National Geographic

Chasing After Allosaurus

A little more than a year ago, in the corner of a Salt Lake City tattoo parlor spattered with sci-fi ephemera and fantasy art, I watched as artist Jon McAffee inked an Allosaurus onto my arm. The bloody art was a celebration of a dream realized and a promise to myself.

The giant, sauropod-rending theropod Allosaurus is the state fossil of Utah, and a symbol of why I transplanted myself to the state. I moved west for the dinosaurs. But the tattoo represents more than that. I’m not content only writing about dinosaurs. I need to seek them out; to dig them from their resting places and contribute something to our understanding of prehistory. Allosaurus – the most common terror of 150 million year old Utah – was at the top of the list of the dinosaurs I wanted to meet among the badlands.

I had coaxed dinosaurs from rock before I was artistically scarred, and spent much of the summer of 2012 continuing my search. But I was always in the wrong rocks to find any trace of Allosaurus. I scuffed over and scratched at the 220 million year old Triassic rock of Utah and New Mexico – early dinosaurian days when their kind was small and had only a marginal role in the habitats in which they lived – and ambled over the 75 million year of strata of Grand Staircase-Escalante National Monument, searching sections of stone that record a profusion of non-avian dinosaurs near their Cretaceous curtain call. These exposures were far too early and too late, respectively, to contain any sign of allosaurs or any other of my Jurassic favorites.

For my third western summer, I resolved to get to the Jurassic. I had to. Besides being the heyday of dinosaur giants, I had developed a growing affection for Allosaurus. The “different reptile” has often been treated as a lesser predecessor of Tyrannosaurus, a mere shadow of the bone-crushers that would come later. Yet rare specimens suggest that Allosaurus reached sizes comparable to the more celebrated Cretaceous carnivore, and the abundance of their remains in Jurassic rock hinted that Allosaurus were quite successful and formidable predators of their time. I wanted to find one. So during a lull in my June schedule, I signed up to help pull a few more bones out of a Jurassic-age bonebed in the alien landscape outside Hanksville, Utah. The site was dominated by young sauropods – little long-necked herbivores of the Apatosaurus sort – but at least I’d be in the right temporal territory to stumble across some sign of Allosaurus.

But not long before I was due to strike east for Hanksville, I got an email from Bureau of Land Management paleontologist Mike Leschin. Would I be interested, Leschin asked, in visiting the Cleveland-Lloyd Dinosaur Quarry to see new excavations run by University of Wisconsin Oshkosh researcher Joe Peterson? I tried to keep the exclamation points in my response to a minimum. Not only is Cleveland-Lloyd another Jurassic mass burial tucked within the cracked and colorful exposures of Utah’s San Rafael Swell, but the site is totally dominated by Allosaurus.  Based on bare bones, a minimum of 46 Allosaurus of different ages were entombed here, and that’s only counting the fraction of the site that has been exposed to date. Yes, I replied to Leschin and Peterson; I’d be delighted to drop in at the CLDQ.

I had seen the historic quarry’s bones before. Last November, for a behind-the-scenes event at the Natural History Museum of Utah, I stood in front of a long row of cabinets carefully piled with the distinctive black bones of Cleveland-Lloyd so I could show off some Allosaurus jaws to visitors. Most of these bones were collected over decades of sporadic work by different institutions. The University of Utah was the first to work the site, pulling about 800 bones from the sandstone in 1927, and was followed by a Princeton University team that extracted a further 1,200 fossils between the summers of 1939 and 1941.

Ultimately, the UU purchased the Princeton collection and re-opened the site during the 1960s, upping the collected total to over 10,000 bones from this single site. With the efforts of paleontologist James Madsen, Jr. and others, the dinosaur graveyard became a National Natural Landmark in 1965. More than that,  Madsen used the slew of bones in the UU collections to eventually write the definitive monograph on the anatomy of Allosaurus fragilis, and casts created from Cleveland-Lloyd bones became the definitive image of the dinosaur. When artist Glendon Mellow went about designing my Allosaurus tattoo, he went to the Royal Ontario Museum to study a reconstruction based on bones from the eastern Utah quarry.

