The Rise and Fall of the Dinosaurs

by Steve Brusatte

  You might think this discovery would have encouraged paleontologists from throughout Argentina to flock to Ischigualasto in some kind of mad dinosaur rush. But it didn’t happen. After Reig and Bonaparte’s expeditions ended, things got quiet. The late 1960s and 1970s were not a prime time for dinosaur research. There was little funding and, believe it or not, little public interest. Things picked up again in the late 1980s, when a thirty-something paleontologist from Chicago named Paul Sereno put together a joint Argentine-American team of other ambitious young guns, mostly graduate students and junior professors. They set out in the footsteps of Romer, Reig, and Bonaparte, the latter meeting with the group for a few days to guide them to some of his favorite sites. The trip was a rousing success: Sereno found another skeleton of Herrerasaurus and many other dinosaurs, proving that Ischigualasto still had plenty of fossils to give up.

  Three years later, Sereno was at it again, bringing much of the same crew back to Ischigualasto to explore new territory. One of his assistants was a wisecracking student named Ricardo Martínez. While out prospecting one day, Martínez picked up a fist-size hunk of rock covered in a gnarly frosting of iron minerals. Just another piece of junk, he thought, but as he reached back to toss it aside, Martínez noticed something pointy and shiny sticking out of the cobble. They were teeth. Glancing back at the ground, dumbfounded, he realized that he had plucked the head off the nearly complete skeleton of a dinosaur, a long-legged, lightly built speed demon about the size of a golden retriever. They named it Eoraptor. Those teeth poking out from the skull turned out to be highly unusual: the ones in the back of the jaw were sharp and serrated like a steak knife, surely to slice through flesh, but the ones at the tip of the snout were leaf-shaped with coarse projections called denticles, the same type of tooth that some long-necked, potbellied sauropod dinosaurs would later use to grind plants. This hinted that Eoraptor was an omnivore and possibly a very early member of the sauropod lineage, a primitive cousin of Brontosaurus and Diplodocus.

  I met Ricardo Martínez many years later, around the time that I first laid eyes on the gorgeous skeleton of Eoraptor. I was an undergraduate student at the University of Chicago, training in Paul Sereno’s lab, when Ricardo came to work on a clandestine project, later announced as yet another new dinosaur from Ischigualasto, the terrier-size primitive theropod Eodromaeus. I took a liking to Ricardo right away. Paul was running an hour late, stuck in traffic on Lake Shore Drive, and Ricardo was literally twiddling his thumbs, hunched in the corner of the lab office. It was an incongruously disengaged posture from a man who very quickly revealed himself to be the very type of hot blooded, fast-talking, fossil-loving typhoon that I longed to be. He kind of looked like the Dude from The Big Lebowski: wild tangled hair, beard thick around the mouth, interesting fashion sense. He regaled me with stories of working in the wilds of Argentina, recounting with theatrical hand gestures how his hungry crew would sometimes hunt down stray cattle on their ATVs, delivering killing blows with the business end of their geological rock hammers. He could tell I was developing a romantic attraction to Argentina and told me to look him up if I ever came to visit.

  Five years later, I took him up on the offer when I attended the hardest-rocking scientific conference I’ve ever had the pleasure of speaking at. Usually conferences are fairly stale affairs, held in Marriotts and Hyatts in cities like Dallas and Raleigh, where scientists gather to listen to each other speak in cavernous banquet halls that usually host weddings, drinking overpriced hotel beer while catching up on field stories. The conference that Ricardo and his colleagues hosted in the city of San Juan was anything but. The dinner on the last evening was legendary, like one of those hedonistic house parties in a rap video. A local politician adorned with a sash opened the proceedings, managing to make an outrageous quip about some of the foreigners in attendance. The main course was a phonebook-size slab of grass-fed beef, washed down with copious amounts of red wine. After dinner was dancing, for hours, fueled by an open bar with hundreds of bottles of vodka, whiskey, brandy, and a local firewater whose name I can’t remember. At about three a.m., there was a break in the proceedings while a make-your-own taco bar was assembled outside, a tasty change from the humidity of the dance floor. We staggered back to our hotels as dawn broke. Ricardo was right. I would love Argentina.

