Sauropod femur largest ever found at quarry
The straps slowly, slowly grew taut as Mike Perry nudged the gas on the F-150. One end of the thick straps was looped over the truck’s trailer hitch, the other strategically circled around a sizable white blob in the Mygatt-Moore Quarry at Rabbit Valley.
Except it wasn’t just any ol’ blob: Inside four layers of plaster and burlap were two articulated vertebrae, meaning that in fossilization the bones remained in roughly the same position that they were in life. About a foot in diameter, they belonged to a sauropod — the class of long-necked, quadrupedal plant eaters.
Friday morning, a cadre of Museum of Western Colorado volunteers and staff circled the dusty pit where the vertebrae and a femur had been discovered four summers ago. Perry, former executive director of the museum, gently pushed the gas and there was a moment of breathless suspense.
Would the vertebrae bundle break away along an already-existing fracture? Would the bones stay in place within the plaster wrapping? And, most importantly, would the femur stay where it was or topple without the brace of the vertebrae?
Because while the vertebrae are tremendous, the femur is an incomparable treasure: a 6-foot, 7-inch sauropod bone, one of the biggest ever found at the quarry, belonging to a giant up to 90 feet long. In fact, the discovery of the vertebrae led to finding the femur, when volunteers dusting off the back bones happened across another bone that just kept going and going.
So, after four seasons of slowly, painstakingly unearthing and protecting the bones — months and months of minute, meticulous work in the baking desert sun — it was time Friday to take the vertebrae to the lab at Dinosaur Journey in Fruita.
“We’re prepared for worst-case scenarios,” explained Julia McHugh, who on Monday became the museum’s new curator of paleontology, as volunteers did some last-minute chiseling at the base of the vertebrae bundle. “It was a really wet spring, so it’s really fractured inside the femur jacket and there’s a chance it could start to fall when we pull the vertebrae out. We’ll brace it and hope the vertebrae jacket breaks away along a fracture.”
The vertebrae were extracted using a technique called pedestaling, McHugh said, in which a trench twice as deep as the plaster jacket was dug down around the bones. Then, the dirt was undercut so that the bundle would, it was hoped, pop away like the cap off a mushroom stem.
To that end, volunteers Tom Lawrence and Tom Schroer braced metal chisels under the vertebrae jacket, pounding them with mallets to loosen the entire bundle from its bed of brown-gray mudstone and shale. The vertebrae had lain in that spot for about 152 million years — since the late Jurassic, McHugh said — in the Brushy Basin member of the Morrison Formation.
After the final undercutting, and after working straps between the vertebrae and femur jackets, the moment of truth. Perry tapped the gas a tiny bit more, the taut straps quivered and then an audible crack as the vertebrae jacket popped away from the femur, which remained in place.
Volunteers Dale Jones and Kay Fredette beamed and McHugh raised her arms and cheered. Field coordinators Chris Racay and Rob Gay hurried into the shallow pit to collect the few bone fragments that had fallen off as the vertebrae jacket split away from the femur, placing them in gallon Ziploc bags that had been labeled beforehand.
The work and worry wasn’t over yet — a team of six had to gently turn the vertebrae jacket over so it could be dragged out of the pit and lifted onto a trailer for transport to Dinosaur Journey.
Once in the lab, the bones might begin to tell a deeper story: whether they belong to an apatosaurus, as theorized. Whether the dinosaur died at that spot, on the banks of a still, seasonal pond, or whether perhaps an allosaurus scavenged the carcass and dragged it to that spot.
“Fossils are part of our natural heritage,” McHugh said, adding that they, and the area in which they’re found, tell a story spanning millions of years and encompassing changes big and small.
So, when the vertebrae bundle made its exit from the pit Friday morning, Fredette smiled and said, “This is a good day.”