Maiasaura, Montana's Good Mother Lizard

May 9, 2014

Small, croaking chirps emanated from a tidy pile of mounded vegetation. A huge hulking dinosaur raised its bony skull to investigate and plodded to the mound. With a careful nudge, the dinosaur, a Maiasaura, uncovered her hatchlings with her wide duckbill-like nose. The chirps grew louder and louder as the first hatchling’s brothers and sisters emerged as well. What once were 30 large eggs had become a group of hungry dinosaurs imploring their mother for a meal.

The baby Maiasaura could not walk to find their own food—they were born altricial, meaning that they were not fully developed and could not fend for themselves, much like human babies today. These baby Maiasaura depended on their mothers for everything from protection to food.

This Maiasaura, Latin for “Good Mother Lizard,” knew precisely where to find good food in this area. For years she had been returning to this very spot to lay her eggs. In the late Cretaceous shrub land, the Maiasaura grazed among Troodons and other herbivorous dinosaurs and beneath pterosaurs, weaving her 3-ton, 30-foot-long body through conifer shrubs, collecting food for her new hatchlings. Grazing animals typically bring to mind modern-day cows munching on grass, but in the late Cretaceous era, around 70 million years ago, grass did not exist, and would not evolve for another 10 to 15 million years. The mother Maiasaura filled her mouth with cycads, horsetails, and various conifers, and brought them back to her nest. The little Maiasaura may not have had strong legs yet but they did have strong teeth to munch down wood fibers and other plant material. Because of their mother’s good care and the abundance of nutritious flowering plants on the landscape, the young Maiasaura were able to grow from 1 foot to 10 feet within the first year!

Maiasaura gathered in huge herds, which offered them protection against one of the most feared group of dinosaurs of the era—the iconic Tyrannosaurs. Large herds provided safety in much the same way that herds of bison or caribou do today, and, like caribou, Maiasaura were likely migratory, traveling long distances to forage and returning to the same nesting spot each year to lay their eggs and raise their young.

One large nesting ground was located near Choteau, Montana, in the Willow Creek Anticline of the Two Medicine Formation, a sedimentary rock formation that makes up the broken badlands east of the Rocky Mountain Front. This area has been dubbed “Egg Mountain” for the high concentration of eggs that paleontologists have discovered there. Maiasaura was first discovered by amateur paleontologist Marion Brandvold and then described and studied by paleontologists Jack Horner and Robert Makela in the late 1970s. These researchers found fossilized unhatched embryos as well as a number of intact nests, which led to many discoveries about the behavior and biology of the Maiasaura and other duck-billed dinosaurs. These findings really changed many peoples’ perception of how dinosaurs may have raised young. It turns out, dinosaurs 75 million years ago raised their young in a very similar way to many modern-day birds, their descendents!

Maiasaura lived up until the end of the Cretaceous Era, about 65 million years ago, which was ended with a great asteroid strike in the Yucatan Peninsula in Mexico, an area now called the Chicxulub (chik-shoo-loob) Crater. This great impact and a changing climate were likely responsible for the extinction of about half of the species on the earth at the time, including Maiasaura. Virtually no land-bound dinosaurs existed after the Cretaceous mass extinction and the start of the Tertiary Era.

We owe much of our understanding of dinosaur behavior to Maiasaura. Montana has even chosen it to be the state fossil, and it was the first fossil in space as well, flying on the Spacelab 2 mission in 1985. Maiasaura is also a special dinosaur to me. Not because it has flown in space or the important discoveries that were made from it, but because it is the Good Mother Lizard and I, myself, have a Good Mother Human.

(Broadcast: "Fieldnotes," 5/11/14, 5/12/14, and  5/3/16. You can hear the program on the radio Sundays at 12:55 p.m., Tuesdays at 4:54 p.m., and Fridays at 4:54 p.m., or listen via podcast.)