Fossil Friday #13 – Tunicates

Colourful tunicates! Credit: Nick Hobgood

If you have even had the chance to see or feel a tunicate, you’ll know they’re weird little creatures. At first glance, the tunicate resembles a sponge, with an exhalent and inhalent opening. They’re often found in similar environments, encrusting rocks, ships, and docks. Like sponges, many species of tunicates are also colonial, colourful, and generally unassuming, which is why you may not have noticed, or even heard of, tunicates.

Despite their initially similar appearance, sponges and tunicates couldn’t be more different. For starters, if you give them a gentle touch, you can immediately feel a difference. Sponges will often be soft, porous, and somewhat flexible, whereas most tunicates feel solid, firm, and gel-like (kind of like a gel-cushion you’d buy for your shoes). If you have ever accidentally stepped on a tunicate, you might have received a shot of water back, hence why they are often called “sea-squirts”. Stick them under a microscope, or even look at them with a magnifying glass, and you should start to notice that tunicates are much more complex animals than sponges. This is because while sponges are the simplest of all animals, not even having cells organized into tissue, tunicates belong to the phylum which has the most complex animals of all: the Chordata.

For those of you that are familiar with the word “chordate”, you might be surprised. That’s because the phylum Chordata is our own phylum, including all vertebrate animals. That’s right: tunicates are your closest invertebrate relatives! Chordates include all animals which have a notochord at some point in their development. Notochords are stiffened (but flexible) rods that run along the dorsal (back) side of the animal, and provide structural support for muscles and bone. Most vertebrates only have a notochord early in their embryonic life-stages (although some adult fish still have them), and adult tunicates also lose their notochords.

Generalized chordate- Credit: OpenStax

Larval tunicates (called “tadpoles”) have a well-developed notochord, which allows them to be very strong swimmers. They use their notochord as a “push-pull” point for their little muscles. Tunicate tadpoles are attracted to light, non-feeding, and have a very short larval stage (it takes a lot of energy to swim so much!). Being a strong swimmer is therefore very important for finding a suitable environment in which to settle. After as little as a few hours, the tadpoles will start to swim down and try and find a place to settle. They settle “tail-up”, and the tail/notochord begins to resorb as they undergo metamorphosis.

Adult tunicates look very different than their tadpoles. The organs are near the base, and the majority of the body consists of a large feeding organ called the pharyx or “gill-basket”.  Food particles are trapped as water is drawn in through the inhalent opening (atrial siphon in the diagram below), and through slits in the gill-basket. The entire body is covered in a sheath called the tunic, which is filled with an acellular jelly-like substance called tunicin (I love it when terminology makes sense).

The fossil record for tunicates is very, very poor, and specimens from the Cambrian and Carboniferous that were once considered tunicates have since been found to be organisms from other phyla (Chen et al. 2003).  However, there are several well-preserved fossils of a critter called Shankouclava from the Early Cambrian of southern China that are still considered tunicates (Chen et al. 2003). Considering tunicates are the “base” of our own phylum, this find is a pretty big deal, and shows that the group has had little change over more than 500 million years! (check out their paper for some neat images!)

References and Links:

OpenStax, Chordates. OpenStax CNX. Apr 29, 2013 

Baker, A.L. et al. 2012. Phycokey — an image based key to Algae (PS Protista), Cyanobacteria, and other aquatic objects. University of New Hampshire Center for Freshwater Biology. 16 Feb 2018.

Chen, J., D. Huang, Q. Peng, H. Chi, X. Wang, and M. Feng. 2003. The first tunicate from the Early Cambrian of South China. PNAS (14) 8314-8318.


Fossil Friday #12 – The Black Turban Snail (AKA the Greatest Snail There Ever Was)

I’ve been rather quiet on my blog this past year, in part due to an intense workload down in California, studying for my candidacy exam (I passed, phew), the usual suite of conferences and writing, and of course, life. But I’ve also been doing a lot of thinking and reflection on how to be a better science communicator. This year was an immense year of growth for me both as a scientist, and as a human being. The folks of Bodega Marine Lab were amazing, and I learned so much during my time down there about marine science, the importance of collaboration and peers, and how to advocate for science. I am probably going to do a blog or two about my time in California, but I figured I’d start with something familiar.

