Shark week 4: megalodon tooth colonized by boring clams
November 9, 2022
Alert readers probably noticed that I titled the first post in this series “Matt’s first megalodon tooth“, implying that there would be other megalodon teeth to follow. Here’s my second one.
At first glance, this is a pretty jacked-up megalodon tooth. It is pocked with circular and ovoid craters, and has a big fat hole drilled right through it. Hardly collector grade! And in fact that’s what first caught my attention about this tooth — it’s a 6-incher that was being offered for an enticingly low price. But I got even more excited when I clicked past the thumbnail image on the sale site and saw precisely how this tooth was damaged. This is not random, senseless taphonomic battery (ahem); this tooth was colonized by a bunch of boring clams.
Like Adam Savage — and, I suspect, most collectors-of-things — I am fascinated by objects and the stories that they tell. And this tooth tells several stories. First, it’s a huge tooth from a huge shark, a truly vast, multi-ton animal heavier than a T. rex and longer than my house. Second, it’s a fossil that’s millions of years old, evidence of an extinct species from a vanished ecology, one where gigantic sharks and macroraptorial sperm whales hunted small baleen whales, early seals and sea lions, and manatees and sea cows. And third, it’s a relic of another, entirely different ecology, one in which this shed tooth sank to the sea floor and was colonized by a host of smaller organisms, including most obviously hole-boring clams. In effect, this one tooth was a miniature reef, supporting multiple species of invertebrates. The traces left by those invertebrates are themselves ichnofossils, so this tooth is a body fossil with ichnofossils dug out of it. It’s turtles all the way down!
Can we figure out what any of those invertebrates were? Just a few years ago that would have been a challenging task for a non-specialist, but fortunately in 2019 Harry Maisch and colleagues published a really cool paper, “Macroborings in Otodus megalodon and Otodus chubutensis shark teeth from the submerged shelf of Onslow Bay, North Carolina, USA: implications for processes of lag deposit formation”. That paper is very well illustrated, and the figures basically serve as a field guide for anyone who wants to identify similar traces in rocks or teeth of equivalent age. I will take up that sword in a future post.
Incidentally, this is now the biggest tooth in my little collection, just slightly — but noticeably — bigger than my first megalodon tooth: 157mm on the long side, vs 155mm, and 112mm max root width, vs 107mm.
Bonus goofy observation: I strongly suspect that no other megalodon tooth in the world beats this one in simulating a Star Trek phaser.
Reference
Shark week 3: free stuff for the shark-obsessed
November 8, 2022
Couple of fun things here. First, if you’d like to play with — or print — 3D models of megalodon teeth, there are a bunch of them on Sketchfab, helpfully curated by Thomas Flynn, the Cultural Heritage Lead there. As of this writing there are 24 meg teeth in the collection (link), and by my count 14 of them are downloadable, 11 for free and 3 for sale. If you’re not already on the ‘fab, it takes like 2 minutes to create a free account, and then all you gotta do is click on the download icon next to each freely downloadable tooth.
Second, I obviously named this post series after Shark Week on the Discovery Channel, but the sad fact is that Discovery Channel documentaries long ago took a steep nose dive into being mostly garbage. I guess if you like seeing the same footage half a dozen times in a 40-minute documentary, being repeatedly beaten over the head with the same three very basic facts (or, too often, “facts”), and wondering which thing the creators have more contempt for, the actual science or you, the audience, then go ahead, knock yourself out.
If, on the other hand, you like non-repetitive, vibrant footage, non-repetitive, useful and informative narration, and coherent programming you can actually learn from, let me suggest the Free Documentary – Nature channel on YouTube.
“Rise of the Great White Shark – A History 11 Million Years in the Making” is excellent, with tons of great footage and some very nicely-done explanations of the sensory and thermoregulatory adaptations of great whites and other sharks — and, whaddayaknow, a fact-based, non-sensationalized, and still awesome segment on megalodon.
I also learned a lot from “Shark Business”, about the growing ecotourism business of boat- and scuba-based shark tours or shark encounters. Two things in particular stood out: first, because sharks don’t have hands, their exploratory way of interacting with objects in their environment is to give everything a test bite. The vast majority of shark “attacks” on humans consist of a single bite, with a quick disengagement and no pursuit of the human by the shark. It’s just that sharks have super-sharp teeth and incredibly powerful jaws, and even a comparative gentle (to the shark) test bite can leave a person severely injured or dead. That sharks most often don’t intend any harm is probably cold comfort to people who have been subject to test bites, but it’s a useful thing to understand if you’re genuinely interested in sharks.
