Dinosaurs Without Bones (23 page)

“What is it?” she asked.

“I think it’s a dinosaur burrow,” I whispered.

At the time, she was one of only a few people in the world who knew about the fossil burrow in Montana. In fact, Dave, Yoshi, and I had not yet named
Oryctodromeus
, whose remains, along with the
two juveniles, were still encased in plaster and rock. So we were still doing all we could to keep its discovery quiet until it had gone through a scientifically proper vetting process. Consequently, I had not yet told any of my new Australian friends about it and was not about to start now.

Nonetheless, the problem with outwardly expressing curiosity and wonder is that it attracts other people who then want to join in with you. As a result, only a few minutes elapsed before one of several geology graduate students with us, Chris Consoli, saw us standing there and wandered over to ask the same question as Ruth: “What’s that?” I answered truthfully but evasively, “I’m not sure, but it’s an interesting structure.” I then asked him if he would mind being the scale in my photographs, and quickly snapped three shots in succession. He soon strolled away once I supplied no other information about what was there. Ruth then helped me to take a few quick and surreptitious measurements of the enigmatic structure. Mike Cleeland also stopped by and asked about it, and I was similarly nonchalant with him.

These were the only photos I took of the suspected burrow that day, as I really did not want to call much attention to it and we had other work to do in our short time there. All of us wandered about, looking down on bedding planes, glancing above us on the outcrops, and in between at nearby sections of the strata. This perusal was mildly successful, as during our short time there Mike and I found a few faint and incompletely expressed dinosaur tracks, including one that was likely from a large theropod. This meant that it would be worth coming back to look for more and better tracks. I also noted many fossil invertebrate burrows that were about the right sizes for ones made by insect larvae. These were valuable indicators of the original environments there, such as river floodplains that formed from the run-off of spring thaws following polar winters. Yet we saw no bones.

All told, we were at the site for only a little more than an hour before slogging back up the hill to meet our two friends, who wondered how things had gone. Amazingly, we still had enough time
that afternoon to stop at nearby Dinosaur Cove, a world-famous locality for polar dinosaur bones that many of these same Australians accompanying me had quarried in the 1980s and 1990s. We departed just as the sun set over Dinosaur Cove, a long and satisfying day of field work completed.

Later, I studied the three photographs I had taken of the odd structure at Knowledge Creek and could not get over the eerie sameness it held compared to what I had seen in the Cretaceous rocks of Montana. Not knowing what else to do, I sent a photo to Dave Varricchio for him to assess. As expected, he was non-committal about what it meant, but it felt good to share this coincidence with someone else in the know. Nevertheless, one thing was for sure: I had to go back to Knowledge Creek.

So I returned the next year, in July 2007, only a few months after the publication of the paper on
Oryctodromeus
and its burrow. The day that paper came out, I wrote to Pat Vickers-Rich and Tom Rich to finally disclose my secret that they had a possible dinosaur burrow there in the Cretaceous rocks of Victoria. Of course, they were excited about this prospect (albeit understandably skeptical) and encouraged me to come back to Victoria. During this second trip, Mike Cleeland was along for the ride again, but joining us was Lesley Kool and five others. Lesley was a long-time dig-site manager for Pat and Tom, and like Mike is an extraordinarily keen-eyed finder of vertebrate bones.

Mike and Lesley looked at the possible burrow with me and confirmed what I had surmised initially, which was that it contained no skeletal debris. Thus this was going to be pure ichnology, dinosaur burrows without bones. However, it was on this foray that I noticed a second twisting, sandstone-filled structure above the one that had originally grabbed my attention. It was not as completely expressed as the other, with only a former tunnel and lacking a chamber at the end, but was the same width and filled with the same type of sandstone. This time, with much less urgency than the previous time, I carefully sketched, measured, and photographed both structures, documenting them enough so they could be summarized in a paper and evaluated by my peers.

