Egg Mountain

The panel's second dinosaur has worn two names and may take a third. When Jack Horner and David Weishampel described a clutch of nineteen eggs from this ground in 1988, they credited the embryos inside to Orodromeus makelai, a small plant-eater named for Egg Mountain and Bob Makela. Further preparation exposed an embryo's teeth and changed the answer, and in 1996 the pair published a correction naming it Troodon. A year later an adult was described in contact with a clutch, probably brooding. Troodon is now widely treated as a doubtful name, and these eggs may belong to Stenonychosaurus.

What the plaque says

Egg Mountain In 1978, rock - shop owner Marion Brandvold found a group of small bones that paleontologists Jack Horner and Bob Makela later identified as baby bones belonging to a new species of duck - billed dinosaur. Horner and Makela named this new species Maiasaura peeblesorum, the good mother reptile. The site where the Maiasaura bones were found was named Egg Mountain, and has since yielded the largest cache of dinosaur eggs, embryos, and baby skeletons found in the Western Hemisphere. The site has also yielded one of the largest concentrations of adult dinosaur skeletons found in the world. Paleontologists have interpreted this accumulation as a gigantic herd of Maiasaura that died in a catastrophic event, possibly resulting from a volcanic eruption or a hurricane. Besides Maiasaura, a little meat - eating dinosaur named Troodon also nested at the Egg Mountain site. Its eggs indicate that they were brooded similar to birds, by direct contact of the parent. About 76 million years ago, when Maiasaura and Troodon lived in this area, the Rocky Mountains were just beginning to form to the west, and a shallow ocean existed 300 miles to the east. The dinosaurs nested near lakes and streams on a fern covered coastal plain. Maiasaura is Montana's state fossil.

Where it stands

Worth the stop nearby

• Fort Shaw Indian School — 24 mi
  An Army post turned boarding school, whose Native girls went to the 1904 World's Fair as an exhibit and came home champions.

More markers nearby

• Old Agency on the Teton — 9.5 mi
• Blackfeet and Buffalo — 10 mi
• Augusta and Gilman — 16 mi
• Fort Shaw — 24 mi