It’s difficult to resist calling pliosaurs sea monsters. Their long, toothy jaws and strange, streamlined shapes make them dead ringers for what we fear waiting for us in the deep and, for my own part, I’m a little less hesitant to plunge into the ocean knowing that the last of them went extinct over 66 million years ago.
Many pliosaurs are cast in the same role – as big apex predators capable of munching on prey as large, if not larger than, themselves. But not all pliosaurs accomplished these gustatory feats in the same fashion. A new fossil pliosaur described by paleontologist Valentin Fischer and colleagues late last year hints that one carnivore, at least, was accomplishing the same task in a slightly different way.
There was only just enough of the animal, named Makhaira, for Fischer and coauthors to identify it as something new. The reptile’s preservation in 130 million-year-old limestone nodules was not kind to its bones. But the teeth and jaws from the tip of the predator’s snout make it stand out from its relatives. Each tooth of Makhaira had three serrated cutting edges, and the teeth were not as closely-spaced as those of other big-game-hunting pliosaurs. The overall picture is that Makhaira slammed this distinctive dental armory into big prey even though it wasn’t as massive as some of its larger relatives, indicating that pliosaurs were still capable of big bites even at smaller size.
Meaning:Makhaira is a Latinized version of the Greek word for “curved blade” and rossica denotes the animal’s discovery in Russia.
Age: Around 130 million years ago.
Where in the world?: Slantsevy Rudnik, western Russia.
What sort of critter?: A marine reptile known as a pliosaur.
Size: Estimated around 15 feet long.
How much of the creature’s body is known?: A fragmentary skeleton including parts of the jaws, teeth, several vertebrae, and pieces of the hips.
What sort of critter?:Atychodracon is a plesiosaur – a four-flippered marine reptile distinct from dinosaurs.
Size: Approximately 16 feet long.
How much of the creature’s body is known?: Casts of a complete skeleton, two partial skeletons, and an intact complete skeleton.
Claim to fame:Atychodracon was a casualty of war. On November 24th, 1940, German bombers hit the Bristol City Museum and Art Gallery, totally destroying the original, spectacular specimen. But all was not lost. Thanks to photos and casts made of the skeleton, paleontologist Adam Smith has been able to determine that this animal – originally described as a species of Plesiosaurus – belonged to a previously unknown genus of marine reptile. And while the original skeleton cannot be replaced, fossil finders have turned up additional specimens of Atychodracon. The “unfortunate dragon” has been revived.
[Note: This is a continuation of the Paleo Profile feature I started over at Dinologue.]
Bones are symbols of death. That makes sense. Before X-rays and CT scans allowed us to look inside ourselves, we’d only see our skeletons after death and decay had stripped everything else away. Not to mention that poison labels, the Jolly Roger, and visages of the Grim Reaper have all reminded us of our eventual fate. But while these associations aren’t wrong, they suffer from being one dimensional. Bone isn’t just about death. For some creatures, bone is a giver of life.
On the surface, the phrase “bone-burrowing worm” sounds like something David Cronenberg thought up. Perhaps, had they been discovered sooner, the body horror director would have used them. The invertebrates weren’t found until the year after The Fly debuted, pocking the skeleton of a whale that had perished off the California coast. In time, these specialized worms – known by the scientific name Osedax – became known as central players in the succession of “deadfall” critters that make their living on bodies that sink to the bottom. The end of one life enriches countless others.
But when did Osedax start drilling their way into the deceased? Pinholes in fossil whale bones, bolstered by estimates of genetic divergence among living worm groups, showed that Osedax – or very similar annelids – have been sinking their roots into undersea skeletons for millions of years. For as long as there have been whales, it seems, there have been worms that could take up residence on their remains.
Whales were not the first creatures to trade life on land for one spent entirely at sea, though. Starting around 245 million years ago, about 190 million years before the earliest whales took their first dip in the water, multiple marine reptile groups slid into the seas. Those disparate forms – the fish-like ichthyosaurs, quad-paddled plesiosaurs, sea turtles, and more – flourished throughout the Mesozoic, the last of these “sea dragons” going extinct about 66 million years ago. Surely these marine reptiles died and sank to the bottom just as whales do today. Is it possible that Osedax evolved to inhabit their bones and only later continued the tradition with whales?
The recent discovery of modern deadfalls sent paleontologists searching for more ancient equivalents. And they found them. A pair of plesiosaurs excavated from the 86 million year old rock of Japan hosted late stage deadfall communities where snails grazed on mats of bacteria, and, last year, Plymouth University paleontologist Silvia Danise and colleagues reported on a 145 million year old ichthyosaur from southern England that documented how the marine reptile hosted a changing array of scavengers. Yet no one was able to find signs of Osedax. The oldest confirmed traces of the worm were 30 million years old, and it was unclear whether the worm hadn’t evolved in the time of the marine reptiles or whether its taphonomic calling cards were absent from the known finds. Now, in a new Biology Letters paper by Danise and Nicholas Higgs, paleontologists have their answer.
Osedax have been taking advantage of deadfalls since the Cretaceous. The evidence, Danise and Higgs report, can be seen on an upper arm bone of a plesiosaur and two sea turtle bone fragments found in the 100-93.9 million year old sediment of England. The Cretaceous bones bear burrows that correspond to those made by modern Osedax species, showing a narrow opening to the surface with a glob-like chamber beneath. Even though the worms themselves didn’t become preserved, the traces of their osteological feast give them away.