Because nearly everyone in our group was exhausted by the hike down but still faced a climb up, they took off as I did this tedious but necessary work. Roger Close, a young geology graduate student, stayed with me and assisted where needed before we also walked out. At the top, Lesley, her husband Gerry, and several others who had made the round trip greeted us with big grins and happily announced that they never needed to visit Knowledge Creek again.

Life got in the way throughout most of 2008 for me to do anything with these hard-earned data, until a burst of writing during the 2008–2009 holiday break from teaching duties between semesters resulted in a manuscript. I decided to author the paper by myself, because if it turned out to be totally wrong, I would own all of the failure. My interpretations of the field observations were risky because, unlike the Montana burrow, the structures did not hold any accompanying dinosaur bones.

However, in the paper I made sure to thoroughly explain the reasons why some polar dinosaurs
should
have burrowed as a behavior that would have allowed them to overwinter during cold, dark, harsh times in polar environments. For one, the Cretaceous rocks of Victoria abounded with evidence for hypsilophodonts, small ornithopods morphologically similar to
Oryctodromeus
and
Orodromeus
in North America. For another, such dinosaurs were too small to have migrated long distances between seasons. Thirdly, many modern polar vertebrates, from puffins to polar bears, burrow into dirt or snow to take refuge in those harsh environments. Consequently, in January 2009, I sent the paper to the journal
Cretaceous Research
and kept fingers, toes, and thumbs crossed that it would be received favorably.

The paper was reviewed in a timely way and fortunately was not rejected outright. Still, the reviewers and editor expressed concern about its content, requiring responses to specific points. As mentioned before, this is where many scientists might give up on both revising and resubmitting a manuscript, without the guarantee of acceptance. However, I had already planned to go back to Australia and promptly put Knowledge Creek on my itinerary to answer a
few questions, such as the exact nature of the sedimentary rocks surrounding the structures I claimed to be dinosaur burrows.

Thus my third (and perhaps last) visit to Knowledge Creek took place in May 2009. This time only three of us went: my wife Ruth (her second visit); Mike Hall from Monash University of Australia, an experienced field geologist who also was an expert on sediments and sedimentary rocks; and myself. Mike had never been there, and it had been long enough for me that we became disoriented and displaced—some might call it “lost”—on the way down to the site. This was a disheartening déjà vu for Ruth, echoing her experience from three years previous with me and other geologists, and justifiably shaking her faith in our navigational abilities. Her unease grew more pronounced when Mike proposed that we circumvent the nearby sheer sea-cliffs by following a wallaby trail through the thick coastal scrub forest. Travails notwithstanding, we made it to the site okay, and once more Ruth and I stood together on the nearly flat marine platform of Cretaceous strata of Knowledge Creek. This time we had plenty of daylight ahead of us, though, and Mike’s help as a geologist to double-check my field results.

This trip was well worth it, as we noted what might have been yet a third partially preserved dinosaur burrow. It was shorter than the other two but almost the same diameter and had a similar sandstone fill. This implied that all three had once been hollow structures and had likely been filled by the same sedimentary processes at the same time. Elsewhere on the outcrop, in strata above the supposed dinosaur burrows, we also measured and otherwise documented dozens of invertebrate trace fossils, all small-diameter burrows. With only three of us there, we even had enough time after my data collection to explore our gorgeous surroundings.

It was a magical experience, a sense of wonder evoked by walking on the remains of polar rivers from more than 100 million years past, as waves from a present-day sea churned violently against these same rocks just behind us. All paleontologists who have done field work end up having favorite places where they feel lucky to
learn and realize something new about the history of our planet. Knowledge Creek had become one of mine.

Once back in the U.S., I finished the revisions of the manuscript, wrote a rebuttal to the reviewer remarks that nearly eclipsed the length of the manuscript itself, inserted a mention of a possible third burrow at the same site, and resubmitted it. Gratifyingly, the editor accepted the paper the following week, which had the title “Dinosaur Burrows in the Otway Group (Albian) of Victoria, Australia, and Their Relation to Cretaceous Polar Environments.” Unexpectedly for me, though, the accepted manuscript was also posted online only a week after that, which meant that science reporters began calling me, asking about these dinosaur burrows in Australia, the oldest interpreted from the geologic record.