Anyone who has ever been tide-pooling along the rocky intertidal of the Pacific coast of Canada or the US has probably come across a little blackish-purple snail, often with an eroded apex that can look either pearly or orange, called the black turban snail. Its scientific name is Tegula funebralis (although this is hotly debated, and it should probably be called Chlorostoma funebrale, but I’m not going to get into that). During a low tide, you can find them by the hundreds, clustered around the bottoms of rocks, or in tide pools, munching on their favourite algae.

Tegula funebralis – the black turban snail

Marine intertidal ecologists are very familiar with this little snail, and most of us are unusually fond of it. Why? It’s hard to explain, but somehow this non-descript little snail, with its little black foot (body) and curious epipodial tentacles that will explore you as it wobbles across the palm of your hand, is very charismatic. It is unusually long lived for such a small snail (up to 30 years), has been used for countless studies, and is commonly found in teaching labs and touch tanks at aquariums (not as scary as in Finding Dory). Some scientists refer to it as the “most noble snail”, and there has even been an article that lightly suggests that Tegula can explain the logic of the universe. I tend to agree.

Collecting Tegula funebralis

Tegula is a large genus, consisting of some 30-odd extant (living) taxa found all around the Pacific, including other species such as the brown turban snail, Tegula brunnea, which looks similar to T. funebralis, or a pretty, light coloured one called the dusky turban snail, Tegula pulligo. You can distinguish T. funebralis primarily by its purplish-black colour, eroded apex that will expose the pearly nacre of the shell, and crenulated ornament along the top margin of the whorl (spiral), although this is not always present. T. brunnea is similar in colour, and is also found in the intertidal (lower), but will be more brown than purple, does not have the eroded apex, and for living snails, will have a bright orange band on its foot that is not present in T. funebralis.

The fossil record of the Tegula genus extends back as far as the Cretaceous, to a creature called Tegula jeanae (Squires and Saul, 2005), which interestingly looks a lot like Tegula funebralis. As many Tegula are found either in the intertidal, or in the shallow subtidal, their fossil record isn’t the best, as these environments usually erode, rather than become buried. However, there is some nice material, particularly of T. funebralis, from the Plio-Pliestocene of southern California. Interestingly, I discovered from curators at the Natural History Museum of LA County Invertebrate Paleontology Collection that while most fossils lose their colour, even from the Late Pliestocene (~12,000 – 126,000 years ago), T. funebralis retains its dark purple colour, making it very easy to spot among the drawers of dusty, beige fossil shells. In addition to fossil material, there is also a lot of archaeological material from shell middens, as Tegula has been used for food by people all along the coast (Erlandson et al. 2015).

behemoth tegula
A behemoth Tegula funebralis with 9(!) repair scars

Not only is Tegula a cute little snail and excellent experimental animal, it is also important ecologically. Being one of the most common and abundant intertidal snails, it is food for lots of animals, such as sea stars, crabs, octopus, and even birds. One of the reasons we study it so much in the Leighton Lab is because populations of T. funebralis often have lots of repair scars from crab attacks, meaning we can study how this crab-snail interaction is affected by things like wave-energy, environment, other potential prey, and even ocean acidification (which is what I am exploring for my dissertation). Unfortunately, OA studies have found that T. funebralis is in trouble (e.g. Jellison et al. 2016). From the results of my experiments, it is in huge trouble (Barclay et al. 2017 – stay tuned for updates!). And if something happens to Tegula, it could be detrimental for intertidal ecosystems. Think of it this way: without Tegula, there would be a lot less food for predators, which puts more pressure on other prey animals and could disrupt populations their populations, potentially messing up the “food chain” or established interactions within the whole ecosystem.

Tegula funebralis about to become a snack for a hungry sea star – credit: Darrin Molinaro

So the next time you happen to visit the Pacific coast, keep your eyes out for the black turban snail. Once you spot one, you’ll notice them all over the place. Lightly twist one off a rock and place it in your palm. If you are gentle and patient, it will venture out of its shell and explore your hand. Remember that they are in trouble due to climate change, and will need our help to make decisions that will work towards protecting them and their environment. And if you see a piece of kelp washed up, try feeding it to them. It’s their favourite snack, and it’s fun to watch their little raspy radula (tongues) hard at work. We could all benefit from taking to time to just sit, soak in their rocky intertidal home, and explore life at a “snail’s pace”.