A reconstruction of Allosaurus menaces visitors to the CLDQ visitors center. Photo by Brian Switek.

A reconstruction of Allosaurus menaces visitors to the CLDQ visitors center. Photo by Brian Switek.

Other teams have picked at the site on and off through the years, and other dinosaur species have been found there. (The Ceratosaurus that joins the Allosaurus on my arm, for instance, is based on specimens found at Cleveland-Lloyd, and the small carnivores Marshosaurus and Stokesosaurus were described from material first found in the deposit.) Yet, despite the wealth of fossils in the boneyard and the persistent mystery of why any one place should be so rich in Allosaurus, the Cleveland-Lloyd quarry has often been forgotten or neglected. Perhaps, as had for so long been the case with the Hanksville-Burpee quarry further south, the familiarity of the Late Jurassic dinosaurs enclosed within the rock failed to spark the interest of researchers who were out to find new species from other ages.

But I couldn’t wait to join Peterson’s group. I had driven out to the quarry once before – on a sweltering June afternoon last summer – to see the recently-built visitors center and the exposed bones inside a small metal building propped up over part of the original quarry. Dinosaur National Monument, it’s not, but I’m dinosaur-crazed enough that I was still enthused at seeing dusty bones poking out of the stone and carefully-arranged replicas marking the places of fossils already excavated. If I was going to have any chance of turning up a bit of Allosaurus, there was no surer bet than working the Cleveland-Lloyd quarry.

There was just one snag. Peterson was working at Cleveland-Lloyd during the same week that I had signed up for Hanksville. I didn’t want to back out on the Burpee Museum of Natural History crew, but I couldn’t give up on Allosaurus. So I made a lopsided compromise. I decided to cut off the last day of my time in Hanksville to skip camps and join Peterson’s efforts. At least the quarries were close – only a three-hour stint from each other along Utah’s Dinosaur Diamond byway system.

I met Peterson and his van full of undergraduate assistants next to the high-kicking Utahraptor just outside Price, Utah’s Prehistoric Museum. Inside, the reconstructed representations of the dinosaurs found at Cleveland-Lloyd were slowly having their spines straightened and limbs re-adjusted to bring the old mounts into accord with 21st century dinosaur visions, but I’d have to come back to see them some other time. The museum was closed for the evening, and there were as-yet-uncovered bones pulling me after Peterson’s lead on the highways and dirt roads out to camp.

For the past few days, I had worked with a crew who – depending on their personal comfort needs – stayed in campers or motels and went out every night for dinner. Peterson’s camp was more like what I was accustomed to – a scattered array of tents and a fire ring, just over the hill from the quarry visitor center. Camp, sweet camp. For a night, anyhow.

After setting up my tent and presenting Peterson with a bottle of whiskey – I believe that good field etiquette requires a tribute of booze to host camps – I asked the Wisconsin-based paleontologist for his interpretation of what happened at Cleveland-Lloyd. At other Jurassic quarries, seasonal droughts and local flooding seem to explain the tangled distributions of dinosaur bones. But what was it about this one particular spot that was so attractive to Allosaurus?

In Utah, at least, there are almost as many hypotheses as there are experts. The Natural History Museum of Utah, where I typically volunteer, devotes an entire interactive display to the competing ideas. Where some see a death trap – a sucking mire that enticed hungry Allosaurus with the scent of putrefying flesh – others see the victims of a drought, an assemblage created by mass poisoning, or the strewn remains of animals that died elsewhere, expanded with gases from decomposition, and were carried like reeking balloons by water flow in a process called “Bloat and Float.” No one has been able to make an irrefutable case for any of these scenarios.

Sunset from the CLDQ camp. Photo by Brian Switek.

Sunset from the CLDQ camp. Photo by Brian Switek.

Since Peterson has been coming out to Cleveland-Lloyd for a few weeks the past few summers to specifically study what happened to the Allosaurus, I wanted to hear his view. Aside from his team, the quarry rests undisturbed for the whole year – a locality rich with possibilities that have only been barely realized in the 86 years since the first UU team dug in here.

