If you have ever been shell collecting on a tropical vacation, you have probably come across a cone snail. These snails are popular among collectors because of their often highly polished and colourful, patterned shells. Cone snails are a type of gastropod (snail), which mostly belong to a single genus, Conus (although there are several other genera within the Family Conidae). The group has been around since the Miocene (about 55 million years ago), and can be found in tropical and sub tropical fossil localities all over the world. We have some in our lab from the Pinecrest Beds of Florida that still have some colour (about 4 – 2 million years old)!
But while cone shells may be beautiful, the animal itself is deadly. All gastropods have a special feeding organ called a radula (usually for wrasping and rough like a cat’s tongue), but in the case of cone snails, the radula has been modified into a harpoon, complete with a venom gland.
What might a little snail need a venomous harpoon for, you ask? Oh, just for paralysing and then eating FISH. Cone snails harpoon their victims, causing almost instant paralysis, and then basically swallow them whole. Cone snails are considered one of the deadliest animals, and the venom can be fatal for humans. In other words, NO TOUCHING!
Last week in my Fossil Friday post, I featured a brachiopod specimen I called “The Champ”. If you are not a palaeontologist, you have likely never heard of a brachiopod, and may assume it is some obscure group of little interest. To be fair, if you are a modern biologist, it is true that brachiopods are of limited significance (yes, brachiopods still exist today, but in small numbers and obscure habitats). However, for the palaeontology crowd, brachiopods have been the subject of much study, as they are arguably one of the most common groups of marine invertebrates throughout the Palaeozoic. In fact, brachiopods are unique in that we know more about the fossil critters than those still alive today.
So what is a brachiopod? In simple terms, it is a two shelled marine invertebrate, much like a clam or mussel. But having two shells is about all clams and brachiopods have in common. One of the first ways we teach students to differentiate brachiopods and clams is to look at the symmetry of the two shells. The plane of symmetry in clams runs between the shells (there is a left and right shell), whereas the plane of symmetry in brachiopods runs down the midline of each shell (there is bottom and top shell which are bilaterally symmetrical).
Brachiopods belong to their own phylum, whereas clams are a class within the phylum Mollusca (which also includes octopods, snails, and several other smaller groups). Brachiopods are also part of a larger group of organisms called lophophorates, all of which have a special organ called the lophophore. The lophophore is a coiled organ with many cillia (tentacles) which actively beat and pump water, providing respiration, and drawing food towards the mouth (located at the base of the lophophore). Brachiopods are therefore considered “active” filter (suspension) feeders, in that they actively pump the lophophore to pull tiny bits of food out of suspension. There are two other groups within the lophophorates, bryozoans and phoronid worms, which I will discuss another time.
Another important bit of anatomy that is unique to brachiopods is a fibrous (sometimes muscular) organ called the pedicle, which protrudes from a hole near the back of one shell, and helps to attach the brachiopod to the substrate/surface like an anchor or sucker. Pedicles can be very strong, and the attachment is usually permanent. For the brachiopod pictured above, if you tried to pick it up, you would likely rip the shells away from the pedicle and the rest of its internal organs (so if you are ever lucky enough to spot one, please be gentle!).
There are two main groups of brachiopods: the Inarticulata (above left image), and the Articulata (above right image). Inarticulates have a large, muscular pedicle, which they use to burrow into soft sediments, leaving only the very top of the shell exposed, whereas articulates have smaller, more permanent pedicles, which help to anchor and keep the brachiopod elevated above the substrate. Atriculate brachiopods generally do not deal with mud and sediment very well (although check out Richardson 1981 for a further discussion of pedicles and mud). The chemical structure of the shells is also different, with inarticulate shells not as likely to preserve in the fossil record. Inarticulate brachiopods are known as “living fossils”, in that they have barely changed since they first appeared in the late Cambrian. Articulates, on the other hand, are very diverse and abundant throughout the fossil record (although only 3 groups have managed to survive to today). Some articulates can be shaped like potato chips or have lots of spines, be as big as baseballs or smaller than a fingernail, and even have only one shell. Most palaeontologists, including myself, study articulate brachiopods.
So why should you care about brachiopods?
There are endless reasons that brachiopod workers could go on about why brachiopods matter, but I will give you a few, based on my experiences.
Most importantly, however, is that brachiopods can be used for studies in conservation palaeobiology (for most of the reasons I list below). Conservation palaeobiology is a new, hot field in science which seeks to use palaeontological data to help ecologists and biologists figure out how to preserve modern ecosystems that are facing pressures from human-induced change (i.e. climate change).
