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.
Like looking at the rings of a tree to determine events in the tree's life, Erickson and other researchers have determined they are able to inspect the age and information about organisms using the same process.
Just by looking at layers in teeth. Erickson told the Washington Post in 2017: “You can basically just count those up and figure out how long it took dentition to form. Dentition is the arrangement or condition of teeth in a particular species, and it should help determine life cycles.
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.
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.
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.