Armed to the Teeth: Bites from Forgotten Sharks

As the 31-day stretch of August rapidly rushes to completion, and the balmiest days of summer fade into the imminent, cool veil of fall, 2014 also discards one of its temporal landmarks associated with these heat-stricken days. If you think I am referencing something remotely anapestic and evoking chest-fluttering nostalgia of long-forgotten, canicular childhood summers, then think again. Because I am, of course, talking about Shark Week.

Yes, that now-legendary bit of the Discovery Channel’s summer programming line-up, a selachimorph-centered festival that is closing in on three decades running, has now passed us by, ending but two weeks ago. Years ago, Shark Week initially appeared to be driven with the mission statement of Discovery in mind, one rooted in the dissemination of fundamentally educational, science-based material in an entertaining manner. This incarnation of Shark Week was the one I was fortunate enough to grow up with, and this week was a boon to my insatiably science-curious child brain, one that my neurons practically salivated over in Pavlovian form right around the time the last traces of abandoned, burnt out firecrackers left July’s dirt. The gift of science education excellence was instrumental in the development of my eventual fascination (and career trajectory) with biology, and I credit the old-school Discovery Channel’s programming with much of the inspiration and intrigue about the natural world that gilded my early days.

At the age of four, my shark ID skills were solid. However, my artistic skills were still…er….buffering.

So, given the intimate intellectual relationship I have with Shark Week and Discovery, watching what both entities have become in recent years feels like a steel-toed kick to the kidneys. There are a laundry list of offenses, and all of them hit on a single formula; the sacrifice of ethics and scientific accuracy in favor of mythology and adrenal-gland massaging codswallop; a grand invasion of heart-pumping, flash and sparkle nonsense programming based on approximately zero micrograms of actual science, all as an ill-conceived motion to inflate ratings. Some examples of Shark Week contrived falsehoods? Well, there’s this lovely bit of mass hysteria-inducing, publicity-hungry deceit initiated by cries of “oh no! Lake sharks! *wink wink*.” Also, there’s that time Discovery trotted out this steaming, embarrassingly unscientific pile of horseshit. Oh, there’s also that other time they made an entire special up. Or how about how the network can only seem to convince scientists to do Shark Week specials with them if they straight-up con them into doing so?

Others (linked above) have done a splendid job of calling out the network’s recent, fraudulent Shark Week habits, so this post isn’t going to be yet another dart in that already well-pockmarked board, but what I want to address is loosely tied to Shark Week’s newfound adoration of Megalodon (well, specifically an adoration of tricking viewers into believing the very extinct shark is still patrolling the deep…now for two years in a row).

“Megalodon”, or to be more accurate Carcharocles megalodon (or Carcharodon megalodon, it depends on what paleontologist you ask) is a popular beast, and thus is an obvious choice for many an examination by television networks (in mockumentaries or not). The extinct shark species is popular for damn good reason, too. C. megalodon was an animal of such outlandish proportions that it doesn’t seem like it could ever have existed, and yet it did, for more than 26 million years, dying out right around the time our ancestral line first harnessed that hot, orange, light-producing stuff that eats up wood (followed swiftly by the invention of S’mores and crappy ghost stories). This was a shark that, according to the most conservative estimates, exceeded 45 feet in length, and had a pair of cartilaginous bear trap-esque chompers big enough to gulp down a Ford Fiesta without even scratching the paint on its immense, triangular teeth.

And oh yes, those teeth. Those frisbee-sized blades that festooned its jaws in a ragged chain of despair. Those famous teeth, for which the animal is named (megalodon basically means “giant fucking tooth”), combined with a body bigger than a goddamn school bus, have enraptured the imaginations of young and old alike, and contemplation about what it would be like to encounter such a surreal, monstrous animal in the flesh is unavoidable.

But, here’s the deal with ol’ Megs…outside of its status as by far the largest shark that ever lived, and definitely one of the biggest predators to ever exist (getting edged out by the sperm whales alive today)…as far as we can tell, there’s nothing insanely unique about its biology. Granted, one of the most fascinating things about C. megalodon is that we don’t know that much about it. Even the size of the thing is sort of up in the air, seeing as how the scientific community has only fragmentary remains (teeth and a handful of vertebrae; the cartilaginous skeletons of sharks don’t fossilize as readily as bony skeletons, so this dearth of recorded remains is not that unusual) from which to base their calculations; estimations range from the 40s of feet in length to more than 60 feet…which in my book is the difference between “we’re going to need a bigger boat” huge and “I’m going to need a new pair of pants” huge.