Brachiopods are probably the single most common fossils for the majority of the history of life. That means brachiopod workers often have data sets that are well into the thousands, which can have great statistical power for answering lots of questions, especially when it comes to things like changes to community diversity through time, and how communities deal with things like mass extinction events (kind of like the one we are currently experiencing). You just can’t do that with most vertebrates (no offense to all my vertebrate colleagues. We all know T. rex is rad, right?).
Because they are so common, brachiopods are a great for studying how biotic interactions can develop or change through time. For example, brachiopods are a major source of food for shell crushing fish and crustaceans, as well as some shell-drilling snails. We can use evidence of predation to observe any changes to the success or frequency of attacks through time, which can not only shape the evolution of the brachiopods, but also their predators. Plus, no food = no predators.I also look at the relationships between brachiopods and the organisms that encrust them to try and determine the nature of the relationship (parasitism, mutualism, etc.) over time. Understanding how brachiopods can develop a relationship with their encrusters provides many insights into how other organisms relate.
Throughout the fossil record, brachiopod numbers and diversity get whacked several times. A lot of brachiopod workers try to figure out what it is about each group (body shape? geographic spread? diversity?, etc.) that either causes them to go extinct, or allows them to survive. For example, there is a catastrophic mass extinction at the end of the Permian (much worse than the extinction that killed the dinosaurs), and most brachiopod groups are decimated. However, a few manage to survive, but never become as diverse or as common as they were during the Palaeozoic. At the same time, molluscs such as clams become much more abundant. Many researchers have dedicated their entire careers to try and explain why brachiopods are never able to recover, and why molluscs seem to “take over”.
Brachiopods have relatively simple, but highly varying shapes, which allows us to study the mechanisms of how shape relates to lifestyle (i.e. the study of functional morphology). To use a very simple example, sponges are usually shaped like tubes because it allows water to pass through them and over their cells just like a chimney sucks out smoke. We can do lots of experiments that help us determine the basic physics of how brachiopods interact with moving water, which can tell us how they feed and live (e.g. Alexander 1984; LaBarbera 1977, 1978). Shape relates a lot to how any organism survives and thrives in its environment, and can be applied to the evolutionary history of most groups of organisms, from plants to dinosaurs.
Did I mention we probably know more about the fossil brachiopods than the modern brachiopods? I’ve been studying brachiopods for about six years, and have yet to see a live one. In fact, most modern brachiopod researchers rely on palaeontological literature as a basis for their studies. That doesn’t happen very often. Fun fact for those of you that read this far: brachiopods may be poisonous. There is this urban legend people always bring up about some professor that fed his/her students some brachiopods, and they ended up in the hospital (Taylor and Lewis, 2005).
TL;DR – Brachiopods are neat, and very useful for solving modern biological problems. And potentially poisonous… so don’t eat them…
Alexander, R., R. 1984. Comparative hydrodynamic stability of brachiopod shells on current-scoured arenaceous substrates. Lethaia 17:17–32.
Barclay, K. M., C. L. Schneider, and L. R. Leighton. 2013. Palaeoecology of Devonian sclerobionts and their brachiopod hosts from the Western Canadian Sedimentary Basin. Palaeogeography, Palaeoclimatology, Palaeoecology 383–384:79–91.
LaBarbera, M. 1977. Brachiopod orientation to water movement. 1. Theory, laboratory behavior, and field orientations. Paleobiology 3:270–287.
LaBarbera, M. 1978. Brachiopod orientation to water movement: functional morphology. Lethaia 11:67–79.
Richardson, J.R. 1981. Brachiopods in mud: resolution of a dilemma. Science 211:1161–1163.
Taylor, P. D., and Lewis, D. N. 2005. Fossil Invertebrates. Harvard University Press.
Welcome to the first of many Fossil Friday posts! Each week, I’ll feature a new invertebrate fossil or group, along with pictures and a little bit of info. I will do longer posts about various fossil groups as part of my regular blog.
If you ever have any suggestions for critters you’d like to see, please leave comment!
Fossil Friday July 22/16
*Disclaimer – This post contains a lot of self-citations. I promise it won’t always be so, but I’m starting the blog with something familiar…*
My first Fossil Friday post is one of my favourite little brachiopod specimens that I’ve ever come across. I’ve affectionately nick-named it “The Champion/Champ”, which is how it is now known in our lab. The Champ is a brachiopod called Pseudoatrypa lineata from the Devonian of Alberta, and has been used for many different experiments in the lab.
