Australia: The Land Where Time Began

A biography of the Australian continent 

Cephalopods

Cephalopods of the Soom Shale, South Africa

Orthocone cephalopods

Of the orthocone cephalopods found at the Keurbos Farm site 14 have been described (Gabbott, 1999). The body chamber has been preserved in all specimens, and the fragmocone has been preserved in some of the specimens. The phragmocone is the remainder of the shell containing the gas chambers. Among the specimens found at the site the largest body chamber is 103 mm (4 inches) long, the longest phragmocone is 243 mm (9.5 inches) long and 44 mm (1.7 inches) wide at its widest point, indicating that the largest specimen would have been a bit less than 350 mm (14 inches) long. As the aragonite of all the original fossils has been dissolved they have been preserved as very flattened moulds. There are some features of the orthocones that have been exceptionally well preserved, such as the radulae, the rows of teeth used by the orthocone in feeding that were preserved as external moulds of teeth. The epizoans that were attached to the orthocone shells in life have been previously described. It is rare for the radulae of fossil cephalopods, most known specimens being from Mesozoic ammonites rather than from cephalopods of Palaeozoic age. The only Palaeozoic radulae reported to date are from Mazon Creek, Illinois, of Upper Carboniferous age and deposits from the Silurian of Bolivia. This makes the Soom Slate radulae the oldest known to date for this group.

Among the cephalopods there are 2 known types of teeth, in nautiloids there is a row of 13 elements and in coleoids (squids and cuttlefish) and ammonoids. The nautiloid from Mazon Creek has 13 elements, so is presumed to be a nautiloid, and the orthoceratid from the Silurian of Bolivia, that is believed to have had 7 elements, that suggests the relationship between this orthoceratid and coleoids and ammonoids. In the cephalopod from the Soom Shale there appear to be only 4 visible elements, though it is possibly more elements that were either not preserved or are hidden by the 4 visible elements, the result being that the Soom Shale specimen does not contribute to the understanding of the evolution of the radulae in the cephalopod.

Sources & Further reading

  1. Selden, Paul & Nudds, John, 2004, Evolution of Fossil Ecosystems, Manson Publishing.

Links

  1. The Cephalopoda
  2. Cephalopod Images

 

 
Author: M. H. Monroe
Email:  admin@austhrutime.com
Last updated 12/03/2012

 

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading