The Cretaceous Parks of the Colorado Plateau: the story of a Dino-Dig wraps up

Continuing the story of our 1994 dino-dig, in which we learned the truth of uncovering new scientific knowledge. We were re-opening the quarry where the raptor Deinonychus had first been discovered. After nearly a week of hard digging we were approaching the bone layer, but work was pre-empted by a heavy rain and hail-storm that drenched the area. We had found nothing to speak of, but in the days that followed the storm, bones began to appear.

Our first effort to actually discover bone involved Karma Craig, whose previous efforts had netted us a near tornado, scorpions, rattlesnakes and deer-van collisions. Knowing of his power, we got him to say the words "I wonder what it would be like to find dinosaur bones?". His Karma was strong, and later that day he stumbled over some tail vertebrae (second picture) of a Tenontosaurus, the large iguanadon-like plant-eater that appears to have been the main prey of Deinonychus. Soon after, another member of the party found an odd boulder that turned out to be the carapace of a turtle (third picture; the matching half of the carapace was later found to be already ensconced in the Museum of the Rockies). I had walked past a pile of rocks for a week before it occurred to me that we were in mudstones, and that rock chunks shouldn't be there; they turned out to be the bones of an anklyosaurus relative. And several members of our party wandering on the other side of the gully found a partial Deinonychus claw and numerous other scattered bone fragments (fourth picture).

Meanwhile, the diggers had reached the bone-level of the main pit. Tensions were high as the professionals climbed in with their dental picks and brushes and went to work. What would come to light? Whole skeletons of Deinonychus locked in a death embrace with their victims? Well, no, we didn't find that; we found a single claw, which fell to pieces upon exposure, and was lost. But that's what happens, I guess. We were quite thrilled with our other discoveries.

Just the same, there was one more discovery to be made in our last days on the site. That story follows soon!

The Cretaceous Parks of the Colorado Plateau: the story of a Dino-Dig

What was your favorite dinosaur when you were a kid growing up?

Before I distracted myself with a series of geo-memes, I was telling the story of my sole experience with a real dino-excavation, as part of my long-running "short" history of the Colorado Plateau. The first posts explained how we got invited to assist on the dig, and some of our adventures on the way to Montana. Today is an explanation of what we were looking for.

As far as I can tell, I am one of the old-timers of the geoblogosphere, so my childhood memories include T-Rex, stegosaurus, brontosaurus (yes, I know the name is wrong...), triceratops, and pteranodons (yes, I know the ptera-animals aren't dinosaurs, but I didn't know it at the time). As far as my five-year-old self was concerned, they all lived at the same time, fought with each other, were sluggish and cold-blooded, and died out because the superior mammals ate their eggs.

In the 1980's and 1990's, public perception of the dinosaurs was changing, due in part to the movie "Jurassic Park", but really because of the extensive work of numerous paleontologists, some of whom were talented at presenting their work to laypeople through such books as The Dinosaur Heresies (Robert Bakker), and Digging Dinosaurs (John Horner). A sort of dinosaur renaissance followed, and with a vast increase in research into the lives (and deaths) of the dinosaurs, the total number of dinosaur species was doubled.

One of the opening salvos in the new perception of the dinosaurs was a report by John Ostrom in 1969 about his discovery of deinonychus fossils in association with a tenontosaurus at a quarry near Bridger, Montana (the picture above is adapted from Ostrom's report; it was drawn by Robert Bakker, who was his research assistant for years). The velociraptors, popularized (and vastly enlarged) in the movie Jurassic Park, were actually no bigger than a german shepherd. The closely-related Deinonychus would have been a bit closer to the size of the creatures in the movie, although Utahraptor would have been even closer. At Ostrom's quarry, at least four individual raptors died along with the large plant-eating tenontosaur, leading to speculation that the predators had attacked the much larger creature together (and had died in the process). The result of Ostrom's analysis was that at least some of the dinosaurs were closely related to the birds, that they were agile and warm-blooded, and that some may have cooperated in bringing down prey. These were revolutionary and controversial ideas at the time.

So, what were we up to in 1994? We were going to help reopen John Ostrom's quarry! The distinctive hill is called the Shrine site (although we were also told it was named for a particular part of the original ranch owner's wife's anatomy), and is located in the badlands near Bridger, Montana. It is an exposure of the Cretaceous Cloverly Formation, which is related to the Cedar Mountain Formation on the Colorado Plateau, and is composed of sand and silt deposited on a muddy river floodplain. The idea of pack behaviour among dinosaurs remains a controversial subject, and by digging further into the side of the hill, we hoped to find more evidence concerning these predators of the early Cretaceous.

We couldn't have asked for a more dramatic setting. Besides the vivid colors of the nearby badlands, we had a skyline view of the high Beartooth Mountains that form the eastern edge of Yellowstone National Park. To the east rose the Pryor Mountains, and a few miles beyond, the Bighorn River (yeah, the Custer's Last Stand one). The picture of the camp above hardly does it justice (all that pre-digital photography with cheap cameras).

We met the professional crew, Geoff and Desmond, and a couple of amateur dino-diggers from the Bay Area, and starting looking over the quarry site. We knew our role; it was to remove the side of the mountain so the bone people could get to the bone layer with their brushes and dental picks. As Arlo Guthrie put it, we came armed with shovels and picks and implements of destruction. We set up camp, and made dinner. Work would commence the next morning....

Ostrom, J. H. (1969). "Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana". Peabody Museum of Natural History Bulletin 30: 1–165.

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!