My university media folks and I scrambled to put together a press release, and we used edited video footage from Knowledge Creek to accompany it as a sort of modern-day newsreel. As of this writing, the video had the most views of any in the history of my university, and the press attention was flattering. So two places in the world—Montana, USA and Victoria, Australia—had been proposed as sites with dinosaur burrows, with the hope that more would be added to this list in upcoming years, as paleontologists now knew what to look for.

“Mythbusting” a Dinosaur Burrow

Many scientists welcome media attention or other forms of interacting with the public, whether through lectures or writing popular-outreach pieces such as magazine articles or blog entries. Yet a mantra I often preach to my students and try to put into daily practice is that these attempts at public outreach and communication do not necessarily make our science truer. As I mentioned previously, science does not prove, it disproves. Hence, paleontologists who live up to this ideal by testing their own results—treating their work to the same degree of scrutiny and skepticism as they would their rivals’ research—always impress me. It is an intellectual honesty
we all need to practice, such as in interpreting the indirect evidence represented by dinosaur trace fossils.

Along those lines, Dave Varricchio assigned an undergraduate student of his, Cary Woodruff, to do just that. Woodruff’s job was to test whether the
Oryctodromeus
bones could have been buried while in the den (that was the original hypothesis) or whether they were carried in from outside (that’s the alternative hypothesis). If they were moved from outside of the den, this would be a strike against these dinosaurs having lived and died there and would have cast doubt on their having been the original burrow inhabitants. Instead, their dead remains may have been tossed into a big hole, burrow or not, that just happened to be in the area when a river overflowed back in the Cretaceous.

So in an experiment straight out of the popular TV show
Myth-busters
, Woodruff joined PVC piping and set up scaffolding to make a half-sized version of the burrow. He then made up mixtures of sand, mud, and water, and used rabbit bones as a proxy for the dinosaur bones. Thirteen times he ran the experiment, in which he filled a plastic bucket with sediment and poured it down the hole. Sometimes rabbit bones were added to this sedimentary stew, but other times he placed the bones inside the artificial burrow chamber first, then decanted. Out of the thirteen times he did this, six resulted in the same sort of jumbled distribution of bones in the burrow chamber that Dave had observed with the original
Oryctodromeus
bones and their sedimentary matrix. Four of these arrangements were made with the rabbit bones already in the den, and two came from outside, with the bones in the bucket.

Four to two: we win! Except not really, because science is not a game in which simple scores decide which hypothesis is the better one. These results still meant the bones feasibly could have been deposited into the burrow and that the
Oryctodromeus
bones could have come from somewhere else outside of it. Woodruff then tried to disprove this hypothesis by scrutinizing the original
Oryctodromeus
bones, seeing whether they held any nicks, scratches, or dents from having been bounced along the bottom of a stream.
Many dinosaur bones bear such evidence, telling how those parts may have traveled far from the spot where a dinosaur died. However, in this instance the bones had no such marks. This lack of evidence implied that the bones of this probable parent and offspring did not travel far at all. They either died together just outside of the burrow, or in it.

But wait: Could the burrow have belonged to some unknown burrowing predator that scored a super-sized meal one day by taking down an adult and two juveniles of the same species? Then maybe it dragged these bodies into its burrow to nosh on them, left its partially consumed dinner in the burrow, and was conveniently somewhere else when its prey’s bones were buried by the flooding of a nearby river? For that idea to have more support, though, more trace fossils were needed, such as toothmarks on the bones. Yet none were to be found. Thus, considering the happenstance of bones from an adult and two juveniles of the same dinosaur species being together, no signs of long-distance transport of those bones, no evidence of anything chomping on the bones, and all of the aforementioned ichnological evidence showing a match between the burrowmaker and the burrow, the hypothesis that this
Oryctodromeus cubicularis
was a burrowing, denning dinosaur still stands. So far, so good.