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 is located about ten miles west of here. Egg Mountain has 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.
Slide toward Today to fade the historical sheet and see the modern map underneath.