Even though there are concerns with determining growth rates, some scientists have tried to estimate the numbers. In particular, the growth rates were calculated for species where there is fossil evidence from both eggs and adults, using the maximum growth rate of living reptiles as a guide.

For example, an adult Protoceratops, a ceratopsian of the Cretaceous period in Mongolia, weighed approximately 390 pounds (177 kilograms); the hatchling weighed approximately 0.95 pounds (0.43 kilograms) (it’s assumed the hatchling weight was 90 percent of the egg weight). From this data, the researchers calculated the time the young Protoceratops needed to reach adulthood was approximately 26 to 38 years. On the other end of the size scale was an adult Hypselosaurus, a sauropod of the Cretaceous period in France. This large dinosaur weighed approximately 5.8 tons (5.3 metric tons) at adulthood; the hatchling weighed approximately 5.2 pounds (2.4 kilograms). The scientists calculated the time need to reach adulthood for this animal at 82 to 188 years.