Phylum Mollusca (6)



Early Paleozoic cephalopods were mostly straight-shelled and attained a length of up to 27 feet. Later cephalopods developed a coiled shell. Four major suture patterns developed in cephalopods, reflecting the nature of the interface between the septa and the chamber wall:


1.Nautiloid. This straight suture pattern is exhibited in cephalopods from Paleozoic to recent times.


2.Goniatite. This pattern consists of curved sutures and is found only on Paleozoic cephalopods,


3.Ceratite. This curved and crenulated pattern is found on cephalopods from the late Paleozoic to the early Mesozoic.


4.Ammonite. This highly crenulated pattern is found only on Mesozoic cephalopods. Ammonites became extinct with many other groups of organisms at the end of the Mesozoic.


Belemnites were relatives of the modern squid and possessed cigar-shaped internal calcite supports that are found as fossils in late Mesozoic and early Cenozoic strata.