I am an ichnologist, someone who studies the traces and trace fossils left by life: tracks, trails, burrows, and other indirect signs of behavior. Modern and ancient traces alike interest me, as these lend insights on how behavior has changed through time (or not).
About six weeks ago, I shared the happy news of our discovering dinosaur tracks at Milanesia Beach, Victoria, which turned out to be the largest collection of polar
dinosaur tracks known in the Southern Hemisphere. Those tracks were found during
the month-long excursion (May-June 2010) along the Victoria coast that inspired
the start of this blog. And although we found heaps more trace fossils, the
tracks constituted out most important scientific find. So even though we have a
but more science to do, this is as good of a time as any with this blog to say,
“Catch you later” and make a transition both geographical and temporal.
The Great Cretaceous Walk
has been very, very good to me. But it’s time to take a pause in all of the
walking and talking about the Cretaceous of Australia, and look closer to home (Georgia)
and at this time in the present (otherwise known as “now”). Photo by Tom Rich, and taken on
May 28, 2011 (Day 2) of our month-long field survey of the Cretaceous trace
fossils of Victoria.
(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-toedtheropod 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!”
Because of the sparse and uneven record of dinosaurs in Australia, their fossil footprints are more valuable here than anywhere else on Earth.
- Thomas H. Rich and Patricia Vickers-Rich, A Century of Australian Dinosaurs (2003).
The Preamble
Dinosaur tracks are hard to find. This humbling realization struck me during the third week of a month-long field excursion in May-June 2010, while doing field work along the craggy coast of Victoria, Australia. Why was I there, engaging in such an apparently fruitless quest? Paleontologist Tom Rich of Museum Victoriahad invited meto look for trace fossils made by dinosaurs and other Cretaceous animals that might be preserved in the rocks of Victoria. Yet as was often the case with looking for fossils of any kind, there were no guarantees of success. He and I had already searched more than a hundred kilometers of coastal cliffs and platforms east of Melbourne, and were then working our way through sites west of there.
Here are four three-toed dinosaur track,s preserved on a block of sandstone at Milanesia Beach, Victoria (Australia). They’re faint, but there – look closely for all four. These tracks were probably made by small theropods on a river floodplain during a polar summer about 105 million years ago, when Australia was close to the South Pole. On June 14, 2010, I discovered the block that contained these tracks, and a few hours later, Greg Denney found another block with more tracks. This is a big deal, as they represent the greatest number of polar dinosaur tracks found in any one place in the Southern Hemisphere. It’s enough to make you want to do a happy dance. Scale bar in photo (lower left) = 10 cm (4 in).
Way back in June 2010, after completing nearly a month of field excursions exploring the Cretaceous rocks of Victoria, Australia, I had adjusted to a daily routine of expectations. These were, in no particular order: difficult access, high coastal cliffs, thick brush, dangerous waves, slippery rocks, lots of walking (and looking), and only a few trace fossils at the end of each day to show for all of this effort. Here is an artistic rendering of what it felt like out there most days:
Claude Monet’s Gros Temp à Étretat [Rough Weather at Étretat], 1883, in the National Gallery of Victoria, looking oddly familiar to me after lots of field work on the Victoria coast during their winter. I’m the one trying to hold onto my hat.
Another realization gained from field work in Victoria is that fossil bones are rare there. In all of our walking along the coast and scrutinizing more than 100 km (60+ miles) of coastline, Tom Rich (Museum of Victoria) and I did not find a single piece of bone. This hard-earned insight made me appreciate all the more the exceptional nature of those places in the Victoria with abundant bones. Moreover, the bones that have been found came at a considerable cost, especially in terms of human labor (see Dinosaur Cove for an example).
Dave Pickering, a curator and fossil preparator at the Museum of Victoria, who has a bone to pick with you. And as small as this bone is, it could have taken a few hundred hours of prospecting in the Cretaceous rocks of Victoria before someone found it, followed by yet more hours of preparation. Next time you see Dave or any volunteer who looks for fossils on the Victoria coast, please buy them a beer or its monetary equivalent.
