Dracorex (top, left) and Stygimoloch (top, right) were previously considered separate species, but Horner thinks they are just juvenile forms of Pachycephalosaurus (bottom). Stygimoloch is at a stage just prior to sexual maturity, with the bony dome of the adult starting to develop.
Credit: Holly Woodward/Montana State University
MY CLAIM TO FAME is that I've had a dinosaur specimen named after me. In mid 2009 I visited a dig with palaeontologist Jack Horner, famous for discovering the first nests of baby dinosaurs and for providing technical advice on the Jurassic Park movies. And it was on that dig in the sweeping badlands of eastern Montana that he discovered my namesake: a juvenile Triceratops.
I met up with Horner at Montana State University in Bozeman, where he is curator of palaeontology at the Museum of the Rockies. And in fact he looked dressed for a Jurassic Park set, much as I'd expected him to, with a khaki shirt tucked into blue jeans.
Despite the straggly grey hair and thin silver glasses, he looked much younger than his 63 years. Pleasantries over, I hopped into my hired 4WD and followed his red pickup truck for five hours, straight into the land of the dinosaurs - a place called Hell Creek.
I knew I was in for an adventure from the moment we arrived and Horner forgot to put the handbrake on before getting out of his truck. I watched in horror as it rolled towards me, but he quickly leapt back in, emerging soon after as though nothing had happened.
I climbed out of my car into the heat and dust and gazed into the endless sky and mountain peaks. The jagged, easily eroded slopes and sparse vegetation of Montana are not only serene, they also make fossil hunting relatively easy. As I allowed the beauty of the landscape to consume me, I understood that in Hell Creek I was in dinosaur heaven.
Mark Goodwin, assistant director of the Museum of Palaeontology at the University of California, Berkeley, tells me that part of what sets Horner apart from other fossil hunters is that he "has had a lot of novel approaches to things". One of these novel approaches is a project that aims to collect numerous specimens of a single dinosaur species, which I am shortly to learn much more about.
Horner first made a name for himself in the 1970s, when he discovered entire nests containing baby dinosaurs and eggs of a duck-billed species at nearby Egg Mountain. He named the species Maiasaura, meaning 'good mother lizard', since the find provided some of the first evidence of extended parental care in dinosaurs.
"It suggested that these dinosaurs hatched out of their eggs and remained in their nests for a period of time in which the babies at least doubled in size," says Horner. To remain helpless for so long, he argued, the dinosaurs would have needed a parent to feed them.
At the time the finding was controversial - but now Horner and Goodwin have a new controversy to shake things up. Their work suggests that palaeontologists have significantly overestimated the true number of dinosaur species.
The idea is that dinosaurs may have undergone morphological changes during development that were more significant than anyone realised. In their latest report, published in the journal PLoS One in October 2009, they suggest that two Hell Creek species described by other palaeontologists - Dracorex hogwartsia (with a spiked dragon-like head and named after the wizarding school in the Harry Potter books) and Stygimoloch - are not distinct species at all, but juvenile stages of the dome-headed species Pachycephalosaurus.
They realised that juvenile dinosaurs could be quite different from adult dinosaurs while studying the skulls of heavily armoured Triceratops that once lived around Hell Creek, and first published their evidence in the Proceedings of the Royal Society B in 2006.
"Juveniles and adults of these dinosaurs look very, very different … and literally may resemble a different species," says Goodwin. "But some scientists are confusing morphological differences at different growth stages with characteristics that are taxonomically important. The result
is an inflated number of dinosaurs in the late Cretaceous."
Part of the problem is that we have too few specimens of each species to compare, says Horner. "Early palaeontologists recognised the distinction between adults and juveniles, but people have lost track of looking at ontogeny - how the individual develops - when they discover a new fossil. Dinosaurs are not mammals, and they don't grow like mammals."
Currently, around a dozen species of dinosaur are known from the Hell Creek formation, but Horner keeps subtracting numbers from their ranks, condemning them to a different kind of extinction. A few duck-billed hadrosaurs dropped out recently; so did a small, slender-headed theropod called Nanotyrannus, now accepted to be an adolescent T. rex.
In fact, Horner thinks that a third of all described dinosaur species may have never existed, particularly in groups with elaborate head ornaments that changed throughout development and at sexual maturity.