  Before the debauchery of that evening, I spent several days in the collections of Ricardo’s museum, the Instituto y Museo de Ciencias Naturales in the lovely city of San Juan. Most of the riches of Ischigualasto are kept here, Herrerasaurus, Eoraptor, and Eodromaeus among them, but also many other dinosaurs. There’s Sanjuansaurus, a close cousin of Herrerasaurus that was also a fierce predator. In another drawer is Panphagia, similar to Eoraptor in being a primitive miniature cousin of the later colossal sauropods, and Chromogisaurus, a larger Brontosaurus relative that grew up to a couple of meters long and was something of a middle-of-the-food-chain plant-eater. There are also the scrappy fossils of a dinosaur called Pisanosaurus, a dog-size animal that shares some features of the teeth and jaws with the ornithischian dinosaurs—the group that would later diversify into a vast range of plant-eating species, from the horned Triceratops to the duck-billed hadrosaurs. And they’re still finding new dinosaurs in Ischigualasto, so who knows what new characters will be added if you are lucky enough to visit.

  As I was pulling open the specimen cabinet doors, carefully removing the fossils to measure and photograph them, I felt like something of an historian, one of those scholars who spends dark hours in the archives, scrutinizing ancient manuscripts. The analogy is deliberate, because the Ischigualasto fossils are indeed historical artifacts, primary-source objects that help us tell the story of deep prehistoric pasts, millions of years before monks started writing on parchment. The bones that Romer, Reig, and Bonaparte, and then later Paul, Ricardo, and their many colleagues, have pried from the lunar landscape of Ischigualasto are the very first records of true dinosaurs, living, evolving, and beginning their long march to dominance.

  These first dinosaurs weren’t quite dominant yet, overshadowed by the larger and more diverse amphibians, mammal cousins, and crocodile relatives that they lived alongside on those dry, occasionally flooded plains of the Triassic. Even Herrerasaurus probably wasn’t at the top of the food chain, ceding that title to the murderous twenty-five-foot-long crocodile-line archosaur Saurosuchus. But the dinosaurs had arrived on the scene. The three major groups—the meat-eating theropods, long-necked sauropods, and herbivorous ornithischians—had already diverged from each other on the family tree, siblings setting out to form their own broods.

  The skull of Eoraptor and the hand of Herrerasaurus, two of the oldest dinosaurs.

  Photo courtesy of the author

  The dinosaurs were on the march.

  2

  Dinosaurs Rise Up

  Coelophyis

  Chapter Title art by Todd Marshall

  IMAGINE A WORLD WITH NO BORDERS. I’m not channeling John Lennon. What I mean is, envision a version of Earth where all of the land is connected together—no patchwork of continents separated by oceans and seas, just a single expanse of dry ground stretching from pole to pole. Given enough time and a good pair of shoes, you could walk from the Arctic Circle across the equator to the South Pole. If you ventured too far inland, you would find yourself many thousands of miles—tens of thousands, even—from the closest beach. But if you fancied a swim, you could take a dip in the vast ocean surrounding the big slab of land you called home and, theoretically at least, paddle from one coast all the way around the planet to the other coast without having to dry off.

  It may sound fanciful, but this is the world the dinosaurs grew up in.

  When the very first dinosaurs, like Herrerasaurus and Eoraptor, evolved from their cat-size dinosauromorph ancestors some 240 to 230 million years ago, there were no individual continents—no Australia or Asia or North America. There was no Atlantic Ocean separating the Americas from Europe and Africa, no Pacific Ocean
on the flip side of the globe. Instead, there was just one huge solid unbroken mass of land—what geologists refer to as a supercontinent. It was surrounded by a single global ocean. Geography class would have been easy in those days: the supercontinent we call Pangea, and the ocean we call Panthalassa.

  The dinosaurs were born into what we would see as a totally alien world. What was it like to live in such a place?

