Scan detects identifier for gender of stegosaurs

BILLINGS – Evan Saitta, a rising senior at Princeton University who has been digging dinosaur fossils north of Billings for five years, made the history books Thursday.

While scanning a series of 150-million-year-old stegosaur fossils at Billings Clinic, he made a breakthrough step in finding a way to differentiate between male and female stegosaurs.

The elephant-size herbivores have two pairs of defensive tail spikes and two rows of plates that run along their spines. At a dinosaur quarry in the Little Snowy Mountains about two hours north of Billings, Saitta and a number of other researchers have unearthed the remains of four stegosaurs.

In the past, many unearthed stegosaur plates have been wide and oval shaped, said Saitta, a native of Ponte Vedra Beach, Fla.

“And we have found four of these,” he said. “But what’s exciting is that we also found, basically, the exact opposite – we found tall, narrow, almost pointed plates, too.”

Saitta’s idea was that males and females have differently shaped plates. The first step in proving that hypothesis came while he and other researchers and analysts were using a CT scanner at Billings Clinic.

Using the scanner, they were able to see inside the plates and spot canals in the bones that showed the differently shaped plates both came from adult stegosaurs.

“The question is which is female and which is the male,” Saitta said. “But there are some ways to test this, and that’s going to be the next step.”

Female birds and dinosaurs store calcium deposits in their bones before they lay eggs, he explained, so finding these deposits in a stegosaur’s bones could indicate its gender.

“Whether or not we see that is kind of luck of the draw,” Saitta said, because the calcium deposits would only be found if the female stegosaur died shortly before laying eggs.

Scanning the fossils at Billings Clinic ties in with the educational and research aspects of the Billings Clinic Foundation’s mission, said Jim Duncan, president of the organization.

The Little Snowy Creek stegosaur dig is unique for a couple of reasons, Saitta said.

“This site is the furthest north of any late Jurassic dinosaur site,” he said. “It’s older than most dinosaurs you find this far north.”

People have been digging up stegosaur fossils for more than 100 years, but the site north of Billings is the first place where multiple stegosaurs have been found together, he added.

“The thing that’s so unique about this is that it’s in our own backyard,” said Duncan, who recently visited the dig and helped unearth some stegosaur fossils.