After we arrived at the Hell Creek tent city, Horner introduced me to his gang of 30 dinosaur hunters - some professional palaeontologists, others students and volunteers. Liz Freedman, a petite graduate student, directed me to my home for the next few days: a tiny orange tent, which made up for its dimensions with a spectacular view of a lake.
It was the weekend of the 4th of July and Horner's team - halfway through the digging season - were eagerly awaiting the eight cases of beer he'd brought out to the camp to help them celebrate U.S. Independence Day.
Every northern summer of the past decade, Horner and his team have gone on a dinosaur-hunting spree largely aimed at collecting as many specimens as possible of single species: Triceratops.
"Most people look for new dinosaurs and unusual ones, but we want an enormous collection of one single dinosaur species, so we can learn about their growth and behaviour," says Horner.
Before they started the collection of Triceratops, currently numbering 60-something individuals, nobody knew what a juvenile looked like or how fast they grew. But now the fossils hint that they were social animals.
"Dinosaurs, like birds and many mammals, retain 'neoteny' - that is, they retain their juvenile characteristics for a long period of growth, which is a strong indicator that they were very social animals, grouping in flocks or herds with long periods of parental care," Horner explains.
In September 2009, Horner and his graduate student John Scannella presented some of their findings regarding the development of Triceratops at a meeting of the Society of Vertebrate Palaeontology in Bristol, England. The presentation outlined evidence that the three-horned species Torosaurus is not a distinct creature, but is in fact a fully mature Triceratops.
Triceratops, it now seems, had a skull shape that changed throughout their lives. "The horns above its eyes curve backwards when they are juvenile. The horns point forward when they are adults, and the points become flattened," says Horner.
"When fully grown, they also have holes in their frills." Several studies in the Journal of Vertebrate Palaeontology reveal how the large frill was used in display and to signal sexual maturity, and also how the frills and horns first develop at an early age.
"If Horner is right about Triceratops and Torosaurus [not being separate species], it will be relevant to this bigger question of how fast the dinosaurs went extinct," says Matthew Carrano, curator of dinosaurs at the Smithsonian Institution National Museum of Natural History in Washington DC.
"If dinosaurs were doing fine, and there were a lot of species up to the very end, then they died because of the asteroid. But if dinosaurs were already declining, when the meteor hit it may have been the final straw."
Depending on the elevation, the fossils at Hell Creek can be anywhere between 65 and 68 million years old, meaning they have direct relevance to uncovering the detailed factors that led to the extinction of the dinosaurs 65 million years ago.
Dracorex was described as a new species in 2006 and even made it on to the front cover of National Geographic. Horner and Goodwin's new study compared the structure of its skull with Pachycephalosaurus and Stygimoloch using morphological analysis and CT scans.
What they found suggested the other two creatures are juvenile pachycephalosaurs with skull bones that are not completely fused; Stygimoloch is at a stage just prior to sexual maturity, with the bony dome of the adult starting to develop.
In both this species and Triceratops the experts believe the animals had so-called 'metaplastic' bones in their skulls that could change shape - growing or reabsorbing throughout life, something like the antlers of deer.
Triceratops may be plentiful at Hell Creek, but so are several other species. Standing at the summit of a hill overlooking the vast, blue Fort Peck lake, on the second day of my trip, Horner points out the spots where a dozen or so specimens of T. rex have been unearthed on the hillside.
He likes to name specimens after people, and among others he points out C-rex, named after Celeste Horner, one of his ex wives, Jen-rex after Jennifer Flight, a former graduate student, and B-rex after Bob Harmon, his crew chief.
Horner says he prefers being alone in the field, but sometimes, like today, he must entertain guests and reporters. Alone or not, each hike represents a chance to find a new specimen to bring back to the Museum of the Rockies.
Later that day, during a hike across the hilly terrain, Horner shouts: "I've found a dinosaur!" It's almost like he has a sixth sense for it. He kneels down for a better glimpse of the finger-sized orange bones, takes note of the exact coordinates using a GPS device and then snaps a picture.
I'm chuffed when Horner decides to name the specimen after me and the three other female visitors. And the 'Four Babes Trike' (short for Triceratops) turns out to be the most ancient juvenile Triceratops ever discovered, at around 68 million years of age.
People have been dinosaur hunting in the Badlands of Montana for over a century. Palaeontologist Barnum Brown spearheaded the first excavations of T. rex fossils in 1902. He collected tonnes of bones by blasting into the hills with dynamite and shipped the fossils east using manpower, horse and carriage, and train.
