Maiasaura Fossils Reveal Most Detailed History Of Any Dinosaur Species

Fossils of the Maiasaura peeblesorum, also known as the good mother lizard, have allowed researchers from Oklahoma State University, Montana State University (MSU) and Indiana's Purdue University to create the most detailed life history of any dinosaur ever known. 

"This is one of the most important pieces of paleontology involving MSU in the past 20 years," Jack Horner, curator of the Museum of the Rockies at MSU, said in a news release. "This is a dramatic step forward from studying fossilized creatures as single individuals to understanding their life cycle. We are moving away from the novelty of a single instance to looking at a population of dinosaurs in the same way we look at populations of animals today."

The fossils used in their study were originally excavated from a bone bed in western Montana. The study was led by Holly Woodward, who did the research as her doctoral thesis in paleontology at MSU.

Researchers examined the fossil bone microstructure, or histology, of 50 Maiasaura tibiae, or shinbones. This revealed information regarding growth rate, metabolism, how old the individual was when they died, sexual and skeletal maturity, and how long a species took to reach adult size.

"Histology is the key to understanding the growth dynamics of extinct animals," Woodward said in the release. "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."

This is the largest and most comprehensive histological study of a single dinosaur species, Woodward noted. In their study researcher revealed the Maiasaura had bird-level growth rates throughout most of its life. Also, its bone tissue closely resembled that of modern day warm-blooded large mammals such as elk.

"By studying the clues in the bone histology, and looking at patterns in the death assemblage, we found multiple pieces of evidence all supporting the same timing of sexual and skeletal maturity," Elizabeth Freedman Fowler, curator of paleontology at the Great Plains Dinosaur Museum in Malta and adjunct professor at MSU, said in a statement.

Maiasauras reached sexual maturity within the third year of their life, the researchers noted. Within eight years, the dinosaurs reached an average size of 2.3 tons as an adult and their mortality rate significantly decreased. When the dinosaurs were young they walked on two legs, but as they got older they began to walk on all fours. Researchers also concluded that Maiasaura nested in colonies, where their environment was warm and experienced long dry seasons due to droughts. Therefore, their diets were made up of mostly rotting wood.

"By looking within the bones, and by synthesizing what previous studies revealed, we now know more about the life history of Maiasaura than any other dinosaur and have the sample size to back up our conclusions," Woodward added. "Our study makes Maiasaura a model organism to which other dinosaur population biology studies will be compared."

Their findings were recently published in the journal Paleobiology. 

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