But here the fossil record would seem to hit a snag. The last whale-sized marine reptiles died out 66 million years ago, and the first fully-marine whales didn’t evolve until about 20 million years later. This bottleneck in the food supply could mean that worms with an Osedax-like lifestyle evolved more than once – just as multiple forms of bone-burrowing beetles have utilized dinosaur and fossil mammal bones – but, more likely, it speaks to how flexible these worms are.
While some marine reptile lines ended by the close of the Cretaceous, sea turtles survived. Osedax could have kept persisting on their skeletons, at the very least. And, from geologically younger finds as well as experimental studies, marine biologists have found that Osedax are not especially picky about whose bones they’re colonizing. A whole whale is great, but cow, bird, or fish bones will do in a pinch. Magnificent giants that paddle through the surface waters have come and gone, but, for over 93 million years, the bone-eating worms have been waiting for them.
If you want to find sea monsters, there’s hardly a better place to look than western Kansas. Not that you’re going to see any live ones slithering around. They’ve been dead for more than 66 million years. In rocks deposited by a warm, shallow sea that once washed over the middle of North America, paleontologists have pulled dozens of marine reptiles that ruled the marine realm while non-avian dinosaurs stomped around on land and pterosaurs soared through the air. And among the most impressive of all were the great mosasaurs.
Enormous aquatic lizards related to today’s monitor lizards, mosasaurs like Tylosaurus and Platecarpus were totally at home in the sea. Descendants of terrestrial reptiles, their limbs had become modified into flippers, their tails took on a downward kink that supported a vertical tail fluke for more push with each sweep, and their scales became streamlined to help them better cut through the water. The largest of their kind reached lengths of 50 feet. But the discovery of many large mosasaurs from the ancient ocean rock of Kansas raised a prehistoric puzzle. Where were the baby mosasaurs?
Early 20th century marine reptile expert Samuel Wendell Williston proposed a handful of different explanations for the absence of wee sea lizards. Maybe mosasaurs had special pupping grounds that were nearer to the shore than the sites preserved in the Kansas stone, or perhaps the gravid mothers swam up rivers to drop their broods in the relative safety of fresh water. Then again, Wiiliston suggested, perhaps mosasaurs clambered back onto beaches to lay eggs in the way that sea turtles do today.
What Williston didn’t consider was that baby mosasaurs had already been found. At least two were in the collections of the Yale Peabody Museum of Natural History by the time Williston wrote his 1904 report on mosasaur behavior. The trouble was that the little lizards had been mislabeled.
The exact circumstances of when the fossils were collected is unclear. It seems that they were found in the approximately 88 million year old rock of western Kansas sometime in the late 19th century, at the height of the “Bone Wars.” The skull bones were so light and delicate, however, that they were cataloged as “Aves indeterminate” – seemingly fragmentary examples of the toothed birds Yale’s Othniel Charles Marsh described from rocks of about the same age.
Yale paleontologist Daniel Field and his coauthors have now corrected the misattribution. In the pages of Palaeontology, the researchers briefly describe the fossils as baby mosasaurs that probably stretched just a little over two feet long, or about 22% of expected adult size.
The fossils add to the growing body of evidence that – in the Western Interior Seaway, at least – baby mosasaurs were born out in the open ocean. The deposits the youngsters were found in was hundreds of miles from the nearest Cretaceous shore, meaning that they were not hanging out in a nursery. Added to other fossils – such a purportedly pregnant mosasaur that has yet to be formally described and a forerunner of mosasaurs called Carsosaurus found with young inside – the Yale babies suggest that mosasaur mothers gave live birth in open water.
And the new study offers another lesson. During the Bone Wars era and decades of fossil expeditions that followed, many paleontologists were concerned with acquiring the biggest and most impressive fossils. The grand halls of eastern museums needed petrified celebrities to fill their scientific trophy rooms. Little fossils were either ignored in the field or, if collected, were given little interest in the lab. But now it seems that “missing” parts of prehistoric creature’s lifecycles and many hitherto unknown species are being recovered amongst the meeker fossils within museum collections. We know about the giants. Now it’s time to learn the stories of the small.
Whales can poop almost anywhere they want. They have the entire ocean to relieve themselves in, so most of the planet can theoretically be their toilet. Yet, despite having a near-universal lavatory pass, cetaceans often relieve themselves near the surface. In the words of marine biologists Joe Roman and James McCarthy, many whales feed in the deeper tiers of the sea to then return to the surface and release “flocculent fecal plumes” – cetacean clouds that may create what Roman and McCarthy call a “whale pump“.
The researchers laid out their logic in a 2010 PLOS ONE paper. Our planet’s seas are constantly recycling themselves. Showers of marine snow send organic matter cascading down to the sea floor, and zooplankton excrete poop full of nitrogren, phosphorus, and iron in deep water as they go about their regular up-and-down migration through the water column. This is a downward “pump” of resources. But other organisms can also bring some of these elements back from the deep. Whales and other marine mammals, Roman and McCarthy hypothesized, replenish the surface waters with their excrement.