Sipping a bit of bourbon from a plastic cup and lit by the orange and purple sunset behind the outcrop, Peterson said that he currently favors the “Bloat and Float” hypothesis. Forgetting about the preponderance of Allosaurus, he explained, the geology of the site and distribution of the bones suggests that the dinosaurs within were transported and tossed together at this one place. Rather than being a deadly predator trap, a drying watering hole, or a toxic quagmire, the Cleveland-Lloyd quarry might be the burial ground for tragedies that unfolded elsewhere on the Jurassic landscape.

But then Allosaurus stomps back into the picture. Why are over 75% of the Cleveland-Lloyd dinosaur bones referable to Allosaurus of all ages? Other Jurassic bonebeds are dominated by herbivores and seem to more closely represent our expectations of the Jurassic landscapes we revive from the fossil record – long-necked sauropods, armored stegosaurs, and other plant-pluckers everywhere, with a rare carnivore lurking among the conifers or brashly tearing strips of muscle from a downed Camarasaurus on the fern-covered floodplain. But, Peterson pondered aloud, what if Allosaurus was far more common than we ever expected? Maybe the African savanna model – innumerable big herbivores, relatively few carnivores – doesn’t apply to the Late Jurassic.

I’m not sure Allosaurus was so ubiquitous and social to readily explain over 46 individual animals – and probably many more – dying en masse at some distant site and floating downriver into an osteological pileup. For one thing, dinosaurs such as Allosaurus grew quickly and apparently had hot-running metabolisms (even if we don’t know all the details of their physiology yet). How would an enormous flock of Allosaurus possibly find enough food to eat, or even manage to share a single kill?

But maybe Cleveland-Lloyd represents a kind of event that we can’t yet tease out from the fossil record, or even a circumstance that we will never know. Could all these Allosaurus come together – over one season or many – to this particularly place to lek or otherwise attract mates? Or might there have been a mass die-off of huge sauropod dinosaurs, providing a feast that somehow turned tragic and later scattered the bones of the toothy revelers? Whatever the immediate causes of their death and deposition, we’re still left with the perpetually-vexing question of why so many Allosaurus are found here and are rare elsewhere.

My addiction to technical quandaries temporarily sated, campfire conversation turned to paleo gossip and lurid tales of other camps. (Someone could write a Hunter S. Thompson-esque account of the boozing and lascivious behavior of paleontologists in the field, Peterson suggested.) After dark, the team members sleepily walked back to their tents over the rough cobblestones of the campground, leaving only me and one of the annual Cleveland-Lloyd interns awake. We continued to chat for a while, watching the fire slowly dim, when the intern saw a pair of red lights zip along the road in front of camp, accompanied by the grinding of tires over dirt. This was well past midnight, and the camp wasn’t expecting any other visitors. The lights carried a concerning possibility – maybe someone was planning to rob the quarry.

Dinosaur theft and vandalism is frustratingly common. The problem isn’t only restricted to far-off sites in the Gobi Desert, where thieves snatch scientifically-important specimens and funnel them to black market dealers. Rock shop owners hungry for new items and selfish passersby who want a piece of their own dinosaur will raid quarries for whatever they can break off and carry. Even worse are the lackwits who simply smash and shatter. This has made paleontologists wary of quarry visitors. We want the public to visit our sites, to see the science of dinosaur excavation in action, but outreach also runs the risk of giving hints to those who wish to steal and destroy.

The intern roused a friend from his tent and the pair of them drove off to see if they could spot the intruder. They were expecting to find ATV tracks around the fences and locked quarry buildings. Half an hour later, they came back to camp without seeing a definite sign of any fossil rustlers. Worries at least somewhat relieved, those of us left awake retired to our tents for the night.

After slathering myself with sunscreen and packing some water, crackers, and jerky for lunch, I had my choice of duties the next day. I could go with Peterson to see a new fossil site nearby, work in the quarry building open to the public, or dig in a second fossil shack that is used for storage most of the year and, I was told, smelled of packrat pee. I picked the public quarry. With so little time at Cleveland-Lloyd, I wanted to devote my hours to searching for Allosaurus bones away from rodent odors.

