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!”

Tuesday, August 9, 2011

The Dinosaur Tracks of Milanesia Beach: Part I

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 Victoria had invited me to 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).