Troddon formosus was a predatory dinosaur with good grasping arms and hands and a mouth full of coarsely serrated teeth

fun to perform but whose results are impossible to verify. Yet as I gazed into the oversize eye sockets of the Troddon\ birdlike skull, trying to imagine the long, slender snout receding and the low forehead growing wider, I found myself wondering what exactly the world would look like today if some of the events that shaped the natural history of dinosaurs had taken a slightly different turn. In my opinion, the extinction of Maiasaura, Hypacrosaurus, and their kin was neither as neat nor as unavoidable as the doomsday meteor theory would have us believe. Like all organisms, dinosaurs were subjected to a complex and dynamic array of forces, and though the forces are now largely understandable in and of themselves, their consequences, being dependent on untold numbers of contingencies, were not always or even mostly inevitable. Something as unimportant, seemingly, as a small shift in the climate—producing fewer droughts along the upland coastal plains, for example—could have profoundly altered the fortunes of certain dinosaur lineages in the late Cretaceous period. When I look into the holes where the Troddon's eyes once looked out at an earlier and very different world, I don't see a reflection of myself, as those who study primates often claim, but I do see a reflection of something more fun damental: my condition, our condition, the tenuous hold all living things have on existence. And but for the aimless grace of natural history, there lay the last member of my kind, buried in a mudstone graveyard, yet another evolutionary experiment come to an end.

The Troodon skull was not the only thought-provoking fossil among the new additions to our collection. With the approach of winter came our seasonal change in activity and orientation. Home from the hunt, back from the excitement of the chase, we would retire, somewhat fatter after ten weeks of Mel's fabulous meals, to the laboratory and for the next several months ponder our specimens, methodically studying their every aspect—their shapes and sizes, internal makeup and structure, how they fit together as full skeletons, how the animals the skeletons represent might have moved, their probable behavior, the roles they played in the ecosystems they inhabited. What did the fossils tell us about the lives of dinosaurs on the coastal plain during the late Cretaceous? That was the question behind everything we did during the winter of 1988-1989. While Pat, Carrie, Bob, and preparator Allison Gentry, assisted by volunteer Bea Taylor, began the laborious task of removing the plaster jackets and preparing the specimens, I reviewed the results of our four seasons on the Blackfeet Indian Reservation.

Overall, the most notable development since leaving Egg Mountain concerned the thrust of our research: It now ran on two equally important tracks, neither of which showed signs of ending soon. The first stretched all the way back to our earliest days at the Willow Creek anticline and carried through to our most recent excavation—the nesting horizon at Blacktail Creek North. In Hypacrosaurus stebingeri we had found a dinosaur whose behavior we could compare with that of Maiasaura. It wasn't a perfect match, to be sure, but the hypacrosaur material was so comprehensive and rich I felt confident that by the time we completed our study of it, teasing out all of the relevant implications, we would be able to say whether our original ideas about reproduction and the treatment of babies among duck-billed dinosaurs had been wrong.

The second research track started at Dino Ridge Quarry, in the Landslide Butte badlands, ran through Canyon Bone Bed and on to Hillside Quarry along the Two Medicine River. The three new horned dinosaurs and the new gryposaur gave me reason to believe that we might be able to answer questions that no one before had been able to address, much less resolve: What was the rate of evolution among dinosaurs? What were the mechanisms that drove their evolution? Our journey along this track had scarcely begun, however, and I was eager to move ahead, to see what lay around the next bend. Specifically, we needed more fossils, as well as a more thorough understanding of the large-scale environmental events that occurred on the coastal plains during the Cretaceous period, which is to say, we also needed to see more sedimentary rock.

So the following season, the summer of 1989, we went back to the Blackfeet Indian Reservation for what would turn out to be our last major field effort in the Two Medicine Formation. As part of his doctoral research, graduate student Scott Sampson had taken an interest in the horned dinosaurs of Landslide Butte. He wanted to investigate in particular what role the diverse headgear played among such highly social, plant-eating dinosaurs. Were the neck shields and spikes weapons of defense against predators? Or were they used primarily for sexual display and nonlethal sexual competition between rival males, as is the case among gregarious horned animals today? In the second week of June, Scott and a small crew reopened Canyon Bone Bed, while Pat Leiggi and another small crew assisted in the effort by reopening Dino Ridge Quarry. Meanwhile, graduate student David Varricchio, Allison Gentry, and a third crew established a camp on the Carroll Ranch along Badger Creek, then resumed the excavation of Jack's Birthday Site. Also working on a dissertation, Dave planned to spend the summer trying to determine the type of environment the site represented and what exactly happened to the animals assembled on that ridge. Jason, Carrie, and I pitched our tents on Birch Creek, which forms the southernmost border of the reservation. From there we could reach the Blacktail Creek region much easier than from the river, the approach we had used the previous two seasons. Our camps were spread from one end of the Blackfeet Nation to the other, yet all of us were either exploring or excavating within the top three hundred feet of the Two Medicine Formation.

During the next several weeks the exploring party—Jason, Carrie, and I—found a number of important specimens in the vicinity of Blacktail Creek: the skull and partial skeleton of an Achelousaurus and numerous areas containing Hypacrosaurus and Troddon eggs, embryos, and babies, along with several Hypacrosaurus and Prosaurolophus bone beds. Tiny islands of rock surrounded by vast sea-swells of grass, the new sites were not promising enough, however, to warrant further digging, at least not until we had finished excavating our other quarries, principally, Jack's Birthday Site, where Dave, Allison, and their crew were recovering the remains of almost every kind of dinosaur that had been found previously in the upper part of the Two Medicine Formation. Besides fossil concentrations of Troddon, Hypacrosaurus stebengeri, and Prosaurolophus blackfeetensis, the name I gave to the new duck-billed dinosaur first seen at Westside Quarry, near Landslide Butte, they found scattered skeletal elements representing, among others, ankylosaurs and Daspletosaurus, a theropod very similar to Tyrannosaurus, though not quite as large. Nondinosaur fossils included turtles, whole freshwater fish, frogs, lizards, birds, and pterosaurs (the flying reptiles that were close relatives of dinosaurs). In an area between Jack's Birthday Site and the Badger Creek camp, graduate student Vicki Clouse discovered an intact Daspletosaurus skull and a Daspletosaurus leg, complete from thighbone to claws. No other parts of the animal could be found. Bob Harmon and a small crew excavated the specimens during the final days of the 1989 season.

Also by that time, Dave had assembled a tentative but fascinating scenario for Jack's Birthday Site. As Ray Rogers had done at the Landslide Butte quarries, he measured and characterized the sediments in and near the ridge and conducted a taphonomic investigation of the fossils uncovered at the site, which is to say, he mapped the positions and conditions of the bones. Taphonomy,

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