Honestly, C. megalodon was cool and all, but it was basically just a Hulked-out version of any large lamniform shark (Lamniformes being the order of sharks to which great whites and makos belong). The animal is more or less like a great white had a run in with Rick Moranis and his growth ray, with maybe some very subtle differences in proportions…and a slightly different taste in prey…like taking on goddamned whales instead of comparatively diminutive sea lions. Yes, C. megalodon was something of a specialized whale killer…a shark exquisitely well-adapted to slaughtering and consuming the most massive animals of all time.

So sure, it’s teeth were heart-stoppingly big, and robust, and belonged in the titanic jaws of a beast of celebrity status….but they were just relatively standard lamniform teeth ratcheted up in size, with some limited modifications for slicing through several hundred cubic feet of whale flesh and bone at a time (increased thickness and bigger, deeper roots). For an animal so well-known for its mouth, it certainly didn’t have the most unique pearly whites among extinct sharks. The diversity of prehistoric sharks, and the diversity their feeding adaptations (which often are very divergent from today’s sharks), are woefully unappreciated, at least in comparison to C. megalodon, which is a remarkable shark due to its size and power…but I can think of a couple examples of long-extinct sharks that have far more interesting things going on at their eating ends.

Take Cretoxyrhina mantelli, for example, pictured below in this reconstruction by paleo-artist Dmitry Bogdanov, which given this speculative coloration, appears to be a shark that has deceptively splashed its belly in paint in a desperate attempt to mimic a great white shark.

I blame unrealistic standards of shark intimidation in the media.

Cretoxyrhina wouldn’t have had to try too hard to look like the most powerful predatory shark of today’s oceans (the great white), considering that they were very close relatives and reached similar sizes (although Cretoxyrhina likely got even larger, topping out at around 23 feet (7 meters) or more in length). Cretoxyrhina was a member of the same taxonomic order of sharks that great whites and C. megalodon belonged; Lamniformes, a group of sharks characterized by relatively conical snouts, five gill slits, and a mouth that sits behind the eyes. Cretoxyrhina was part of different family of sharks than today’s sea lion tossers, but they were more or less cut from the same evolutionary mold.

Cretoxyrhina patrolled global shallow seas between about 80 and 100 million years ago, meaning that it was separated from the most ancient great white sharks by the same immense length of time that modern humans are separated from the last of the dinosaurs. One of the places it called home, and where many high-quality fossil remains have been discovered, was Kansas. Cretoxyrhina didn’t frequent the Sunflower State because it craved barbecue and pursued the smells wafting out of Kansas City by crawling through wheat fields Land Shark style. Cretoxyrhina has fossils coming up in the heartlandiest part of America’s heartland because during the Mid-Cretaceous era, this entire region was covered by the Western Interior Seaway, a great swath of saltwater that divided North America longitudinally into two giant landmasses, running unbroken from the Gulf of Mexico to the Arctic Ocean. The notion that Kansas, and much of the American Mid-West, was a sea bed tens of millions of years ago isn’t that surprising considering that the region is flatter than twenty year-old can of Crystal Pepsi. It’s flatter than Bernie Lomax’s ECG. Flatter than that dusty, unused piano in your grandmother’s guest room. Flatter than how a joke about twerking falls at an AARP convention. What I’m trying to say is that Kansas is flatter than shit (and honestly, it’s kind of a dull, featureless, oppressive shithole, both due to the aggressive summer heat and the legions of hyperreligious, bug-fuck insane, freedom-fried inhabitants…sorry Kansans).