My corner of the quarry. Photo by Brian Switek.

My corner of the quarry. Photo by Brian Switek.

After Peterson’s quick tour of what he and his team were working on this year, I lifted the latch to the orange gate in the public quarry building and found a cramped spot just to the left side of the shady structure. I had to constantly watch my step so as to not to trample on a pair of Allosaurus femora – thigh bones – uncovered a few days before. Despite the thousands of dinosaur pieces already exposed over the course of decades, fossils were still crowded just below the sandstone surface of the rock.

I struck bone almost immediately. A few scratches of an awl and a thin piece of black bone seemed to pop from the surrounding stone. I followed the usual process of pick, brush, vinac until the fragment was secure. Much like my experience at Hanksville earlier in the week, I had found yet another weird, thin enigma.

Poking and swiping at the sandstone, I still believed that an Allosaurus claw, hip fragment, or skull element was just beneath where I was working. I scored and popped off the rock to only find more small bones, fragments and tubular bits of belly ribs technically known as gastralia. The student next to me chose her spot more wisely. Every fifteen minutes, or so it seemed, she found another isolated Allosaurus element. Some volunteers have all the luck.

At least the gnats weren’t bad. Say the word “Gnat” around a paleontologist, and if they don’t immediately shriek “WHERE?!”, they’ll take on a grim expression as they remember bug bites past. Growing up, “gnat” was a term for the gently swirling clouds of insects I often saw in the backyard twilight or along forest paths. In the field, gnats are vampires that can immediately pinpoint your weak spots, almost imperceptibly take their blood meals, and then flit around your face and ears as if they are trying to drive you mad. Applying bug spray almost seems to encourage them, as if you’re challenging them to a fight. A mosquito may buzz away from the scent of DEET. A gnat will want to bathe in it.

Allosaurus femora found during this year's excavations. Photo by Brian Switek.

Allosaurus femora found during this year’s excavations. Photo by Brian Switek.

Mercifully, a stiff and persistent breeze kept the gnats at bay for most of my time in the quarry. A different kind of annoyance came from the building next door. The undergrads blasted dubstep and death metal in their private excavation. Fair enough for them, but the muffled music was just distracting enough to become almost as irritating as the occasional visits from gnats. Peterson, who was working at my feet, suggested that we crank up our own soundtrack by putting an iPhone inside a metal bucket amplifier. His choice: The Doors. Whenever someone in one of his quarries played The Doors, Peterson cheerfully explained, someone found something good.

The Lizard King’s band was about halfway through the hypnotic jam of “L.A. Woman” when a flick of my awl turned up something shiny in the grey grit of the ancient sandstone. I knew that the black sheen could only be part of a dinosaur’s dental toolkit. “Huh, I think I’ve got a tooth”, I said, and handed the fossil into Peterson’s outstreched hand before even cleaning it off. From the size and little dimples along the edge, I suspected that I had found nothing more than a broken bit of an Allosaurus tooth. Not a bad find, I thought, but not so impressive as the fossils everyone was finding around me.

“This is weird”, Peterson said, turning over the tooth in his hands. I hadn’t found part of an Allosaurus tooth. The shape was all wrong, and the serrations I thought I saw were enamel wrinkles along a squared-off and tapering crown. The anatomy was totally wrong for a carnivore, and didn’t fit any of the sauropods, either. Peterson and I exchanged ideas. Could the tooth be from a Stegosaurus? Or a bipedal, beaked dinosaur called Camptosaurus? What if it’s something new? Peterson had never seen someone uncover such a tooth before from the quarry. Who did the mystery fossil belong to?

Peterson ran up to the visitors center to compare the tooth with the casts of Stegosaurus and Camptosaurus on display. The petrified remnant didn’t seem to match either, he reported back. For one thing, the tooth was way too big – the tooth crowns of Stegosaurus and Camptosaurus were about the size of the rounded head of a fabric pin, while the Jurassic piece I’d discovered was bigger than my thumbnail. If the tooth was from either of these two candidates, the individual would have been a giant.