  First, let’s think about the physical geography. The supercontinent spanned an entire hemisphere of the Triassic Earth from North Pole to South. It looked something like a gigantic letter C, with a big indentation in the middle where an arm of Panthalassa cut into the land. Towering mountain ranges snaked across the landscape at odd angles, marking the sutures where smaller blocks of crust had once collided to build the giant continent, the pieces of a jigsaw puzzle. This puzzle wasn’t put together very easily or very quickly. For hundreds of millions of years, heat deep inside the planet pushed and tugged on the many smaller continents that were home to generations of animals long before the dinosaurs, until all of the land was globbed together into one sprawling kingdom.

  And what about the climate? No better way to put it: the earliest dinosaurs lived in a sauna. The Earth was a whole lot warmer back in the Triassic Period than it is today. In part, that’s because there was more carbon dioxide in the atmosphere, so more of a greenhouse effect, more heat radiating across the land and sea. But the geography of Pangea exacerbated things. On one side of the globe, dry land extended from pole to pole, but on the other side, there was open ocean. That meant that currents could travel unimpeded from the equator to the poles, so there was a direct path for water baked in the low-latitude sun to heat up the high-latitude regions. This prevented ice caps from forming. Compared to today, the Arctic and Antarctic were balmy, with summer temperatures similar to those of London or San Francisco, and winter temperatures that barely inched below freezing. They were places that early dinosaurs and the other creatures with whom they shared the earth could easily inhabit.

  If the poles were that warm, then the rest of the world must have been a hothouse. But it’s not as though the entire planet was a desert. Once again the geography of Pangea made things much more complex. Because the supercontinent was basically centered on the equator, half the land was always scorching in the summer while the other half was cooling down in the winter. The marked temperature differences between north and south caused violent air currents to regularly stream across the equator. When the seasons changed, these currents shifted direction. That kind of thing happens today in some parts of the world, particularly India and Southeast Asia. It’s what drives the monsoons, the alternation of a dry season with a prolonged deluge of rain and nasty storms. You’ve probably seen images in the newspaper or on the nightly news: floods drowning homes, people fleeing from raging torrents, mudslides burying villages. The modern monsoons are localized, but the Triassic ones were global. They were so severe that geologists have invented a hyperbolic term to describe them: megamonsoons.

  Many a dinosaur was probably swept away by floodwaters or entombed by mud avalanches. But the megamonsoons also had another effect. They helped divide Pangea into environmental provinces, characterized by different amounts of precipitation, varying severity of the monsoonal winds, and different temperatures. The equatorial region was extremely hot and humid, a tropical hell that would make summer in today’s Amazon seem a trip to Santa’s workshop by comparison. Then there were vast stretches of desert, extending about 30 degrees of latitude on either side of the equator—like the Sahara, only covering a much broader swath of the planet. Temperatures here were well into the hundreds (over 35 degrees Celsius), probably all year long, and the monsoonal rains that pounded other parts of Pangea were absent here, offering little more than a trickle of precipitation. But the monsoons exerted a great impact in the midlatitudes. These areas were slightly cooler but much more wet and humid than the deserts, far more hospitable to life. Herrerasaurus, Eoraptor, and the other Ischigualasto dinosaurs lived in such a setting, smack in the middle of the midlatitude humid belt of southern Pangea.

  Pangea may have been a united landmass, but its treacherous weather and extreme climates gave it a dangerous unpredictability. It wouldn’t have been a particularly safe or pleasant place to call home. But the very first dinosaurs had no choice. They entered a world still recovering from the terrible mass extinction at the end of the Permian, a land subject to the violent whims of storms and the blight of blistering temperatures. So did many other new types of plants and animals that were getting their start after the mass extinction cleared the planet. All of these newbies were thrust onto an evolutionary battlefield. It was far from certain that dinosaurs were going to emerge triumphant. After all, they were small and meek creatures, nowhere near the top of the food chain during their earliest years. They were hanging around with lots of other species of small-to-midsize reptiles, early mammals, and amphibians in the middle of the food pyramid, fearful of the crocodile-line archosaurs, who held the throne. Nothing was handed to the dinosaurs. They were going to have to earn it.