The Western Interior Seaway was an ocean that teemed with a rich diversity of marine life, and provided Cretoxyrhina with a smorgasbord of flavorful, finned fauna upon which to dine…and dine it did, with a set of some of the most impressive teeth to evolve in the hundreds of millions of years of shark prehistory. These knife-like teeth, some two inches long and numbering more than thirty in each jaw not counting the replacement teeth “on deck” (compared to the twenty-five or so in great white jaws), are graced with a unique characteristic of their construction; the presence of an unusually thick, resilient enameloid (similar to enamel, the hardest, outermost covering of human teeth) coating. These teeth had the impeccable sharpness common to predatory sharks in general, combined with an unprecedented toughness. Cretoxyrhina was equipped with teeth that were particularly good at biting into very hard, bony or shelled things over and over again, and successfully cutting them into manageable, bloody chunks. For this reason, Cretoxyrhina is commonly called the “Ginsu shark”, referring to the famous, supposedly exceptionally sharp cutlery hard sold via infomercial in the 70s and 80s.

It’s perhaps incredibly fortunate for Cretoxyrhina that it had this buzzsaw of a mouth at its disposal. The Mid-Cretaceous oceans, especially in the bountiful, warm, shallow waters of the Western Interior Seaway, were full of “difficult” prey items and “worrisome” predator competition…and by “difficult” and “worrisome” I mean that they would make today’s most effective and brutal marine predators jettison the contents of their bowels into the water column in a fit of terror. Middle America some 90 million years ago was a lukewarm cauldron full of an assemblage of aquatic monstrosities that appear to be lifted straight from the sketchbook of a deranged 8-year old child. Among them was Xiphactinus, a voracious, needle-toothed fish with a dramatic, bulldog-like under-bite and a body the size of a Chevy Tahoe. There were also plesiosaurs like Elasmosaurus, whale-sized, snake-necked reptiles that look more like something hunting in the subterranean oceans of Naboo than something that actually existed on Earth at one time. The seaway also was home to sea turtles that weighed more than two tons, and a number of mosasaurs like TylosaurusFor those unfamiliar, mosasaurs were a group of marine lizards that reached their heyday at the tail end of the Cretaceous, and were basically a hellish amalgamation of crocodiles, eels, and sharks…but blown up to the size of an orca. Wherever mosasaurs swam, they, understandably, were among the most dominant predators in their ecosystem. Similar throngs of animals were found in epicontinental seas (inland seas and seaways) and continental shelves (areas offshore where the continental plate is submerged in the sea; more shallow than the middle of the oceans), prime Cretoxyrhina habitat, the world over.

The “Ginsu shark” may have been an impressive fish, with its gob full of diamond-tipped blades and imposing bulk, but it was just one of many giant predators in the tepid Cretaceous oceans.

So, there was a glut of flesh, bone, and teeth during this time; on land there were still the big, non-avian (non-bird) dinosaurs, and in the seas, gigantic reptiles and fish. Cretoxyrhina was likely superbly adapted to exploiting food sources in these treacherous waters via its uniquely effective bite. Flourishing in a sea full of big, armored, active animals means you have to have the capacity to take a shot at just about anything…and it appears as though Cretoxyrhina did just that. Cretoxyrhina teeth and bite marks are found in just about every big animal it shared the water with; Archelon, the largest sea turtle to have ever existed, got jacked up by this shark…the shark tore into giant pleisosaurs….and even went after the biggest and least-fuck-withable things around, mosasaurs. It is often hard to tell from the fossil evidence whether or not affixed teeth or scarring on bone is the result from an actual attack and feeding, or simple posthumous scavenging. However, there are examples in the fossil record of Cretoxyrhina making a failed attempt at a kill of a mosasaur, evidenced by the mosasaur’s vertebrae having shark teeth embedded within the bone, where the injury became infected, subsequently healed, with the bone growing over the tooth like a tree trunk slowly enveloping a fence over decades. Think about that for a second; mosasaurs, a predator group so heinous that it likely had an impact on the decline of entire orders of other humongous, fang-toothed, marine reptiles like pliosaurs and ichthyosaurs, were a menu item for Cretoxyrhina. Even if most of its interactions with the largest predators and prey in the ocean were, realistically, opportunistic events where it fed on small, young, or sick individuals, or just devoured the dead…the Ginsu shark assuredly occasionally used those incredible teeth against things that were very big, very strong, and very dangerous.

