Fossil Friday #4 – Ammolite: Alberta’s Fossil Gemstone

Polished ammolite.  Photo credit: http://www.gemselect.com/other-info/rare-ammolite.php

If you think diamonds are the most beautiful of the gemstones, you have clearly never seen ammolite.  Ammolite is an iridescent, opal-like gem that comes in an amazing range of vibrant colours that cover the complete visible spectrum.  The only fossil that can be commercially mined and sold in Canada, ammolite is made from the shells of an octopod-like creature called an ammonite.

An ammonite shell made of ammolite.  Photo credit: http://www.canadianammolite.com/AmmoliteFacts.html

Ammonites are a type of cephalopod, the group that includes the smartest and largest of the invertebrates, such as octopods, squid, and cuttlefish.  While most cephalopods today have no external hard parts, for much of the Paleozoic and Mesozoic, shelled cephalopods were common, and could often reach sizes comparable, or greater than that of today’s giant squid.  Like modern cephalopods, ammonites were voracious predators, although they were often the prey of large marine reptiles, such as mosasaurs.  Along with ammolite, in Alberta, we often find ammonites that have teeth marks in their shells from marine vertebrate predators.

An ammonite with teeth marks from the Royal Tyrrell Museum.  Photo credit: https://www.flickr.com/photos/tyrrellmuseum/6883571350

Ammonites went extinct at the end of the Cretaceous, along with their predators, the large marine reptiles, and the dinosaurs.  Today, there are only two small genera of shelled cephalopods left in the oceans, including a delightful little creature called Nautilus.

Nautilus. Photo credit: http://www/zoo-rostock.de/de/tiere+park/unsere_tiere?tierwelten/darwineum/nautilus

Not all ammonites produce ammolitic shells, at least, not in a commercially productive sense.  Ammolite is mostly produced by a specific genus of ammonite, Placenticeras, from the Bearpaw Formation (Late Cretaceous) of Alberta and Saskatchewan.  The world’s only ammolite mine is near the city of Lethbridge in southern Alberta.  Most ammolite is mined in pieces, which are made into jewelry, but if an intact specimen is uncovered, it will likely be sold as is.  There is one absolutely stunning specimen on display at the Royal Tyrrell Museum in Drumheller.  Ammolite is a great reminder that Alberta has more to offer palaeontologists and fossil enthusiasts than just dinosaurs.

Ammolite specimen at the Royal Tyrrell Museum.  Photo credit: https://www.tonmo.com/threads/royal-tyrell-ammolite-ammonite.15768/

For more information about ammolite, please check out the following article by Mychaluk et al. (2001): http://freeshipping.www.canadianammolite.com/SP01.pdf#page=5

Any questions or comments?  Suggestions for future Fossil Friday posts?  Let me know by leaving me a comment, or visiting my contact page!

Fossil Friday #3 – Encrusters!

Today’s Fossil Friday is a sneak peak into the little world of encrusters.  Encrusters, known in the scientific community as epibionts, or sclerobionts, are organisms which attach and live on other organisms.  In modern oceans, the most obvious example of encrusters, or epibionts, are barnacles (see picture below).  Encrusters need a hard surface on which to live, and so other organisms often make great substrates.  The organism acting as the substrate for the encruster is called the host.

EncrustedScallop3
Encrusting organisms on a scallop host

Encrustation is a great way to study biotic interactions.  We often think of encrusters as fowling organisms (things that clog up pipes or ruin the sides of ships), and it is true that they can be very detrimental (parasitic) to hosts.  For example, if your mouth parts become clogged or permanently closed from an encruster, you are likely in big-time trouble.  Sometimes the weight and loss of streamlined shape from lots of encrusters can also seriously harm a host.  As a potential solution, some organisms can prevent encrustation by having soft surfaces or a mucus lining to prevent encruster attachment.

A very unhappy host (sea turtle).  Image credit: islandeyenews.com/wp-content/uploads/2015/09/DSC_0200-copy.jpg

However, some hosts, like decorator crabs, actively attract epibionts as a means of camouflage.  Hosts might not be visible to predators if covered in encrusters, and hosts might not even smell like anything tasty to their predators.  A camouflage benefit to the host can lead to strong mutualisms, or even co-evolution of epibionts and hosts.

A very happy host.  Can you see the decorator crab? No? That’s what it wants.  Image credit: hbdivegirl.com/wp-content/uploads/2010/10/Decorator-Crab.jpg

Fossil encrusters (sclerobionts) and their hosts can be used to study how close biotic interactions develop over time.  For example, a lot of the work done in our lab looks for associations between encrusters and hosts that coincide with a decrease in predation rates.  If we are able to find that an increase in encrusters = a decrease in predation, that is pretty good evidence that the encrusters are acting as camouflage for the hosts.  However, I have also seen cases where the encruster clearly killed the host because it encrusted over its feeding parts or openings.  Having encrusters is a bit of a dangerous game.

The Champion 4
Sclerobionts encrusting a brachiopod host

Encrusters will always hold a special place in my heart, as they were my introduction to real research when I was an undergrad, and they were a large part of my MSc thesis.  Even now, I still love popping a fossil under a microscope and discovering complex biology occurring at an entirely different scale.  It’s like a little scavenger hunt.

Plus, there is something very impressive about tiny critters being preserved for hundreds of millions of years…