The other thing that jumped out at me is the 50-second segment that starts at 7:45, in which a tour guide is shown pushing on the snouts of great white sharks with his bare fingers as they approach the boat. The sharks roll their eyes back, open their mouths, and seem to go catatonic for a bit. Although they don’t make this connection explicitly in the doc, sharks generally roll their eyes back when they go in for a bite, presumably to protect their eyes from the object they’re sampling. I wonder if the nose touch signals to the shark that it’s bite time, and it rolls its eyes back, opens its mouth, and waits for something to bite down on. It seems like a useful thing to be aware of in case a shark is ever coming at you — a gentle push on the snout might put the shark into zombie mode for long enough to get out of the way. On the flip side, if you push the shark’s snoot and don’t get out of the way, it might be super-primed to take a hunk out of you. Note: I am not a shark expert, this is not professional advice, and I assume no liability if a shark eats your arm off. I just thought it was an interesting bit of shark biology that could conceivably pay off in an emergency.
Is this really going to be a whole week of shark posts? Beats me! I’m making this up as I go. Let’s find out.
Shark week 2: great white teeth redux
November 6, 2022
Cast (white) and fossil (gray) great white shark teeth, lingual (tongue) sides.
Something cool came in the mail today: a fossil tooth of a great white shark, Carcharodon carcharias. The root is a bit eroded, but the enamel-covered crown is in great shape, and it’s almost exactly the same size as my cast tooth from a modern great white.
The labial (outer or lip-facing) sides of the same teeth.
I got this for a couple of reasons. One, I wanted a real great white shark tooth to show people alongside my megalodon tooth (for which see the previous post). Extant great whites are quite rightly protected, and their teeth are outside my price range when they are available at all. Fortunately there are zillions of fossil great white teeth to be had.
Also, the cast great white tooth has been kind of a disappointment. It’s so white that it’s actually a letdown, visually. Tactilely it’s great, with all kinds of subtle features on the crown especially, but those features are almost impossible to see or photograph. In the photo above, you can make out some of the long, smooth wrinkles in the enamel of the cast tooth, but the median ridge, which is dead obvious on the fossil tooth, only shows up under very low-angle lighting on the cast. The fossil tooth is just a more interesting and more informative specimen, material and origin aside. Now that I have it, I might try either staining or painting the cast tooth, to see if I can rehabilitate it as a visual object.
This fossil tooth is also noticeably thicker than the cast tooth. I don’t know if that’s serial, individual, population, or evolutionary variation. In the last post I contrasted the proportional thinness of the cast tooth with the robustness of the megalodon tooth; this fossil tooth might fare a little better if subjected to the same comparison. I should have thought to do that when I was taking these photos.
Speaking of comparisons, here’s megalodon to remind everyone who’s boss. There’s no scale bar here, but the cast great white tooth is 65mm from the tip of the crown to the tip of the longer root, and the meg tooth is 155mm between the same points.
Now I have a gleam in my eye of assembling a couple of sets of fossil teeth: one to illustrate the evolution of the modern great white from its less-serrated ancestors, like this diagram from the great white Wikipedia page, and one to illustrate the evolution of megalodon from its side-cusped ancestors, like this diagram from the megalodon page — presuming that current hypotheses for the two lineages are accurate. If I ever get either set done, I’m sure I’ll yap about it here.
Matt’s first megalodon tooth
November 5, 2022
I got this thing a while back. I’d always wanted one, and it really does spark joy.
First up: what should we call this critter? AFAIK, the species name has never been in doubt, it’s always been [Somegenus] megalodon. That genus has variously been argued to be Carcharodon (same as the extant great white shark, Carcharodon carcharias), Carcharocles, Otodus, Megaselachus, and probably others. From my limited reading, the current consensus seems to be converging on Otodus, for reasons that seem reasonable to me, but I’m hardly an expert on this problem. It’s not that I think it’s unimportant, more that the generic identity of [Somegenus] megalodon has been historically labile, and as a non-expert I hesitate to come down firmly behind any of the hypotheses. If it’s still Otodus megalodon in another decade, I might take a stand. If you want to do a deep dive on this, check out Kent (2018: 80-85). In the meantime, I’m going to refer to it informally as ‘megalodon’, without italics. Although the actual genus name Megalodon was tragically wasted a fossil clam (true story), I’m confident that no-one, scientist or layperson, will misunderstand when I refer to the humongous extinct megatoothed shark as megalodon.
