The Great Cretaceous Walk Takes a Rest

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.

Who Made the Three-Toed Dinosaur Track?

In paleontology, occasionally a scientific hypothesis rules for several decades or more and enters the public realm, becoming part of popular lore. Nonetheless, science is always changing, which means that what we took for granted as a “true” story can be upended in a way that surprises everyone, perhaps even the paleontologists doing the revising. Such is the situation with the “giant-stalking-theropod-dinosaur-causing-a-dinosaur-stampede” story of the Lark Quarry dinosaur tracksite in Queensland (Australia). This tale has been reigning for more than 30 years and is known worldwide by paleontologists and laypeople alike, but now faces a makeover in the light of new evidence.

Here are some dinosaur tracks from Queensland, Australia. The dinosaurs that made them had three toes on their rear feet, and walked only on those two feet (bipedally). So were these from theropod dinosaurs or ornithopod dinosaurs? Don’t know? Then I guess you’ll have to read more, won’t you? Display is at the Museum of Tropical Queensland in Townsville, Queensland (Australia). Note the stylish sunglasses (lower right) for scale.

Luck, Preparation, and Opportunity: Part II

"You won't find anything."

This assurance came from Tom Rich as he drove, and me as his sole passenger on a quick trip to the Victoria coast. At his invitation, we were traveling together to Flat Rocks, the Dinosaur Dreaming dig site near Inverloch, Victoria. It was late February 2006 and the last weekend of the dig season there. It was a privilege for me to witness the closing of yet another successful field season and meet some of the people associated with Dinosaur Dreaming. But at the same time I was entering an intellectual unknown.

Dinosaur Dreaming, February 2006

I had been in Australia for less than three weeks, on a sabbatical from Emory University for the first time in 16 years. The primary reason for my being there was to work with Patricia (Pat) Vickers-Rich on a geoscience-education project, but I was open to any other opportunities that might arise. So when Tom asked me if I would like to come with him to the coast, I emphatically said “yes,” albeit with a blend of awe, excitement, and trepidation. The last of these feelings stemmed from my being in a new place, with new people, and new rocks (an example of how “old” becomes “new” in geology). The still-healing fractured tibia in my right leg, the result of a biking accident only a month before, also reminded me to take it slowly, and I had brought a walking stick with me to help with traversing the flat platform of rock. (Yes, the person who first named “Flat Rocks” must have had a lack of imagination that day.)

Flat Rocks, near Inverloch, Victoria.

Tom’s pessimistic statement came in response to my observing that in 14 years of work at the Flat Rocks site, a source of some major paleontological discoveries, no trace fossils had been detected, yet I expressed hope that I would find some there. His pessimism, though, was based on what was known then. The only trace fossil described from Early Cretaceous rocks both east and west of Melbourne was a single, small dinosaur track from the Otway Group, in rocks dated at about 106 million years ago and from Knowledge Creek. Pat and Tom found this track in 1980, during their only time to Knowledge Creek, a place they swore they would never visit again because of its remoteness and difficult access.

No fossil burrows, not even those of invertebrate animals – such as insects or crayfish – had been reported from kilometers of expansive Cretaceous outcrops. Invertebrate trace fossils, especially burrows, are normally the most common trace fossils in any given sedimentary rock sequence, and I thought it was unusual that none had been described after more than 100 years of geological research in this area.

Fortunately for both of us, Tom was wrong. I found two isolated large theropod dinosaur tracks the first day, the first such tracks discovered from this site, then found fossil crayfish burrows the day after that.

Fossil crayfish burrows at Flat Rocks, Strzelecki Group, 115-120 million years old. Burrows were filled with a differently colored sand while the surrounding sediment was still soft, and both sediments later cemented to form sandstones. Photo scale = 10 cm (4 inches).

I promptly celebrated this discovery by sitting on them.

Me sitting on Cretaceous fossil crayfish burrows: photo by Gerry Kool.

Although the dinosaur tracks were nice to find, I actually was more excited about the second day’s discoveries, for reasons explained later. The fossil crayfish burrows led to a paper that took nearly two years to write and publish, but one that was well worth it for its contributing to the solution of a 130-year-old evolutionary puzzle first posed by famed evolutionary scientist Thomas Huxley.

This new knowledge thus alerted future dig crews to start looking for more trace fossils, and especially dinosaur tracks. Sure enough, the next year, in February 2007, an undergraduate student, Tyler Lamb, found a third large theropod track, only 5 meters (16 feet) from the dig site.

Large theropod dinosaur track, preserved as a sandstone fill of an originally concave feature, and weathered out in bold relief. Yup, same photo scale as in the previous picture.

The humbling realization for everyone after this find was that hundreds of volunteers and professional paleontologists had walked across this track for nearly 15 years, unknowingly putting their feet on the same spot where a dinosaur had stepped 120 million years earlier. Hence my own luck, preparation, and opportunities enabled others to make their own discoveries, using the same winning combination of fortune, knowing what to look for, and circumstance.

Tomorrow, Tom and I leave together for Inverloch and will walk over the same rocks, more than four years ago, with both of us expecting to be surprised by what we find. The next post should be about our progress, but also be looking for one that explains why the fossil crayfish burrows were more important to science than the dinosaur tracks, and how these were connected to Mr. Huxley.