Saturday, October 10, 2009

A is for ammonite

I may have mentioned to some of you that the other day I woke up with a single sentence on my lips: "A is for Anomalocaris", my Cambrian super-predator BFF.  This thought launched a brilliant/horrible idea: A blog series/potential children's book on aquatic creatures from A-Z!  Fabulous!  So, starting today, I present you with A, which is not in fact for anomalocaris, but AMMONITE.

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What's an ammonite?

Ammonites are extinct cephalopods, related to celebrated extant creatures such as octopus, squid, cuttlefish and the relative who they most superficially resemble, the nautilus.  Sadly for us, the ammonite has been extinct for quite a while; they got iced along with the dinosaurs during the Cretaceous–Tertiary extinction event, which happens to be the most recent mass extinction event in the history of Earth.  And when I say "most recent", I am implying that there have been more, because, well, there have been more.

Anyway, despite becoming extinct, ammonites had a pretty sweet run of it.  Let's consult our handy-dandy Chart of Geologic Time:

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I have colored the right vertical section of the chart in tasteful hot pink to show the 435 million year run of the ammonites.  As you can see, dinosaurs of any real sort were only around for roughly half of that. 

Also, if you've ever wondered what period of geologic time we're currently in, we're in the Cenozoic Era, Quaternary Period, Holocene Epoch; it's that very thin sliver of time topping the rest of the history.  Cephalopods have owned the earth for far longer than any of us hairless primates have been trundling around, and it's likely that they will continue to do so after we're gone.

Cryptic quasi-apocalyptic suppositions aside, ammonites, like their descendants, were numerous.  Currently, the worldwide biomass of squid exceeds the worldwide biomass of humans; that is, there is more living squid matter than living human matter.  Bear in mind this is just for squid, this isn't even counting all the other cephalopods

Ammonite fossils are distributed worldwide and make very useful index fossils, special fossils that can be used to date different strata of rock because they are specific to a particular time period.  Given the long reign of the ammonite, in this case specific species of ammonite are used as the rock-clocks.

So what's great about them?

#1) They are named after the Egyptian god Amun/Ammon, who was often depicted with ram's horns.  People thought that ammonite fossils resembled coiled ram's horns, thus they are called ammonites.

#2) They were ridiculously diverse in terms of shape and size.  Along with the traditional nautilus-shell-looking ammonites, there were crazy variations.  This gallery depicts a large variety, and this thread from good ol' TONMO (The Octopus News Magazine Online; if you have more than a passing interest in cephalopods, you need to join this site NOW) has a number of images of the nipponites, the squiggliest of ammonites.

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Illustration based on nipponite fossils

#3) They are the source of ammolite, a rare and lovely gemstone.

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Gem-quality ammolite is found in some ammonite fossils deposited in a region once covered in a shallow inland sea that stretched from  "...Alberta to Saskatchewan in Canada and south to Montana in the USA.", according to Wikipedia other ammolite resources.  It is iridescent like an opal and is the official gemstone of the Canadian province of Alberta.

Personally, ammolite (and opals, natch) is one of my favorite gemstones and there is no shortage of websites out there with examples of their ammolite jewelry.  I think it looks better in fossil format, personally; patterns and colors can be viewed here at the Gem Society's page on ammolite, which provides much more comprehensive mineralogical information than I am providing here. 

BONUS LINK: Here's a Russian site with all sorts of colorful ammonite fossils, including some with pyrite (fool's gold).

#4) They are a natural example of the spira mirabilis.

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The spira mirabilis, the "miraculous spiral", is known by approximately 8 billion different names.  These names include "logarithmic spiral", "equiangular spiral", "growth spiral" and others.  For the specific mathematic properties of this curve, I suggest consulting Wolfram MathWorld's page on the topicThis site is messier, but has interesting examples of the curve in nature.

#5) They range widely in size!

Ammonites can be tiny...

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....or very large.

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And numerous!

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I leave you with a few ammonite links:

-Site about large chalk ammonite fossils viewable at Peacehaven, in the UK.  There are other interesting fossilized creatures there, too.

Beautiful gallery that shows the diversity of ammonite shapes and shells from all over the world/time.  At the bottom, there's a gorgeous iridescent blue shell that's not to be missed.

-This website can direct you if you're interested in purchasing ammonite fossils, or samples of ammolite.  They are not cheap.  More are available here.

-FAQ on Fossil Cephalopods from the venerable Cephalopod Page, presented by Dr. James B. Wood

-Article on nautiloids by Phil Eyden from TONMO.


  1. I feel tingly. What is that?

    I think that's learning.

    From an artistic point of view, the ammolite is fantastically beautiful, and the nipponites border on nightmare fuel in a very good way! There is just enough "doesn't look quite right" to them, like they would fit right in swimming around the slumbering Cthulhu.

  2. An aquatic A-Z is a fantastic idea! Kudos for starting off with ammonites, too. I actually live in Southern Alberta, and once when I was was about 6 we were driving when my Dad (a geologist) pulled the car over and made everybody get out. Lying right beside the road were BILLIONS (slight exaggeration) of ammonite fossils. After that, I learned all about them and pretty much thought they were the coolest thing since sliced bread.

  3. ! I would love to see an ammonite field (and have a geologist dad, for that matter)! I visited the Houston Natural Science Museum the other day and while in the paleontology exhibit my mother kept saying things like "Oh! These were on our farm!" about ammonites other Paleozoic beastie fossils on it. Apparently nobody ever thought to investigate this before, for some reason? I'm going to see if I can't investigate that further and work on trying to angle myself to inherit that land (hopefully distant) future. That sounds horrible, but IT'S FOR SCIENCE!!1

  4. these are lovely, we do not have large amonite collections here in Nigeria like the ones i have seen in the box, if that was true, i would do anythng to get 1m close to it, i love these finding and i'm a collector as i am a geologist. we need to have many of these properly preserved so the generation to come wouldn't hear that they once were there but due to construction which preceded the civilization and urbanization all were lost....sad story, and no,..splendid

  5. i am emmanuel etim okon as i am anonymous, a nigerian softrock geologist, and i love to keep memories alive, thanks

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