Sunday, August 14, 2011

Discovering the Dinosaur Tracks of Milanesia Beach

(In my previous entry, I described the start of a day in the field – June 14, 2010 – at Milanesia Beach, Victoria (Australia), just hours before Tom Rich, Greg Denney and I discovered the largest assemblage of polar dinosaur tracks in the Southern Hemisphere. In that entry, I also pointed out how few dinosaur tracks had been documented in Victoria before then, which also meant very few polar dinosaur tracks had been found in the Southern Hemisphere. This background gave some context on why this find is a big deal, paleontologically speaking. So, would you like to want to learn how these tracks were discovered? Then read on.)

As Tom Rich, Greg Denney, and I walked down Milanesia Beach the morning of June 14 2010, my thoughts were about the dearth of dinosaur tracks found thus far in Victoria, Australia. Geological research of these Cretaceous-age rocks had been going on for more than 100 years, and paleontological studies there had been particularly intense during the past 30 years. Yet during that time, only four definite dinosaur tracks had been discovered in all of the extensive Cretaceous outcrops of coastal Victoria. Moreover, all of these were individual prints, with no dinosaur trackways showing at least two sequential steps. The previous three weeks of field work Tom and I had done along the coast seemed to bear out this notion that dinosaur tracks were rare here, even scarcer than their bones.

Nonetheless, I also tried to shake a premonition, experienced only a half hour after arriving at Milanesia Beach, that we might find dinosaur tracks there. Rest assured, this hunch was not inspired by séances, Ouija boards, psychic-pet hotlines, or any other forms of necromancy. Instead, it was based on our seeing the physical sedimentary structures and small invertebrate trace fossils (burrows) that told me we were looking at the former deposits of river floodplains. These environments would have been perfect for preserving dinosaur tracks. Regardless, I reminded myself to just be a cold, clear-headed, objective scientist: you know, a pessimist.

 A few more of the dinosaur tracks of Milanesia Beach, Victoria (Australia). Three size categories were there: small, medium and large, all made by three-toed theropod dinosaurs. Greg Denney found the ones shown here, which he discovered by recognizing how this rock matched another one with dinosaur tracks that I had found just a few hours before. Please buy him an adult beverage next time you see him, slap him on the back, and say, “Good on ya, mate!”

Just to dissipate these inward distractions, I decided to look intently at more of the small invertebrate burrows in the outcrop along Milanesia Beach. At this point, Greg abandoned me, and I didn’t blame him. He walked ahead to join Tom, who was already several hundred meters east of us, searching for bones, teeth, or other bodily remains of fossil vertebrates.

Meanwhile, I took some more photographs and measurements of the burrows we had only found 20 minutes before. Once that was done, I ambled leisurely, scanning both the outcrop and large boulders strewn across the beach. While walking, I carefully picked where my feet landed, having learned the hard way that these rocks often had nearly invisible slippery surfaces caused by slimy algal overgrowths. I had already fallen a few times during more than a hundred kilometers of walking along the Victoria coast, and did not want to add another bruise, bump, or scrape to my three-week-old collection.

Walk this way, but be careful. The boulders of Milanesia Beach and other rocky shorelines of the Victoria coast, aided by their algal friends, can become hazardous when prospecting for fossils.

To this day, I don’t know why, but one large, rectangular block of rock among dozens along the shoreline compelled me to stop and take a moment to stare at it. All I can imagine now is that this sensation stemmed from more than ten years of tracking animals in the sands and muds of the Georgia barrier islands and other places in the world, a collective experience that led to a subliminal recognition of something real, something worth noticing on the periphery of my vision. I looked to my left, then down at the top surface of the boulder.

There was a small, three-fold impression, looking vaguely like the middle three fingers of a human hand. It was close enough to touch, so I did. My own three middle digits molded to the indentations, confirming what my eyes had seen but not quite believed. It was a small dinosaur track.

