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Cephalopod Awareness Days: Finally Some Fossils

October 12, 2012

Greetings Blogophiles! Well, we made it. Today is the last official day of Cephalopod Awareness Days; phew. Fossils! I’m a paleontologist, who actually does research on fossil cephalopods, but I tend to work on the parts of them nobody ever thinks about, such as fossilized squid pens and cuttlebones.  However, as I’ve already mentioned these in previous blogs, today we will focus on ammonites and belemnites. Oh goody!

Photo of Sphenodiscus sp. , an ammonite

Sphenodiscus sp. is an ammonite fossil found in Cretaceous sediments of North Carolina and elsewhere. Photo by Trish Weaver

Belemnites, now here’s a fossil that brings back fond memories for me. Back when I was a young paleontology student, my classmates and I would spend many late night hours in the paleontology lab trying to memorize the Latinized names of tray upon tray of invertebrate fossils. Invariably someone would stick the belemnite in their mouth and pretend to smoke it. Someone else would usually say “hey, don’t Bogart that belemnite!” Yes, paleontologists are often pathetic in their attempts at humor. Belemnites were squid-like organisms with an internal shell called a guard or rostrum. This is the part that is usually preserved and looks an awful lot like a bad cigar.

Photo of two belemnite guards or rostra

The guards of belemnites are an internal shell. These are also found in Cretaceous sediments of North Carolina and elsewhere. Photo by Trish Weaver

Ammonites are extinct cephalopods that have an external shell. Ammonites are usually strongly coiled and look, superficially, very similar to nautiloids. However, if you were to examine them more closely, you might notice that the partitions between the chambers are much more complex. Turns out ammonites are more closely related to coeloid cephalopods (squid, octopus and cuttlefish) than they are to nautiloids.  Ammonites differ from nautiloids in their septa (the dividing walls that separate the chambers), by the nature of their sutures (where the septa join the outer shell wall), and in general by their siphuncles. Bacculites is an ammonoid genus that has a nearly straight external shell and also has very complex suture patterns.

Photo of a pyritized ammonite

Pyritized ammonite from Europe. The original shell material has been replaced by pyrite. Photo by Trish Weaver

Here are the fast facts;

  • Ammonites first appear in the Devonian Period and go extinct at the end of the Cretaceous.
  •  Bacculites appeared in the Cretaceous, were wide-spread then went extinct at the end of the Cretaceous.
  • Ammonites are great index fossils
  • Bacculites males may have been a third to a half the size of the females and may have had much lighter ribbing on the surface of the shell.
  • Bacculites fossils are very brittle. They are most commonly found broken in half or several pieces, usually along suture lines. Individual chambers are sometimes referred to as “stone buffaloes” (due to their shapes).
  • Belemnites first appeared in the Lower Jurassic Period and went extinct by the end of the Cretaceous.
  • In medieval Europe, fossilized ammonites were thought to be petrified coiled snakes, and were called “snakestones” or “serpent-stones.”
  • Belemnites had ten arms, an ink sac, beaks and large eyes.
Photo of Bacculites sp.

Bacculites sp. is a straight shelled ammonite. Notice the almost leaf-like pattern of its sutures.

We have finally come to the end of Cephalopod Awareness Days. I sincerely hope that you enjoyed this series of blogs and if you managed to learn anything along the way that’s even better. Perhaps next time you see a cephalopod, you will be more aware of it. If it is a live one, I can almost guarantee, unless it is sleeping, it is aware of you. Cheers!

Photo of Octopus rubescens swimming forward in algae disguise. ©Roger T. Hanlon used with written permission

As if waving goodbye, Octopus rubescens is swimming forward in algae disguise. Photo: ©Roger T. Hanlon used with written permission.

One Comment leave one →
  1. October 12, 2012 11:55 am

    Reblogged this on NC Museum of Natural Sciences Blogs and commented:

    by Trish Weaver

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