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Matt Kolmann is currently a grad student at the University of Toronto and is an absolute “flat shark,” enthusiast. His work with rays has created some stunning imagery, which at first glance might appear like artwork, but in reality is a new insight into the lives of elasmobranchs. Matt uses CT scans to better understand the functional morphology (form and structure of animals and plants) , ecomorphology (is the study of the relationship between the ecological role of an individual and its morphological adaptations), evolutionary morphology ( how adaptations of form and structure have evolved over time and why) ( are all sub-disciplines within biology) to learn how an organism has adapted or evolved to function within a particular niche or ecosystem. Essentially this means by better understand the structure of an animal both internally and externally, we can better understand the role it plays in a particular ecosystem and how this role has changed, if at all, over time. Thank you Matt for sharing this amazing science with us! To learn even more about Matt’s work you can check out his WEBSITE or follow him on Twitter.
1. What is your favorite species of shark and why? What is your favorite species of ray?
Hmmm, that’s a tough question. Of all the sharks I’ve seen, I have a particular fondness for lantern sharks (Etmopteridae) – they’re bioluminescent and potentially use the photophores on their bellies to mask their body profile, kind of like using light as a cloaking device to hide from predators! Even their spines “light up!”
Favorite ray… that’s even tougher! I think the Xingu River ray (Potamotrygon leopoldi) are particularly neat. These guys are found exclusively in the Rio Xingu in Brasil – a river that has rapids and clear waters for most of its length. These rays have evolved to feed on snails and gastropods there (the Xingu has a strange, almost marine-like ecosystem, with sponges even!) – so they have these very large, stout jaws to crush prey. In addition, they’re stunningly beautiful – with bright white spots (called ocelli) on black skin.
2. What is one species of elasmobranch you would like to see in the wild?
I have been dying to see a Porcupine ray (Urogymnus asperrimus) up-close. They are the only member of their genus in the family Dasyatidae and unlike the rest of these rays, they don’t have a venomous barb. They are, however, covered with many thorny scales called denticles.
3. Can you tell us a little bit about your current research?
My research examines how Neotropical freshwater river rays (Potamotrygonidae; potamos- Gr. for “river” and trygon- Gr. for “stingray”) have adapted to living in the Amazon River and other South American tributaries. I am particularly interested in how quickly these rays have evolved into different species, and how these species seem to specialize on eating different prey. In some cases, these literal river rays eat things that no other elasmobranchs eat – like insects! Other members of Potamotrygonidae only eat fish, while still others only eat snails. Understanding what happens when animals leave one habitat, in this case, marine coastal waters, and transition to a new habitat – freshwater rivers – can teach us a lot about how evolution works. So I have to figure out, by comparing DNA sequences from different species, how all these rays are related to each other (sort of like a family tree) and then try to understand how their anatomy (jaws, fins, etc) relates to their ecology (what they eat and where they live) according to their genealogical history – sort of like finding out why you might look like your relatives, but also a little different.
4. What made you want to study sharks and rays?
I started off being interested with sharks and rays from an anatomy perspective – I knew that sharks had skeletons made of cartilage, not bone like other fishes, and I wondered how this affected their day-to-day lives. In particular, I wondered how some rays and sharks fed on mollusks, like clams and snails, if their skeleton was presumably so flexible. Take a second and pinch the tip of your nose and wiggle it from side-to-side – that’s cartilage. Now, imagine trying to crush a scallop or clam with jaws made out of that – it wouldn’t be very easy. As it turns out, these rays cheat! The cartilage in sharks and rays is very different from cartilage in other vertebrates and in many ways comparable to bone, being both stiff & strong materials.
5. What got you started doing CT scans on sharks and rays?
Many of the animals I’m interested in are difficult to capture, tend to being quite large, and in many cases, protected due to habitat loss and threat from commercial extraction. I didn’t feel like collecting more of them was feasible or ethically responsible – so I had to use specimens from museum collections. These specimens have been collected over hundreds of years and are typically quite rare or fragile. Computed tomography (CT) scans are non-invasive and non-destructive, so it was a perfect way to collect data on internal anatomy (the jaws and related head skeleton, in this case) for my research. CT scans are essentially many, many layered x-ray photographs which are then combined into a single 3D model of the animal. Areas of these x-ray photographs are darker or lighter in color depending on the density of the material they hit – that’s how we can map the skeleton in 3D! CT scans are beautiful in their own way, so it was a fun process as well.
6. What has been your favorite species to scan?
The Cowtail Ray (Pastinachus sephen) is just a weird ray. It has a really funny jaw design – with an extended “lip” of cartilage that protrudes out the front – and round, flat almost domed teeth. The top jaw is curved to fit (we say “occlude”) against a matching, curved lower jaw. We think these curved jaws help the rays break and eat large crabs, but we’re not sure yet.
7. What is one of the coolest things you have learned from your research?
I have to say, scanning that Xingu River ray was really exciting, I’m sort of enamored with that species. Its jaws are very similar to Cownose rays (Rhinoptera) and Eagle rays (Aetobatus), despite not being closely related. It was very exciting that my theories had been supported – a lot of rays eating similar prey (mollusks) should very similar – despite being only distantly related. Both Eagle rays, Bat rays, and the Xingu River rays eat “hard” stuff – and their jaws and teeth look very much alike – big, blocky, and with teeth that interlock to form a single tooth “plate.” When unrelated animals look alike because they have similar ecological roles, we call this “evolutionary convergence” – meaning that for some characteristics, animals tend to evolve a good design and stick with it.