After a quick inhalation of breath and almost trembling, I dared to look at the rest of the rock, scanning from left to right. More patterns of three came into focus, one after another, each identified faster than the previous one. Within about 5-10 seconds, I realized the bumpy surface was loaded with dinosaur tracks. Instead of shouting “Eureka!” or some similarly noble and dignified sentiment, I whispered a much shorter synonym of the phrase, “Hallowed excrement!

The slab of rock that made me ready to buy a slab of beer to celebrate. It has at least 16 dinosaur tracks on it, although some are so shallow that you can’t see them very easily in the first photo (top), and at least two are only represented by paired clawmarks. With a little bit of digital enhancement, though, you can then see some of the fainter ones (middle image), and I later mapped track locations (bottom). That map is now a testable hypothesis, and potentially could be disproved or otherwise modified in the future by me or someone else. That’s science, folks.

One of footprints – a chicken-sized one, only about 7 cm (2.8 in) long – was close to the edge of the slab. With my heart beating faster, I then did something I almost never do with modern tracks, which was to backtrack. I shifted my focus behind the track nearest me to see if any similar preceded it. Sure enough, there was another one of the same size, aligned with the previous one. Halted briefly by disbelief, I backtracked one more time. Another track was exactly where it should be, at a distance nearly identical to the space between the other two, although slightly off the line of travel. One, two, three steps in sequence, showing a slight rightward turn. A preserved motion from more than 100 million years ago, made by a small theropod dinosaur on a river floodplain during a polar summer. It the first known dinosaur trackway in all of southern Australia, and the first polar-dinosaur trackway from the Southern Hemisphere.

The first known dinosaur trackway from southern Australia, made by a chook-sized theropod dinosaur, about 105 million years ago and probably during a polar summer. While walking, it decided to turn slightly to the right. At first I speculated it did this because it moved around an irregularity in its landscape caused by two overlapping dinosaur tracks on its right. That idea didn’t make it through peer review, though. Again, that’s science, folks. Scale = 13 cm (5 in) long.

But there was no time to celebrate. I needed to get to work and do something that went beyond mere discovery. I looked more closely, and felt the rock surface to augment what my eyes told me. Following this, I began sketching what was there and marking locations of the tracks, using graph paper in my geological field notebook to make a scaled drawing that served as a “track map.” Unlike taking photographs, drawing forced me to look at the rock and its fossil tracks repeatedly, carefully, and critically, a time-honored observational technique I teach to my students.

This method soon paid off, for within about 10 minutes, I found a few more tracks, subtle ones that either consisted of very faint toe impressions or were missing parts. For instance, two tracks were only evident as paired marks made by sharp claws from two toes. A quick, initial count yielded about 14 tracks, all showing three or fewer toes. The surface itself only had an area of about 0.7 m2 (7.5 ft2), so it held a lot of information in a small space. This was a busy little piece of real estate during the Early Cretaceous.

A small indulgence in 21st century technology that was necessary, though, was to use a handheld GPS unit to determine the location of this rock. With this, it quickly determined the latitude-longitude coordinates of where I was standing. These were saved as a waypoint but also written in my notebook, just in case the GPS unit somehow ended up in the seawater that just happened to be crashing in waves behind me.

My staying in one spot for nearly 45 minutes and writing in a notebook provoked some curiosity in Greg, who left Tom and came back down the beach to see what was holding my attention. He was all smiles as he walked up to where I was seated, which was on another boulder in front of the track-bearing slab.

“What’d you find?” he asked cheerfully.

I grinned back, gestured toward the slab surface, and said with a mixture of pride and awe, “Dinosaur tracks.”

Greg’s jaw dropped, and he briefly looked like a stunned mullet as his eyes took in what was there. In silence, I thoroughly enjoyed watching him re-discover each dinosaur footprint, a wonderful moment to share with a field compatriot. Once he regained his voice, he exclaimed, “Wow, this is fantastic!” Yes, it was.

