Pikes Peak Pebble Pups

Pikes Peak Pebble Pups

Monday, July 30, 2012

Recent Fossil Finds From the Morrison Formation

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.
The dinosaur bone (Figure 2) is from an unknown species, and yields clue as to where the dinosaur died. The dimensions of the gastropod fossil and dinosaur bone are shown in Table 1.

Table 1: The Dimensions of the Fossils

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 S. Veatch
The dinosaur bone has not been identified or dated, as of the writing of this paper, but it appears to be a fragment of a large bone, and it is attached to an extremely fine-grained sandstone, which may give clues about how the bone was preserved. The dinosaur bone is shown in Figure 2. Agate has formed within the Haversian canals and can be seen at either end of the fossil bone. Haversian canals are the tiny, interconnecting, longitudinal channels in bone tissue through which blood vessels, nerve fibers, and lymphatic vessels pass.
Overall, these are two magnificent fossils and fascinating finds that help us reconstruct ancient worlds that have long since passed into deep time.

References Cited:

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/

About the author:
Zach Sepulveda is a junior member of the Colorado Springs Mineralogical Society where he helps the program leaders with instruction and demonstrations. Zach is currently working on a biology of dinosaurs program and a multitude of writing projects, including the fine art of poetry.

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Through this blog pebble pups and junior members of the Colorado Springs Mineralogical Society can access their lessons, work on assignments and projects, and receive details about field trips in the Pikes Peak Region. This Internet program is also suitable for young people who are interested in Earth science but do not live near a rock club or gem and mineral society or for young people anywhere who want a deeper dive into these topics. The only requirement is that all participants must be members of the Colorado Springs Mineralogical Society and must fill out the CSMS membership form (under important websites) and send their registration and membership fee in. Steven Veatch is the senior instructor and will need an email from you with your name, address, phone number, and permission from your parents to participate in this program.