Cretoxyrhina wasn’t the baddest bastard under the waves, but outfitted with a bite that could cleave several inches of bone in an exposed mosasaur flipper as effortlessly as a light saber carving through a gelatin salad, it sure as shit acted like it was. C. megalodon may have chiefly fed on giant whales…but baleen whales don’t have the ability to fucking bite back, and for that reason, Cretoxyrhina’s comparably courageous habit of recklessly targeting actual, real life sea monsters as food, as if it’s filming an episode of Jackass, receives an award for Heftiest Gonads of Shark Prehistory, at least in my book.

A second shark with a special set of teeth actually lived in the Western Interior Seaway during the same era as Cretoxyrhina, but this shark fed itself in a way not often associated with anything vaguely related to the common conceptualization of how a “shark” is supposed to make a living. A major part of this reason is because this shark had teeth that looked very similar to these:

Less with the “serrated death dagger” and more with the “wrinkly elbow” look

These teeth belong to a species of shark in the genus Ptychodus. Ptychodus was one of the last remaining examples of a group of sharks known as hybodonts (order Hybodontiformes). Hybodonts evolved more than 300 million years ago, and were incredibly common throughout the “age of the dinosaurs”, but eventually were out-competed by more sophisticated, less primitive sharks and died out sometime near the end of the Cretaceous. At the very end of their time on Earth, some bizarre, specialized forms had evolved, and Ptychodus was one of them.

Ptychodus had a set of jaws packed with rows of flat, bottle cap-shaped teeth arranged in a dense formation that resulted in a functional “plate” in both upper and lower jaws, opposing each other. This meant that Ptychodus obviously had a vastly different dental set up compared to other contemporary sharks, with much of the jaw toothless, save for this odd battery of bumpy hubcaps crammed together at the very front of the face.

It also meant that it had jaws that weirdly resembled the human female reproductive system.

It is thought that these mouths full of molars were an adaptation to feeding upon a very specific, and very locally abundant quarry; shelled animals, particularly clams. This type of feeding on tough, hard-shelled organisms, involving using broad teeth and powerful jaws to crush the shell outright, is known as “durophagy”, and outside of the limited number of species of bullhead sharks, it is not a strategy employed by modern sharks. We don’t know a whole lot about what they looked like and how they behaved, but given what we know about living sharks that have slow-moving prey that stay close to the bottom, we can surmise that Ptychodus had similar characteristics, in that it was likely slow-swimming (since hunting clams and urchins and other spiny, shelled critters doesn’t exactly require much chase) and resembled sharks with similar habits, like a nurse shark, for example.

This dietary specialization is unique, but one species of Ptychodus, Ptychodus mortoni, unearthed in Kansas several years ago, takes the entire game to a whole other level by being huge, based on calculations from fragmentary remains. How huge? Ten meters huge. That’s longer than a lot of sailing yachts.

P. mortoni was among one of the largest sharks of all time (and certainly one of the largest durophagous creatures of all time), and if it were alive today, it would only be exceeded in mass by whale sharks and the occasional basking shark…so it must have been eating bucket loads of clams to sustain itself, right? Not necessarily, at least not the types of clams you and I are familiar with. The Western Interior Seaway was also inhabited by a giant organism of a different stripe; Platyceramusthe most titanic genus of clam to ever sit, boringly, in the loose silt at the bottom of the sea. It was a clam with a shell that, at its smallest was bigger than your bulkiest, most airline-unfriendly piece of luggage, and at its largest, could fill an entire living room. A single individual could produce enough clam chowder to quell the hunger of a hundred famished New Englanders. Platyceramus was so insanely colossal that it served as a micro-ecosystem in and of itself, being utilized as protection for scores of fish, as well as a substrate for other shelled animals to attach and grow. This mega-mollusk, which makes the giant clams of today look like dinky, littleneck clams, was likely splintered by the insatiable car compactor jaws of P. mortoni, and the great underwater fields and reefs of these clams that once lined the shores running up and down the soon-to-be Great Plains could have been a major source of food for such a giant fish.