Putting my scientist hat back on (covering up the stylish paleontologist hat), I then decided to test some of these preliminary results. I asked Greg, a non-paleontologist but a skilled observer, to point to everything he thought was a dinosaur track. Within a few minutes of studying the surface, he quickly identified nearly every one I had detected, with only a few misses. “Nice job!” I told him, and we then went over his test results, just like I would with any eager and talented student of mine.

Tom soon joined us. Like Greg, he also wondered what had held our interest so raptly, and he asked the same question: “What’d you find?” My reply to him, though, was slightly different, as I got a little professorial and answered his question with a question: “What do you think is there?”

Tom coolly looked at the rock surface, bringing to bear more than 40 years of paleontological experience, with more than 30 of those years spent studying the Cretaceous rocks and fossils of Victoria. A moment passed, then he pointed to the best-preserved dinosaur track, and said matter-of-factly, “Looks like a dinosaur track.”

I smiled. “Yes, it is. See any others?”

One by one, he pointed to each track, and like Greg, found nearly every one I had identified. This was a great example of a little scientific principle called repeatability: that is, a scientist should be able have her or his results repeated independently by other scientists.

But I wasn’t through with Tom, and asked him to take a close look at the little, chicken-sized track nearest me. “Anything special about it?”

That stumped Tom. “Help me out. What am I supposed to see?”

“Look behind it. See anything like it?”

He quickly put his finger on the small track preceding the one nearest me.

“Good. Anything behind that one?”

“That one,” he said, putting his finger on another identically small-sized track.

I smiled again, something I was doing a lot of that day. “It’s a trackway,” I shared, letting understated brevity speak for its importance.

When that little bit of information sunk in, Tom allowed himself the indulgence of a very small, almost Mona Lisa-like smile. I had already pointed out the trackway to Greg, but he kept silent as he enjoyably watched Tom go through much of the same interrogation he had just experienced. After all, it’s always better to watch someone else take a test than to take one yourself.

So with this affirmation from my field partners spurring me on, I resumed with taking measurements and writing notes, then took some photographs. Greg helped with the data collection, acting as a scribe with my field notebook as I measured lengths, widths, and depths of the footprints with digital calipers. As we did this, I could tell Tom’s mind had gone somewhere other than gathering data about the dinosaur tracks. At some point, he asked to borrow my tape measure, and he immediately went about measuring the length, width, and thickness of the slab. He sat down, wrote in his notebook, and then revealed what he was thinking.

“Greg, do you think we could get a front-end loader down here to take this up?”

I was surprised by Tom’s question, but shouldn’t have been. As an ichnologist, I’ve never been much of a collector. My work normally consists of describing, measuring, and photographing trace fossils, recording their locality information, then bidding adieu, sometimes never seeing them again. After all, I don’t have a museum with storage space or research labs at my disposal, let alone collection managers and the means for collecting large, heavy rocks. On the other hand, Tom has all of these amenities available to him, along with a collecting permit. Why did he have a collecting permit? We were actually in Great Otway National Park, which meant that no fossils could be taken without the written permission of the Australian government.

Thus Tom had made a perfectly valid inquiry. He wasn’t planning to let this big hunk of rock stay here on Milanesia Beach, but instead was already plotting how to put it in Museum Victoria. His scribbling consisted of back-of-the-envelope calculations of the approximate length, width, and height measurements, which yielded volume, which was then multiplied by density of the rock – sandstone interbedded with siltstone, which was about 2.7 g/cc, or more than 2.5 times the density of water. This yielded an estimated weight of about 700 kg (1,500 lbs) for the rock in front of us.

Amazingly, nearly a year later, in early June 2011, Tom, with the help of Pat Vickers-Rich, their daughter Leaellyn Rich, Greg Denney, David Pickering (Museum Victoria), and personnel from Parks Victoria succeeded in carrying out his quixotic goal of transporting this block of rock with dinosaur tracks safely off the beach. It and the other block containing dinosaur tracks from the same site were then transported and deposited in Museum Victoria in Melbourne, where they are now stored for future reference and further study.