Tegula funebralis in their intertidal habitat credit: Steven Lonhart (SIMoN

Literature Cited (and other cool links):

Barclay, K. M., Gaylord, B., Jellison, B.M., Shukla, P., Sanford, E., and Leighton, L.R. 2017. Impact of ocean acidification on shell growth and strength of two intertidal gastropods exposed to the scent of predation. Western Society of Naturalists 98th Annual Meeting

Erlandson, J. M., Ainis, A. F., Braje, T. J., Jew, N. P., McVey, M., Rick, T. C., Vellanoweth, R. L., and Watts, J. 2015. 12,000 Years of Human Predation on Black Turban Snails (Chlorostoma funebralis) on Alta California’s Northern Channel Islands. California Archaeology 7:59-91.

Jellison, B. M., Ninokawa, A. T., Hill, T. M., Sanford, E., and Gaylord, B. 2016. Ocean acidification alters the response of intertidal snails to a key sea star predator. Proceedings of the Royal Society B 283:20160890

Squires, R. L., and Saul, L. R. 2005. New Late Cretaceous (Santonian and Campanian) gastropods from California and Baja California, Mexico. The Nautilus 119:133-148

At A Snail’s Pace – Bay Nature – a great article in which Tegula explains the logic of the universe

WoRMS – World Register of Marine Species – Tegula Tegulidae – has great pictures!



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.

Fossil Friday #8 – Science Literacy Week

It’s Science Literacy Week here in Canada, so in celebration, this week’s Fossil Friday post is a short compilation of some great books and reading resources for anyone interested in palaeontology, ecology, evolution, and even the Canadian Rockies.

Here’s a list of some of my favourite natural science related books:

(1) A Natural History of Shells.
Vermeij, G. J. 1993. Princeton University Press, Princeton, New Jersey.

This one is probably my favourite textbooks of all time.  If you like evolution, palaeontology, or ecology, go read everything by Geerat Vermeij.  He is a genius and arguably one of the top scientists in the world right now.

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(2) Fossil Invertebrates
Richard S. Boardman, R. S., Cheetham, A. H., and Rowell, A. J. 1987. Blackwell Scientific Publications, Oxford.

There is another book by the same title published by Taylor and Lewis in 2007.

(3) Fossil Invertebrates
Taylor, P. D., and Lewis, D. N. 2007. Harvard University Press, Cambridge, Massachusetts.

Paul Taylor is another leader in the field, and has done a lot of work on encrustation/biotic interactions.  I recommend many of the papers he and Mark Wilson have written.

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(4) Invertebrate Palaeontology and Evolution.
Clarkson, E. N. K. 4th edition. 2008. Blackwell Scientific Publications, Oxford.

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(5) Geographical Ecology: Patterns in the Distribution of Species.
MacArthur, R. H. 1984. Princeton University Press, Princeton, New Jersey.

This one is pretty math-heavy, but it is considered a classic, and one of the last things MacArthur wrote (he died quite young). MacArthur was another genius and is generally regarded as the top ecologist of all time (he, along with E. O. Wilson, came up with major ecological theories, such as island biogeography).

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(6)Predator-Prey Interactions in the Fossil Record.
Eds. Kelley, P. H., Kowalewski, M., Hansen, T. A. 2003. Kluwer Academic/Plenum Publishers, New York, New York.

Full of really interesting chapters on a large variety of animals from a lot of different authors.

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(7) Handbook of the Canadian Rockies
Gadd, B. reprint 2016. Corax Press, Canmore, Alberta.

I’ve included this one because it covers everything from plants, to birds, to geology, and even humans!  Great for a general audience, and a super fun, informative, and entertaining read!


(7) Living and Fossil Brachiopods.
M. J. S. Rudwick. 1970. Hutchinson University Library, London

A must-read for anyone studying brachiopods.  It might be a bit outdated, but it is very comprehensive and easy to read.

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There are lots of other classics out there, such as anything by S. J. Gould, M. Rosenzwig, etc., etc., etc.

What are you reading right now?  Anything to add to my list?  Leave me a comment, and happy reading!

Fossil Friday #6 – Predation and Drill Holes

Predation is a pretty big topic in palaeontology, but not as straight forward as you might expect.  We all have this image in our head of the T. rex from Jurassic Park feasting on another dinosaur (or perhaps the lawyer on the toilet), but where does that information come from?  Unlike in Jurassic Park, humans were never alive to actually witness a T. rex eating a Triceratops, so how can we be certain those interactions ever occurred?

