The subject matter of this short essay is a rare, agatized snail fossil from the Jurassic Period that was found in the Morrison Formation, and a dinosaur bone of an unknown species, also from the Morrison. Both specimens are from Colorado. The Morrison Formation is a sequence of sedimentary rocks that contains many Late Jurassic fossils. Iconic dinosaurs such as Allosaurus fragilis, Diplodocus longus, and Brachiosaurus altithorax have been found in this layer of Jurassic sediment.
The aquatic gastropod (Figure 1) is about 165 million years old, and is assigned to the Valvatidae, a taxonomic family of small, fresh water gastropods known as the valve snails. These have an operculum ("The gastropoda"). The operculum is like a trapdoor attached to the upper surface of the foot and closes the opening of the shell when the soft parts of the snail are retracted inside. The snail is assigned to the species Valvata scabrida ("Humboldt State University," 2002). This snail lived in a Jurassic freshwater pond or lake.
|Figure 1: Photomicrograph of a Valvata scabrida. Gastropods are characterized by the possession of a single (often coiled) shell. Photo ©2012 by S. Veatch.|
Fossil Length Width Height
Valvata scabrida 43.18 mm 2.86 mm 45.72 mm
Dinosaur bone ~ 145 mm ~ 43 mm ~ 40 mm
As shown in Figure 1, the gastropod shells are replaced by agate, in a process known as agatization, which also occurs in other types of fossils. Agate is a beautiful material that is often used in jewelry.
|Figure 2: The unidentified dinosaur bone. Photo ©2012 by |
Overall, these are two magnificent fossils and fascinating finds that help us reconstruct ancient worlds that have long since passed into deep time.
The gastropoda. (n.d.). Retrieved from http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/gastropoda.php
Humboldt State University Natural History Museum: Jurassic Period. (2002, October 15). Retrieved from http://www.humboldt.edu/natmus/Case_indexes/Case_jpgs/Jurassic.web/
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