The researchers based their case on an array of cetacean observations. Whales must surface to breathe, the physiological consequences of diving and surfacing make it likely that marine mammals will let it all go near the surface, and observations of crappy clouds have shown that they dissipate through the water rather than sink. And even though whales sometimes feed in the upper portion of the sea, they often dive deeper to reach dense pockets of fish and invertebrates. These hard-to-reach resources are key to Roman and McCarthy’s proposal. Whales feed on deepwater prey that are taking up elements from far below. After a bit of digestion, the whales then jettison some of those elements in shallower waters and leave plankton to recycle the slightly-used nitrogen.
Seals and sea lions might do their share, too. If you’ve ever smelled a pinniped colony at the height of breeding season, you’ve probably cursed your sense of smell. What the blubbery mammals spill onto the shore can be washed back into the sea, emanating the ecological reek of seal-processed fish and squid returning nitrogen to the water.
It’s one thing to theorize from an armchair, though, and quite another to get out on a boat and collect some whale feces. That’s exactly what Roman and McCarthy did to further investigate their idea, taking 16 samples of billowy poops from the Gulf of Maine. All of the samples contained significantly more ammonium – a nitrogen-rich waste product – than the surrounding water. Based on these analyses, Roman and McCarthy suggested that whales could be responsible for dumping 2,3000 metric tons of nitrogen into the Gulf of Maine every year. The amount was probably even higher before commercial whaling tried to sate its hunger for the massive mammals.
And seagoing beasts may only be continuing a trend that was in place long before they took to the water. At this past weekend’s PaleoFest at the Burpee Museum of Natural History, paleontologist Ryosuke Motani pointed out that marine reptiles were doing the dive-and-surface shuffle hundreds of millions of years before the hoofed ancestors of whales were even a glimmer in natural selection’s eye. Some of these marine reptiles – such as the fish-like ichthyosaurs – were some of the first deep-divers, Motani pointed out, and they could have played an ecological role similar to what Roman and McCarthy have suggested for whales. So perhaps it’s too narrow to talk about “whale pumps” or “marine reptile pumps” feeding the seas. Those are just more academically-acceptable ways of talking about “poop pumps”.
Textbooks aren’t known for their originality. They build on the basics, and often include the same standard examples from one generation of students to the next. (I haven’t checked, but I wouldn’t be surprised if the fox terrier clone is still creeping somewhere.) That’s why ichthyosaurs are a textbook staple.
Mesozoic “fish lizards”, ichthyosaurs were marine reptiles that independently became adapted to a life at sea around 200 million years before dolphins. Despite their distance from the oceanic mammals in both time and evolutionary history, though, ichthyosaurs look enough like dolphins for the two to be practically inseparable in textbooks. They’re a striking example of convergent evolution – two lineages independently evolving extremely similar anatomy from different starting points.
But how similar are the two, exactly? An Opthalmosaurus looks kind of like a bottlenose dolphin, sure, but stopping at superficial similarities isn’t very scientific. Here’s where a new Biology Letters study by National Museum of Natural History paleontologist Neil Kelley and U.C. Davis’ Ryosuke Motani offers an opportunity to see whether such resemblances are only skin deep.
Kelley and Motani focused on skulls of marine tetrapods – descendants of the four-legged vertebrates that crawled out of the swamps over 360 million years ago. They’re an ideal group for such comparisons because all of them – from seals to turtles to whales – had terrestrial ancestors that eventually took on life in the seas. By combining skull, jaw, and tooth measurements from 69 living species with data on what they actually eat, Kelley and Motani were able to pick out how form relates to feeding.
As it turns out, skull anatomy is a fairly good predictor of feeding style regardless of ancestry. For example, herbivores like the marine iguana, green sea turtle have short skulls with larger areas of attachment for powerful jaws muscles to crop and crush vegetation. Species that snatch up fish and squid, on the other hand, tend to have longer, toothier snouts better-suited to “snap feeding” and swallowing prey whole. Apex predators such as the saltwater crocodile, leopard seal, and orca fell in-between, characterized by elongated jaws and relatively deep skulls that give them the power to tear apart larger prey.
Despite diverging far back in the prehistoric past, creatures as distantly-related as iguanas and dugongs have evolved similar skull shapes to cope with similar diets. And with this proof-of-concept in place, the same technique can be applied to the fossil record. Paleontologists will able to investigate the similarities, and differences, between ichthyosaurs and dolphins, and perhaps even gauge how marine reptiles like different species of mosasaur may have been able to coexist by picking different items off the marine menu. There are plenty of prehistoric secrets embodied by evolution’s greatest hits.
Look into the jaws of a Mosasaurus and you will gaze into a nightmare. The seagoing lizard’s curved teeth stand in a line that point backwards to the throat, an extra set of piercing teeth on the roof of the mouth guaranteeing that any journey into the mosasaur’s mouth was a one-way trip. Mosasaurus clearly had the bite of a carnivore. But what did it actually eat? That’s a tale that cannot be told be teeth alone, and, fortunately for paleontologists, a lovely little Mosasaurus provides a partial answer to the question.
In 2008, workers at Alberta, Canada’s Korite International Ammolite Mine uncovered the bones of a marine reptile. Paleontologists from Canada’s Royal Tyrrell Museum quickly excavated the skeleton, but it was only after careful preparation and study that is became clear that they had uncovered a fossil with a complex story to tell. The poor little mosasaur, dead for over 75 million years, was preserved with its last meal and signs that it, too, had become food.
