Notorynchus cepedianus is a member of Hexanchiformes (cowsharks), a clade widely considered to be among the more primitive of the living sharks. J. Frank Daniel, in his classic work "The Elasmobranch Fishes", used the anatomy of Notorynchus as the basis of comparison for other sharks and rays. The specimen shown here is in fact one of Daniel's originals from the California Academy of Sciences, and is remarkably well preserved.

The imagery on this page is the basis for a paper entitled Morphology of the braincase in the broadnose sevengill shark Notorynchus (Elasmobranchii, Hexanchiformes), based on CT scanning, by J.G. Maisey. (2004, American Museum Novitates, 3429, 1-52). The abstract is as follows:

A detailed description is presented of the neurocranium in the hexanchiform shark Notorynchus cepedianus, a primitive modern elasmobranch (neoselachian). The study is based on high-resolution CT scanning and digital imaging, which revealed both the external and internal morphology of a wax-impregnated braincase. Besides providing new data concerning Notorynchus and neoselachians generally, the investigation also provides a control for establishing the reliability of morphological observations of fossil elasmobranch braincases based on CT scans. Many of the features described here have considerable phylogenetic potential, although comparative CT scan data are still unavailable for most modern and extinct elasmobranchs.

This specimen, a braincase impregnated with paraffin wax, was brought to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. John Maisey of the American Museum of Natural History. Dr. Maisey wanted to examine the architecture of the endocranial cavity and the skeletal labyrinth (the large space occupied in life by the membranous inner ear). It was important to establish the extent to which the skeletal labyrinth conforms to the inner ear as a control for the study of the skeletal labyrinth in fossil sharks. The braincases of several different extinct elasmobranchs have now been scanned for comparison with Notorynchus

The elasmobranch inner ear is highly specialized toward low-frequency phonoreception, and many derived elasmobranch characters can be recognized in the skeletal labyrinth. One of the most obvious is separation of the posterior semicircular canal; it remains connected to the rest of the labyrinth only by a single opening, and the canal forms an almost complete circuit. This and other modifications of the labyrinth can be recognized in the CT imagery, and the morphology of the skeletal labyrinth and other endocranial spaces can be reconstructed with great accuracy using various image processing techniques.

The specimen was scanned by Richard Ketcham and Matthew Colbert on 12 March 1999 along the coronal axis for a total of 492 512x512 pixel slices. Each slice is 0.25 mm thick, with an interslice spacing of 0.25 mm and a field of reconstruction = 95 mm.

Literature

Cappetta, H. 1987. Chondrichthyes II: Mesozoic and Cenozoic Elasmobranchii; pp. 44-50 in H.-P. Schultze (ed.), Handbook of Paleoichthyology Vol. 3B. Stuttgart, Fischer.

Compagno, L. J. V. 1973. Interrelationships of elasmobranchs; pp. 15-61 in P. H. Greenwod, R. S. Miles, and C. Patterson (eds.), Interrelationships of Fishes. Academic Press, London.

Daniel, J. F. 1934. (first published in 1922) The Elasmobranch Fishes. University of California Press, Berkeley, California.

Maisey, J.G. 2001. Remarks on the inner ear of elasmobranchs and its interpretation from skeletal labyrinth morphology. Journal of Morphology 250:236-264.

Notorynchus cepedianus on FishBase

Notorynchus cepedianus on The Australian Museum Fish Site

Notorynchus cepedianus on the Shark Database of the Shark Foundation (Hai-Stiftung)

Learn more about Hexanchiformes at ReefQuest Expeditions

None available.