Using high resolution CT scanning (HRCT), scientists are able to image 3D structures from inside well-preserved fossils. In this example, the cochlea in the inner ear of Phocageneus, a 13-million-year-old shark-toothed dolphin from North Carolina, was imaged. Features such as the number and spacing between the coils of the cochlea that have been associated with ultrasonic hearing in living whales are already present in this 13-million-year-old specimen. By comparing this specimen to the inner ears of fossil dolphins and whales from other times, scientists think that ultrasonic hearing evolved with echolocation in the first toothed whales, and that hearing at higher frequencies began even earlier, in the ancestors of toothed whales.
The fossil dolphin was scanned using HR-CT to produce a three- dimensional model of the inner ear using a computer. The cochlea measures 10.56 mm at its widest point, and is shown in apical view.
Manuel Martinez-Caceres PhD, Jonathan Geisler PhD and Morgan Churchill PhD, Dept. of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY.