I recently unveiled a new tier of Patreon rewards: 3D printed shark and ray models!For $17 per month, you will get a monthly 3D printed educational model of different shark or ray parts in the mail, and you’ll be supporting my efforts to provide these models to schools for free.
This month’s reward is a tooth from Hexanchus griseus, the bluntnose sixgill shark, a member of the cowshark family!This particular specimen was scanned by Dr. Lisa Whitenack as part of her Ph.D. dissertation work on comparative evolution and biomechanics of shark teeth.
Learn more about the bluntnose sixgill shark and it’s unusual shaped teeth below!
Here’s what the 3D printed model looks like- please note that it is enlarged and not actual size!
And here’s what the actual teeth look like, from photos I took at the Seattle Aquarium’s education collection:
1.Most shark species have 5 gills slits, but bluntnose sixgill sharks have, um, six gill slits. Which is, um, why they’re called that. Their scientific name “Hexanchus” translates to “six gills”. There is also a group of sharks called sevengill sharks, if anyone would care to guess how many gill slits they have. And while we’re talking about gills, no, not every shark species needs to constantly swim in order to breathe! Forcing water over your gills by swimming is called “ram ventilation,” but many shark species are capable of manually pumping water over their gills using a method called “buccal pumping,” as explained in this How Stuff Works blog post.
I asked Jenny Bigman, a Ph.D. candidate working on shark gills at Simon Fraser University, to explain more about shark gills:
“In all fishes, gills are the primary site of oxygen uptake. Most sharks have 5 gill arches, with 9 sets (called hemibranchs) of gill filaments. Each shark has hundreds of filaments and each filament has hundreds of lamellae. Lamellae are the site of gas exchange and are vascularized (have blood vessels). Water flows over the filaments and past the lamellae, where oxygen from the water is diffused into the bloodstream of the animal. No one really knows for sure why most sharks have 5 gill arches and a few species have more than 5. I am trying to get samples of sixgill and sevengill sharks to see how their gill surface area compares to sharks with only 5 arches. Although I’m not sure if sharks with more gill arches have a larger gill surface area (comparably) OR they have the same gill surface area (comparably) and just spread it out over more arches, I would hypothesize that sharks with more arches have larger gill surface area because they live in hypoxic (low oxygen) environments.” – Jenny Bigman, Simon Fraser University
2. Bluntnose sixgill sharks usually live in the deep sea, and have been observed at depth of almost 2,500 meters, according to Fisheries and Oceans Canada! They were the sharks that were featured in a particularly dramatic scene in Blue Planet 2. They are a wide-ranging and highly-migratory species found throughout temperate and tropical seas. They’ve been known to eat diverse prey including seals, swordfish, hagfish, mahi-mahi, and even smaller sharks.
3. Sometimes sixgill sharks come into shallow enough water that they interact with SCUBA divers! Typically, this happens with smaller individuals, and almost always at night when they come into shallower waters to feed. There’s a great PBS documentary about this, featuring the Seattle Aquarium’s research team. I reached out to Dr. Shawn Larson, the head of Conservation Research at the Seattle Aquarium and the leader of the Seattle Sixgill research project, and here’s what she had to say:
” The Seattle Aquarium has been studying sixgill sharks (Hexanchus griseus) since 2002 in the Salish Sea. Sixgill sharks are large predatory sharks that typically live in waters deeper than 200 meters. They are thought to live long lives (up to and over 100 years) and are found in every ocean of the world. Adult females sixgills near maximum size of 5 m and weighing 1000s of kg have been found periodically in the relatively shallow inland waters of Puget Sound giving birth. These neonate and juvenile sixgills are then stay in the inland waters of Puget Sound and the Georgia Basin using it as a nursery area. Once they approach adult size and age (3 meters for a male and 4 meters for a female) they leave the nursey area for the deeper open ocean. The sixgill sharks that the aquarium has studies over the years have been the juveniles inhabiting Puget Sound. We found that they inhabit relatively small home ranges (less then 12 km) year round until they leave for the open ocean. These young sixgills live in these small home ranges with a group made up of primarily their brothers and sisters. When the aquarium studied these sharks in the early 2000’s there were many young sixgill in the area (over 100 in Elliott Bay alone). Since 2008 most of the sharks that were being studied have left for the open ocean. We still see some sixgills in Puget Sound but not at the levels we saw in the early 2000’s. The aquarium is still conducting research and taking diver sightings information to document the next time sixgills are seen in large numbers in Puget Sound.” – Dr. Shawn Larson, Seattle Aquarium
4. Bluntnose sixgill sharks are considered to be Near Threatened by the IUCN Red List, but are a species of Special Concern under Canada’s Species at Risk Act (Bluntnose sixgills are the largest commonly-seen shark in Canadian Pacific waters). They are sometimes caught as bycatch and are part of several sport fisheries. Their meat and oily livers are commercially valuable. They used to be caught throughout the Pacific coast of North America to make sandpaper out of their skin and vitamin A supplements from their liver (at that point they were called “mudsharks.”)
5. So what’s up with their weird teeth? Here’s what Dr. Lisa Whitenack had to say.
“Sixgill teeth are really good at sawing back and forth (like a steak knife), and not so good at just puncturing (biting down) on soft prey. Sixgills eat a lot of larger prey when they’re big, so having teeth that can help carve out manageable chunks of prey is helpful! Sixgill teeth are weird compared to what we typically think shark teeth should look like. The sharks we tend to see on tv and in magazines tend to have broad triangular serrated teeth, or thin fang-like teeth. It turns out that shark teeth come in a huge variety of shapes and sizes – some like our molars, some tiny, some big, some with multiple points, some that look like a rip saw blade from a circular saw. And if you go back into the fossil record, across their 400 million years, there are few triangular “typical” teeth! So, to me, there is no weird shark tooth.” – Dr. Lisa Whitenack
Want to get your own 3D printed sixgill shark tooth, and support my efforts to provide these models to schools for free? Support me on Patreon! You can also support me at a lower tier without getting these rewards, and all support is appreciated.