Now, for anyone who is used to literary tricks of the trade in journalism or other forms of story-telling, you probably see a set-up here, where I give you one premise – the Cretaceous of Victoria – then shatter it by wielding the exact opposite situation – the Cretaceous of Queensland. Yes, that’s right, the old “compare-and-contrast” device, which is right up there with the “overcoming incredible odds, only to succeed through hard work and moral fortitude” Horatio Alger story.
(Incidentally, the realist in me enjoys puncturing such stories by pointing out that Horatio Alger was actually Horatio Alger, Jr., a second-generation Harvard man, who probably had the hired help pulling up his bootstraps for him. Fortunately for American literature, Mark Twain, a contemporary of Alger, had satirical responses to such stories: “Poor Little Stephen Girad” and “The Story of the Good Little Boy”), when he wasn’t already writing about trace fossils (specifically, fossil tracks of giant ground sloths).
American satirist Mark Twain, who had little tolerance for Horatio Alger, Jr.'s stories, and occasionally reported on possible trace fossils made by giant ground sloths, or, alternatively, Nevada legislators and Old Silurian asses, with the distinction purposefully blurred. Photo from Wikipedia Commons.
So I plead guilty to falling into the cliché of contrasts, but only partially. As befits a continent that straddles three time zones and about 30° of latitude – from Tasmania to tropical Queensland – Australia is teeming with environmental and geological contrasts. When you travel from the southern part of mainland Australia (Victoria) to the northern part (Queensland), some differences are expected, and indeed there are many.
Australia’s a country and a continent, mate. Image from Google Maps and modified by me.
For example, the Cretaceous of Queensland is often represented by: wide, flat areas; deeply eroded rocks with few actual outcrops; and no nearby ocean waves. (Or at least, not now. Go back 100 million years, then yes.) So this is indeed remarkably different from paleontological explorations in the slightly older Cretaceous rocks of Victoria, and requires a bit of an attitude adjustment one going from one to the other.
The outback of central Queensland (top) versus the Victoria coast (bottom). Spot any differences? Photo on top is by Ruth Schowalter, who was driving shotgun at the time.
Nonetheless, the human-perceived differences of conducting field work in Queensland versus Victoria largely end there. Paleontologists still have to work very hard to find bones or trace fossils in the Cretaceous of Queensland, just like in Victoria, although it definitely requires a different kind of effort. And even though rocks in this region of Australia have yielded some significant fossils through the years (especially in the past few years), you still need to have the right search images for finding them, and lots of human labor to recover and prepare them. More about that aspect will be discussed in future entries, and we will especially the logistical differences between finding and handling a leg bone of a small juvenile ornithopod dinosaur, versus that of an adult sauropod.
No rugged individualism is allowed when you find sauropod limb bones in the Cretaceous of Queensland. Rather, mateship is encouraged and necessary. “Gorgeous George” of the Australian Age of Dinosaurs (AAOD) Centre near Winton for scale (more about him and his mates at the AAOD later).
Perhaps what is most remarkable about paleontology in Queensland, though, is how much it has suffused into the outback culture there in just the past few decades. For example, despite more than 30 years of intensive research on dinosaurs and other fossils from the Cretaceous of Victoria, Australia’s “Dinosaur Trail” is located in Queensland. The three outback towns of Hughenden, Winton, and Richmond roughly define a triangle containing rocks rich with Cretaceous fossils, marine and terrestrial, comprised of plants, invertebrate animals, and vertebrate animals. Another outback town with a good collection of Cretaceous fossils to see is in Boulia. For younger fossils, hailing from the mere Cenozoic Era, there is also the city of Mt. Isa. These fossils are from the world-famous Riversleigh deposit, holding geologically younger and exquisitely preserved body fossils of marsupials from the Oligocene through the Miocene Epochs, from about 25-15 million years ago.
So upcoming entries will be about those places in Queensland and their fossils, told from the perspective of a Yank paleontologist, a stranger in an even stranger land, yet one that was very friendly, had many fantastic fossils to see, and (most importantly) no shortage of beer.
