With the brim of his battered cowboy hat tipped down against the sun, Doug Wolfe scans the dusty ground as he heads up a small arroyo in New Mexico's Zuni Basin. There's not much to look at. The gullies here are so dry and the buttes so barren that little more than a few small stunted pines and the odd rattlesnake can scrape out an existence. Still, Wolfe keeps coming back here, month after month, searching for evidence of a time when this desert landscape was lush, green, wet, and dense with dinosaurs.
A rough artistic montage of bones from a dinosaur nicknamed Fred suggests the 3-foot-tall carnivore was fleet-footed. Paleontologist Doug Wolfe says the newly discovered coelurosaur also "likely had a fairly large brain for its body plan."
At the top of the ridge, the paleontologist hunkers down beside a cylindrical boulder streaked with crumbling crystalline rock. He runs his fingers along a series of weathered growth rings. The boulder, a massive fossil, was once the stump of a tree. Wolfe estimates it reached a towering height of some 60 feet about 90 million years ago, part of a thick forest dappled by ancient relatives of the magnolia and fig families. It's a stretch of the imagination, but the arid badlands that reach toward the horizon once were verdant wetlands. Over there, across a broad floodplain, a silty brown stream once meandered lazily on its way to a nearby sea, unburdening itself of sediment. Close by, box turtles burrowed by the edges of a large pond where carnivorous fish armed with needle-sharp teeth basked in the sun like logs, as crocodiles glided by in the shadows. Wolfe shakes his head, as if to throw off the easy disbelief, then says: "It would have been like the Gulf Coast here, with lots of rain and lots of vegetation."
Wolfe has pieced together a remarkably detailed picture of that wild, moist world by analyzing thousands of bone fragments collected by a fossil-hunting team that includes his wife, Hazel, and their son, Christopher, 11. At the site of an ancient pond, just one small part of an ancient boneyard, Wolfe and his team have begun to reconstruct an entire ecosystem. Among their discoveries is a dinosaur paleontologists have never encountered before— a two-legged meat eater 3 feet tall and 6 feet long, with serrated teeth like miniature steak knives and claws that may have been suitable for climbing trees.
The Zuni Basin is littered with such surprises, although many of the finds are in bite-sized pieces. In the pond, for example, "a lot of the stuff may have gone through the digestive gut of crocodiles," Wolfe says. Reassembling the pieces is slow work, but so far Wolfe and his colleagues have discovered three previously unidentified dinosaur genera, including a feathered herbivore, roughly 13 feet tall and 20 feet long, that seems to have been a bizarre cross between Tyrannosaurus rex and a turkey. Another curiosity is an early horned dinosaur, about the size of a small cow, with teeth capable of shearing off tree branches. Wolfe's team has also collected remains of two other dinosaur species, plus fragments of turtles, monitor lizards, and three varieties of fish. There may be much more. Early mammal experts will soon begin screening the tiny fossil bones of primitive marsupials. Meanwhile, paleobotanists are poring over the fossilized stumps of immense trees still rooted in the ancient forest floor. "Wolfe has got a virtual graveyard of things," says Spencer Lucas, curator of paleontology at the New Mexico Museum of Natural History and Science. "It's not like someone just went out and found one skeleton and that's all we're ever going to know."
Diminutive Hell -RaiserFred was much smaller than his distant cousin Tyrannosaurus rex but was still a terror. "These things may have been ganging up on large predators," says Wolfe. He and his fellow researchers first thought the creature resembled a raptorlike dromeosaur but now think it was a coelurosaur, a more primitive theropod. Wolfe and his colleague Jim Kirkland sent fossil casts and photos to artist Maximo Salas to aid in the creation of this reconstruction, which remains a work in progress. The claws and grasping digits of the lithe little dinosaur are incomplete on this preliminary 3-D model.
Sculpture by Maximo Salas
The diverse discoveries at Zuni Basin are already shedding light on a host of long-standing questions, from dinosaur origins to dinosaur migrations. Moreover, Wolfe and his team have cracked open a time portal that offers an unprecedented glimpse of life during the middle Cretaceous Period, an era of global warming when a dramatic rise in sea levels left much of the world's landmass underwater. In years to come, the team's painstaking reconstruction of the ancient wetlands at Zuni Basin may supply clues to a puzzle that increasingly preoccupies modern science: What effect did cataclysmic climate changes have on the world's biota? "If you want to find out how bad things could get with global warming," says Wolfe, "then the middle Cretaceous is the time to study."