Pretty soon, palaeontologists flocked here for dinosaur fossils, skimming the surface of the formation for the largest and most impressive to display as trophies of their toils. In the late 1990s, Horner changed the game.
His Hell Creek project brought together a multi-disciplinary team to learn about how dinosaurs lived during the Cretaceous (from 65 to 145 million years ago) and also to find out as much as possible about the whole ecosystem.
During the Independence Day weekend, Greg Wilson, stationed in the camp next to ours, came over for a beer. Wilson, an assistant professor at the University of Washington in Seattle, is no stranger to Horner's camp. He joined the Hell Creek project as a graduate student, researching mammal fossils.
"This is the cushiest camp. We have Internet access, telephone lines, electricity, and special trailers for cooking and VIP guests," says Wilson. There's a town of 30 tents. And there are often celebrities coming through, he says. Geologists and experts on ancient plants, snails and clams and many other topics gather to build up an entire picture of the environment and ecology of the period.
Even outsiders looking in know how critical the Hell Creek project has been in painting a picture of how dinosaurs lived. Paul Sereno is another veteran palaeontologist based at Chicago's Field Museum of Natural History. He says that what Horner is turning up about the variation within dinosaur species is key information.
"Ever since Darwin, we have appreciated that individual variation is the stuff of evolution," he says. "The skeleton is the single best source for evolutionary information, often mapping in sync with genetic changes."
Lawrence Witmer, an anatomist at Ohio University in Athens, U.S., agrees about the significance of the project: "One specimen from a species of an extinct animal is seldom complete. To understand extinct species, we need a sample of more than one specimen to get a sense of variation," he says.
ON MY THIRD and final day on the dig, I wake at 4.30 am with the Sun already bright in the sky. I climb out of my tent to enjoy the crisp morning air and by 6 am the entire crew is gathered around the breakfast tables. The food is terrible, but I'm happy to rough out the conditions for a couple of days.
The rest of the fossil hunters, however, have been here all summer and are clearly a dedicated bunch. They only shower once a week, constantly fend off biting insects and have to protect themselves by chopping off the heads of the rattlesnakes that regularly meander into the campsite.
On Sundays, they travel back to civilisation to take that shower, eat a meal at the local bar and watch TV at the Garfield Motel in the small town of Jordan, a half-hour drive from camp.
After breakfast, we divide into groups and set off to see some of the 24 digs in operation this summer. I am assigned to the group that will pay a visit to 'Duckytail', a hadrosaur with a tail that was broken at some stage in the animal's life, but later healed. I walk over to a four-wheel drive pickup truck, identical to one that featured in the opening scenes of Jurassic Park III.
In fact, Horner tells me that the film's director, Joe Johnston, copied the entire Hell Creek camp for the movie - right down to the vehicles. After a bumpy 30-minute drive along dirt roads, we park and hike through a kilometre-and-a-half of snake-infested meadows to the quarry site.
Duckytail is kept underneath a black tarp to protect the freshly exposed bones from the weather. As the covering is stripped back I'm amazed to see so much of the skeleton still intact. The crew unload their tools - rockhammer, ice picks, dental picks, paintbrushes, kneepads and whisk brooms - and begin clearing away the dirt. I grab a chisel and hammer and do my bit to help.
To protect the exposed parts of the bone a chemical called Vinac is used to coat the fossils. A top jacket is applied using burlap and plaster and the site's location and the date are written on the jacket. Once the top of the bone is covered, the crew dig underneath the fossil.
"They come to me with a childlike admiration of dinosaurs," Horner says of his hardworking team, "but when they work with me, I want them to think about dinosaurs more intellectually."
It was this intellectual thinking that led Horner and his team to question the notion that all the new dinosaurs found recently are distinct species; a question that led to one of the most significant discoveries to come out of dinosaur palaeontology in recent years.
Most days, Horner works alone, with his head down to the ground. When he finds a new specimen, his eyes light up - perhaps just as they did when he found his very first fossil bone at the age of eight. "I'm persistent. The more I walk around and stare at the ground, the more dinosaur bones I will find," he says.
Each new specimen fills in just a little bit more of our understanding of how these ancient beasts lived. And many more remain to be discovered in the Hell Creek formation - little slivers of bone exposed in the hillsides, waiting for someone with Horner's sixth sense to sniff them out.
Boonsri Dickinson is a science writer in New York City and a former Cosmos intern. John Pickrell is the former editor of Cosmos Online.