Described by Takuya Konishi and colleagues in the Journal of Vertebrate Paleontology, the marine reptile was a relatively small specimen of Mosasaurus missouriensis. This species was first discovered during the early 19th century, and was recently revised when a long-lost snout piece was finally reunited with the rest of a historic specimen. But the new animal includes parts not previously seen. The Mosasaurus was preserved so delicately that Konishi and coauthors were able to identify the cartilaginous rings of the lizard’s trachea, as well as the sternum. Even though some parts of the back half of the body had gone missing, the rest of the skeleton is stunning in detail.
And not all the bones in the block belonged to the Mosasaurus. The paleontologists found various fish bones in the lizard’s gut and beneath the reptile’s skeleton. These were part of what was once a three-foot-long fish called a grinner.
The bones had not been washed in after death. Bite marks on some of the fish bones, as well as the positioning, indicate that the unfortunate fish was the mosasaur’s last meal. Other mosasaur skeletons have yielded gut contents, too, but this is the first time anyone’s found such scraps inside Mosasaurus itself.
Better still, the forensic details of the fish bones may allow paleontologists to figure out how this Mosasaurus ate.
Even though the mosasaur’s head was only two feet long, and shorter than the fish itself, the reptile probably could have swallowed the grinner whole. But the scatter of bones are a clue that the fish met a more violent end. The mosasaur nabbed the fish and chunked it into more manageable pieces, Konishi and colleagues suspect, swallowing each morsel in turn.
Not all mosasaurs fed this way. Konishi and coauthors point out that a skeleton of a different mosasaur named Prognathodon, found in the same area at the same geologic level, had remains of fish, a sea turtle, and possibly an ammonite in its stomach when it died. Prognathodon was eating hard-shelled stuff, or, was a “Crunch” feeder rather than a “Cut” feeder like Mosasaurus.
The jaws of the mosasaurs seem to match these menu items, Prognathodon with a stouter lower jaw and teeth that show wear from tougher fare. Additional mosasaurs with intact gut contents will be needed to see whether these two individuals really represent the preferred feeding habits of their respective species, but, Konishi and colleagues suspect, differing diets may have allowed these two species of mosasaur to inhabit the same stretch of the sea.
Despite their status as apex predators, though, mosasaurs wound up as meals, too. The Mosasaurus found in the ammolite mine didn’t survive long after dining on grinner, and, soon after settling to the bottom, the lizard’s body was scavenged by at least three sharks. Two left their teeth as calling cards, and a third carved a bite into the mosasaur’s bone. In fact, Konishi and coauthors propose, the large shark may have even contorted the Mosasaurus skeleton into its final position, dragging the tail beneath the body as it chomped along. At least the sharks didn’t have much time to do their work. Sediment soon buried the Mosasaurus, eventually sealing the details of carnivorous Cretaceous life into the rock.
Evolution is great at producing novelty. Every organism that has ever lived – from the first cell to the grass on your lawn and the blue whales in the sea – is a testament to that. But evolution can also repeat itself. From disparate starting points, evolution can spur some lineages to serendipitously converge on similar forms or behaviors. Among these replays – arguably among evolution’s greatest hits – are no less than five varieties of marine crocodile.
None of these seabound reptiles exist today. True, saltwater crocodiles and even American alligators can be seen at sea, but they are not as tied to the ocean as the prehistoric crocodylomorphs that spent most – if not all – of their lives in the marine realm. These salty archosaurs all lived between 199 and 34 million years ago, with each of the five groups representing independent oceanic invasions.
But why did seagoing crocodiles keep evolving and going extinct? What regulated their rise and fall? Part of the answer, University of Bristol paleontologist Jeremy Martin and colleagues suggest, may be the constantly-changing temperature of the ocean.
Paleontologists have floated a number of explanations for the recurring rise and crash of marine crocodiles. These range from a lack of complete fossil sampling to major sea changes wherein ocean chemistry drastically restructured marine life. But in their study, Martin and coauthors compared the varying diversity of marine crocs to a pair of possible explanations – shifting sea levels and changes in the sea surface temperature.
The reach of the ocean appears to have little to do with marine croc evolution. That’s probably because these carnivores were able to catch a broad variety of prey and even make forays into freshwater habitats, Martin and colleagues suspect. Changes in surface sea temperature offer a better fit.
Starting with an Early Jurassic group called thalattosuchians, almost every lineage of crocodylomorph to slip into the seas did so during a time of warm surface temperatures. The crocs crashed when sea temperature dipped. With the exception of one lineage, Martin and colleagues found, the marine crocs followed a pattern seen among their close relatives.
Fossil crocodylomorphs are often taken as a rough proxy for warm habitats. During a global heat spike 52 million years ago, for example, alligators lived in the Arctic, and paleontologists can track how gators followed warm temperatures down the latitudes as the global climate cooled. That’s because the prehistoric crocodylomorphs, like their living relatives, had a physiology in which their body temperature was regulated by the outside the environment. They were ectotherms. To survive, they had to follow the heat.
But one group didn’t behave like the rest. Metriorhynchoid crocs became intricately-adapted to ocean life, their limbs modified to flippers and their tails bearing large, vertical flukes. They may not have been able to return to land at all. And, Martin and coauthors found, they proliferated during a time when Jurassic sea temperatures were dropping.