Following field work in Victoria, Ruth and I went on holiday for our last few weeks in Australia, first to Sydney (New South Wales), then to Queensland. As Ruth and many other spouses/partners can attest, though, there’s one drawback with going on vacation with geologists or paleontologists. And that’s their insatiable drive to see more rocks or fossils. In that respect, then, Sydney seemed safe, being a big city with heaps of concrete and steel covering the good bits (geologically speaking). But Sydney also has great (and free!) museums, containing all of the items that catch the attention of the earth-inclined, and even has some outcrops of cross-bedded Triassic sandstone along its world-famous shorelines, including in front of the Sydney Opera House.
Why do photographs of the Sydney Opera House always omit the Triassic sandstone in front of it? This just goes to show you how even geologists can be temporarily distracted by dazzling architecture.
But how could a geologist not notice that the oldest brewpub in Australia – The Lord Nelson Brewery – is located in a part of Sydney called The Rocks? Out of a sense of scientific duty, we had to go there and sample a few of their brews, too.
A close-up of some of the local Triassic sandstone along a stairway in The Rocks part of Sydney, showing a transition from planar to rippled to some gorgeous convoluted bedding, the last a result of soft-sediment deformation, made before the sediment was cemented into rock. I can’t remember if this was seen and photographed before or after the visit to the brewery, which de facto means it was after.
Nonetheless, our main reason for going to Sydney was to view art, which was already plentiful, but made more so by a biannual art event named (oddly enough) The Biennale. Venues hosting art associated with this event were scattered throughout parts of the central business district (CBD) of Sydney, but most works were either at the Museum of Contemporary Art or on Cockatoo Island, which is located just north of the Sydney Harbor Bridge. For those of you who revel in using both sides of your brain and want to learn more about an artist’s perspective on this year’s artworks, please read Ruth’s take on it (written under her persona of Hallelujah Truth).
We also took in a few hours of the Australian Museum, which has a nicely done section on Australian indigenous cultures (including art styles of different regions), and the obligatory dinosaur hall, which seem to be required of all major natural-history museums. Nonetheless, I was pleased to see how the dinosaur-hall exhibit – which thankfully was not just about dinosaurs, but included other biota, even from outside of the Mesozoic Era – included much information based on the Cretaceous of both Victoria and Queensland.
A reconstruction of Qantassaurus intrepidus, the only dinosaur named after an airline (Qantas), but more importantly is a small ornithopod dinosaur that lived in southern Victoria during the Early Cretaceous Period, about 105 million years ago. Sadly, this detailed reproduction is mostly speculative, as this species is represented by only a few isolated bones, which also took considerable human labor to uncover.
A reconstruction of another small ornithopod from the Early Cretaceous of Victoria, Leaellynasaura amicagraphica. Unlike Qantassaurus, this dinosaur was named after a person (Leaellyn, daughter of paleontologists Tom Rich and Pat Vickers-Rich) and the friendship of the National Geographic Society, respectively. Also unlike Qantassaurus, Leaellynasaura is represented by a partial skull, as well as bones from below the skull.
Note the presence of a villainous raptorial claw entering the frame, about to victimize this poor, defenseless little dinosaur. Might be a good idea to duck into a burrow for safety, eh?
An ankylosaur is loose in the Australian Museum! What a waste! Oh, the humanity!The ankylosaur is Minmi, named in honor of creator spirits in indigenous cultures of northern Australia. Minmi is the most complete ankylosaur in Australia, and its skeleton was discovered in Early Cretaceous rocks of central Queensland, dating from about 95 million years ago.
As loyal readers know, I now have a little bit of experience with the Cretaceous rocks of Victoria after walking over a great amount of these (hmmm, some of those key words might be worked into the name for a blog some day). In contrast, I have much less experience with the Cretaceous of Queensland, which actually is far more extensive and produces vastly greater numbers of fossils than Victoria.
Now, I am not being disloyal to Victoria when I make such a statement: it’s just a fact, supported by the near-constant discovery and recovery of skeletons of large dinosaurs and marine reptiles. For example, last year the world learned about just how special Queensland dinosaurs were, when the Australian Age of Dinosaurs Centre unveiled three new species: two beautiful sauropods and one very nasty-looking theropod (and I mean “nasty” in a good, wholesome Janet-Jackson sort of way). Much, much more about those dinosaurs and the Centre will be discussed in a future entry.
