| Summary: | Toothed whales (Cetacea: Odontoceti) are the most diverse group of modern cetaceans, originating during the Eocene/Oligocene transition ~38 million years ago. All extant odontocetes echolocate; a single origin for this behavior is supported by a unique facial source for ultrasonic vocalizations and a cochlea adapted for hearing the corresponding echoes. The craniofacial and inner ear morphology of Oligocene odontocetes support a rapid (Simocetus and Olympicetus suggest an ability to generate ultrasonic sound, until now, the bony labyrinths of taxa of this grade have not been investigated. Here, we use µCT to examine a petrosal of a taxon with clear similarities to Olympicetus avitus. Measurements of the bony labyrinth, when added to an extensive dataset of cetartiodactyls, resulted in this specimen sharing a morphospace with stem whales, suggesting a transitional inner ear. This discovery implies that either the lineage leading to this Olympicetus–like taxon lost the ability to hear ultrasonic sound, or adaptations for ultrasonic hearing evolved twice, once in xenorophids and again on the stem of the odontocete crown group. We favor the latter interpretation as it matches a well-documented convergence of craniofacial morphology between xenorophids and extant odontocetes. Tiff stack of CT slices of CCNHM 1000 Zipped tiff stack of leveled CT slices of close-up of the bony labyrinth based on microCT scan of CCNHM-1000 petrosal. Files generated in VGStudioMax 2.2 from original CT data volume. CCNHM1000-imagestack.zip CCNHM–1000 inner ear endocast model Digital endocast of the bony labyrinth (inner ear) of CCNHM-1000; 3D model in STL format. STL generated in VGStudioMax 2.2. CCNHM1000_inner_ear_endocast.stl Part 1 of the NSI Volume data files Zipped section of 3D volume files of original CT data of CCNHM 1000 close-up scan of the inner ear. All files of this series should be extracted and used together. CTdata1-CCNHM1000.zip Part 2 of NSI Volume data files Compressed section of 3D volume files of original CT data ...
|
|---|