An intense, temperamental man, with a musician's neatly trimmed goatee and a driving, headstrong energy that belies his 42 years, Wolfe clearly revels in the richness of the new finds. Geologists who surveyed the area during the early 1980s turned up thick slabs of fossilized plant leaves and hefty seams of dark black coal but didn't detect fossil lizards, turtles, or fish, much less the massive bones of larger beasts. Paleontologists had long doubted the area would ever yield any significant dinosaur bones, but Wolfe's first prospecting trips left him convinced there was treasure in the parched landscape. While studying for his master's at the University of Colorado at Boulder in 1983, Wolfe and his friend Jim Kirkland, a fellow graduate student, discovered a tiny shred of ankylosaur armor and a fragment of dinosaur rib bone in a crumbly band of middle Cretaceous rock. Wolfe returned years later for weekend fossil-hunting expeditions, exploring nearly every major canyon and outcrop of the basin accessible from public roads. During one of those surveying weekends about five years ago, he and colleague Bob Denton, a paleontologist at the New Jersey State Museum, spied a hidden section of badlands that looked promising. It contained strata that had yielded bits of bone elsewhere in the area and outcrops that were accessible.
Two weeks later, Wolfe and his family found four localities sprinkled with bone. Even when the weather turned miserable on the second day, the family pressed on. In the late afternoon, Wolfe spied some white specks on a small butte. His son, Christopher, then 7, ran ahead and excitedly called his father to take a closer look. Wolfe was startled to find bits of a massive dinosaur horn scattered on black shale. He felt as if he had just walked into an enchanted world. Out of habit, he glanced down at his watch. It had stopped earlier that morning, "and it was really strange," he recalls, "because as we were driving away, my watch started again."
From the outset, Wolfe suspected he had uncovered a major find. He had already dated the relevant strata in the basin by detecting certain well-studied marine fossils of known ages in the overlying and underlying rock. Although any dinosaur skeletons from the middle Cretaceous Period in North America are rare finds, Wolfe knew diverse ecosystems would likely nourish an exotic variety of fauna. His study of the complex paleogeography of Zuni Basin during the middle Cretaceous suggested it was an intricate landscape of ponds, streams, swamps, and forests as well as advancing and retreating coastlines. So he called his old friend Jim Kirkland and asked him to help put together a team of excavators and fossil preparators.
Bony ChroniclesBy removing the stony matrix from fossils, preparators have revealed the telltale signatures of three new dinosaurs: 1) the horn of Zuniceratops christopheri, the earliest brow-horned dinosaur; 2) the claw of an Asian immigrant, Nothronychus mckinleyi, a giant long-necked herbivore; and 3) the snout of the yet-to-be-formallynamed coelurosaur Fred, who may have climbed trees.
The first bone bed the team dug up was full of dinosaur parts, a crushed jumble of carcasses that had been swept up by a raging torrent 90 million years ago, then snagged in a downstream logjam. Identifying specimens in an ancient mishmash can be tricky. As Wolfe and Kirkland sorted through splintered fossil fragments, they were particularly mystified by a wafer-thin bone and some large vertebrae that were riddled with air pockets, like the bones found in birds. Then they reexamined a hooked claw they had originally identified as a tyrannosaur talon and noticed something startling: Both the claw and the birdlike bones resembled skeletal fragments from an obscure Asian family of beasts called therizinosaurs.
These "scythe lizards" had long puzzled paleontologists. The oddest ones brandished 3-foot-long claws resembling pitchfork tines. They defied classification for decades. The first fragmentary specimen, excavated in the Gobi Desert during the 1940s, was initially described as a giant turtle, then later was thought to be a member of the family of plant-eating dinosaurs known as prosauropods. In recent decades, the discovery of more bones, teeth, and fragments of fossilized skin bearing impressions of pinfeathers has led researchers to conclude that therizinosaurs were feathered and closely related to the carnivorous tyrannosaurs and allosaurs.
Specimens were few and far between. To obtain an expert opinion on the mysterious wafer-thin bone he found, Wolfe took a cast to a paleontology conference in Utah and showed it to American Museum of Natural History paleontologist Mark Norell and Royal Tyrrell Museum of Paleontology researcher Phillip Currie, both of whom had worked extensively in China. Norell and Currie agreed that the cast resembled the ischium (the posterior pelvic bone) of a therizinosaur. "We subsequently found teeth, the shoulder assemblage, and other stuff to nail the diagnosis," says Wolfe, "but it was a pretty big leap, because these animals were not known in the Americas."
Now described and named Nothronychus mckinleyi, the new therizinosaur is the largest of the dinosaurs identified so far in Zuni Basin. Measuring 20 feet in length from the top of its feathered head to the tip of its stout tail, it almost certainly walked upright— like Godzilla— rather than tilted over in a posture apparently favored by its celebrated relative, T. rex. Clearly built for comfort rather than speed, N. mckinleyi boasted an immense potbelly and in all likelihood moved with a shuffling, waddling gait. It also was likely covered in shaggy plumage like an emu and had a tiny beaked head equipped with miniature serrated teeth. "Just imagine a big feathered, brightly colored thing with claws and a teeny-tiny head lurking toward you," says Wolfe.