Perhaps the metriorhynchoids were stuck. They were so quickly adapted to an exclusively marine life that the only evolutionary paths open to them laid in the seas. Then again, Martin and colleagues write, perhaps metriorhynchoids like the fearsome Dakosaurus had a way to cope with cooler marine temperatures. Maybe, like some other marine reptiles, the metriorhynchoids were able to keep their body temperatures several degrees above the ambient water temperature. Further study is needed to find out, but metriorhynchoids may have been hot-running crocs.
No one has ever found marine crocodiles from sites that sat near the poles, though. Whether ectothermic or warm-bodied, seagoing crocs were restricted in time and space by the warmth of the seas. Crocs slid into the sea during warm times, and they disappeared when the chill set in.
The last of the truly marine crocs died out over 34 million years ago. Among these holdouts were the dyrosaurids – crocs that survived the fifth mass extinction and enjoyed the global hothouse that came in the disaster’s aftermath, only to disappear as sea temperatures again fell. But thanks to our addiction to fossil fuels, we’re rapidly recreating the hothouse conditions under which the marine dyrosaurids thrived. As we warm the world’s seas, perhaps marine crocs will evolve anew.
When I was a fossil-crazed tyke, I used to spend hours flipping through a set of LIFE Young Readers Nature Library books my parents had purchased. The multicolored collection was one of my earliest introductions to natural history and science, and all the time I spent with those pages seared a few illustrations onto my memory. One of the most frightening depicted the blue outline of a man projected against the black and white grimace of a monstrous marine reptile with a gape as tall as the human silhouette. This dragon, according to the caption, was Kronosaurus – a 42-foot-long, quad-paddled carnivore that ruled the seas of Cretaceous Australia around 100 million years ago.
I’m a little surprised the book’s simple illustration didn’t give me nightmares. To think that the seas once held a sharp-toothed giant that could snap me up in one quick bite… And even though more recent estimates have downsized Kronosaurusto around 30 feet long, that has barely diminished my imagination’s ability to imagine the destruction the toothy reptile was capable of.
Kronosaurus wasn’t an aberration or evolutionary one-off. It was one of many imposing marine reptiles called pliosaurs. Cousins of the famous, long-necked plesiosaurs, the pliosaurs kept the four-flippered body plan but typically bore huge heads with elongated jaws. They spanned much of the Mesozoic – about 150 million years from their Triassic origin to their Cretaceous extinction – and the largest of them were probably in the neighborhood of 30 to 40 feet long. The biggest were the most massive flesh-eating marine reptiles of all time, but despite the ferocity apparent in their bones, an essential aspect of their predatory lives has remained little-studied – just how did pliosaurs employ their powerful jaws?
To answer this mystery, University of Bristol research associate Davide Foffa worked with a team of paleontologists and visualization experts to create a digital model of a Jurassic pliosaur’s jaw. The animal they chose was a well-preserved specimen of the roughly 155 million year old Pliosaurus kevani found in Dorset, England’s Weymouth Bay. While many other species of Pliosaurus are represented by fragments, this particular seagoing reptile is known from a nearly-complete skull that stretches over six feet long. That’s roughly the size of the Kronosaurus skull that entranced my childhood self.
After using CT scans to create a digital model of the Pliosaurus kevani skull, including reconstructing parts of the lower jaw and cranium that are missing, Foffa and coauthors modeled the extent of muscles used to close those jaws and further investigated how the skull would have coped with forces that would have been caused as the predator twisted or shook its skull to rip apart prey. What they researchers found questions the image of pliosaurs as the rapacious big game hunters they’re often portrayed as.
Just how hard Pliosaurus kevani could chomp differed according to what part of the jaw was doing the biting. While bites at the front part of the jaw were in the relatively meager 2,000 to 4,000 pound range, back jaw bites spiked between 6,000 and 11,000 pounds. That’s pretty impressive, and in the same ballpark as estimates for Kronosaurus, the extinct alligatoroid Deinosuchus, and Tyrannosaurus. As far as prehistoric giants go, Pliosaurus kevani was a prominent member of the bite club.
Despite such a strong bite, though, Pliosaurus kevani had a relatively weak skull. Estimates of skull strength using techniques called beam theory and Finite Element Analysis showed that the predator would likely damage its skull if it tried to twist off chunks of flesh or shake prey to death. And despite my childhood awe at the gape of Kronosaurus, the similarly-sized Pliosaurus kevani could have only swallowed prey 30 inches in diameter or less. Anything larger would have to be broken down into smaller bits. With shaking and twisting being so risky, how could Pliosaurus have done so?
Foffa and colleague propose an alternative way for Pliosaurus to process prey. Instead of violently tearing at or throttling prey, the researchers suggest, big pliosaurs probably nabbed prey and hefted it to the back of the jaw. That’s where all their power was. With the prey positioned just so, they chomped and chomped and chomped until their victim died and started to go to tatters. Whatever couldn’t be swallowed whole was repeatedly gnashed until the dismembered parts were small enough to gulp.