With that out of the way: wow, that’s a big freakin’ tooth! Here it is again with a scale bar.
The serrations on the sides are very cool. The edges are worn a bit in places, and that plus the visible notch on one side of the tooth (upper left in the photo above) suggests that this tooth was used, as opposed to being a replacement tooth that rotted out of the jaw before it ever had a chance to be deployed. Where ‘used’ means ‘used to punch and then tear immense holes in other animals’. Pretty wild to think about ancient whales dying on this very tooth.
I use this thing at outreach events, and I got a cast tooth of a modern great white shark for comparison. Those great white teeth are 10 bucks at Bone Clones, so I got a bunch of them and gave them to nieces and nephews as stocking stuffers.
Here’s a labeled version. From what I’ve been able to determine (i.e., shark people, please correct me if I’m wrong!), most shark teeth ‘lean’ away from the body midline. Upper teeth of megalodon tend to be very wide, with wide, shallow angles at the base, whereas lower teeth are more dagger-shaped and have a more pronounced basal angle. I’m pretty sure this meg tooth is a lower, and we’re looking at the lingual (tongue) side in this photo (more on that in a bit), so the tooth is facing the same way we are. I think that makes it a left lower tooth. The great white tooth is a probably a left upper, although great whites apparently have one tooth position that leans mesially instead of distally, so I could have that one wrong-sided. The ‘bourlette’ is an area of exposed orthodentine between the root and the enamel that covers the tooth crown (Kent 2018: 86). This tooth is not in perfect shape, there’s been some peeling of the enamel just above the bourlette.
I think this photo makes the size-comparison point even more clearly.
Worth noting: if the hypothesis that megalodon belongs in Otodus is correct, the similarities between megalodon and the great white shark are convergent; megalodon teeth are Otodus teeth that lost their side-cusps, and great white teeth are basically wider, serrated mako teeth. That level of convergence shouldn’t be surprising to anyone who has seen a thylacine skull. Still, this photo makes it very obvious why Louis Agassiz assigned megalodon to Carcharodon, the great white shark genus, when he named the species back in 1843: the two look a lot alike. (Also: Agassiz didn’t have all the transitional fossils that we do now.)
Boomerang thought, added in post: at least, megalodon teeth look a lot like the upper teeth of great whites. The lower teeth of great whites are much narrower and more mako-esque.
A couple of features worth noting here. The mesial margin has a little wrinkle, which cannot be damage because the serrations follow the in-folded contour. This seems to be a minor developmental anomaly that is pretty common in megalodon teeth. The distal margin has a distinct notch, also mentioned above, which probably represents feeding damage sustained in life.
Arguably this side-view is even more striking; the megalodon tooth is 2.38 times the length of the great white tooth (155mm vs 65mm on the long side), but more than three times as thick (29mm vs 9mm max thickness), and the blade of the tooth stays proportionally thicker over more of its length. This tooth was built to do some work.
Am I fanboying here? Sure, a little (and not for the first time). Giant extinct monsters are exciting, and I’m happy to celebrate that while also wanting to know more about how they lived.
The thing that surprised me the most while reading up on shark teeth is how they are oriented in the jaws. I’d always assumed that the convex faces (toward the bottom of the above photo) faced outward (labial or lip-facing), and the flat faces (toward the top of the above photo) faced inward (lingual or tongue-facing), but it’s actually opposite. In the photo above, the labial or outward faces are up, and the lingual or inward faces are down. I’m sure this is old hat to shark people, but it hurts my head. Most teeth I know of have their convex faces outward, like human incisors and tyrannosaur premaxillary teeth. Plus, instinctively it seems like predator teeth should curve toward the back of the mouth, but with their flat labial faces and convex lingual faces, most shark teeth seem to curve toward the front (I realize that they may have been placed in the jaws so that they still pointed backwards overall). I was so surprised by this that I did a lot of checking before bringing it up in this post, but it’s clear even in really good photos of live great white sharks with their mouths open. There’s no bigger story here, just me confronting my own misapprehension about animal morphology. Still seems weird.