However strange and ungainly, N. mckinleyi was ingeniously suited to the lush life of Zuni Basin. While researchers have suggested that the therizinosaurs of Asia were giant insectivores that fed by rooting out termites with their long spikelike fingers, N. mckinleyi's body plan apparently was more like that of another extinct herbivore— the ground sloth. Like the sloth, it could lift its arms high over its head, a great asset for a forest dweller, and had sturdy hooked claws that would have been useful for grasping branches. N. mckinleyi's huge gut, moreover, could have served to digest vast quantities of vegetation. "We've got some of the first really abundant flowering plants and fruits," says Wolfe, "and maybe these animals went after them."
The Wolfes— Doug, Chris, Hazel, and their dog Dina— have been hunting fossils together for five years. "We thought we'd be lucky to find some crocodiles," says Doug. "We didn't ever think we would find this many dinosaurs."
In the same ancient logjam that yielded N. mckinleyi, Wolfe and Kirkland have also uncovered an intriguing new species of horned dinosaur, the oldest ever recovered from North America. Named for Wolfe's son, who was the first to spot its bone, Zuniceratops christopheri was a slender animal about the size of a small cow. Furnished with a beak and protected by two prominent brow horns as well as a frill above the head like a triceratops, the dinosaur walked on all fours and likely possessed a daunting battery of sturdy teeth, whose shearing motion could have been designed for pruning branches off trees. "They did not just selectively eat leaves," says Wolfe. "These things could probably chomp through wood as thick as your arm. Now, whether that's to get to the tender leaves or that is what they were really eating, I don't know."
Cretaceous CatastropheGlobal warming during the middle Cretaceous accompanied a dramatic rise in sea levels that left vast stretches of North America underwater. The Zuni Basin of New Mexico became a coastal swampland, where smaller cycles of cataclysm played out 90 million years ago. First drought struck the region, forcing large herbivores to congregate around ever-diminishing watering holes and creeks. Many died.
Illustration: Matt Zang
So far, the fossil-hunting team have found nary a trace of a large predator in the Zuni Basin, and that strikes Wolfe as curious. Along a coastline filled with large and presumably savory herbivores, one would expect to find at least one large carnivore— a dagger-toothed tyrannosaur capable of crushing the head of a therizinosaur, or a fleet-footed allosaur equipped to chase down nimble-footed prey. Such creatures typically shed their incisors quite often, but after five years of quarrying and screening, Wolfe and his colleagues have yet to net one tooth from a large carnivorous dinosaur.
Cretaceous CatastropheThen floods struck, sweeping carcasses downstream. Doug Wolfe's sketches (below) show how bones became tangled in an ancient logjam, creating a jumbled dinosaur graveyard.
Illustration: Doug Wolfe
Even so, the riverbanks and watering holes of the basin were not devoid of saurian dangers. The team's quarrying has produced two partial skeletons of a new species of meat eater, a delicate 6-foot-long dinosaur that seems to be a diminutive cousin of T. rex. Slender and long-legged, the little predator, which Wolfe has playfully nicknamed Fred, would likely have served much the same role in the ecology of the middle Cretaceous as the coyote or wolf does today. "It was probably part of a guild of small predators that performed an important function— preying on small animals and perhaps being scavengers." While removing the surrounding rock from one of the skeletons, fossil preparator Harold Bollan found what looked to be the creature's last dinner— a plant-eating lizard whose strong lashing tail would have given its attacker a serious fight. "You can just imagine this 6-foot-long dinosaur wrestling with a 3-foot-long monitor lizard," says Wolfe.
Classification studies by University of Maryland paleontologist Tom Holtz have yet to suggest just how the small predator captured prey. But one feature of the animal's anatomy— its dexterous claws— suggests an intriguing possibility. "I will probably get shot down for this, but it's possible that they were climbing trees," says Wolfe. "Hiding in trees would be a great ambushing strategy. If you are a small meat-eating critter, that's where the mammals and birds are going to be."
With their slothlike arms, shaggy plumage, and tree-shearing teeth, some of the dinosaurs of Zuni Basin seem as strange and fanciful as the creatures of Dr. Seuss. But that sense of peculiarity, argues Spencer Lucas of the New Mexico Museum of Natural History and Science, stems from our general lack of knowledge of terrestrial life during the middle Cretaceous. Similarly, when the first dinosaur fossils were collected in the 1820s and 1830s, the Victorian public had never seen anything quite like the giant reptiles with their bizarre frills, horns, and claws. "The animals looked awfully odd because nobody could have ever guessed that they had been around," says Lucas.
