By Azadeh Ansari, CNN: Everyone knows dinosaurs were gigantic, but they grew from tiny embryos just like birds do. What were these extinct reptiles like at this early stage of development?
Scientists have found some new clues that could shed light on this age-old mystery.
In a study published Wednesday in the journal Nature, scientists said they have discovered the oldest known collection of fossilized dinosaur embryos.
"In a way, I think we have set a new standard for dinosaur embryology," said paleontologist Robert Reisz, the lead study author.
Scientists found these dinosaurs grew extremely fast in comparison to present-day living animals and even flexed their muscles while still in the egg.
The bigger the spaces between primary bone cavities, the faster an animal grows. These bone cavities house soft tissue responsible for blood vessel generation.
"In other animals, about 15% to 45% of the embryo bone tissue is made up of these soft tissue cavities; in these dinosaur fossil samples, we found the cavities to make up roughly 60% of the bone tissue," Reisz said.