But long before dinosaur bones were found in abundance in Queensland and new dinosaur species were described, people had found something even more important in central Queensland, and I say that with the fully biased opinion of an unrepentant ichnologist. That would be the Lark Quarry dinosaur tracksite, located about 110 kn (60 miles) south of Winton.
This tracksite is arguably one of the most important in the world (and yes, I will argue in favor of that designation, and yes, you will lose if you take up a contrary view). In a relatively small area on a single bedding plane are more than 3,000 dinosaur tracks preserved in natural relief. That in itself is remarkable, but the tracksite also records a few moments of dinosaurian behavior not interpreted from anywhere else in the world. More about that will be explored later, too.
So the following entries, based on our two weeks in Queensland, might be more aptly titled: The Great Cretaceous Drive, as not so much walking was done while we drove many kilometers in the outback. Fortunately for marital stability, there was a lot of paleontologically inspired art along the way too. So Ruth and I were able to combine our interests to each learn about why the Cretaceous of this part of Australia is also rich in stories that inspire our creative juices. So stay tuned for some juicy revelations, coming up soon!
(Field work along the Victoria coast ended last month, and now my wife – Ruth – and I are on holiday in Queensland, Australia. Strangely enough, we are still very much interacting with the Cretaceous in Queensland, so look for future entries dealing with that. The following is the last of the Victoria entries.)
The last day of field work in the Cretaceous of Victoria was on Wednesday, June 23, and it was mercifully laid-back and casual in comparison to our field experiences at Rotten Point andDinosaur Cove the day before.
Mike Hall had left Apollo Bay the night before for home (which was in Melbourne), and Greg Denney was not joining us in the field, either. So it was just Tom Rich, my wife Ruth, and me going out on this fine day, one of the nicest weather-wise we had encountered during my month of field work in Victoria. Not surprisingly, we had some wild and wooly days during the course of a month: after all, it is winter there.
Our goals were to briefly scout two localities in the westernmost part of the Otway Ranges, which by happy coincidence were relatively close to The Twelve Apostles. This was Ruth’s third visit to this part of Victoria, yet she had not seen these natural wonders of Australia, the scenic centerpiece of the Great Ocean Road (albeit it was nowhere near the “center” of the drive, but more like the end of it if traveling from Melbourne). Tom insisted that Ruth would not miss The Twelve Apostles this time, a very gracious offer on his part, and justifiable for me as a geological-education stop. My students at Emory University can look forward to my showing them photos in their environmental geology class this upcoming September, whether they like it or not.
The Twelve Apostles, dwindling in number now but perhaps someday being joined by new seastacks through constant weathering and erosion. The ocean giveth, the ocean taketh away.
On the way to these seastacks, we first stopped at Moonlight Head, which was a bit difficult to pinpoint. In trying to find it, Tom had mistakenly conflated Moonlight Head with Wreck Beach, which led us to Moonlight Head, but it was not the same place he recalled, which we later found out was Wreck Beach. Wreck Beach he had visited only a few years ago, but he clearly remembered that 300+ steps were needed to reach the beach from the carpark. And of course, you had to climb back up those same steps if you wished to see the carpark again. (Life is full of choices, except when it’s not.)
Anyway, Moonlight Head was our first stop, and we parked the vehicle in a small space in front of a sign announcing that we were indeed at Moonlight Head.
Moonlight Head: The Sign. Note that the sign does not prohibit the use of wombats and explosives, a gross oversight by the park service, indeed.
We walked for only five minutes before stopping at a gorgeous overlook of the Victoria coast. Green coastal forest and scrub undulated downward to the sea, and far off in the distance were the tectonically tilted strata of the Otway Group, beseeching us to visit them and look for Cretaceous trace fossils.
Alas, its siren call fell on deaf ears, as our peals of laughter drowned it out. Our shared amusement was provoked by the thought of our walking for the next few hours downhill on a trail to such a faraway land – with no promise of trace fossils awaiting us there – then turning around and walking back up. Today was not the day for such athleticism or time consumption, especially with Wreck Bay and its 600+ steps happening later in the day. So with the GPS unit, I duly noted our position on the overlook, we took some photos, marveled at the scenery, and unceremoniously departed.
