by Brian Switek
Those parasites have been found inside the petrified scat of carnivorous dinosaurs. In 2006, the paleontologists George Poinar and Arthur Boucot broke down a coprolite from an especially rich dinosaur site in Bernissart, Belgium. They scrubbed the specimen, ground it down into grains, suspended it in hydrochloric acid solution, spun the mixture in a centrifuge, placed it in hydrous hydrofluoric acid, centrifuged the products again, and so on, until the scientists had a concentrated dinosaur-poo residue that could be readily viewed under the microscope.
When Poinar and Boucot zoomed in, they found parasites. Tiny cysts indicated the presence of Entamoeba—a widespread genus of microorganisms that can be harmless or cause disease, depending on the species. And there were also eggs from both trematode and nematode worms. The prehistoric parasites were not identical to living species, but were similar enough that they could be identified. The little hitchhikers hadn’t changed very much in 125 million years, and they indicated to paleontologists that dinosaurs were warm hosts to many familiar microorganisms.
Dinosaurs were assailed from the outside, too. While prehistoric lice are relatively few and far between, a combined approach using the known fossils and genetic data estimated that the major varieties of lice present today began to proliferate around 100 million years ago. Feathered dinosaurs had been around for at least 60 million years at that point, not to mention all the fuzzy mammals, and the boom among feather lice hints that the wingless insects had found plenty of homes. Dinosaur feathers were suitable homes for the parasites, just like the plumage of modern birds. With any luck, a sharp-eyed paleontologist will someday be able to pick one of these nits from the fossilized feathers of one of the beautifully preserved dinosaurs found in China’s ash beds.
Dinosaur lice shared their world with ticks, mosquitoes, and other biting, burrowing insects. We don’t know how many of these annoying invertebrates actually fed on dinosaurs (it’s not like anyone’s had the pleasure of catching one of the little biters in the act). But in the increasing array of possible parasites, there is one variety whose bloodsucking tools were so powerful that they would have been overkill on anything but a dinosaur. In early 2012, the Chinese Academy of Sciences paleontologist Diying Huang and his team announced that they had discovered huge, 165-million-year-old fleas. Granted, the fleas were only relatively gigantic—the largest was still just under an inch long—but to any potential victim, that’s certainly big enough. Unlike their modern relatives, these fleas couldn’t jump. They had heavy-duty mouthparts studded with saw-like projections, and this sturdy equipment led the researchers to propose that the tools went to work on dinosaurs. The fleas were probably annoying ambush predators, they argued. The terrible fleas would wait for a dinosaur to amble by before scuttling out to latch onto their host, feed, and disappear back into the undergrowth.
Cataloging the list of dinosaur pests and parasites is a relatively new area of interest, though. For the most part, paleopathology has focused on injuries directly seen in dinosaur bones.
There’s an entire book devoted to the various types of dinosaur pathologies, one that I like to occasionally flip through to remind myself of how dangerous dinosaur lives must have been. Organized by Tanke and the pathologist Bruce Rothschild, the volume carries the charming title Dinosores: An Annotated Bibliography of Dinosaur Paleopathology and Related Topics—1838–2001. Everything from biting insects to bone damage finds a place in the catalog. Highlights include early-twentieth-century speculations that dinosaurs got so large and weird because of glandular disorders, that a suite of bone fractures were attributable to rough dinosaur sex, and that they were poisoned by everything from arsenic and botulism to strychnine. The comprehensive list includes possible cases of spina bifida, osteomyelitis, necrosis, and gout.
Dinosaurs were even afflicted by cancer. Tumors both benign and malignant have turned up—not at such a rate that there’s any indication that dinosaurs were suffering an increased cancer risk near their extinction, but we’ve indeed determined that this disease was present hundreds of millions of years ago. Tanke and Rothschild identified a benign tumor in the bone of a Jurassic dinosaur found in Utah, and in 1998 Rothschild and other scientists discovered metastatic cancer in another Jurassic dinosaur, this time from Colorado. Multiple cases have been found over the last ten years or so, most of them in hadrosaurs from the Late Cretaceous period.