Anti-predatory adaptations, such as armour, spikes, frills, are a good first clue that something is trying not to be eaten.  Even better, though, is the actual evidence of an interaction preserved on the hard parts of either predator, or (more often) prey.  For example, there is a really nice specimen of a Triceratops at the T. rex Discovery Centre in Eastend, SK, where you can see tooth marks from a predator.

Tooth marks in bone (T. rex Discovery Centre, Royal Saskatchewan Museum, Eastend, SK)

Unfortunately for vertebrate palaeontologists, bigger animals are not as abundant, so the occurrence of such fossils is really special and rare.  With invertebrate palaeontology, we have a bit of an easier time.  One type of predation trace preserved on invertebrate prey is called a drill hole, which is a hole in the shell of a prey animal created by predatory gastropods (snails).

Fossil bivalve shell with drill hole from a predatory snail (Pinecrest Fm., Late Pliocene)
Drilled fossil gastropods from the Pinecrest Fm. (Late Pliocene, Florida)

If you remember my post about cone snails, I mentioned that gastropods have a special feeding organ called a radula, which is usually rough like a cat’s tongue and used for scraping food.  In the case of drilling gastropods, they have another organ called an accessory boring organ (ABO), which secretes material to soften the shell of their prey as they scrape with their radula.  One of the more common predatory snails is called a naticid (moon snail).  They can get to be very large (bigger than a softball), and have a giant foot that they use for both moving, and grappling their prey.

A fossil naticid (moon snail) from the Pinecrest Fm. (Late Pliocene)


Image result for live naticid
A live naticid with its giant foot of nightmares. Image credit:

Drill holes can be used to study many aspects of predation and predator-prey dynamics.  For example, we can look at how often prey are being attacked and see if there are predator preferences (Yanes and Tyler 2009).  Or perhaps there is evidence of anti-predatory adaptations, such as spines (Leighton 2001), or a lack of edible parts (Tyler et al 2013).  Drill holes can even be used for taphonomic studies (everything that happens from the moment an animal dies to the time the fossil is discovered), such as how drill holes affect the transportation and deposition of shells (Molinaro et al. 2013).  drill-hole-2

Predators are not always successful, and will sometimes get interrupted, perhaps even by a predator of their own.  Such interruptions produce incomplete drill holes, which can also be used to determine the success rates of predators, or the intensity of predation upon the drillers themselves (Chattopadhyay and Baumiller 2010).

Incomplete drill hole on a modern naticid.

Some predators will even recognize different prey types and attack each in a particular manner, producing sterotypic drill holes that are in a consistent location unique to that prey (Leighton 2001).  Not only that, but they can be highly cannibalistic, and will often eat smaller members of their own species (Chattopadhyay et al. 2014).  Basically, if they are able to grapple you with that huge foot, you are in trouble.

Stereotypy of drill holes in smaller, modern naticids (cannibalized)

TL,DR: Drill holes have an extensive fossil history, and are very useful for studying predator-prey dynamics and how predation has evolved.  Stay tuned for a future blog post on another type of predation trace: repair scars…


Chattopadhyay, D., and Baumiller, T. K. 2010. Effect of durophagy on drilling predation: a case study of Cenozoic molluscs from North America. Historical Biology. 22:367-379.

Chattopadhyay, D. Sarkar, D., Dutta, S., Prasanjit, S. R. 2014. What controls cannibalism in drilling gastropods? A case study on Natica tigrinaPalaeogeography, Palaeoclimatology, Palaeoecology. 410:126-133.

Leighton, L. R. 2001. New example of Devonian predatory boreholes and the influence of brachiopod spines on predator success. Palaeogeography, Palaeoclimatology, Palaeoecology. 165:54-69.

Molinaro, D.J., Collins, B.M.J., Burns, M.E., Stafford, E.S., Leighton, L.R. 2013. Do
predatory drill holes influence the transport and deposition of gastropod shells?
Lethaia. 46:508–517.

Tyler, C. L., Leighton, L. R., Carlson, S. J., Huntley, J. W., Kowalewski, M. 2013. Predation on modern and fossil brachiopods: assessing chemical defenses and palatability. Palaios 28:724-735.

Yanes, Y., and Tyler, C. L. 2009. Drilling predation intensity and feeding preferences by Nucella (Muricidae) on limpets inferred from a dead-shell assemblage. Palaios 24:280-289.