Wow, what fantastic Cretaceous outcrops! If only we felt like visiting them. Whoa, look at the time! Shouldn’t we be having a cuppa about now?
A little bit of backtracing in the vehicle brought us to a fork in the dirt road where we had originally taken a left, so now we took a right, which led to Wreck Beach. Fifteen minutes later, we arrived at a small carpark and got out to take a look. Yes, this was the place Tom had seen a few years before, and yes, the steps were there. A sign informed us of the precise number, which was 366, but for those people who like precision in their lives, more steps were required to walk from the vehicle to the start of the steps. Falsities abound when you live your life as an accountant.
Down we went, and quickly. Cretaceous sandstones and conglomerates were to my right and left, so I arbitrarily chose to go right. Cross-bedded sandstone was followed by more cross-bedded sandstone, which in turn was succeeded by cross-bedded sandstone. The lithological monotony was interrupted briefly by thin conglomerates, which were composed of broken bits of shale and fossil plant debris. After walking for about 20 minutes, no trace fossils made themselves apparent to me. All I saw was very nicely defined stratification, unsullied by burrows. A month of field work had led to my being able to discern which rocks were most likely to have trace fossils, and these were not those rocks. Ruth and Tom likewise saw no evidence of biological activity preserved in the rocks, either.
This space was left intentionally blank. That’s because I took no pictures of the rocks along Wreck Beach, out of protest at the lack of trace fossils there.
Soon we turned around, went back to the steps, and worked our way up, which took twice as long as going down, a result of that phenomenon known to some people as gravity (which is, after all, just a theory).
The way up from Wreck Beach, however many steps it might be.
Oh well – good exercise, fresh air, more rocks seen, and another locality in the Otway Ranges placed in the category of “There ain’t no trace fossils here.” And it was our last official stop in the Otways, and the last official stop of The Great Cretaceous Walk. After Wreck Beach, it was off to the Twelve Apostles (for which Ruth was grateful), and then to Melbourne for the night, before heading off to Sydney for a few days of rest, relaxation, and a big-city experience that was both interesting and jarring in its juxtaposition with our time along the Victoria coast.
But is this really the end? Not really, and I really mean that (for once). Following Sydney, Ruth and I made our way to Queensland for more vacation, but we passed through the Cretaceous of outback Queensland area, including a pilgrimage to Winton and the world-famous dinosaur tracksite, Lark Quarry, that is “only” 110 km (60 miles) south of town, as well as a visit to the very exciting Australian Age of Dinosaurs Centre just east of town. So keep tuned for a few more steps taken in The Great Cretaceous Walk in Australia. Will there be other years in Victoria, with more walking along Cretaceous outcrops? We shall see. In the meantime, on to New South Wales and Queensland!
Me, with my hand on the Tertiary Period and my feet in the Cretaceous Period at Dinosaur Cove, symbolizing how we oftentimes straddle great spans of time of which we cannot conceive nor comprehend. Also, I was trying really hard not to slip down the outcrop, and needed to hold onto something. Photo by Ruth Schowalter.
In this episode of The Great Cretaceous Walk, I combine the latest in avant-garde filmmaking with geological investigations and inspirations. Please use for contemplative and meditative purposes, but feel free to add your own soundtrack.
The Cretaceous rocks we saw yesterday here in Victoria, Australia gave us a reason to ponder temperature and climate, but in a much grander way than just saying the words, “global climate change.” I cogitated on this matter while enduring the harsh, ravaging effects of the Victorian winter here.
Thinking cold thoughts, post-field work version. Sorry for the omission of a beer, if at least for scale.
Yet despite what we observe here today, this part of southern Australia was connected to northern Antarctica 120 million years ago – during the Early Cretaceous Period – and the rocks here hold clues that reflect environments close to 75° S. (Just in case one of my students is reading this and furiously converting those degrees into Fahrenheit on his/her iPhone, those degrees are not for temperature, but latitude, and the South Pole is 90° S of the equator.)
Paleogeographic map from about 130 million years ago, during the Early Cretaceous Period. So if you think Australia is “Down Under” now, go back to the Cretaceous and see what you think, mate! Map from Ron Blakley’s fantastic paleogeographic map site, hosted by Northern Arizona University.