If you want to know more about how megalodon lived, I’ve included links below to some papers on its size (Shimada 2019, Shimada et al. 2020, Cooper et al. 2020, 2022, Perez et al. 2021), breeding habits and life history (Miller et al. 2018, Shimada et al. 2021, 2022), evolution (Shimada et al. 2016, Kent 2018, Perez et al. 2018), and paleobiology (Maisch et al. 2019, Ballell and Ferron 2021, Miller et al. 2022, Sternes et al. 2022). This is a highly idiosyncratic collection based on like one evening of messing around on Google Scholar. I’m sure I missed tons of important work, so feel free to recommend more refs in the comments.
Oh, like virtually everything else on this site, these photos are freely available under the CC-BY license, so if you want to use them, modify them, etc., go nuts.
References
- Ballell, A. and Ferrón, H.G. 2021. Biomechanical insights into the dentition of megatooth sharks (Lamniformes: Otodontidae). Scientific Reports 11(1): 1-9.
- Cooper, J.A., Pimiento, C., Ferrón, H.G. and Benton, M.J. 2020. Body dimensions of the extinct giant shark Otodus megalodon: a 2D reconstruction. Scientific Reports 10(1): 1-9.
- Cooper, J.A., Hutchinson, J.R., Bernvi, D.C., Cliff, G., Wilson, R.P., Dicken, M.L., Menzel, J., Wroe, S., Pirlo, J. and Pimiento, C. 2022. The extinct shark Otodus megalodon was a transoceanic superpredator: Inferences from 3D modeling. Science Advances 8(33): p.eabm9424.
- Kent, B.W. 2018. The cartilaginous fishes (chimaeras, sharks, and rays) of Calvert Cliffs, Maryland, USA. The Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA. Smithsonian Contributions to Paleobiology 100: 45-157.
- Maisch IV, H.M., Becker, M.A. and Chamberlain Jr, J.A. 2020. Macroborings in Otodus megalodon and Otodus chubutensis shark teeth from the submerged shelf of Onslow Bay, North Carolina, USA: implications for processes of lag deposit formation. Ichnos 27(2): 122-141.
- Miller, A., Gibson, M. and Boessenecker, R. 2021. A megatoothed shark (Carcharocles angustidens) nursery in the Oligocene Charleston Embayment, South Carolina, USA. Palaeontologia Electronica 24(2): 1-19.
- Miller, H.S., Avrahami, H.M. and Zanno, L.E. 2022. Dental pathologies in lamniform and carcharhiniform sharks with comments on the classification and homology of double tooth pathologies in vertebrates. PeerJ 10: e12775.
- Perez, V.J., Godfrey, S.J., Kent, B.W., Weems, R.E. and Nance, J.R. 2018. The transition between Carcharocles chubutensis and Carcharocles megalodon (Otodontidae, Chondrichthyes): lateral cusplet loss through time. Journal of Vertebrate Paleontology 38(6): e1546732.
- Perez, V.J., Leder, R.M. and Badaut, T. 2021. Body length estimation of Neogene macrophagous lamniform sharks (Carcharodon and Otodus) derived from associated fossil dentitions. Palaeontologica Electronica 24(1): a09.
- Shimada, K. 2019. The size of the megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), revisited. Historical Biology 33(7): 904-911.
- Shimada, K., Chandler, R.E., Lam, O.L.T., Tanaka, T. and Ward, D.J. 2016. A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the ‘megatoothed’clade. Historical Biology 29(5): 704-714.
- Shimada, K., Becker, M.A. and Griffiths, M.L. 2020. Body, jaw, and dentition lengths of macrophagous lamniform sharks, and body size evolution in Lamniformes with special reference to ‘off-the-scale’gigantism of the megatooth shark, Otodus megalodon. Historical Biology 33(11): 2543-2559.
- Shimada, K., Bonnan, M.F., Becker, M.A. and Griffiths, M.L. 2021. Ontogenetic growth pattern of the extinct megatooth shark Otodus megalodon—implications for its reproductive biology, development, and life expectancy. Historical Biology 33(12): 3254-3259.
- Shimada, K., Maisch IV, H.M., Perez, V.J., Becker, M.A. and Griffiths, M.L. 2022. Revisiting body size trends and nursery areas of the Neogene megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), reveals Bergmann’s rule possibly enhanced its gigantism in cooler waters. Historical Biology: 1-10.
- Sternes, P.C., Wood, J.J. and Shimada, K., 2022. Body forms of extant lamniform sharks (Elasmobranchii: Lamniformes), and comments on the morphology of the extinct megatooth shark, Otodus megalodon, and the evolution of lamniform thermophysiology. Historical Biology 1-13.