Not all dinosaur diagnoses are on the mark. It’s difficult enough to accurately identify disease today, much less in patients millions of years old (always get a second opinion from another paleontologist). Some of the earliest reports of dinosaur disease were influenced by the way scientists saw dinosaurs at the time. One of my favorite cases was described by the early-twentieth-century pathologist Roy L. Moodie. Even though paleontologists had noticed damaged dinosaur bones before, Moodie was one of the first researchers to fully catalog the wide array of pathologies found among fossil creatures in his influential book on the subject, simply titled Paleopathology. Among other fossils, Moodie highlighted two tail vertebrae from a sauropod similar to Apatosaurus. The size and shape of the bones showed that they came from near the end of the tail, but they didn’t articulate with each other normally. A blob of inflamed tissue sat between two of the terminal tailbones. “The mass resembles closely the tumor-like masses seen on oak trees,” Moodie wrote, and noted that such injuries could be seen in other dinosaur tails as well. Moodie invoked the sloth of the huge sauropods to explain how such an injury might have occurred. The tip of the dinosaur’s tail “might be seized by one of the carnivorous dinosaurs and vigorously chewed for some time before the owner of the tail was able to turn his huge body and knock the offender away,” he explained. Supposing that the sauropod’s tail hadn’t been significantly shortened, he reasoned, the bacteria that surely proliferated in the Jurassic swamps quickly infected the wound down to the bone.
Moodie’s scenario was based on the commonly held idea at the time that huge sauropods were painfully stupid and were bound to live their lives in fetid swamps. He was wrong that sauropods were so sluggish and dim-witted that Ceratosaurus could simply bolt up to a sauropod tail for a quick and easy meal, but right that the tailbones of these dinosaurs were relatively delicate and prone to injury, and that in this and other ways their size and grandeur did not exempt them from what Shakespeare called “the thousand natural shocks / That flesh is heir to.” Moodie observed, “The study of the lesions so far known among fossil animals indicates nothing new in the nature of pathological processes but simply extends our knowledge of disease to a vastly earlier period than had previously been known.” While not all diseases present today existed in the Mesozoic, the signs of trauma and pathology among dinosaurs and other prehistoric creatures are familiar ones. The afflictions dinosaurs faced are still with us now.
The array of lesions, fractures, bite marks, fused bones, and other pathologies that Moodie, Rothschild, and other paleopathologists have identified show that dinosaurs were not impervious ultra-beasts. The fact that they were susceptible to injury and disease just like any other large vertebrate makes them all the more real. A pristine dinosaur skeleton, free of pathology, doesn’t seem as authentic. A dinosaur with healed fractures or infected bones underscores the fact that the animal was once truly alive, and each injury goes back to some prehistoric event that we can at least trace the outlines of.
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One dinosaur that I feel especially sorry for is Big Al, a teen Allosaurus. Like Sue and Jane, Big Al was an apex predator of his time, and suffered multiple injuries. Discovered in 1991 near the abundant Jurassic age Howe Quarry in Wyoming, Big Al was astonishingly complete, but his skeleton showed those telltale signs that he was badly beaten. The paleontologist Rebecca Hanna cataloged the dinosaur’s injuries and found that he had nineteen abnormalities—from ribs and fingers damaged by trauma and infection to vertebrae damaged by more mysterious causes. None of the injuries directly caused the dinosaur’s death, according to Hanna, but many of t
hem hindered Big Al’s ability to hunt. A fracture and resulting bone infection in Al’s right hand were so bad that the dinosaur’s second finger probably ached when he flexed it. And injuries on Al’s left foot—still visible as an open abscess on his main weight-bearing toe bone, which would have suppurated, oozed pus, and hurt—hampered his ability to chase down prey. Big Al suffered a variety of painful injuries, but then again, the suite of pathologies also testifies to how resilient he was.
A roadside dinosaur stop just outside of Arches National Park records the steps of a dinosaur who knew Big Al’s pain all too well. There is no sign or other hint that dinosaur ghosts are nearby; driving on State Road 191 past the towering red rock bluffs outside Moab, Utah toward I-70, the route to the tracksite is a dirt road that abruptly joins the main highway around mile marker 148.7. The first time I drove there, I wasn’t entirely sure my little car was going to make it on the rough road. But I couldn’t say no to dinosaur tracks.