Tom measuring the first block of dinosaur tracks on Milanesia Beach, plotting how to bring ‘em back alive, er, well, you know what I mean. Photo stolen brazenly from Dinosaur Dreaming.

In this video (produced by Museum Victoria), Tom explains the scientific significance of the Milanesia Beach dinosaur tracks, although he’s giving this explanation from the relative comfort of a storage room at the museum in Melbourne. Watch further, and you’ll see both Tom and Greg helping with the recovery of both blocks containing the dinosaur tracks, which were put on a small front-loader and carried up the trail from the beach.

Oh, right. There was a second block of dinosaur tracks. Greg discovered that one. With that, he handily provided yet another reason why academic paleontologists are extremely dependent on non-academic folks to make significant contributions to our science. Greg’s discovery was also a lesson in hubris for me. I was so giddy (and more than a little prideful) about finding the first block, I didn’t bother to look around to see if any more like it were nearby.

Greg did. So while I was self-satisfyingly writing field notes about the tracks on the first block, and imagining future fame (perhaps even an appearance on The Colbert Report), he was looking at every nearby boulder. Suddenly, at some point he started acting like a larrikin, and ran around the beach looking for a piece of driftwood. Within a few seconds, he found a 2” X 4” board (you’d be surprised at what washes up on some of these beaches), and quickly placed one end under a boulder less than 2 m (6.5 ft) away from where I sat. Clearly inspired by Archimedes, he started to flip the rock by using the board as a lever.

“Greg, what are you doing?”, I asked, as Tom and I watched him with slightly alarmed curiosity.

“This rock is the same as that one!” he shouted gleefully.

As if watching a tennis match, Tom and I swiveled our heads back-and-forth between the slab with the dinosaur tracks and the one Greg was attempting to turn over. He was right: they matched perfectly, although this one was upside-down, with its uppermost surface hidden from view. Realizing that Greg had, indeed, not turned into a galah, we ran over to help, and got the block turned over.

On its top surface were more dinosaur tracks. I pulled out a small brush from my field vest and cleaned off the distracting modern beach sand on its surface, and we then stared at the lithified sand from a 105-million year-old floodplain. Sure enough, some of this Cretaceous sand had been molded into the three-toed shapes of dinosaur feet. So only three hours beforehand, when we first descended onto Milanesia Beach, only two confirmed dinosaur tracks had been found in the Eumeralla Formation of western Victoria. Now we had 24. You could say we were having a good day.

The second block of dinosaur tracks from Milanesia Beach, minutes after Greg Denney discovered it. It has at least eight tracks on it, probably all of them from theropods, and its layering and rock types perfectly match those of the first block with dinosaur tracks I had found three hours before. With this slab, the number of dinosaur tracks discovered at Milanesia Beach went up about 50%, and our respect for Greg went up immeasurably.

About a week later, Greg Denney demonstrates how he found the second slab and its dinosaur tracks at Milanesia Beach by using a lever to move weighty rocks. Here he is assisted by my wife Ruth, who had just arrived in Australia a few days before (but looking completely unaffected by jet-lag).

Greg’s method for finding the tracks was both simple and brilliant. He had noticed the thickness of the first block, its thinly interbedded sandstones and siltstones, and a gray siltstone a little more than halfway down its thickness, looking much like a different ingredient in an otherwise monochrome layer cake. He then glanced around to see if any other boulders shared those traits, and matched one of them with the one in front of me. Seeing that the gray siltstone bed was less than halfway down its thickness, he correctly surmised that it was wrong-side-up, and intuited that the dinosaur tracks could be on its top surface. He was right.

