At the Proctor Lake site in Texas, skeletons of hundreds of young and adult dinosaurs, all of the same species, are found in rocks over 110 million years old. Good skeletons of adult dinosaurs are rare, especially for this geological period, and juveniles are even rarer. Dr. Dale Winkler of Southern Methodist University is excavating and studying this assemblage to gain insight into the changes in behavior, feeding, and locomotion that occurred in these animals during their growth. These bipedal plant eaters (ornithopods) from Texas are small for dinosaurs (about 3-4 meters long), but related kinds found in Texas and many that evolved afterward are much larger. Determining how and why these evolutionary changes took place is important for understanding the relationships between groups of dinosaurs. Recent technical advances allow images of specimens to be entered into a computer by video camera for precise and rapid measurement and for storage and exchange of data. This new method along with statistical techniques will be used to determine if the process of evolving to larger size (over millions of years) follows the same pathway as the growth of an individual during its life. To learn more about dinosaur behavior and life history, computer methods will also be used to help demonstrate subtle differences in shape between male and female skeletons. Knowing the sex of the dinosaur specimens will reveal much about their nesting habits and social structure. Dinosaurs, like other reptiles, probably grew throughout their lives, so there have been many difficulties in recognizing the age of dinosaur specimens (hatchlings, juveniles, adults). Because body shape usually changes during growth, young and adult dinosaurs of the same species may look different and may mistakenly be called different species. Studies of changes in species diversity through time and other evolutionary topics are clouded by this problem. To help solve this dilemma, the excellently preserved Proctor Lake samples will be used to map the shape changes that can be expected during an individual dinosaur's development. Also, changes in internal bone structure that occur during growth can be correlated with the changes in body form. Quantifying both of these changes as a percent of the largest adult size may provide a system for determining the growth rate and age of other dinosaur specimens for which a growth series is not available. The results of this research will provide tools to understand how dinosaurs lived and diversified, ultimately dominating land faunas for over 150 million years.
