These mollusks appeared in the Late Cambrian and continued until the Early Triassic.
Shell description
The shell resembles a miniature Nautilus, with greatly overlapping, rounded whorls, in which the last whorl completely encompasses the others, leaving either a very narrow umbilicus on either side, or none at all. At the aperture of the shell is a slit, which results in a sort of low ridge that runs along the length of shell. The shell has a low profile and these possibly were active, fast-moving molluscs.
Taxonomy
1960 taxonomy
Knight et al. 1960 in the Treatise on Invertebrate Paleontology[4] consider the Bellerophontidae a very large family made up of a number of subfamilies and tribes.
The 1960 classification places the family Bellerophontidae in the order BellerophontidaUlrich & Scofield, 1897.
Recently, Peter J. Wagner presented cladograms which divide this assemblage into a number of different groups, as well as combining the Bellerophontidae with the family Sinuitidae.[5] while Bouchet & Rocroi (2005)[3] places Sinuitidae as a family in superfamily Bellerophontoidea.
Bouchet & Rocroi, on page 271 (2005),[3] also state that the assignation of "symmetrical univalved mollusks "bellerophonts" either to Gastropoda or to Monoplacophora or Tergomya is controversial." In other words, it is not yet certain whether bellerophonts are in fact real gastropods, they might be monoplacophorans or they might belong to a group (Tergomya) that is closely related to the gastropods, but not actually gastropods.
^McCoy F. 1852. A synonpsis of the classification of the British Palaeozoic rocks, with a systematic description of the British Palaeozoic fossils in the Geological Museum of the University of Cambridge with figures of the new and imperfectly known species. Parker & Son, London, 661 pp., 25 plates. Bellerophontidae is at page 307.
^ abcdeBouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. ISBN3-925919-72-4. ISSN 0076-2997. 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278
^Knight J. B., Cox L. R., Keen A. M., Batten R. L., Yochelson E. L., & Robertson R. 1960. Systematic descriptions [Archaeogastropoda]. In Moore, R. C. (ed.) Treatise on Invertebrate Paleontology. Part I. Mollusca 1, Geological Society of America and Kansas University Press, Colorado and Kansas.
^Wagner P. J. 2001. Gastropod phylogenetics: progress, problems and implications. Journal of Paleontology 75: 1128-1140.
Further reading
Linsley, R. M. 1978. Locomotion rates and shell form in the gastropoda. Malacologia 17, 193-206
Moore, R.C., Lalicker, C.G., and Fischer, A. G., (1952), Invertebrate Fossils, McGraw Hill Book Company, New York; 766 pp.