Pliosaurus wasn’t a marauder that only targeted the biggest game, though. To the contrary, Foffa and coauthors point out that gut contents show that cephalopods and sharks made up a large part of the pliosaur diet, while turtles, other plesiosaurs, and the odd dinosaur – perhaps washed out to sea – were rarer menu items. Apex predators they were, but pliosaurs were not monsters hellbent on consuming the biggest and most dangerous creatures they swam alongside. These extraordinary reptiles were generalist predators who had a specific way of catching and pulverizing the abundance of prey that flourished alongside them in the Mesozoic seas.
Nothing opens up the possibility for evolutionary oddballs to emerge quite like a mass extinction. The worst such catastrophe – the Permian-Triassic mass extinction, about 252 million years ago – so dramatically cut back the world’s biodiversity that the relatively few survivors stepped into an open world where entirely novel forms of life could evolve.
Triassic reptiles, in particular, underwent an evolutionary explosion in the aftermath of the disaster, and within that proliferation multiple lineages of the scaly vertebrates started to slide into the sea. Fish-like ichthyosaurs, shell-crushing placodonts, and the quad-flippered ancestors of plesioaurs were among the most famous lineages to take the plunge, but paleontologists have recently started to turn up even odder marine reptiles from the early days of the Triassic. The zipper-mouthed Atopodentatus, named earlier this year, was once such Triassic weirdo, and just last month Xiao-hong Chen and colleagues added another to the list – Parahupehsuchus longus, an aquatic reptile whose body was encased in a tube of bone.
There’s nothing quite like this highly-armored reptile alive today. With elongated, toothless jaws, stumpy paddles for limbs, a thick torso, and an elongated tail, Parahupehsuchus longus was a bizarre critter belonging to an ephemeral group of Triassic reptiles found in eastern China called the Hupesuchia. And within this group, the 248 million year old Parahupehsuchus longus stands out for having such well-developed anti-predator defenses.
At about twenty inches long and two and a half inches thick, the “body tube” of this Triassic enigma was made of modified ribs and gastralia, or “belly ribs.” The bones expanded so much, in fact, that there’s no space remaining between the ribs, much like a turtle’s shell but evolved totally independently. And this was a stiff structure. Each rib of Parahupehsuchus longus articulated with the spine at two sites, severely limiting how much the ribs could move.
Stout ribs were not the reptile’s only defense. Running along the back of Parahupehsuchus longus was a triple layer of dermal ossicles, or bone armor embedded in the skin. The lower two layers were interlocking triangles, overlain by large, flat bones that span two or three vertebrae each. This extensive armor determined how the reptile could swim. Up and down or side-to-side, the trunk of Parahupehsuchus longus probably wasn’t very flexible, Chen and coauthors point out, so this stiff reptile probably swam by swishing its long tail back-and-forth like modern crocodiles do.
This Triassic curiosity is more than just another strange reptile that sculled through the ancient seas, though. At about 248 million years old, Parahupehsuchus longus was swimming around a relatively scant four million years after the close of the world’s worst mass extinction. That not only points to the rapid invasion of the seas by reptiles, but the specialized defenses of Parahupehsuchus longus means that there were already fearsome superpredators capable of biting sizable chunks out of their aquatic neighbors in the Early Triassic oceans.
The same deposits that have yielded Parahupehsuchus longus, Chen and colleagues point out, also contain an as-yet-unnamed marine predator that stretched nine to twelve feet long. Parahupehsuchus and the other marine reptiles only got to be about three feet long, making them possible prey for the larger animal. And it wasn’t very long before even larger predators menaced the marine realm. By about 245 million years ago – only seven million years into the Triassic – there were enormous, macropredatory ichthyosaurs with wicked jaws. This ramping up of the classic evolutionary arms race between predators and prey means that the world’s ecosystems bounced back quickly after being so vitally damaged. The unusual armaments of Triassic marine reptiles are a sign of life’s resilience in the aftermath of near-destruction.
[For another take on Parahupehsuchus and what that “body tube” is all about, see Andy Farke’s post here.]
The fossil record is replete with wonders. Humungous fungus, dazzling dinosaurs, intricate ammonites, and perplexing protomammals just scratch the surface of such a wide array of fantastic organisms that sometimes it’s easy to become acclimated to the enigmatic and weird. Yet, even then, there are fossils so strange that they make me jolt upright in my seat and think “Wait, what the hell is that?” The latest prehistoric creature to leave me gobsmacked is Atopodentatus unicus.
The roughly 245 million year old marine reptile is beautifully preserved. Uncovered in southwest China and described by Wuhan Institute of Geology and Mineral Resources paleontologist Long Chen and colleagues, the reptile’s nearly complete, nine-foot-long skeleton is laid out as charcoal-colored bones against gray rock. And while not as wholly adapted to an aquatic lifestyle like the eel-like ichthyosaurs found in the same deposits, the stout limbs, hips, and geological context of Atopodentatus hint that this reptile divided its time between land and sea. Then there’s the skull.
Preserved in profile, the cranium of Atopodentatus looks like a bony version of a Scotch tape dispenser. In front of a rounded orbit, the creature’s snout is a downturned hook that creates an arc of tiny, needle-like teeth that are fused to the sides of the jaw rather than sitting in sockets. Stranger still, most of the teeth in the upper jaw faced each other in a split running between the two halves of the upper jaw. Head-on, Atopodentatus had a zipper smile of little teeth.
