MILAN (AP) — A wildlife photographer stumbled upon one of the oldest and largest known collections of dinosaur footprints, dating back about 210 million years to the Triassic Period, high in an Italian national park near the 2026 Milan Cortina Winter Olympic venue of Bormio, officials announced Tuesday.

The discovery in the Stelvio National Park was striking for the sheer number of footprints, estimated at as many as 20,000 over some five kilometers (three miles), and the location near the Swiss border, once a prehistoric coastal area, that has never previously yielded dinosaur tracks, experts said.

“This time reality really surpasses fantasy,’’ said Cristiano Dal Sasso, a paleontologist at Milan’s Natural History Museum, who received the first call from wildlife photographer Elio Della Ferrera after making the discovery.

The dinosaur prints are believed to have been made by long-necked bipedal herbivores that were up to 10 meters (33 feet) long, weighing up to four tons, similar to a Plateosaurus, Dal Sasso said. Some of the tracks were 40 centimeters wide, with visible claws.

The footprints indicated that the dinosaurs traveled in packs and they sometimes stopped in circular formations, possibly as a protective measure.

“There are very obvious traces of individuals that have walked at a slow, calm, quiet rhythmic pace, without running,’’ Dal Sasso told a press conference.

The tracks were discovered by Della Ferrera, who set out to photograph deer and vultures in September when his camera was trained on a vertical wall about 600 meters (nearly 2,000 feet) above the nearest road.

The location, some 2,400 to 2,800 meters (7,900-9,200 feet) above sea level on a north-facing wall that is mostly in the shade, made the footprints, though in plain sight, particularly hard to spot without a very strong lens, Dal Sasso said.

Della Ferra said something strange caught his eye, and he scaled a vertical rock wall with some difficulty to get a closer look.

“The huge surprise was not so much in discovering the footprints, but in discovering such a huge quantity,’’ Della Ferrara said. “There are really tens of thousands of prints up there, more or less well-preserved.’’

The entrance of the park, where the prints were discovered, is located just two kilometers (a mile) from the mountain town of Bormio, where Men’s Alpine skiing will be held during the Feb. 6-22 Games.

Lombardy regional governor, Attilio Fontana, hailed the discovery as a “gift for the Olympics,” even if the site is too remote to access in the winter, and plans for eventual public access have not been made.