The Cretaceous outcrops we have walked across for the past eight days are now at 38° S. This means Australia has moved steadily north in the past 120 million years, and at this rate will reach the equator in another 100 million years or so. This is Reason #1,243 why plate tectonics, as a process, rules.
Granted, mean annual air temperature (MAAT) was much higher during the Cretaceous Period than today, at about 20°C, versus 14.6°C today. (OK, now you can do those conversions to Fahrenheit: that’s 58°F versus 68°F.) Still, it got very cold here during the winters, accompanied by months of darkness each winter, cold enough to freeze the ground, and even form permafrost. (Of course, it’s not frozen now, so it’s not really fulfilling the “permanent” part of permafrost. Unless you count rocks as “frozen,” which I don’t.)
What evidence do they have of frozen conditions here? Well, we could use stable oxygen isotope ratios, which are routinely applied to figure out paleotemperatures. Alas, we are mere underfunded field geologists, not the immortals on Olympus who use geochemistry and other means of witchcraft to pry thermally related secrets from the rocks.
We could also use paleobotany, as fossil plants have growth rings, leaf margins, and the assemblage of plants themselves that reveal much about the environments. Indeed, that has been done, and they match plant assemblages that are typical of MAAT of 8-10° C. But we also are not paleobotanists, however much we wish we were (because paleobotanists so cool, they inspire songs).
So how about good old geological evidence, observable in the field using our unaided eyes and not requiring any fancy equipment, or paleobotanical know-how? Hey, that’s a great idea! Sure enough, three lines of geological evidence support that these environments – inhabited by the likes of dinosaurs, mammals, and the “monster newt” Koolasuchus – were indeed frozen at times. These are:
• “Soil drops.” • Hummocky ground. • Ice wedges.
All of these collectively could be termed as cryoturbation structures, which may sound a little naughty, and for that reason alone they are probably illegal in much of the southeastern U.S., regardless of their identity. Nonetheless, the name literally means, “cold mixing,” which implies that cold and frozen conditions, along with thawing of ice, can mix sediments, like sand and mud.
Here are the “soil drops” viewed in cross section in an outcrop, in which darker sediments (mud) settled into the lighter colored sand. This was caused by ice melting above, which made the mud heavier, then it plopped into the less-dense sand. These structures are at Flat Rocks, the site of the Dinosaur Dreaming dig.
“Soil drops” at Flat Rocks, near Inverloch, Victoria. Photo scale is a wee one, only 10 cm (4 in) long.
Note that they all have flat bottoms, and they flatten out on some unseen surface about 20 centimeters (8 inches) below the top of the “drops.” This imaginary plane is where the permafrost below them halted their progress. Think of the permafrost acting like the plastic liner of a kiddie pool, thus preventing chocolate pudding from going below it while two consenting adults wrestle above. (OK, I have to work on that metaphor.) Anyway, I have looked carefully at these structures at Flat Rocks during several previous visits there, and lacking any other reasonable explanation, I am convinced that they are what other geologists have interpreted.
Hummocky ground forms the same way as the “soil drops,” only they are more symmetrical, with the troughs of the “hummocks” bottoming out above a permafrost layer. Yesterday, we saw a beautifully exposed example of such a horizon in an outcrop near Kilcunda, Victoria, outlined by a thin, black layer of coal.
A hummocky-ground horizon in vertical section, with its bottom marked by the black line; scale is about 20 cm (8 in) long.
Very close to these at the same outcrop, less than 100 meters (330 feet) away, were the ice wedges. These, of course, are not to be confused with “ice wedgies,” which I suffered at the hands of bullies all through elementary school. (Yeah, but who’s laughing now?). Ice wedges are formed by water freezing in sediments that, as the ice expands, wedges it apart and forms fractures. Here are some of the structures, filled with lighter-colored sandstone, which makes them stand out in the finer-grained and darker shale.
Ice wedge, filled with sandstone in shale, vertical section. (It’s that snaky looking thing in the middle.) Scale is the same as before.
Ice wedge, filled with sandstone in shale, but this time seen from above (what we geologists suggestively call the “bedding plane.") Yup, same scale.
