Fossil Friday #11 – Crinoids: the Ocean’s Feather Dusters!

The modern ocean is full of scary, disgusting, bizarre, awesome, and adorable organisms (multiply that by several thousand times, and you can cover prehistoric oceans too). While crinoids might not strike terror into your heart, they are pretty strange animals, which are often mistaken for plants at first glance (the name crinoid means “sea lily”).  I personally find them somewhat adorable (living, swimming feather dusters?  I mean, come on).

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Fossil and modern crinoids.  Image credit:

Crinoids are a class of echinoderms, the group which includes creatures like sea stars, urchins, sand dollars, and sea cucumbers.  Echinoderms are characterized by having some form of five-sided symmetry, and a system of thousands of tiny appendages called tube feet, which allow the organisms to move and feed.  Many echinoderms have five or more arms which are lined with tube feet, often improving their ability to catch food.  Another characteristic of echinoderms is that they have a skeleton formed in the middle layer of the skin, just like vertebrates, which actually makes echinoderms our closest invertebrate relatives.  Most other invertebrates have a skeleton which forms in the outer layer of skin, like the exoskeleton of an insect.

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Echinoderms!  Top left is a crinoid.  Image credit:

Crinoids are composed of three or four main sections: the holdfast, stalk (sometimes), calyx, and arms.  At the base of the animal is a kind of root system, which is used for attachment onto a surface or substrate.  This is called the holdfast (get it? It holds the crinoid fast/tight to something.  I love it when terminology makes sense).  Some crinoids then have a stalk, which leads to the head, including the mouth and anus, which is called a calyx.

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Anatomy of a crinoid.  Image credit:

Why the feather duster analogy for crinoids?  Coming from the calyx, crinoids have a lot of very thin, long arms, with secondary arms (called pinnules) that look like the main barb and secondary filaments on a feather.  The pinnules on a crinoid’s arm are covered in long tube feet, which act like a net to catch food particles out of the water.  The tube feet then move food down the arm to the mouth, which is located on the calyx.  The overall effect is that crinoid arms look like a bunch of feathers.  Hence: feather duster of the sea.

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A beautiful modern crinoid.  Image credit:

As I mentioned, modern crinoids can, indeed, swim, flicking their arms to paddle through the water.  They do get tired fairly easily, so swimming isn’t usually sustained for more than a minute or so.  Some crinoids can also walk or drag themselves along the ocean floor.  This is especially advantageous if they get knocked over, covered in sediment, or perhaps need to flee a predator.  Check out this YouTube video of a swimming crinoid in action:

While most modern crinoids just have the holdfast, calyx, and arms, the majority of fossil crinoids also had a stalk.  The stalk gives them the appearance more of a pinwheel than a feather duster.  The stalk is comprised of a series of disks (called columnals) which are stacked on top of one another, and elevate the calyx high above the ocean floor, much like the trunk of a tree.  Imagine a series of poker chips (the cheap plastic ones with the ridges along the edge) stacked on top of one another, with a hole in the middle and a string (liagment) passing through and holding them together.  That is basically the stalk of a fossil crinoid.  However, not that long ago, modern, stalked deep sea crinoids were discovered, leading to the group being termed “living fossils”.

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A close up of crinoid columnals.  Image credit:



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Modern, stalked, deep-sea crinoids.  Image credit:

Given the nature of a crinoid’s skeleton, which is composed of many tiny pieces, just like the bones of vertebrates, we usually don’t see intact crinoids in the fossil record.  Instead, we more commonly find crinoid columnals, and other disarticulated pieces, scattered among our other fossils.  Sometimes, you can find the calyx still intact, but they are often still very fragile.  There are some beautiful examples of completely intact crinoids, but these are somewhat rare, and require exceptional preservation, just like the conditions needed to find intact vertebrate skeletons.

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Dense crinoid columnals in rock.  Image credit:


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Beautiful intact crinoids.  Image credit:

Crinoids may seem like an obscure group now, but they were one of the dominant ocean invertebrate groups until they were badly decimated by the end-Permian mass extinction, which wiped out about 85 – 95% of all living things, and is the worst mass extinction event ever recorded on Earth.  Luckily, crinoids did manage to recover a bit, and you can now enjoy pictures and videos of the ocean’s very own feather dusters and pinwheels.

