#60 - The Famous Egg Mountain Fossil Site near Choteau, Montana

Diagram courtesy of Montana Geologic Road sign program. A revolutionary discovery . . .
There have been some extraordinary dinosaur discoveries in our state over the past several decades, but the discovery that put Montana on the dinosaur map were found near Choteau in 1977 by Marion Brandvold, owner of the Trex Agate Shop (aka "The Rock Shop") in Bynum, Montana. The following year she showed the bones to paleontologist Jack Horner, and the rest is history. Horner and the late Bob Makela dug up the first nest of baby dinosaurs ever found. Over the next several years Horner and his team team discovered was 14 dinosaur nests in a single area of the site, providing the first strong proof that dinosaurs fed and cared for their young and exhibited complex social behaviors.

Good mothers . . .
The size of the shells indicated that the babies were about 12 inches long at birth, but bones of much larger infants were also discovered in some of the nests. This suggests that these dinosaurs cared for their young, unlike modern sea turtles that lay their eggs in the sand and leave the babies to fend for themselves. Furthermore, the teeth of the infants showed signs of wear, suggesting that the adults brought food to the nests. As a result, the newly discovered species (a type of duckbilled dinosaur) was named Maiasaura peeblesorum - Maiasaura is Greek for "good mother lizard", and Peebles honors the families of John and James Peebles, on whose land the finds were made.

Social colonies, nesting grounds . . .
Many of the nests were found at two locations called "Egg Mountain" and "Egg Island". These were small islands when the eggs were laid, yet the dinosaurs kept their nests separated by 23 feet, the approximate length of an adult Maiasaur. This suggests a type of cooperation typical of animals that live in groups. Nests at these two sites were found at three different levels, separated by layers of sandstone. Apparently the islands were nesting grounds that the Maiasaurs returned to year after year.

Term: paleontology

For a more detailed article about Egg Mountain, CLICK HERE.

Below: Illustration of a herd of Maiasaura walking along a creekbed, as found in the semi-arid Two Medicine Formation fossil bed. This region was characterized by volcanic ash layers and conifer, fern and horsetail vegetation. (Wikipedia)