Palaeos Invertebrates: Mollusca: Cephalopoda: Order Belemnitida (original) (raw)

Order Belemnitida Zittel 1885

(="Belemnoidea")

Jurassic to Cretaceous periods

Introduction

Belemnites are prehistoric squid-like cephalopods that flourished in Mesozoic seas. Like squids, belemnites possessed an ink sac and ten arms. Both squids and belemnites belong to the group of molluscs known as Coleoidea, mostly fast-swimming creatures with a soft body and internal reduced shell (or in the case of the octopus no shell at all). Belmnites were among the earlier members of this group, and probably ancestral to modern forms.

In appearance and habits, a live belemnite would have greatly resembled a modern squid. It differed But it differed in that it had a more developed internal shell. This is made up of a hard pointy end, the **rostrum**or guard (see photo below) a chambered part (like a short straight-shelled nautiloid) in the middle, the phragmocone, and a long blade-like extension at the front, the proostracum("fore-shell"). The solid conical rostrum, is the strongest part of the shells are often preserved as fossils. The phragmocone and the proostracum are far more rarely preserved.

Belemnites also possessed hooks rather than suckers on their tentacles. Belemnite hooks are commonly found in the fossilized stomachs of marine reptiles that preyed upon them, such as ichthyosaurs.

Most belemnites were medium-sized creatures, similar in size and shape to a modern-day squid. One large form however, Megateuthis, which is found in the Jurassic of Europe and Asia, had a rostrum measuring 50 to 60 centimeters in length, making the overall shell up to 2 meters, which would give the living animal an estimated length of 3 metres or more (depending on the length of the tentacles).

After flourishing in huge numbers for millions of years, the belemnites were wiped out, along with many other forms of life, during K-T mass-extinction, sixty-five million years ago.

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page uploaded 27 September 2002
checked ATW040726
(originally uploaded on Kheper Site 12 October 1998)
page by M. Alan Kazlev
this material may be freely used for non-commercial purposes