It’s unknown exactly what brought an end to P. mortoni. During the latter part of the Cretaceous, hybodont sharks were being outpaced by “newer models” of sharks, generally speaking, but given P. mortoni’s level of dietary specialization, traumatic ecological competition doesn’t seem too likely, unless some other giant durophagous fish rears its head in the Kansan fossil record. It’s also unclear if this shark was a victim of the same extinction event that leveled the non-avian dinosaurs, marine reptiles, and pterosaurs. A third route for its extinction might be linked to its selective diet, and the fact that, as of right now, has never been found outside of the range of the Western Interior Seaway. The seaway eventually closed as the Cretaceous transitioned into the Paleocene, and with it went all the habitat that made such rich grounds for an endless supply of outsized clams. It is possible that even if this last holdout of the hybodont family line managed to slip past millions of years of competition and an abrupt, catastrophic, global extinction event…it could have fallen victim to the incredibly common ecological and evolutionary phenomenon of being exceptionally good at a far too few number of jobs; the biggest species of Ptychodus did a wonderful job of scooting along the bottom of the ocean, shattering clam beds like a steamroller making its way through a ceramics class…but once the clams are gone, unemployment hits swiftly. Unfortunately, ecological unemployment tends to be irreparable, and fatal.

Either way, much like the limelight awash C. megalodon, both these other noteworthy sharks and their astonishing bites are forever lost to the lonely, backward expanse of time. It’s been many tens of millions of years since Cretoxyrhina last unwisely harassed the most decidedly inedible animals to ever evolve on this planet. Ptychodus hasn’t lazily busted open a couch-sized clam in almost that long. No modern human has ever had the undoubtedly epic experience of seeing these three animals alive, and barring the eventual invention of time travel, no human ever will. These animals, along with their incredible teeth, feeding behaviors, and overall biology, are quite dead.

We should consider ourselves lucky that a diversity of groups of sharks made it out of the Mesozoic era and arrived at the present day, continuing their several hundreds of millions of years of existence in our oceans. Multiple lineages of sharks today depart from the archetypal “tooth torpedo” form many of us have assigned to sharks, and engage in a wide array of unique feeding strategies. Unfortunately, many of these sharks are also threatened with extinction. Some hammerhead sharks use their hammer-shaped cephalofoil, armed with a high density of electroreceptive sensors, like a finely tuned metal detector, searching for the slightest signs of stingrays partially buried in the sediment at the bottom of the sea, which are then pinned down in a flash of cartilage-on-cartilage savagery and ingested after being rooted out from their hiding place. These remarkable sharks are also distinctly endangered, with two species currently regarded by the IUCN as endangered, and another as vulnerable. The whale shark, an enigmatic, beautifully serene animal that feeds entirely on plankton via filter feeding in a very unstereotypical fashion (for a shark), equipped with a mouth shaped like an envelope slot and with its closest relatives consisting of tiny, bottom-dwelling, camouflage-embracing sharks, is also the world’s largest “fish”, growing to more than 40 feet in length. It too is considered to be vulnerable to extinction, with major causes of concern of population decline stemming from fisheries that target the sharks, to habitat loss and depletion of the quality of feeding waters. The river sharks of the genus Glyphis are remarkable solely for the fact that they live completely within freshwater river systems, unlike any living sharks (bull sharks are renowned for their ability to access fresh and brackish water, but these sharks depend on saltwater for reproduction and are therefore not truly freshwater animals). River sharks are so rarely sighted (and as a consequence, so poorly understood) that it’s possible we haven’t identified all members of the group yet, and some of the ones we know about are undoubtedly critically endangered, especially those constricted to heavily polluted and overtaxed river basins in Southeast Asia. Sawfish, while not actually sharks (they are instead rays), grow to very shark-like body sizes and use an amazing, tooth-studded, electrosensor-lined bill to detect and stun/impale prey from its position on the muddy bottoms of lagoons, estuaries, and river deltas. Not a single accepted species of sawfish isn’t immediately endangered with extinction.

It is far too late to observe Cretoxyrhina or Ptychodus, but the exceptional elasmobranchs I listed above are modern. They exist as a part of our present day world, at least for now. Whether or not they begin to fade into the permanence of the fossil record, one by one, is largely up to us.

Image credits: Tooth intro image, Cretoxyrhina, Ptychodus teeth, Ptychodus jaw

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2014. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.

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