OMNH 1670, a fat shark, the past, and the future
December 20, 2017
I have used this photo in loads of talks, but as far as I can tell, this is the first time I’ve put it up on SV-POW! (I am certain that, having said that, someone will find a previous instance – if so, consider this an extremely inefficient and lazy form of search.) The vert is OMNH 1670, the most complete and nicest dorsal of the giant Oklahoma apatosaurine, probably a D5 or D6. That’s me back in 2004. Photo by my then fellow grad student in the Padian lab, Andrew Lee. I’m 6’2″ and have normally-proportioned human arms, but if you’re trying to figure out the scale, that vert is 135cm tall, with an anterior centrum face 38cm tall by 46cm wide (partly reconstructed but probably accurate). See this post for more details and a fairly exhaustive list of measurements.
Here’s a stupid thing: roughly 2-3 times a year I go to the field or to a museum and get hundreds of SV-POW!-able photos. Then I get back to the world and catch up on all of the work that piled up while I was away. And by the time I’m done with that, whatever motivating spark I had – to get some of those photos posted and talk about the exciting things I figured out – has dissipated.
Case in point – this bitchin’ shark, prepped in ventral view, which I saw last month in the natural history museum in Vienna. Look at that fat, muscular tail – this shark is swole.
That’s dumb. And this blog is in danger of slipping into senescence, and irrelevance.
So here’s my New Year blog resolution for 2018: I’m getting us back to our roots. I, or we – I am taking this plunge without consulting with Mike (surprise, buddy!) – will post a new, never-posted-before photo, at least once a week, for the whole year. It may not always be a sauropod vertebra, but if often will be, because that’s what I have the most of, and the most to yap about. And I will try to write something interesting about each photo, without lapsing into the logorrhea that has too often made this blog too exhausting to contemplate (at least from this side of the keyboard).
Wish me luck!
Amazing free comparative anatomy resource. Also, sharks (also for free).
February 29, 2016
Functional Anatomy of the Vertebrates: An Evolutionary Perspective, by Liem et al. (2001), is by some distance my favorite comparative vertebrate anatomy text. When I was a n00b at Berkeley, Marvalee Wake assigned it to me as preparatory reading for my qualifying exams.
This scared me to death back then. Now I love it – sharkitecture!
The best textbooks, like Knut Schmidt-Nielsen’s Animal Physiology (which deserves a post or even series of its own sometime), have a clarity of writing and illustration that makes the fundamentals of life seem not only comprehensible, but almost inevitable – without losing sight of the fact that nature is complex and we don’t know everything yet. FAotV has both qualities, in spades.
Where vertebrae come from. Liem et al. (2001: fig. 8.4).
I’m writing about this now because Willy Bemis, second author on FAotV, has just made ALL of the book’s illustrations available for free on his website, in a series of 22 PowerPoint files that correspond to the 22 chapters of the book. All told they add up to about 155 Mb, which is trivial – even the $5 jump drives in the checkout lanes at department stores have five to ten times as much space.
Aiiiieeee – a theropod! Aim for its head! Liem et al. (2001: fig. 8.17).
Of course, to get the full benefit you should also pick up a copy of the book. I see used copies going for under $40 in a lot of places online. Mine will have pride of place on my bookshelf until I enter the taphonomic lottery. And I’ll be raiding these PPTs for images from now until then, too.
Countercurrent gas exchange in fish gills – a very cool system. Liem et al. (2001: fig. 18.6).
So do the right thing, and go download this stuff, and use it. Be sure to credit Liem et al. (2001) for the images, and thank Willy Bemis for making them all available. It’s a huge gift to the field. Here’s that link again.
Dangit, if only there was a free online source for illustrations of shark anatomy… Liem et al (2001: fig. 10.12).
But wait – that’s not all! Starting on June 28, Dr. Bemis will be one of six faculty members from Cornell and the University of Queensland teaching a 4-week massively open online course (MOOC) on sharks. Freakin’ sharks, man!
“What did you do this summer? Hang out and play Nintendo?”
“Yep. Oh, and I also took a course on freakin’ sharks from some awesome shark experts. You?”
As the “massively open” part implies, the course is free, although you have the option of spending $49 to get a certificate of completion (assuming you finish satisfactorily). Go here to register or get more info.
Reference
- Liem, K.F., Bemis, W.E., Walker, W.F., and Grande, L. 2001. Functional Anatomy of the Vertebrates. (3rd ed.). Thomson/Brooks Cole, Belmont, CA.
Sauropod Vertebra Picture of the Week 