  DURING MANY SUMMERS, I’ve journeyed deep into the subtropical arid belt of northern Pangea, on the hunt for fossils. Of course, the supercontinent itself is long gone, having gradually fractured into our modern continents during the more than 230 million years since the primeval dinosaurs started their evolutionary march. What I’ve been exploring is a remnant of old Pangea that can be found in the sunny Algarve region of Portugal, at the very southwestern corner of Europe. During those formative years when dinosaurs were navigating the megamonsoons and boiling heat waves of the Triassic, this part of Portugal was only 15 or 20 degrees north of the equator, about the same latitude as Central America today.

  As with so many adventures in paleontology, it was a random clue that put Portugal on my radar. After our first jaunt together in Poland, visiting Grzegorz and studying fossils of some of the dinosauromorph ancestors of dinosaurs, my British buddy Richard Butler and I developed something of an addiction. We became obsessed with the Triassic Period. We wanted to understand what the world was like when dinosaurs were still young and vulnerable. So we scoured the map of Europe looking for other places where there were accessible rocks of Triassic age, the type of sediments that could conceivably contain the fossils of dinosaurs and other animals living alongside them. Richard came across a short paper in an obscure scientific journal, describing some scraps of bone from southern Portugal that were collected by a German geology student in the 1970s. The student had been in Portugal to make a map of the rock formations, a rite of passage for all undergraduate geology majors. He had little interest in fossils, so he threw the specimens in his rucksack and hauled them back to Berlin, where they languished in a museum for nearly three decades until some paleontologists recognized them as skull pieces of ancient amphibians. Triassic amphibians. That was enough to get us excited. There were Triassic fossils in a beautiful part of Europe and nobody had been looking for them for decades. We had to go.

  That tip brought Richard and me to Portugal in the late summer of 2009, the hottest part of the year. We teamed up with another friend, Octávio Mateus, who wasn’t even thirty-five years old at the time but was already regarded as Portugal’s leading dinosaur hunter. Octavio grew up in a little town called Lourinhã, on the windy Atlantic coast north of Lisbon. His parents were amateur archaeologists and historians who spent weekends exploring the countryside, which just so happened to be strewn with Jurassic dinosaur fossils. The Mateus family and their ragtag band of local enthusiasts collected so many dinosaur bones, teeth, and eggs that they needed a place to put them, so when Octávio was nine years old, his parents started their own museum. Today, the Museu da Lourinhã houses one of the most important collections of dinosaurs in the world, many of which have been collected by Octávio—who went on to study paleontology and become a professor in Lisbon—and by his ever-expanding army of students, volunteers, and homegrown helpers.

 
It was fitting that Octavio, Richard, and I set out in the August heat, because we were chasing the fossils of animals that lived in the very hottest and driest sector of Pangea. But it wasn’t very good strategy on our part. For several days, we hiked through the sun-baked hills of the Algarve, our sweat soaking the geological maps that we hoped would lead us to our treasure. We checked out nearly every speck of Triassic-age rock on the maps and relocated the site where the geology student had collected his amphibian bones, but all we saw were fossil crumbs. As our week in the field drew to a close, we were hot and exhausted, and staring down the barrel of failure. On the verge of defeat, we thought we should take one more hike in the area where the geology student made his discovery. It was a scorcher of a day, the thermometer on our handheld GPS units reaching 120 degrees Fahrenheit (50 Celsius).

  After an hour or so of prospecting together, we decided to split up. I stayed near the base of the hills, scrutinizing the fragments of bone scattered across the ground in a desperate attempt to trace them to their source. I had no luck. But then I heard an excited voice scream from somewhere up on the ridge. I detected a hint of a lyrical Portuguese accent, so it must have been Octávio. I rushed toward where I thought the voice was coming from, but now there was nothing but silence. Maybe I was imagining things, the heat playing tricks on my brain. Eventually I saw Octávio in the distance, rubbing his eyes like someone woken up by a phone call in the middle of the night. He was stumbling, giving off a bit of a zombie vibe. It was weird.