Dinosaur tracks (Dakota Sandstone, Lower Cretaceous; Dinosaur Ridge, Colorado, USA) 85 : 無料・フリー素材/写真
Dinosaur tracks (Dakota Sandstone, Lower Cretaceous; Dinosaur Ridge, Colorado, USA) 85 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Dinosaur tracks in the Cretaceous of Colorado, USA.Dinosaur Ridge is a section of Colorado's Dakota Hogback, a north-south trending ridge of eastward-dipping, Mesozoic sedimentary rocks. Triassic, Jurassic, and Cretaceous rocks are present, tilted during the Laramide Orogeny in the Cenozoic.This exposure consists of structurally tilted beds of the Dakota Sandstone, a Lower Cretaceous succession of nearshore terrestrial to intertidal to shallow marine quartz sandstone deposits. The eastern side of Dinosaur Ridge has a spectacular sandstone bedding plane with hundreds of dinosaur footprints. Researchers have identified 325 dinosaur footprint at the site, made by about 37 individual dinosaurs. The sediments probably represent a tidal flat that bordered the ancient Western Interior Seaway. The track makers were principally iguanodontid dinosaurs and a small theropod dinosaur. The tracks have been stained gray with charcoal to make them easier to see - the charcoal doesn't harm the tracks. Freeze-thaw weathering is destroying the tracks, and a building over this outcrop has been proposed.This dinosaur tracksite is next to a modern freeway - Interstate 470. As such, the dinosaur tracksite is often called the "Cretaceous 470" or "Dinosaur Freeway". This is part of a series of dinosaur tracksites that occur from Wyoming to New Mexico along the western edge of the Western Interior Seaway and the eastern edge of the Rocky Mountains - this is the "Dinosaur Freeway Megatracksite".Dinosaur tracks were discovered here in 1937 during road construction, but they were found a little downhill from here. This particular bedding plane was exposed in the 1950s and 1960s. Easy access resulted in theft of some dinosaur tracks and some museum extraction (Denver Museum of Natural History). One stolen track was recovered by a Colorado State University student who found it being used as a residential doorstop - it's now at the Dinosaur Ridge visitor center. The area became "protected" in 1989.The most common track type here is Caririchnium leonardii, which was made by iguanodontid (ornithopod) dinosaurs. The pes (hindfoot) track is tridactyl - 3 toes - and no heel (all dinosaurs walked on their toes). Pes impressions range from about 9 to 20 centimeters wide. The manus (forefoot) tracks are small in comparison. The iguanodontid tracks are mostly adult footprints, but some juvenile tracks are present.Another track type at the site is Magnoavipes, which was probably made by a theropod or ornithopod dinosaur. Some unidentified tracks are present at the top of the outcrop. Other fossils in the area include crocodilian tracks, plants (seed pod and tree molds - with possible Teredolites borings), bivalves, and invertebrate trace fossils (Zoophycos, Arenicolites, Diplocraterion, vertical burrows, etc.).Stratigraphy: Dakota Sandstone, Albian Stage, upper Lower CretaceousLocality: eastern side of Dinosaur Ridge, between Interstate 70 and the town of Morrison, west of Denver, north-central Colorado, USA |
| 撮影日 | 2009-06-15 15:56:30 |
| 撮影者 | James St. John |
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