As Cheng and colleagues say in the title of their paper, this is a “highly specialized feeding adaptation.” But for what? Chomping down on fish seems unlikely. The reptile’s tiny teeth would have been too delicate for struggling prey, the researchers note, and muscle attachment sites on the bones suggest that Atopodentatus wasn’t capable of biting hard.
Filter feeding seems a better option for the unusual Atopodentatus apparatus. In a fashion similar to living gray whales, Cheng and coauthors hypothesize, the Triassic reptile may have swum to the muddy bottom of the shallows and turned its head sideways to scoop sediment into piles. Then, scratching or grasping with that hooked upper jaw, Atopodentatus could have strained worms, small crustaceans, and other morsels through its toothy sieve. Nightmarish as Atopodentatus looked, only tiny invertebrates had much reason to fear.
Testing such a scenario is the tricky part. Gut contents and maybe even traces Atopodentatus left behind as the reptile dredged the seabottom could help paleontologists investigate how the “peculiar-toothed” reptile ate. For now, how the ancient swimmer employed such an unprecedented dental apparatus is still open to investigation. I’m grateful that such petrified puzzles exist. For as much as paleontologists have discerned about life’s past, there are likely even odder discoveries yet to be made. Ain’t evolution grand?
Top image by Julius Csotonyi. And for another take on Atopodentatus as an embodiment of a Lovecraftian horror, see this post at The Bite Stuff.
Bones don’t lie. But they don’t tell the whole truth. Certainly not for prehistoric creatures. The bones paleontologists are constantly coaxing from stone and scrutinizing in museum collections are often the only clues to animals that have long since lost their flesh. Putting that flesh back onto the remaining osteological framework relies on the scars, ridges, depressions, and other clues that testify to the intimate relationship between soft tissues and skeletons.
Not all clues are equally easy to read. In the 19th century, when paleontology was still an infant science, artists and researchers often envisioned the impressively-ornamented Irish Elk as having a relatively flat back with a neck held up at a right angle to the rest of the body. It wasn’t until much later that the discovery of prehistoric cave paintings showed naturalists what they had overlooked. Those spines were anchor points for ligaments and muscles that connected to the back of the herbivore’s head. The connective tissue and bone created a prominent hump, and, as paleontologist Stephan Jay Gould pointed out in an essay on the ungulate, the enormous deer didn’t strike a pose with such an erect neck as the classic skeletal illustrations depicted. If the cave paintings are to be believed, the hump was present in both sexes and prominently colored a reddish brown. Early paleontologists didn’t have the advantage of drawing Irish Elk from life, of course, but the conservative tradition of illustrating prehistoric creatures with their skin spun tightly over skeletons had obscured a striking feature of the living animal.
Cave paintings will only get us so far. Back to the last Ice Age, more or less. Given that our species and the last of the non-avian dinosaurs were separated by 66 million years, we can be certain that there’s no hope of finding Tyrannosaurus painted onto a cave wall somewhere, no matter with religious fundamentalists say. Plesiosaurs are in the same predicament. These quad-paddled marine reptiles thrived in the seas while dinosaurs dominated the land. That’s why they often show up in packs of plastic prehistoric animals and, to the ongoing frustration of vertebrate paleontologists, are often confused for dinosaurs. And in those representations, plesiosaurs often have a uniform look. Since the early 19th century they’ve been regarded as being like “a snake drawn through the body of a turtle”, with their tails little more than a cylindrical appendage that apparently had trailed behind the animals like pieces of rigid spaghetti. This may not have been so. Some plesiosaurs may have had tail fins.
From the time that Victorian naturalist William Conybeare named Plesiosaurus on the basis of a nearly-complete skeleton in 1824, the way that these reptiles propelled themselves through the seas has been clear. Plesiosaurs of all types – from the small-headed and long-necked to the large-headed and short-necked – flapped and flew through the water with their four large flippers. This mode of swimming was starkly different from the side-to-side, fish-like manner of most other marine reptile lineages. Plesiosaurs must have been beautiful, graceful swimmers. And with such prominent paddles, there was no important role for their apparently cylindrical tails.
But in 1895 the German paleontologist Wilhelm Dames reported something strange. Around the body of a plesiosaur he named Seeleyosaurus guilelmiimperatoris, Dames reported two curious stains that seemed to be remnants of the plesiosaur’s soft tissue. One, on the trailing edge of a paddle, appeared to be part of the plesiosaur’s right front flipper. The other was a roughly triangular smudge left on the stone around the tail.
Dames took the curious fossils as faithful remains of the plesiosaur’s soft tissues. Along with the skeleton, he published a life restoration of Seeleyosaurus with a diamond-shaped tail and a mischievous grin. But attempts by paleontologists to see what Dames himself observed have been stalled by a simple fact of historical preservation. For some reason, seemingly now forgotten, the possible remnants of soft tissue were painted over. To remove the obscuring layers may risk removing the tantalizing evidence beneath.
No other plesiosaur with such soft tissue clues has been described. While some artists and paleontologists took Dames’ Seeleyosaurus as a cue to speculate on tail fins for other plesiosaurs, the tube-tailed model has held sway. But, in lieu of exceptional preservation, osteological clues may hint at what was lost on Mesozoic seabottoms.
