Inner-ear structure in Morganucodon, an early Jurassic mammal

Authors

  • ANNA GRAYBEAL,

    1. Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology Laboratories, Harvard University, 26 Oxford St., Cambridge, MA 021138
    Search for more papers by this author
  • JOHN J. ROSOWSKI,

    1. Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA 02114
    Search for more papers by this author
  • DARLENE R. KETTEN,

    1. Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139
    2. Cochlear Implant Research Laboratory, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, 243 Charles St., Boston, MA l02114, U. S. A.
    Search for more papers by this author
  • A. W. CROMPTON

    1. Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology Laboratories, Harvard University, 26 Oxford St., Cambridge, MA 021138
    Search for more papers by this author

Abstract

The shapes and dimensions of the cochlear cavities from four petrosals of the genus Morganucoden obtained through sectioning and reconstruction. Morganucodon dates from the early Jurassic and represents many of the earliest known mammal specimens. Each Morganucodon petrosal fossil was embedded in Araldite and shaved with an ultramicrotome to expose the internal structure. Line drawings of the exposed cross-sections were digitized and used to produce three-dimensional reconstructions. The reconstructed Monganucodon cochlear cavities differ from extant mammalian cochleas in several respects: they are uncoiled, shorter in length, and lack the bony lamina which supports the basilar membrane. These three features ar characteristic of extant Aves and Reptilia.

Ancillary