Erickson came to wonder if dinosaur embryos could be studied using a similar method. He started reaching out, and contacted experts at Canada’s University of Calgary and the American Museum of Natural History in New York.
He wondered if there was a way to test his theory. Despite how rare fossilized dinosaur embryos are, both institutions decided they were able to assist Erickson in his research.
When Erickson was a kid, he would help his father, a wildlife biologist and regional director for the Alaska Department of Fish and Game, catch bears. Yes, you read that right.
His dad taught him to age them using cementum rings in their teeth. He would also catch salmon, and age them from the otoliths – their ear bones. When he entered the paleontology field, Erickson found out that not much work had been done using bone ages.
He set out to introduce his childhood technique to the world of dinosaurs and started determining the age of dinosaur skeletons. Skeletons like the famous Sue, the Tyrannosaurus Rex at the Field Museum of Chicago.
Using growth lines in the skeleton, he found something nobody had thought possible since T-Rex bones grow hollow as they age. Erickson was able to find some bones with intact growth lines – Sue apparently perished at the age of twenty-eight.
At the American Museum of Natural History, researchers found the eggs from the Gobi Desert in Mongolia, which according to experts at the time belonged to the species Protoceratops Andrewsi, which is a close relative of the Triceratops.
The Protoceratops Andrewsi doesn't have the three horns so famous among dino fans but did sport the fan of bone and horn that came off the head like a headdress.
At about seven ounces and close to the shape of a potato, the eggs were relatively small and didn't give Erickson a lot to work with. However, a few other specimens gave him plenty of work to do.
These dino egg fossils had been discovered in the Canadian province of Alberta and belonged to the species of dinosaur known as the Hypacrosaurus Stebingeri, which is sort of like a cross between a T-Rex and a duckbill dinosaur. It was a bipedal herbivore and usually grew to about nine meters in length.