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Much ink is spilled on the subject of the extinction of the dinosaurs 65 million years ago. But rather than focus on the demise of these beasts, relatively few people have concentrated on the origin of the dinosaurs. Where did they come from? How did they diversify? Why were they more successful than some of their early contemporaries? When did dinosaurs first get big?
To help answer these questions, a team of graduate students from UCMP, the American Museum of Natural History, and the Field Museum of Natural History are excavating a new locality in northern New Mexico, called the Hayden Quarry. Located at Ghost Ranch, New Mexico, the area is better known as the inspiration for many of Georgia O'Keeffe's paintings. The quarry is found within rocks called the Chinle Formation, which was deposited as river sediments between 220 to 205 million years ago during the Late Triassic Period. The quarry is probably between 210 and 215 million years old.
The Hayden Quarry contains the remains of many different Late Triassic vertebrates, from fish to dinosaurs. Animals found include the large aquatic metoposaurid amphibians, crocodile-like phytosaurs, armored aetosaurs, bipedal early crocodilian relatives, and dinosaurs, among others. What is most exciting about the locality is that it contains a variety of true dinosaurs, as well as their closest relatives. Thus, we have preserved in the Hayden Quarry the transition from dinosaur precursors to true dinosaurs. By understanding how these species fit in the family tree, we can understand the timing of the diversification of the first dinosaurs and their relatives. When we compare the Hayden Quarry to other nearby localities with dinosaurs (for example, the Coelophysis Quarry), we can understand how long or fast it took for dinosaurs to go from being just another group to dominating the landscape.
The rock layers of the Hayden Quarry that preserve vertebrate specimens represent ancient river channel deposits. Thus, we find a variety of specimens, from isolated worn fragments to articulated skeletons. All of these were probably swept into the river channel during flooding episodes and subsequently buried. The team excavates these specific river channel rock layers to discover new fossil specimens.
Very specific layers contain the bones, so the first step in this field season is to remove all the rock above these layers. This year we spent three days removing this rock with picks and shovels with some help from a backhoe. We prepared a flat, stone surface that we can excavate in detail to find the bones. The bones in the Hayden Quarry can be microscopic or up to a foot or more in length. Therefore, we have to excavate very carefully. Common excavation tools include small brushes, awls, and dental picks. These allow us to remove the rock without damaging bones. Because the bones are very fragile, we often coat them with a thin coating of Butvar. This is an acrylic plastic that is dissolved in acetone so that it will penetrate the bones. To safely transport the bones back to the lab, we leave them encased in rock and surround them with a rigid cradle. For smaller bones, this cradle is made of medical bandages (like the ones that doctors put on your arm to immobilize a broken bone). Larger specimens are surrounded by strips of burlap soaked in plaster. A separating layer of damp toilet paper in between the bone and cradle keeps the plaster from permanently sticking to the specimen.
Photo of Randy at the roadcut by Nick Pyenson, UCMP; all other photos by Randy Irmis, UCMP.
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