Oklahoma State University Center for Health Sciences
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OSU-CHS News > 2015

Oct. 8, 2015

Largest dinosaur growth study details life of Montana’s “good mother lizard”


Based on decades of research, a new study provides the most detailed reconstruction of dinosaur life history ever published and recounts the life of Maiasaura peeblesorum, the “good mother lizard,” that lived millions of years ago in Montana.

Holly Woodward Ballard, Ph.D., assistant professor of anatomy at Oklahoma State University Center for Health Sciences, led the research as part of her doctoral thesis in paleontology at Montana State University. She is one of four co-authors of the study recently published in Paleobiology, the quarterly journal of the international Paleontological Society.

 “You can only learn so much from a bone by looking at its shape. But the entire growth history of the animal is recorded within the bone. By looking within the bones, and synthesizing what previous studies revealed, we now know more about the life history of Maiasaura than any other dinosaur,” said Ballard. “Our study makes Maiasaura a model organism to which other dinosaur population biology studies will be compared.”

Other researchers involved in the study are Elizabeth Freedman Fowler, curator of paleontology at the Great Plains Dinosaur Museum and adjunct professor at Montana State University, John Horner, curator of paleontology at the Museum of the Rockies and Regents Professor of Paleontology at Montana State University, and James Farlow, professor emeritus of geology at Purdue University.

The study examines the fossil bone microstructure, or histology, of 50 Maiasaura tibiae to determine information about the growth rate, metabolism, age at death, sexual maturity, skeletal maturity and length of time for a species to reach adult size.

“A sample of 50 might not sound like much, but for dinosaur paleontologists dealing with an often sparse fossil record, the Maiasaura fossils are a treasure trove,” said Ballard. “No other histological study of a single dinosaur species approaches our sample size.”

Researchers discovered that Maiasaura had bird-level growth rates throughout most of its life and that its bone tissue most closely resembled that of modern day warm-blooded large mammals such as elk. Previous studies indicate that Maiasaura were social, nested in colonies and ate rotting wood. While young, the dinosaurs walked on two legs but began to walk on four legs as they grew.

The average mortality rate for Maiasaura under a year of age was 89.9 percent. If they survived their second year of life, they typically enjoyed a six-year window of peak physical and reproductive fitness as the average mortality rate was just 12.7 percent.

“Our study kicks off The Maiasaura Life History Project, which seeks to learn as much as possible about Maiasaura and its environment 76 million years ago by continuing to collect and histologically examine fossils from the bone bed, adding statistical strength to the sample,” she said.

Researchers plan to examine other skeletal elements to make a histological ‘map’ of Maiasaura to determine if different bones in its body grew at different rates.

“This would enable us to study more aspects of its biology and behavior,” she said. “We also want to better understand the environment in which Maiasaura lived, including the life histories of other animals in the ecosystem.”

The Maiasaura Life History Project also will provide opportunities for college students to accompany Ballard during excavations to learn about the fields of ecology, biology and geology and encourage younger generations to pursue careers in science.

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