The Cretaceous Parks of the Colorado Plateau: the Final Discovery

In the last installment of our dinosaur-digging story, we had finally come across evidence that dinosaurs had, in fact, actually lived during the time of the deposition of the Cloverly Formation; we had found deinonychus claws, and bones of tenontosaurs and anklyosaurs. In the final days on the site, we had become fairly sharp at picking out bone fragments on the slopes of the dig site, and two of our party found a fairly significant bone scatter a few yards away from the main quarry.

By working their way up the slope, they found where the bones were emerging, and we started another (much smaller) quarry, and uncovered several dozen bones in situ, of a creature we could not immediately identify. It was smaller than the other species we were expecting to find, and was thus sort of mysterious. We delineated the bone area, and started the process of protecting the exposed bone with "butvar", coating the bones with paper towels and covering the entire mess with plaster. By our last day on the site, we had constructed a giant plaster monstrosity.

The paleo-experts on the dig looked bemusedly at our work, and very politely waited until we had said goodbye and started on our way home before they started tearing off all the plaster and carving the rock mass into smaller parts. The dig was nearly a quarter-mile from the vehicle, and our plaster monster must have weighed 300 pounds! No one wanted to carry it down that hill!

The experts also were nice enough to report on what they found once the specimen had been hauled off to the Museum of the Rockies. Our find turned out to be numerous fragments of a Zephyrosaurus, a species that had been found only once before, and had been named on the basis of a few pieces of the skull, and some vertebrae fragments. We had found leg and claw elements, pieces of a skull, and vertebrae and rib fragments. The animal was a small bipedal herbivore. If your fifth-grader has ever heard of it, it is probably because the kid has a Dinosaur A-to-Z book, and zephyrosaurs are one of the few "Z" dinosaurs!

Images of the bones could be accessed for some time on the Museum website, but they were eventually taken down, so I wonder if they have reconsidered the identification of the specimen. If anyone wants to track it down, it was MOR #759. I would love to know what our creature is up to these days!

The Cretaceous Parks of the Colorado Plateau: the Cedar Mountain Formation

Well, yeah, except that it isn't the Cedar Mountain Formation, and it's not on the Colorado Plateau, and it isn't a park of any kind. If I may explain, the Cedar Mountain Formation is an exceedingly important part of the geological history of the Colorado Plateau, being the only representative layer in the region dating from the early/middle Cretaceous Period. It has also turned out to be a treasure trove of fossils with a rich collection of dinosaurian and other species preserving a time when animals were mixing or being separated from related species in Europe and Asia. So it is really important and all, and every geology field trip should stop and have a look at it and take lots of pictures and stuff. Except that I haven't done so on all of my many trips onto the plateau.

Extensive work on the Cedar Mountain Formation does not seem to have begun until the early 1990's (compare to the Morrison Formation, which was being excavated for dinosaurs in the 1870's). Some two dozen dinosaur species have been found in the unit, including several sauropods, iguanadons, troodons, one of the earliest hadrosaurs (eolambia), and my personal favorites, deinonychus, utahraptor, tenontosaurus, and a zephyrosaurus. At different levels in the formation these dinosaurs share affinities with European faunas while others are related to faunas from Asia. These connections reveal the severing of North America from the former and the linking to the latter during early and middle Cretaceous time.

So what's with the picture above? It is an exposure of the Cloverly Formation near Bridger, Montana. The Cloverly is nearly contemporaneous with the Cedar Mountain Formation, and many of the fossils found within it are similar as well. And I have actually been there, and participated in a dinosaur dig that was a defining life event for me and many of my students. So a few posts will soon follow, describing what we did there back in 1994. Please excuse the somewhat diminished quality of the photography, as these are scans of slides that were taken by a grossly incompetent photographer (me) back in the dark days before digital imaging.

These stories will also serve as my contribution to this month's Accretionary Wedge, hosted by Dave Shumaker at Geology News. The topic of the month is our favorite places to do field work, and was this ever it!

More soon!