A lot of my M.Sc. was based on this guy (or gal). It is very well preserved, so I created a bunch of models of it (made to resemble the weight and density of the original animal’s shell), and ran experiments in a flume (a large tank where you can control the speed and flow of the water). These experiments helped me determine the most realistic life orientation of the original animal, which is important for its interactions with other organisms (see below).
Not only is The Champ an exceptionally well preserved brachiopod, it is COVERED in lots of encrusting organisms. A lot of my undergraduate and M.Sc.theses were based on trying to determine if there were/are any relationships between encrusting organisms and their brachiopod hosts. The life orientation of the brachiopod can tell you the biological significance of the location of encrusters on the brachiopod’s shell (e.g. part of the shell would be resting against the substrate during life, so no encrusters could land there while the brachiopod was alive. Hence, if you observed encrusters on that area of the shell, the brachiopod must have been dead at the time of encrustation). Basically, The Champ is the ideal trophy fossil for many kinds of studies.
If you’d like to learn more about The Champ or the relationships between encrusters and brachiopods, check out some of my publications (Barclay et al. 2015a, and b), or leave a question in the comments.
Biotic interactions are primary forces driving evolutionary change. Whether it is organism trying to avoid being eaten, or two individuals competing for the same resource, the many interactions in which an organism partakes over the course of its life can have a huge impact on that organism’s evolutionary success/fitness (i.e. an organism’s ability to reproduce and pass on genetic material). So how do we as scientists determine the significance of a biotic interaction?
Obviously, if an organism is eaten by a predator, that is “game over” for the organism that was eaten. But what about the predator? It only ate one meal on one day, which may or may not contribute to its overall fitness. The significance of the interaction is clearly different for the two organisms participating. Other, non-lethal interactions can be even more complex. Plants are an obvious example. Most of the time, herbivores fail to eat the entire plant, and therefore the plant may still recover and continue to reproduce. These non-lethal interactions are often of greater interest to biologists, as there are usually individual differences which contribute to the survival of some individuals over others, which can lead to selection of the favourable traits in that interaction over time (e.g. plants and animals with anti-predatory defenses, the bright plumage of many male birds, and even pollinating insects and flowering plants).
The first step in understanding biotic interactions is to understand the nature of the interaction. Let’s assume that we have an interaction between two individual organisms (which may or may not belong to the same species). For each individual, there are three possible outcomes of the interaction: 1) positive, 2) negative, or 3) no effect. Here is a handy chart that is a great teaching tool (from Bronstein et al. 1994):
From the three types of outcomes, there are several types of interactions that are possible. Over the next few posts, I’ll dive into some more aspects detail (I am by no means an expert. It is a huge topic, and each interaction alone could – and has been – the subject of many scientists’ careers). For now, here is a brief overview of each.
Positive/positive interactions: mutualism
Mutualistic interactions have a positive effect for both organisms involved. For example, the interaction between a pollinating insect and flowering plant is mutualistic (the insect gets an energy reward in the form of nectar, and the plant receives a reproductive benefit: pollen carried to and from the flower). Mutualisms can be so extreme that they lead to a symbiotic relationship, such as that of lichen. Lichen is actually a combination of two organisms: a fungus, and an algae/cyanobacteria. The fungus provides structural support and protection for the algae/cyanobacteria, and the algae/cyanobacteria provides food (photosynthesis) for the fungus. Another example would be coral and zooxanthellae in which the coral also provides protection, and the zoxanthellae provide food from photosynthesis.
The drawback of symbiotic relationships is that the two organisms have developed complete dependence on one another, such that if something happens to one organism, the other is also affected. In the case of coral and zooxanthellae, many coral reefs are experiencing “bleaching” in which adverse water conditions cause the coral to expel the zooxanthellae from their cells, causing the coral to turn white. The zooxanthellae cannot survive without living within the coral’s tissue, and the coral often dies from lack of food. As coral reefs are home to major ocean ecosystems, coral bleaching is a huge problem.