So at the end of this little summary of what may be the most obscure topic you’ve ever had the gumption to read, you might justifiably ask, “So what?” The short answer is, these are the only examples of cryoturbation structures known from the Mesozoic Era in the world. Good enough for you? Also, the fact that they are in the same rocks that contain the remains of dinosaurs, mammals, amphibians, and other critters backs up the interpretations that these animals were not only living in polar environments, but environments that were at least occasionally frozen.
Dinosaurs out foraging on a snowy landscape during the Cretaceous winter in southern Australia, while a small mammal watches, remembering all of those “ice wedgies” the dinosaurs gave him. More gorgeous paleo-art by Peter Trusler; originally in Smithsonian Magazine.
And that’s significant, too: no other polar dinosaur site in the world shows such geological evidence, so clearly indicated and exposed such that geologists can just walk up to an outcrop and interpret them. Not only that, we can later that same day go back to the motel and take in some solar therapy, all while imagining those colder times in the Cretaceous of Australia, helped considerably by holding a cold Tasmanian beer.
(Much of the original research done on these cryoturbation structures is described in this peer-reviewed paper: Constantine, A., Chinsamy, A., Vickers-Rich, P., Rich, T., 1998, Periglacial environments and polar dinosaurs: South African Journal of Science, 94 (3).)
Our goal this morning was to walk the rocks of two fossil localities, Potters Hill and Rowell’s Beach, which are both just east of San Remo, Victoria. The weather was excellent, with mild temperatures, a slight breeze off the sea, and mostly blue skies. We threaded our way along the platforms and between boulders below sheer cliffs, and crossed several beaches, one of which was probably Rowell’s. At the end of the morning, the rising tide and waves motivated us to move upslope about 60 meters (200 feet), a nice bit of exercise that lent to some spectacular views of the coastal exposures.
As we walked across these rocks, we were very much aware that they had yielded more than a few bones of an extraordinary fossil amphibian, Koolasuchus cleelandi. This monster newt – well, actually it’s a labyrinthodont, but it’s just fun to say “monster newt” – was nearly 4 meters (13 feet) long, and was likely the top predator of its fresh-water environments. Think of it as the ecological equivalent of an alligator, only it was an amphibian, and living in a near-polar environment.
Koolasuchus cleelandi, as depicted by Australian artíste par excellence, Peter Trusler.
It also was not supposed to be here at this time. Its lineage everywhere outside of Australia had died out nearly 200 million years ago, during the Triassic Period. So when the first bones were found here in rocks from 115-120 million years ago and later identified as belonging to a labyrinthodont, it was a shocking find: the temporal equivalent of finding a Late Cretaceous dinosaur alive today.
Koolasuchus cleelandi is named in honor of two of Victoria’s best fossil hunters, Lesley Kool (who is also the site manager at Dinosaur Dreaming), and Mike Cleeland.
Lesley Kool (on the right), flanked from right to left by Mary Walters and Ruth Schowalter (my wife, frequent field companion, and biggest supporter). Behind them is Flat Rocks, Victoria; photo taken in May 2006. Why the cleaning implements? It’s a long story.
Mike Cleeland (far right – not politically, though), with me (far left – yes, politically) and Chris Consoli (former Monash Univeristy graduate student, now Dr. Consoli) in the middle. Photo taken in May 2006 at Dinosaur Cove, Victoria.
The remains of Koolasuchus are normally found in coarser-grained sedimentary rocks here, such as pebbly conglomerates. This coincidence led to speculations that it lived in fast-flowing streams, similar to modern-day hellbender salamanders (Cryptobranchus alleganiensis) in my home state of Georgia. I could just imagine this gigantic predator sitting on a stream bottom, facing upstream, and just opening its mouth, catching any fish, crayfish, or anything else smaller than it (in other words, nearly everything).
Alas, we did not find any other Koolasuchus bones today, and only a few trace fossils were documented along the way. We did encounter some fantastic scenery, though. So here are a few photos and stitched panoramas, just to give you a sense of what we saw this morning. Not every day has to result in the discovery of a never-before-known fossil, but they can be days filled with an appreciation of geologic beauty.
Tomorrow, more about our latest field endeavors, whether we find anything or not!
