Studying bipedal dinosaur trackways using geometric morphometrics

Abstract

Traditionally, the study of dinosaur tracks and trackways has been helpful to learn about the anatomy of the trackmaker and its biodynamics. The implementation of digital techniques has further allowed delving into elusive evidence, such as the nature of autopod-substrate interaction and to build virtual collections. However, new methods that help to discriminate more objectively traits that lurk undetected within the tracks and the trackways are needed. Geometric Morphometrics (GM) is one of such advanced tools for shape analysis, but it has only been used for the comparison and ichnotaxonomic assessment of isolated footprints, and never for the study of dinosaur trackways. Using 2D GM, we analysed the differences between 75 randomly selected trackways of bipedal dinosaurs from literature, and tested if their variation was associated to the sizes of the trackways and to the estimated speeds at which the latter moved when leaving the trackways. Our results show that the method easily summarizes most of the trackway geometric differences, showing that such variation relates to footprint relative sizes, their orientation and their relative positions within the trackway. Importantly, the multivariate statistics indicated that none such differences could be attributed to ichnotaxa, while they clearly correlated with size, and in a much larger degree, to the estimated speeds at which the trackways were laid. Moreover, size and speed are unrelated, entailing that much of the trackway differences involve the biodynamics of bipedal dinosaurs, irrespective of their trackmaker assignment, plus substrate dynamics. Mireia Costa-Pérez. Departamento de Botánica y Geología, Facultad de Ciencias Biológicas. Universidad de Valencia, Spain. [email protected] José Joaquín Moratalla. Instituto Geológico y Minero de España (IGME), Museo Geominero. Ríos Rosas, 23. 28003, Spain. [email protected] Jesús Marugán-Lobón. Unidad de Paleontología, Dpto. Biología, Facultad de Ciencias. Universidad Autónoma de Madrid, Spain and Centre for the Integration in Paleobiology (CIPb), Universidad Autónoma de Madrid, Spain and Dinosaur Institute, Natural History Museum of Los Angeles County. Los Angeles, CA, USA. Corresponding author. [email protected] COSTA-PÉREZ, MORATALLA, & MARUGÁN-LOBÓN: DINOSAUR TRACKWAYS AND GM 2