I arrived at the little parking lot behind the low hills, and took the short hike up to the site, but I didn’t see the footprints the interpretive sign told me I would. I walked back and forth, searching for them, and returned to the sign hoping that it contained some hint. Then I looked down—I was standing right on top of them. The easiest ones to spot were tracks left by a midsize sauropod. The gently curved tracks looked like an organized series of potholes. Impressive, but not the dinosaur traces I had come to see. The tracks I was looking for ran diagonally in the other direction—a series of large three-toed footprints most likely left by an Allosaurus. I was surprised to see that the tracks weren’t spaced as they should have been. The dinosaur’s steps alternated long and short. This carnivore was limping! The tracks record the movements of a hobbled Allosaurus, and as I found out, this injured dinosaur wasn’t alone in its pain: sites from New Jersey to Australia record the movements of limping dinosaurs.
From broken bones to persistent parasites, injury, irritation, and disease were just a part of dinosaur life. Oddly enough, some paleontologists have turned to these clues to try to explain why the non-avian dinosaurs disappeared at the end of the Cretaceous. When Roy Moodie mapped out the pathologies in the fossil record, the injury curve peaked just before dinosaurs and other forms of Mesozoic life disappeared. Dinosaurs were having more and more accidents, Moodie implied, and “[i]t seems quite probable that many of the diseases which afflicted the dinosaurs and their associates became extinct with them.”
Other paleontologists have tried to pinpoint specific causes—they’ve blamed cataracts, slipped discs, infectious epidemics, and even glandular disorders for the ultimate demise of the dinosaurs. But dinosaurs coped with disease and injury over the entire course of their history without any sign of slowing down or being winnowed into extinction. Something else must have extirpated them from the Earth. Why the non-avian dinosaurs went extinct is one of the greatest murder mysteries of all time.
Ten
Dinosaurs Undone
Of all the dinosaur mysteries, none is so confounding as why there are no descendants of Tyrannosaurus and Triceratops living alongside us today. And to understand that enigma, I knew I had to go to Montana—the resting place of some of North America’s last dinosaurs.
When I finally got out to the dinosaur-rich exposures, though, I learned that cows are not the best company for fossil collecting. Even at a distance, spread out as splotches of black and brown over the Montana ranchland, the cattle, with their ceaseless lowing and grunting, were starting to break my concentration. I tried to tune them out and keep my focus on the ground (or at least keep myself from shouting expletives at the herd at the bottom of the hill). A momentary break in attention can make all the difference between spotting a piece of a dinosaur and stepping on it, unknowingly crushing it back into the ground.
I hadn’t initially planned on doing much prospecting in Montana. I had driven out to the tiny town of Ekalaka from my last road trip stop in Bozeman for a different reason—an appointment with a specific Tyrannosaurus rex. A few months before my move out west, the Carthage College paleontologist Thomas Carr put out a call for field volunteers on Facebook, of all places. Carr needed a few extra hands to help excavate a very young Tyrannosaurus—nicknamed “Little Clint”—that his team had discovered a few years before. I jumped at the chance and asked Carr for a spot. I’d be happy to dig up any dinosaur, but Tyrannosaurus rex? Count me in! Luckily, Carr responded that I’d be welcome to help.
But, as I was disappointed to learn, the young tyrant wasn’t holding audiences. Soon after I rolled onto Ekalaka’s quiet main drag—flanked by garbage cans decorated with sticker letters that spelled out “No Bird or Animal Parts, Thank You”—Carr and his field team delivered the bad news: an exceptionally wet winter had kept streams running high and wide, even into the late July heat. “There’s a flooded stream between us and the Little Clint site that’s about two city blocks wide,” Carr lamented. It cut us off from the dinosaur, and I knew that you don’t mess around with water in the field. I’ve extracted enough mired SUVs to know that even a brief cloudburst can turn smooth dirt roads into quagmires. Little Clint would have to wait for another season. At least the dinosaurian royalty wasn’t going anywhere.
Fortunately, Scott Williams and his crew from the Burpee Museum of Natural History were also working in outcrops around Ekalaka. With Little Clint inaccessible, Carr decided to team up with Williams and look for other fossil sites. I’d have a chance to search for dinosaurs, after all.