At the 2010 Society of Vertebrate Paleontology meeting in Pittsburgh, Pennsylvania, Benjamin Wilhelm made the case for bony clues of plesiosaur tail fins. Over and over again, marine reptiles with upright tail fins – such as ichthyosaurs, mosasaurs, and seagoing crocodiles – evolved a similar set of osteological features to support soft tissue fins. Even better, remarkable sites have sometimes preserved outlines of these tail fins among other marine reptiles. Drawing from this body of evidence, Wilhelm identified skeletal features that are consistent with a tail fin in the skeletons of the plesiosaurs Cryptoclidus and Muraenosaurus. Vertebrae that are compressed from side-to-side near the end of the tail, as well as vertebral spines that change direction to create a kind of rounded hump, are among the features some plesiosaurs share with other marine reptiles with tail fins.
Adam Smith has added another possible candidate to the list of plesiosaurs with tail fins. In a newly-published Paludicola paper Smith argues that Rhomaleosaurus – a plesiosaur with a relatively large skull and a medium-length neck – had two features consistent with a tail fin. In addition to a “node” of two shortened vertebrae where the fin supposedly started, Rhomaleosaurus had a set of compressed vertebrae at the tail tip. The reconstruction included in the paper shows a plesiosaur with a middling, rounded tail fin, but a tail fin all the same.
The trouble with such plesiosaurs is that their tails were not adapted for propulsion to the same degree as the ichthyosaurs, mosasaurs, and marine crocodiles known to have tail fins. Were the vertebrae of Rhomaleosaurus really compressed to support a fin, or do they just look short and boxy because they were near the end of the tail? For Cryptoclidus and Muraenosaurus, too, the bony anatomy wasn’t so prominently suited for tail fin support as other marine reptiles. And with Dames’ Seeleyosaurus surrounded by paint, there’s currently no way to know whether or not his plesiosaur truly had a tail fin, nor why such an appendage evolved.
Just like the old images of Irish Elk with necks held high, though, visions of plesiosaurs with tail fins offer a hypothesis. The same is true for all restorations and reconstructions of prehistoric life. Even the most complete specimen is missing clues, be they bones or the behaviors the animal only performed in life. Further finds will test what has been deduced and supposed so far. For plesiosaurs, the resolution rests with the ongoing search for their kind in rocks lifted beyond the reach of the sea. Maybe, if geological luck is with us, there are plesiosaurs entombed with tatters of soft tissues intricate enough to test visions drawn from their bones.
If you’re talking about Radiohead, “The Bends” is a good thing. Quite the contrary for diving. When a diver surfaces too fast, the pressure of the water changing around them as they go, Nitrogen in their body ekes out as bubbles that can cause everything from discomfort to death depending on where those bubbles go. But this isn’t a problem that started with the invention of the Aqua Lung. The bends have a fossil record that goes back over 220 million years.
Brain, spinal cord, blood vessels – we often think about the bends in relation to soft tissues. But the affliction also causes lesions on bones and around joints. That has left a mark on the skeletons of critters that were diving deep long before us.
In a paper published last year, paleopathologist Bruce Rothschild and colleagues picked out signs of decompression sickness on the skeletons of various ancient marine reptiles. Among the groups vulnerable to the bends were Jurassic and Cretaceous turtles. Now a Triassic turtle brings the bends back even further, giving the pathology a 220 million year history.
The unfortunate animal is Odontochelys semitestacea – an early turtle that still had teeth and was encased by a semi-shell of outer armor on the bottom with broad ribs on top. Possibly the descendant of a land-living ancestor, this unusual turtle’s bones have been found within the petrified wreck of a shallow marine habitat. And on the upper arm bones of the turtle, Rothschild and Virginia Naples report, there is bone damage that is the hallmark of the bends.
Both upper arm bones of the Odontochelys in the study are pocked around the portion that connected to the shoulder. This damage, Rothschild and Naples propose, is a sign that blood circulation around the bone was cut off by the effects of the bends, killing parts of the bone.
But why did this ancient turtle get the bends at all? We may never know what spurred this Odontochelys to rise too fast for the surface. Nevertheless, Rothschild and Naples hazard an explanation. A “gunboat in a sea of fear”, as Thom Yorke put it, may be to blame.
Some ancient predator may have chased frightened Odontochelys into the deep, leaving the turtle to rise too fast or drown. Then again, the situation could have unfolded the other way – with Odontochelys sprinting for the surface to escape – or perhaps the turtle simply made a mistake when young and inexperienced. Whatever happened, Rothschild and Naples suggest, the damaged bones might mean that early turtles lacked the physiological and behavioral tricks modern marine turtles have evolved to circumvent decompression sickness. Poor Odontochelys. All you wanted to do was live, breath… be part of the chelonian race.
A few weeks ago, as we chatted over dinner, some paleo-minded friends and I debated when the safest time to take a dip in the prehistoric oceans might have been. We immediately ruled out the Mesozoic. From the Triassic to the end of the Cretaceous 66 million years ago, the marine realm was dominated by successive arrays of big, toothy, apex predators that crunched prey just as large, if not larger, than they were. Pliosaurs, marine crocodiles, and mosasaurs thrived in ancient seas, each radiation stranger and scarier than what had come before. And, so far as we know, the long tradition of macropredatory marine reptiles started with a roughly 245 million year old ichthyosaur that bore a vicious grin double-edged teeth.