Eager to dispel ignorance about faunal life during the middle Cretaceous, Wolfe and Kirkland are studying the newly unearthed fossils, searching for clues to their ancient evolution. Such studies, say researchers such as Hans-Dieter Sues, a paleontologist at the Royal Ontario Museum in Toronto, are almost certain to shed light on a puzzling transformation that overcame North America's dinosaur populations 90 to 100 million years ago. "Before that time, we had dinosaur faunas that were quite similar to those we know from Europe," says Sues. "But then after that, we increasingly get these strong faunal ties to what is now Central and East Asia." What happened?
A fossil stump rooted in the desert near one of the Zuni Basin bone beds is a relic of a primeval woodland filled with magnolialike trees. "This seems to be one of the first forest habitats of flowering trees that has produced a fauna of large animals," says Wolfe.
The answer may lie in Zuni Basin. Wolfe and Kirkland are turning up tantalizing clues. The key, says Wolfe, could be radical climatic change: The middle Cretaceous was a time of intense global warming. Throughout the world, fiery volcanoes thundered, lofting immense plumes of ash and gas into the air. As a result of this and other complex global atmospheric changes, levels of greenhouse gases soared. Present-day geochemical studies suggest atmospheric carbon dioxide alone rocketed to levels three times higher than those found today. Inevitably, this thick mantle trapped heat. As Earth warmed, sea levels rose by as much as 1,000 feet.
The flooding wreaked havoc with geography. In North America, invading waters formed a sweeping seaway from the Arctic Ocean to the Gulf Coast, dividing eastern highlands from the cordillera, the West's mountainous spine. An ocean severed North America from South America. But in this new water world, the ancient land bridge joining northwestern North America to northeastern Asia remained high and dry. As a result, Asian dinosaurs were free to amble eastward and southward, gradually extending their ranges until they reached land's end in Arizona, New Mexico, and northern Mexico. "You could walk all the way from Russia to here," says Wolfe, "so we were at the very end of the migration route."
At the peak of the flooding, however, there were few lowlands to be found anywhere in North America; the new seaway lapped against the foot of the cordillera. And in such a watery realm, regions like Zuni Basin may have been isolated from other coastal lowlands, becoming virtual islands. Wolfe suggests this may have placed great selective pressure on North America's dinosaurs, weeding out the largest species. "It could be that because we're in this little cul-de-sac, we don't have enough eco-space for a bunch of 30-foot-tall carnivores," he explains. "If you're missing upper stories in the ecology, that tends to show that there's something distressed about the environment. If you go to the Galápagos Islands or the Hawaiian Islands, for example, you're missing entire predatory guilds. There are no snakes, no lizards. Instead you get all these birds, and you have this tremendous speciation because you don't have things keeping them under intensive pressure."
Fossilized bones recovered from Zuniceratops christopheri, a plant eater with a bony head frill, include: 1) a partial squamosal (from head frill); 2) left nasal bone; 3) left premaxilla (bone around nostril); 4) right premaxilla; 5) left maxilla (upper jaw); 6) left brow horn complex; 7) partial orbit (bone around eye); and 8) scapula (shoulder blade).
The intense competition for eco-space in places like Zuni Basin lasted only as long as the flooding. When the world cooled again, the seas retreated, revealing vast stretches of terra firma ripe for colonization. And this, says Wolfe, opened up dazzling new opportunities for animal and plant survivors.
"It's as if you've just downsized every corporation in America and fired the slackers," says Wolfe. "Then you get all these resources, and those most able to adapt flourish." Faced with such ecological bounty, the dinosaurs that remained in Zuni and other coastal regions would have multiplied, giving rise to the brilliant biological diversity seen in the region's new genera.
Climate change and its effect on evolution is something Wolfe often contemplates these days as he walks through arid arroyos and creosote-lined gullies. In a section of badlands that researchers once wrote off as barren, he may have found a Garden of Eden, a lost saurian world fashioned by nature in the face of unprecedented environmental disaster.
The new CretaCeous creatures will be featured on When Dinosaurs Roamed America, a Discovery Channel special that airs July 15.
To see the specimens collected by Doug Wolfe, visit the Mesa Southwest Museum. For information about the museum, call 480-644-4098 or see www.ci.mesa.az.us/parksrec/msm/msmdefault.htm.
For more about Zuniceratops christopheri on-line, see www.dinodata.net/Dd/Namelist/Tabz/Z016.htm.
To learn more about New Mexico dinos, see the New Mexico Museum of Natural History and Science's Web page: www.nmmnh-abq.mus .nm.us/nmmnh/nmmnh.html.
To find out more or to join a discussion on Wolfe's finds, check out the Cleveland Museum of Natural History's Dinosaur Mailing List at www.cmnh.org/fun/dinosaur-archive.