Photo of me studying the dinosaur tracks from the block I found on Milanesia Beach; the block Greg Denney found is in the foreground. Look for the gray band of siltstone in both blocks, which along with the little detail about dinosaur tracks being on their top surfaces shows they were originally part of the same bed. Photo by Ruth Schowalter, taken a week after the initial discovery

Again, there was little time to celebrate, as it was now mid-afternoon on a near-winter day. This meant we were soon going to lose our sunlight, and we still had a long uphill hike ahead of us back to the car park. Tom quickly measured the second slab’s dimensions and figured out its weight. He reckoned it was about 400 kg, smaller than the first one, but still too massive for any (or all) of us to haul up the trail.

I hurriedly photographed the overall surface, conscious of how our light would soon disappear, and started sketching the forms and locations of the tracks on the surface. I also noted any similarities or differences between these newly found tracks and the ones found a few hours earlier. One of the last items on the agenda was to take a few video clips of me talking about the dinosaur tracks, which I knew later could be edited into a informative video. Looking at these clips later brought a smile to my face, because I was trying to be informative and objective, but also couldn't help but show how thrilled I was with what had happened.

A short video that tells about the dinosaur-track discovery at Milanesia Beach that went out with the press release about the peer-reviewed article. The initial video footage was taken by Greg Denney the same afternoon he and I found the two slabs with their dinosaur tracks. That and other footage taken by me and Ruth Schowalter were then edited and produced by Carol Clark of Emory University.

Greg again assisted me in recording measurements, as I used the digital calipers to gather data on the dinosaur tracks from this second block (number of toes, length, width, depth, and so on), and he wrote down the numbers in my field notebook as I read them aloud. Only then did I take close-up photographs of individual tracks with a photo scale next to each, documenting their dimensions and other details.

Much later, back in the comfort of my office at Emory University in Atlanta,Georgia, I re-measured the tracks from photographs to double-check these results, just in case I had misspoken or Greg had miswritten that afternoon. Because I did not know whether I would ever see these tracks again – notwithstanding Tom’s relentless plotting to acquire them – I was being extra careful about making sure the results could be repeated, checked by others, and otherwise pass peer review in the future.

As the sunlight faded, we decided we had enough for now, and vowed to come back the next week to better assess the geological context of the tracks, study and photograph them once more, and figure out how to recover them from this high-energy, wave-filled place.

Our tracks connecting with the dinosaur tracks of Milanesia Beach on the walk home at the end of the day, June 14, 2010.

Milanesia Beach had been very good to us that day, and as we all slogged up the steep trail, we were filled with smiles and excitement. The three of us did indeed come back the next week, along with geologist Mike Hall and my wife Ruth Schowalter. Once the tracks were relocated, I recorded more measurements and descriptions, while the others did a reconnaissance of the local geology.

We knew that some more science had to be done before we could share our finds with the rest of the world, which was that peer-review thing scientists like to talk about. Nonetheless, we were confident that day would come.

Sure enough, exactly one year later – on June 14, 2011 – my coauthors and I - Tom Rich, Pat Vickers-Rich, Mike Hall, and Gonzalo-Vazquez Prokopec - received the good news that our scientific article had been accepted for publication in the journal Alcheringa. Our peers had confirmed what we knew that day one year before: we had just discovered the best assemblage of polar dinosaur tracks in the Southern Hemisphere, the first dinosaur trackway from the southern part of Australia, and extended the geographic range of dinosaur finds in Victoria.

And although these tracks were only a drop in the proverbial bucket when it comes to paleontological discoveries, they help to affirm the most important point about the fossil record: it gets better every day.

(This entry is dedicated to the memory of my nephew, Thomas Schowalter, 1995-2011, who loved animals and nature. This story is for you.)


Peer-Reviewed Article

Martin, A.J., Rich, T.H., Hall, M., Vickers-Rich, P., and Vazquez-Prokopec, G., 2011, A polar dinosaur-track assemblage from the Eumeralla Formation (Albian), Victoria, Australia. Alcheringa: An Australasian Journal of Palaeontology. DOI:10.1080/03115518.2011.597564

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