In the Lab
Collecting fossils is only part of the story. They need to be “prepared”, that is cleaned of their encasing rock so that they can be studied. It takes more time to prepare a fossil than it does to collect it. In the lab, the jacket is partially removed so that the fossil remains cradled by the jacket. The rock may be chipped away using small pneumatic scribes. These scribes have metal tips that vibrate at high speed, thus chipping the rock away. With softer rock, dental tools and awls may be used. As the bone is exposed, its surface is treated with consolidant, and broken pieces glued into place. Eventually, the entire fossil is prepared free and can be studied.
Pneumatic scribe used to remove rock from fossils.
Reconstructing the Paleoenvironment Reconstructing the world of the Cedar Mountain Formation begins with the rocks, because rocks reflect the environment in which they are formed. The most abundant rock in the Cedar Mountain formation are mudstones. This rock is deposited on the floodplain or small ponds on the floodplain . Some of the mudstone has a mottled appearance due to fluctuation of the groundwater during the Early Cretaceous. Color bands often seen in cliff face are ancient soil horizons or paleosols. They are well formed in dry (semiarid and arid) environments. Carbonate nodules in the Ruby Ranch Member. These erode out and liter the ground making walking on slopes rather dangerous. Note the beds of coalesced nodules near the top. Calcium carbonate nodules are common in mudstones of the Cedar Mountain Formation (especially the Ruby Ranch Member as shown above). They form in the soil due to seasonal evaporation of groundwater during the Early Cretaceous. If sediment deposition is slow, carbonate nodules have long time to grow and may coalesce into beds of irregular limestone. Sandstone also occurs in the Cedar Mountain Formation. These were as sand by flowing water, either in river channels or as sediments deposited adjacent to river channels by flood events. Some sandstone bodies actually preserve the position of ancient river channels (left) and these resemble modern counterparts (right). They are exposed when the softer, more easily eroded floodplain mudstones erode away. (See Harris, D.R. 1980. BYU Geological Studies 27:51-66) These ancient channels are important for showing the direction of ancient river flow direction. (adapted from Craig, L.C. 1981.Rocky Mountain Association of Geologists Field Conference Guidebook, p. 195-200). Conifer logs in the Posion Strip Sandstone Fossil logs and wood tells us about the type of vegetation present. Conifers are the dominant tree (some large logs in the Poison Strip Sandstone), but tree ferns are also present based on a unique type of wood called Tempskya. Invertebrate fossils are mostly traces left as insects and other invertebrates crawled and fed on mud, or as termite or ant nests. Body fossils are not yet known, but might some day be found in some of the laminated shales in the Cedar Mountain Formation. Fossilized termite or ant nest. Note the numerous interconnecting tunnels. Death of a Herd Lorrie's Site near Arches National Monument is unusual in that almost all of the 3000 bones collected are of a single species of armor plated ankylosaur. Over 30 individuals of Gastonia are buried here, which suggests a herd had died and was buried at the site. Some of the 3000 bones of Gastonia recovered at Lorrie's Site. Note the lighter colored sediments on the right side. This is a muddy, medium grained sandstone, whereas the greenish-gray sediments on the left is mudstone. The mass of bones were bulldozed by flowing water of a crevasse splay and marks the farthest point of the splay onto the floorplain. The splay is slightly more resistant to erosion than the mudstone, so that the lobes of the splay are visible. Herd of Gastonia What killed them? One suggestion is that they died during a drought. But animals don't die all at once in one place during a drought. Instead, they tend to drop dead over a span of days to weeks leaving carcasses scattered over a wide area. My own idea is that they drowned, either during a flood or while crossing a rain swollen river. Drowned Gastonia Their carcasses accumulated on the floodplain, much like happens with wildebeests that drown during migration. Scavengers and decay left only scattered bones. All that remained after decay and scavenging were scattered bones. Latter floods rearranged bones into current stable positions nearer the river channel. By that, I mean, bones with curvature are oriented so that that were not easily moved again. For example, a curved shoulder blade would be pushed by water currents to be concave side up. We do know that the bones were buried by a crevasse splay (see image above). Such sediments are deposited on the floodplain when the natural levee along a river is breached during a flood. This breach, or crevasse, allows sediment to spill out onto the floodplain. Because the water is no longer confined by the river banks, it spreads out and its velocity drops. This drop in velocity deposits the sediment being carried by the water. Any bones present may be buried. A crevasse splay deposit along the Pearl River, Mississippi. Similar splay sediments buried the Gastonia bones. (Image from Google Earth). 
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