The puzzling tooth I found at the CLDQ. Photo by Brian Switek.

The puzzling tooth I found at the CLDQ. Photo by Brian Switek.

After snapping a photo of the tooth with my phone, I trudged uphill to the visitor’s center myself. Peterson was right. The tooth didn’t exactly match the casts, and was far too large to fit in the jaws of either skull replica. But who else could the tooth be from? The Morrison Formation dinosaurs in eastern Utah are well-documented. If there was some other giant herbivorous dinosaur in Cleveland-Lloyd with such teeth, surely paleontologists would have already found the monster’s bones.

I walked over to where I parked my rental car, one of the few spots with fair cell service, and slowly browsed the web for images of dinosaur teeth for comparison. The fossil I uncovered matched the anatomy of fresh Camptosaurus teeth. The dentition of the cast inside the visitor’s center was replicated as worn-down and didn’t contain all the delicate details of real fossils. But compared to close-ups of other specimens, my tooth fit the pattern. Yet the size of the freshly-uncovered tooth was still strange – might the tooth have been from an especially big Camptosaurus? That question awaits future comparison with fossils already found.

A reconstruction of Camptosaurus at the Brigham Young University paleontology museum. Photo by Brian Switek.

A reconstruction of Camptosaurus at the Brigham Young University paleontology museum. Photo by Brian Switek.

The rest of the day lazily drifted by beneath the quarry building. I didn’t find anything else of interest or importance, despite my goal of at least starting to uncover a truly spectacular fossil. (Earlier in the day, Peterson had jokingly encouraged me to find the Allosaurus hips that he just knew had to be right under my quarry spot. No luck.) After about nine hours in the quarry, everyone was ready to close up the buildings and dig into the dinner that a few volunteers had left to start just a bit earlier. For me, though, this was the end of my Jurassic journey. My rental car was due back in Salt Lake City, and I couldn’t put off the pile of freelance assignments I had left to ferment in my inbox much longer. After having one of Peterson’s Jurassic Park-themed homebrews and trying to avoid the flying bowls of salsa launched by windy gusts funneled by the outcrops through the camp, I packed my tent and started for home. Next year, when Peterson returns to Cleveland-Lloyd and the warm weather brings out the gnats, I’ll renew my pursuit of Allosaurus.

[Many thanks to Joseph Peterson and Mike Leschin for inviting me to join the Cleveland-Lloyd Dinosaur Quarry excavations this year. Next season, I'll set aside more time to help.]

There are 5 Comments. Add Yours.

  1. Jim Kirkland
    June 19, 2013

    Any of the hypothesized causes of this predator dominated death assemblage (as you know, I favor poisoning) are compatible with a float and bloat transportation phase postmortem.

    Anyway, camptosaurs get pretty big. My wife was pepping on one much bigger than that when I met her nearly 30 years ago. It is in the Museum of Western Colorado collections. Bob Bakker had a completed manuscript on it more than 20 years ago in galley proofs though it was never published. I’ll send you a picture of the jaws.

  2. Joyce Koskenmaki
    June 20, 2013

    I completely understand your fascination with this kind of discovery. Thanks for the story.

  3. Gary Raham
    June 20, 2013

    Thanks for the update on Cleveland-Lloyd. It’s been quite a few years since I’ve been there and I never had the opportunity to dig. I have used the mystery of “Why so many Allosaurs?” to invite student interest in the problems of interpreting fossil sites.

  4. Mike Moberly
    June 22, 2013

    It’s interesting for a neophyte like me to read about the excitement and enjoyment you get out of your work. I’ve had the opportunity to go on one dig (paleo-tourist), and would love to do it again, gnat-less if possible.
    I do have to say Jim Kirkland and George Callison where the ones that really got me into it, back at the “company” 20 odd years ago in Irvine… I was the money guy, boo-hiss.

  5. Zshelyz
    July 26, 2013

    Not sure which is more awesome: your Allosaurus tattoo or this blog. : )

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