Dinosaur Dreaming

Preliminary 1998 dig report

Lesley Kool
Dinosaur Dreaming co-ordinator

The 1998 Dinosaur Dreaming dig was, in many ways, very different from the previous four expeditions. When we first began excavating the site in 1994, most of the fossil layer was exposed on the surface of the shore platform, and usually only covered by a few centimetres of sand. Over the last four field seasons, however, the excavation hole has become deeper as we followed the fossil layer into the shore platform.

At the end of the 1997 field season the fossil layer was more than 50 centimetres below the shore platform. When the sand was particularly high, it took up to two hours just to remove the sand brought in by the previous high tide and expose the fossil layer. As we planned to excavate even deeper this year, Nick van Klaveren (the site excavation manager) decided to come up with a system that would prevent some of the sand entering the excavation hole and save us precious time.

Nick spent much of the time between field seasons talking to engineers and other experts to find out what would be the easiest and most environmentally friendly method to keep out the sand. A number of ideas were put forward and rejected for one reason or another. Eventually a plan was visualised that might just do the job. It met all the criteria and worked in theory. We just had to put it to the test.

The best-laid plans...

A certain amount of preparation was necessary before the field trip. This involved obtaining hundreds of plastic feed bags, and filling them with empty plastic bottles, kindly donated by the recycling plant on Philip Island. These were to form the bulk of the fill for the hole. Rolls of steel crab-pot mesh, tarpaulins and steel girders were also purchased.

The now-famous tiny mammal jaw (Ausktribosphenos nyctos), discovered during the 1997 field season, had been found close to the bottom corner of the excavation hole. It was decided that we would concentrate on this area in the hope of finding more mammal bones, but it meant the removal of a large amount of overburden just to gain access to this part of the fossil layer. We originally estimated that both the removal and setting up Nick's system would take about a week. In reality, due to some unforeseen delays and an amount of modification to the sand system, it ended up taking more than three weeks before we were able to begin excavating the targeted area.

Nick's system involved placing rock bolts at one metre intervals around the perimeter of the lower part of the hole, which had been partitioned by a sandbag wall. Once the sand was removed from this part of the hole, and before the hole was inundated by the next high tide, the plan was to fill the hole with bags of empty bottles which were secured by mesh and steel girders to prevent them being washed away.

Problems

The idea appeared sound, but it soon became obvious that some modification was necessary before it would be a viable system. Our first attempt was a disaster. We had placed a tarpaulin under the bags of bottles, which we had hoped we could just peel back when the bags were removed. Unfortunately, so much sand had filtered down through the bags that it took more than three hours to remove the tarpaulin.

The next suggestion was to place tarpaulins over the bags instead. This prevented some of the sand from entering the hole, but it still took too long to clean out. Using only half the number of rock bolts halved the size of the hole; this meant we had less area to uncover and correspondingly took less time. Finally, we placed tarpaulins above and below the bags, enveloping the bags and preventing up to 75% of the sand from entering the hole. Towards the end of the field season, we had become so expert at removing the steel, mesh, bags and tarpaulins that we could clean out the hole in just over one hour. This was all the more amazing considering that the depth of the bottom corner (where we had removed the overburden) was over a metre below the shore platform. Not putting this system in place would have meant between three and four hours digging each day, just to get to the fossil layer in that corner.

Another factor was also introduced this year. Doris Villiers has undertaken to study the taphonomy of this site for her doctoral thesis. This involves studying the bones of all the different animals that have been preserved at this site, and trying to work out how they got there. This also meant studying the sedimentology of the site, so time had to be set aside for her to map the various layers exposed in the working face. Because the face changes each time rock has been removed, Doris had to map it as often as possible, a task that sometimes proved difficult when we only had a few hours to remove rock before the next high tide. The data that Doris collected, however, will prove invaluable in producing a three-dimensional map of the site.

Even with all the delays and time spent perfecting Nick's system, we still managed to catalogue over 500 bones and teeth of dinosaurs, turtles and fish. It is often difficult to identify a bone when it is broken in cross-section and the rest of it is hidden by rock. There were however, a number of larger-than-average hypsilophodontid femora recovered this year that will increase our knowledge of hypsilophodontid speciation. Many small bones were recovered that could be more of our elusive mammal; only time and preparation will tell. Unfortunately, the rate of collection still far outweighs the rate of preparation, and it will be a number of years before most of the material collected during the 1998 Dinosaur Dreaming field trip is prepared.

What next?

With the 1998 field season behind us, we're already planning for next year. We know how we can improve Nick's system to prevent even less sand from entering the hole, and we have already designated the area that we will concentrate on next year. Funding permitted, we will hire a large compressor and a more powerful jackhammer to drill the new holes for rock bolts. This will decrease the time spent on preparing the site and give us more time to concentrate on removing fossil material.

The results of Dinosaur Dreaming 1998 have given us much to work on for future field seasons:

• Nick's revolutionary system to keep the sand out of the excavation hole will save us many hours of back-breaking digging as well as increase our actual excavation time.
• Doris' data will help to construct a clearer picture of how the precious bones ended up where they are.
• Ongoing preparation of the bones and teeth recovered from this and earlier field trips will give us a better idea of the diversity of this area so many million years ago.