Darkfield Digital Image Gallery
Goniatitic Cephalopod Fossil
Cephalopods represent a class of mobile predacious carnivore mollusks that possess a bilaterally symmetrical body, a prominent head, and a modified foot composed of tentacles. The digital image featured below was captured from a relatively low magnification view of a polished thin section from a cephalopod fossil having a goniatitic suture morphology.
View a high magnification image of a Goniatitic Cephalopod Fossil.
During the Paleozoic and Mesozoic eras, cephalopods achieved a great deal of diversity and abundance in marine habitats, with more than 10,000 species in the fossil record, but only two genera that possess skeletons are known today. Among the modern marine fauna, over 650 species of cephalopods have been cataloged, including squids, cuttlefishes, octopi, and the chambered nautilus. The class also includes the genus Nautilus, which contains the only living cephalopod that still retains an external shell.
The cephalopod, whose fossilized shell is presented above, is most likely a member of Ammonoidea, a subclass that evolved from nautiloids during the early Devonian period, about 400 million years ago. These creatures were abundant in the oceans and seas around the world for about 375 million years (as evidenced by the fossil record), but then suddenly vanished at the end of the Cretaceous period. The suture structure of the shell has two main features: saddles and lobes that can be utilized to further classify the fossil. Goniatitic sutures contain lobes that are undivided, ceratitic sutures have serrate lobes, and ammonitic sutures have both lobes and saddles that are finely subdivided.
Cynthia D. Kelly, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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