Positive/negative interactions: Predation, Parasitism, Herbivory Predation (an animal eating another animal), parasitism (an organism infecting a host), and herbivory (usually an animal eating a plant) are all examples of interactions in which one organism benefits in the form of food (and reproduction in the case of parasites), and the other organism is consumed. At first glance, such interactions seem simple enough, but are complicated by non-lethal effects. For example, parasites are more successful when they do not kill their hosts (i.e. the longer the host lives, the longer the parasite benefits from food and/or reproduction). Additionally, as mentioned earlier, most herbivores fail to kill the entire plant, eating leaves or bark and leaving limbs and roots partially intact. Even with predation, non-lethal effects are important. Much of what I and many other palaeontologists study in the fossil record are instances of failed predation where the predator fails to kill the prey (it either escapes, or the predator was interrupted). In the fossil record, failed predation often leaves traces in the form of scars on hard parts (e.g. bite marks, healing fractures, and repair scars on shells). See our paper, Molinaro et al. 2014, for an example.
Negative/negative interactions: Competition
At first, competitive interactions might seem like they should be categorized as a positive/negative interaction (there is usually a “winner” and a “loser” in the interaction). However, even the “winner” experiences a negative effect from the interaction (e.g. two male deer fighting for a mate might injure one another). Competition may be between different species (interspecific competition), or between individuals of the same species (intraspecific competition). There are three main types of competition: 1) interference (direct), 2) exploitative (indirect), and 3) apparent competition. Interference competition usually involves one individual directly trying to gain a resource from another, such a fighting for territory or mates. Exploitative competition is a bit more subtle, and usually involves a form of resource competition, in which organisms compete for limited space or food (one organism taking food means that there is less food for everyone overall). Apparent competition is just that: apparent (not real), and is created by an external factor. For example, if there is a system with one predator and one prey species, and a second prey species is introduced, not only will prey species #1 likely have to compete with prey species #2, but the introduction of a second food source for the predator will increase the predator’s population, resulting in an increased negative effect (predation) on prey species #1, regardless of its interactions with prey species #2 (Holt 1977 is the go-to seminal paper on apparent competition).
Neutral/positive interactions: Commensalism
Commensalism is a relationship in which one organism gains a benefit, and the other is unaffected. This usually occurs when there is a large difference in size between the organisms (the organism receiving the benefit is usually much smaller than the unaffected organism/host). For example, dust mites receive food and habitats from our bedding and dead skin cells, yet we are basically unaffected. Other examples are small fish, such as remora, which attach themselves harmlessly to large hosts such as whales and sharks. The remora then feed off of the food debris from their hosts.
Neutral/negative interactions: Amensalism
Amensalism occurs when one organism is negatively impacted by an interaction with another, unaffected organism. Like comensalism, amensalism often occurs when the organisms in the interaction are very different in size (e.g. an elephant stepping on an insect or small mammal). However, amensalism can also occur when one organism secretes a chemical which harms or kills nearby organisms (e.g. organisms which produce chemicals that kill bacteria, such as bread molds that produce penicillin, or the chemicals secreted by some trees which kill nearby grasses or other vegetation).
Neutral/neutral interactions: Neutralism
Neutralism is a recognized term in biology, but it is not often discussed, as it is hard to explain, or even give examples of, an interaction in which both organisms are completely unaffected by an interaction. It is important to note that neutralism does not mean that there is no interaction. The best example I can think of would be two organisms bumping into one another, then continuing on their separate ways. But even this example may indicate that there is potential competition for space.
There are some other ways of classifying biotic interactions based on whether there are any positive or negative outcomes (e.g. antagonism is sometimes used to describe interactions with potentially negative outcomes, such as competition, and predation/parasitism/herbivory, while facilitation is used to describe interactions where one organism is benefited by another, such as mutualism or commensalism). I personally prefer to use a chart because it is a great teaching tool (put up a blank chart and have students come up with examples for discussion).
As always, such classification systems are merely a human tool for trying to categorize the vast complexity of interactions that exist. Exceptions and variations always exist. As is our lab’s mantra, “nature doesn’t like to follow the rules”.
Bronstein, J. L., 1994. Our Current Understanding of Mutualism. The Quarterly Review of Biology. 69;31-51.
Molinaro, D. J., Stafford, E. S., Collins, B. M. J., Barclay, K. M., Tyler, C. L., Leighton, L. R., 2014. Peeling out predation intensity in the fossil record: A test of repair scar frequency as a suitable proxy for predation pressure along a modern predation gradient. Palaeogeography, Palaeoclimatology, Palaeoecology. 412:141-147.
Holt, R. D., 1977. Predation, apparent competition, and the structure of prey communities. Theoretical Population Biology. 12:197-229.