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Spread across the checkerboard of private ranches and Bureau of Land Management acreage around Ekalaka, exposures of the Hell Creek Formation present snapshots from the last days of the non-avian dinosaurs. The sediments, 65.5 million to about 66.8 million years old, record the reign of Tyrannosaurus, Triceratops, and Edmontosaurus, among others; but these dinosaurs and their close kin, as unstoppable as they might seem, all exited the evolutionary stage at the close of the Cretaceous. What’s left of them rests silently beneath the hooves of grazing cattle and gradually tumbles out of hillsides.
On my first foray into the field on the Carr and Williams expedition, I asked the paleontologist Eric Morschhauser to point out the extent of the Hell Creek Formation so that I could get my bearings. I had read plenty about the Hell Creek, but had never worked there before, and it always takes a day or two for dinosaur hunters to develop a “search image” for the right layers of fossil-bearing rock. Morschhauser waved his hand out toward a wide valley covered in grass and dotted with hills and nubs of exposed rock. “All that out there,” he said, “is Hell Creek.” This was a land of untold opportunity. There were undoubtedly dinosaurs here. We just had to find them.
I got my chance a few days later. Williams led the combined ranks of the paleo teams to a bare, tan mound called simply “Scott’s microsite.” No one was going to find any perfectly preserved, articulated Tyrannosaurus skeletons here: microsites are spots where small, sturdy fossils are found in abundance—fish vertebrae, lizard jaws, and dinosaur teeth. They may not represent the kind of fossil hunting you see on television, but these aggregations of little fossils act as a census of who was around in a particular environment during a short period of time. So, with my bottle of water in hand and incessant mooing of livestock in my ears, I slowly started to scan the ground—looking for a little glint of enamel or color change that might give away a small bone. From a distance, the field crew must have looked like a crowd searching for someone’s lost contact lens without stepping on it. It’s really not that different.
Rain and wind had already done the hard work. Erosion had winnowed the fossils out of the soft sediment and left them all over the ground. Dinosaur teeth were the easiest to find. In an hour of collecting, I had picked up the isolated fang of a small Tyrannosaurus, a Triceratops tooth, and a few slightly curved teeth that belonged to the feathery, sickle-clawed deinonychosaurs. I found a flat spot to sit down and inspected the vestiges of dinosaurian lives long gone. Even thou
gh their avian cousins would survive—even thrive—in the millennia to come, every existing lineage of non-avian dinosaurs simply blinked out of existence. Not a single one was spared.
It’s impossible to know who turned the lights out at the end of the Cretaceous world. We just don’t have the geological resolution to piece together the final moments of that unfortunate creature. But, sitting on the fossil-rich hill, I imagine Triceratops as the final holdout. After all, the hulking, three-horned herbivore is more common than any other type of dinosaur in these deposits. You can hardly spend a day in the Hell Creek Formation without stumbling across some remnant of a Triceratops skull. So, technically, they had strength in numbers in the face of extinction, and could have been the species that defied extinction the longest. Turning over the single Triceratops tooth in my hand—just one component of the prodigious ceratopsian—I envision an old, solitary dinosaur standing in the Cretaceous twilight. One of her horns is broken, and her face is scarred with signs of a hard life in the land of tyrannosaurs. The terminal member of her species, she holds a lonely vigil as the horizon swallows the sun, and the Cretaceous closes. Or maybe, I think, that last Triceratops is a younger animal, confused that his herd has disappeared. He mournfully hoots into the dark night, waiting to hear a return call that never comes.
We’re never going to know what happened. For all we know, the last non-avian dinosaur was one of the fluffy little sickle-claws, plucking strips of flesh from the carcasses of toppled behemoths. But no matter which species persisted the longest, that title is cold comfort given the ultimate extinction of all non-avian dinosaurs. You would think that at least some of these animals would survive. Dinosaurs were highly diverse and lived the world over. Their ultimate extermination is worse than a disaster—it is an abominable enigma reminding us that the universe is indifferent to life and evolutionary magnificence. If natural majesty made any difference in who survived and who disappeared, descendants of Tyrannosaurus and Triceratops should still hang on somewhere today. Extinction doesn’t care a whit how astonishing prehistoric species seem to us.