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The feather dusters of the sea.  Image credit:

As always, if you have questions, comments, or requests for blog topics, please let me know!

For more information on crinoids, check out these resources:


Fossil Friday #10 – Bryozoans!

Bryozoans are the coolest little animals you’ve never heard of.  And when I say little, I mean really little.  As I tell my students, if you aren’t using a microscope, you’re missing the point.  You can’t really see anything without a scope.

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Each of these contains hundreds to thousands of individuals.  Image credit:
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There, that’s better.  Notice the scale bar.  Image credit: https:/

Otherwise know as “moss animals”, these tiny little critters are mostly colonial, and most commonly found in marine environments.  They are generally thought to be related to brachiopods and another group called phoronids, all of which have a specialized feeding organ called a lophophore.  The lophophore is a cilliated (tentacled) structure which actively pumps water/food to the mouth (located at the base of the lophophore).

Most bryozoans secrete a hard skeleton in which they live, much like a coral.  Individuals within the colony are called zooids.  Some types of bryozoans have specialized zooids that only perform one function for the colony, such as providing food, defense, or reproduction.  Because they are colonial, bryozoans are capable of both sexual and asexual (budding) reproduction.  To reproduce sexually, sperm, and sometimes ova, are released into the water column (some colonies with specialized reproductive zooids will keep ova in brooding chambers).

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Fossil bryozoan zooids. Image credit:
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Reproductive zooids (ovicells).  Image credit:

I won’t get into the systematics (grouping) of bryozoans, because it is complicated, and generally unhelpful to the non-specialist (if any specialists are reading this, I apologize.  Just know that I love bryozoans!).  However, there are two basic ways that bryozoan colonies can grow: erect, or encrusting.

Erect colonies grow upright into all sorts of beautiful shapes.  Some grow into simple branching structures that look like trees , and some, like the fenestrates, grow to look like screen doors (but pretty).  Others, like the fossil Archimedes, grow into corkscrew spirals.  A lot of modern erect bryozoans look leafy, like a head of lettuce, or bushy.

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Fossil branching bryozoans.  Image credit: http://www/
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Archimedes close up.  Image credit: 
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Fenestrate bryozoan colony.  Image credit: http://www/

Encrusting forms are usually flattened, but may grow into large bulbous structures.  They can grow into sheets that encrust other organisms, or form large, dense colonies.  Interestingly, during much of the fossil record, the majority of bryozoans grow into erect forms, but in the modern, most bryozoans are flat and encrusting.  These modern encrusting forms are sometimes called “foulers” because they clog up pipes and foul up the sides of ships.

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Encrusting bryozoans. Image credit:

Bryozoans can form colonies of millions of individuals, but still never come close to reaching the size of other colonial animals, like coral reefs.  The result is that bryozoans just never reach the same biomass as other marine fossils, which might make them seem like a somewhat unimportant group, despite being common marine organisms since the Cambrian/Ordovician.  Bryozoans are, however, an important group, and totally rad (in my humble opinion).

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Modern encrusting bryozoans are sometimes really red!  Image credit:

For example, bryozoans are often used to examine how sessile (non-moving) animals interact with one another, or compete for space.  Imagine you are a little larvae that has settled on a susbtrate that is now going to be your home for the rest of your life, and some other larvae settles too close to you, or perhaps on top of you.  If you can’t move, how do you deal with this crowding or lack of space?  As bryozoans are colonial, they are able to respond and grow the colony in all sorts of interesting ways.  Some even have claw-like zooids that can pinch  predators or anyone that gets to close.  Many bryozoans will compete for “superiority” by trying to overgrow the other colony, allowing us to directly examine competitive relationships, something that is usually not possible in the fossil record (e.g. McKinney 1995).

