July 10-12: More Surprises from the South Side
Work at the South Side Ceratopsian site continues to progress. The scattered skeleton continues to emerge from its surrounding mudstone matrix. Mudstone is made from exactly what it sounds like – mud. Specifically, it is made of the compressed mud found along a river bank. When a river floods and breaches its banks, the water spreads out and its flow is generally reduced significantly while it inundates the flood plain. The loss of velocity results in the fine particles of sediment dropping out of the flow, resulting in a big dump of mud on the flood plain after the floodwaters recede. The South Side Ceratopsian skeleton was sitting out on the flood plain when a nearby river flooded. The flood resulted in a fresh deposit of mud that covered up the skeleton, and allowed the slow fossilization process to begin.
In the last few days, we have uncovered more ribs and vertebrae, as well some of the larger and more important bones of the limbs and girdles, including a very nice ulna (from the forearm) and an almost perfect ischium, a bone from the hips.
We have also found some time for prospecting in the badlands surrounding the Milk River. Believe it or not, one of our most reliable crew members turned up another associated ceratopsian skeleton! This one is a few kilometers to the west of our current quarry, and it is also in the lowest part of the Oldman Formation. This is very exciting, and is something that we will definitely go after next year.