The Ear Regions of Archosaurs: The Transition to the Modern Avian and Crocodilian Conditions and Functional Implications for Hearing and Balance in Dinosaurs

Ohio University, Athens OH

Investigators

Abstract

The Ear Regions of Archosaurs: the Transition to the Modern Avian and Crocodilian Conditions and Functional Implications for Hearing and Balance in Dinosaurs Lawrence M. Witmer Ohio University The ear region is a complex area of the head that is concerned with two fundamental functions, hearing and the sense of balance (equilibrium). This project examines the anatomical organization of inner, middle, and outer ears of archosaurs (the group of animals including birds and crocodilians today, and dinosaurs, pterodactyls, and other extinct forms in the Mesozoic Era). The overarching goal is to combine information from animals living today and in the distant past to document the evolutionary changes in the ear that, on the one hand, help us understand how the modern condition arose in ancestors of existing birds and crocodilians, and, on the other hand, provide insight into the behavior, sensory biology, and ecology of fossil groups like dinosaurs. Fossils, however, preserve only hard parts (bones and teeth), and thus a key element of the project is to reconstruct the soft-tissue components of the ear regions of extinct archosaurs, which will then provide a basis for functional interpretation. Hypotheses about the soft tissues in the ear region will be tested in the context of the extant phylogenetic bracket (EPB) approach, whereby the modern relatives (birds, crocodilians, lizards) of the fossil group (dinosaurs) provide information on the relationship between soft tissues and the signatures they leave on the bones. Pertinent soft tissues (inner ear labyrinth, air sinuses, ear drum) will be studied in the modern animals using methods such as dissection, injection, histology, and radiologic imaging to discover the signatures of the soft tissues on bone. Fossil archosaurs will then be surveyed for these specified bony features. CT scanning of literally dozens of pivotal fossil specimens will be a critical tool in that it will not only provide data on features embedded within the skull (inner ear, air sinuses) but also will yield 3D digital datasets from which highly accurate measurements can be made automatically. Some of the specific ear systems studied include (1) the inner ear canals because they are broadly correlated with activity and agility, and their orientation allows reconstruction of preferred head postures; (2) the cochlear duct of the inner ear because it has bearing on broad categories of hearing performance; and (3) the middle and outer ear, including the ear drum, air sinuses, and sound conducting apparatus because they relate to acoustic properties of the ear, and ultimately hearing. This study will impact a number of areas. Numerous undergraduate and graduate students will receive technical and analytical training. The project is highly collaborative, involving many paleontologists and experimentalists worldwide. The extensive radiologic imaging will require development of refined imaging protocols, standardized analyses, specialized workstations, and bioinformatics innovations to deal with the voluminous multi-format digital data. Internet-based means of not only disseminating the data but also manipulating the data will be essential, and will take place in connection with existing bioinformatics hubs. Given the continual K-12 interest in all things dinosaurian, the attention this project will attract will provide new opportunities to use dinosaurs as tools to teach about science in general, with expected venues being media outlets, school or other public appearances, and the internet.