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Overgrowth and competition in bryozoans.  Image credit:

Bryozoans also commonly encrust other organisms, such as brachiopods, allowing us to examine these relationships “in place”, which again, is a rare occurrence in the fossil record  For example, are bryozoans beneficial to their hosts?  Do they provide protection/camouflage from the host’s predators?  Or are they parasitic, and prevent the host from feeding or moving properly?  This is the area of study that I specialized in for my undergrad and M.Sc (check out my publications).

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Brachiopod with encrusters (sheet in the middle is a bryozoan – zoom in!).  Image credit:

I think bryozoans are fascinating, simply because they operate on a fundamentally different size scale compared to most other animals.  They are also very aesthecially pleasing.

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Look at them smiling for you.  What’s not to like?  Image credit: http://www/

Fun tidbit for those of you that read this far: apparently the bryozoan Bugula neritina creates a chemical (bryostatin) which is being tested for use in the treatment of cancer and Alzheimer’s disease.  Can bryozoans get any more awesome?

Want to learn more about bryozoans?  Check out these resources:

McKinney, F. K. 1995. Taphonomic effects and preserved overgrowth relationships among encrusting marine organisms. Palaios. 10:279-282.

Coming soon: Bryozoan Paleobiology by Paul D. Taylor

Fossil Friday #9 – Stromatoporoids vs. Stromatolites

One of the hardest sets of terminology and fossils/structures for students to remember is stromatoporoids and stromatolites.  Not only are the names painfully similar, but they also look very similar, until you get your nose next to them.  Both can be massive (tens to hundreds of metres), both appear finely laminated, and both can be round or bulbous in shape.  The short version is that stromatoporoids (left image below) are body fossils, and stromatolites are more sedimentary structures (right image below).  Hard to tell apart, right?

The longer version:


Stromatoporoids are considered to be an extinct group of sponges that were particularly common during the Silurian and Devonian.  In Alberta, stromatoporoids formed giant reefs during the Devonian.  A large reef formation (biostrome) can be observed in the Moberly Member of the Waterways Formation, which outcrops around Fort McMurray, right underneath the oil sands (McMurray Formation).

Sponges, including stromatoporoids, are the basal group for our own kingdom (Animalia).  Stromatoporoids are usually classified within the sclerosponges, a group which secretes a calcareous skeleton (most other sponges do not have a solid skeleton, but instead make their skeletons from distinct hard pieces called spicules).  The skeletons of stromatoporoids are put down in layers called laminae, and separated into distinct chambers (galleries) by upright pillars.  Water would have flowed through the galleries, where ciliated cells would have drawn nutrients from the water.

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A stromatoporoid showing laminae (horizontal lines), pillars (vertical lines), and galleries (chambers formed from intersections of laminae and pillars).

Often times, a microscope or hand lens is required to see the laminae, pillars, and galleries of stromatoporoids, but occasionally you get really nice preservation, as in the image above (a specimen from the Waterways Fm.), or this specimen below (from the Potter Farm Fm. of Michigan – Devonian).  Another, sometimes more easily observed feature of stromatoporoids, at least when present, are the small bumps that would have been on the outer wall or surface of the animal.  These structures are called mamelons, and would have probably assisted with drawing water into the galleries.


Stromatolites are sedimentary structures which are created when a layer of sticky cyanobacteria traps sediment layer by layer, sometimes creating huge mounds or sheets.  Stromatolites are one of the earliest organically formed structures, dating back to the Precambrian. A new paper by Nutman et al. (2016) found stromatolites in Greenland which they determined to be 3.7 billion years old!


Because stromatolites are formed by algae/cyanobacteria, they are still technically considered fossils, but what is preserved is layers and layers of sediment.  When you look closely at a stromatolite, you will see laminae, but they are not well defined or regular as in stromatoporoids, and they do not have any kind of vertical structure such as pillars or galleries.

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One other cool thing about stromatolites is that they still exist today.  There are some in Shark’s Bay, Australia that are about 2,000 – 3,000 years old!  Check out their website for some more pictures and videos of stromatolites.

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Modern stromatolites of Shark’s Bay.  Image credit:


Nutman, A., P., Bennett, V., C., Friend, C. L. R., Van Kranendonk, M., J., and Chivas, A., R. 2016. Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures. Nature. 537:535–538.