dinosaur had been developing.'
Analysis of a large duck-billed dinosaur called the Hypracrosaurus found their babies took nearly as long as humans' to be born
It was thought the smaller dinosaurs' eggs, based on those hatched by birds, would take 40 days, but the research suggests an incubation period of 83 days – almost three months. The Hypracrosaurs eggs are believed to have taken almost six months, or 171 days.
It is believed the results would apply to all dinosaurs with teeth, ranging from the Tyrannosaurus rex to the stegosaurus. It may also hold the key to why they are not around any more.
Eggs which took so long to hatch would have been more vulnerable to being eaten by smaller dinosaurs, while parents could risk starvation protecting them.
The mass extinction event which led to the death of the dinosaurs is hotly debated, with theories including a massive volcanic eruption and an asteroid hitting the Earth. Either one of these is believed to have thrown up enough dust to block out the sun's rays, massively changing the climate from a warm, mild one to a cooler, more varied one.
It is the dinosaurs' inability to adapt in a world full of scarce resources which may have seen them driven to extinction. The plants they relied on may have been reduced by the lack of sunlight, killing off the smaller dinosaurs and then the larger carnivores which ate them.